System and method of monitoring the recovery of subterranean minerals or metals

Abstract

A method of monitoring and / or optimising the extraction of a target material such as target mineral and / or target metal from a subterranean formation. The method comprises injecting at least one extra

Description

The present invention relates to the recovery of subterranean minerals and / or metals, in particular monitoring the recovery of subterranean minerals and / or metals. Aspects of the inventions relates a system and methods for assessing the recovery of lithium from subterranean formations. Another aspect relates to optimising processes and conditions of a subterranean mineral and / or metal recovery operation. Background to the invention In situ recovery mining is the extraction of useful materials (chemical elements or compounds) from a subterranean location. Typically a first borehole is drilled and fractures or pathways are created to penetrate ores or high concentrations of the target material. A fluid is injected or pumped into the first borehole which travels through porous rock and pathways underground contacting the target material. Depending on the target material a fluid type is selected to interact with the target material to allow extraction and / or mobilisation from the surrounding subterranean geology. The fluid carries the target material with the fluid flow to a second borehole where it is pumped to surface. The material can be extracted from the fluid and the remaining solution may then be treated and circulated back into the first borehole to recover more target material. This process continues until the process no longer recovers a viable amount of target material. This process may facilitate the extraction of target materials from an underground ore without the need for conventional mining involving open-cut mining or underground mining. One example is the extraction of lithium from a subterranean formation such as a geothermal well. An extraction or leaching fluid such as brine fluid is injected into the lithium rich geothermal reservoir. The brine fluid is heated as it passes through the reservoir, the brine fluid interacts with the lithium to extract and carry lithium into a production well connected to the reservoir. The produced heated brine fluid is used to generate electricity and the lithium may be separated from the brine fluid. The separated brine fluid may be reinjected into the reservoir and the process may be repeated. However, there is a risk that the fluid carrying the target material may pass through unknown underground pathways. This can make it difficult to assess whether the target material has been depleted or assess the effectiveness of the extraction process. There is also a risk that unknown underground pathways may divert the extraction fluid and target material which may result in contamination of other areas, especially surrounding groundwaters which can have a negative environmental impact. Summary of the invention It is amongst the aims and objects of the invention to provide a system and method which obviates or mitigates one or more drawbacks or disadvantages of the prior art subterranean mineral and / or metal recovery systems. There is a need to obtain information on subterranean flow paths and to understand the location of target materials, flow paths into, through and / or from subterranean formations containing target material and / or map the migration of extracted target materials through the subterranean flow pathways. It is an object of the invention to provide a system and method to monitor the extraction of a target material from a subterranean location. It is an object of the invention to provide a system and method to understand characteristics of flow paths and to understand how injected extraction fluids are affected by flow path characteristics. It is an object of the invention to provide a system and method to characterise, assess and / or optimise extraction conditions of the target material from a subterranean location. Further aims and objects of the invention will become apparent from reading the following description. According to a first aspect of the invention, there is provided a method of monitoring an extraction of a target material from a subterranean formation, the method comprising: injecting at least one extraction fluid into the subterranean formation; injecting at least one tracer into a subterranean formation; collecting samples of fluid produced from the subterranean formation; analysing the samples to detect the presence or absence of the at least one tracer; based on the measured tracer data monitoring at least one characteristic of the extraction operation. The target material may be a target mineral and / or a target metal. The method may comprise extracting the target material by leaching, dissolving or partially dissolving the target material from the subterranean formation. The method may comprise extracting the target material by mobilising the target material from the subterranean formation. The method may comprise extracting the target material by displacing and / or replacing target material enriched subterranean fluids. The subterranean formation may be selected from the group comprising a geothermal reservoir, a supercritical geothermal reservoir, an enhanced geothermal system, an aquifer, a hydrocarbon reservoir; a well, a mining well, a mining reservoir, a water reservoir and / or a shale reservoir. The subterranean formation may be an active formation. The extraction operation may be conducted at the same time as a subterranean operation such as geothermal energy production, supercritical geothermal energy production and / or a hydrocarbon production. The at least one characteristic of the extraction may be selected from the group comprising identifying and / or characterising a flow path of the extraction fluid in, through or from the subterranean formation; estimating an amount of target mineral and / or target metal in the subterranean formation; and / or estimating a location of high concentrations of target mineral and / or target metal in the subterranean formation. The at least one characteristic of the extraction operation may be determining the efficiency of the extraction operation. The at least one characteristic of the extraction operation may be determining the efficiency of one or more extraction fluid. The method may comprise measuring a concentration of the target material in the fluid produced from the subterranean formation. The method may comprise injecting the at least one tracer into a well in fluid communication with the subterranean formation. The method may comprise injecting the at least one tracer into at least one well in fluid communication with the subterranean formation. The method may comprise establishing a fluid communication between the well and the subterranean formation. The method may comprise establishing fluid communication between the well and the subterranean formation using a well stimulation treatment. The method may comprise injecting two or more distinct tracers into a well in fluid communication with the subterranean formation. The method may comprise injecting two or more distinct tracers into two or more wells. The method may comprise injecting a plurality of distinct tracers into a well. The method may comprise injecting a plurality of distinct tracers into two or more wells. The method may comprise injecting a plurality of distinct tracers wherein each tracer is injected into a different well. The well may be an injection well. The method may comprise collecting or taking samples from a well. The method may comprise collecting or taking samples from at least one production well. The method may comprise collecting or taking samples from at least one injection well. The method may comprise collecting or taking samples from more than one well. The method may comprise collecting or taking samples from more than one production well. The method may comprise injecting at least one tracer into a well in fluid communication with the subterranean formation and collecting or taking samples from the same well. The method may comprise injecting two or more distinct tracers into a well in fluid communication with the subterranean formation and collecting or taking samples from the same well. The method may comprise injecting at least one distinct tracer into a first well and at least one distinct tracer into a second well. The method may comprise injecting at least one distinct tracer into a third well or a further well. The at least one tracer may be detected and its concentration measured by sampling production fluid. The sampling may be conducted at the one or more of said sampling times. The sampling may be conducted downhole downstream of the tracer release apparatus or at surface. Samples may be collected for later analysis. Sampling may be real-time sampling, manual sampling, automated sampling, inline sampling, online sampling, at-line sampling and / or offline sampling. The at least one tracer may be detected by a sampling system. The sampling system may facilitate real time monitoring and / or analysis of the tracer in the production fluid. Samples of the well fluid may be taken at the surface or downhole. The samples may be collected for further analysis onsite or offsite. The method may comprise tracing and / or mapping flow of an extraction fluid through the formation. The method may comprise using the at least one tracer to trace and / or map flow between at least one injection well and at least one production well. The method may comprise using the at least one tracer to determine which injection well is the source of fluid produced at a production well. The method may comprise using the at least one tracer to determine which production well is producing fluid injected in at least one injection well. The at least one tracer may be selected from the group comprising chemical, fluorescent, phosphorescent, radioactive compounds isotope, isotope signature, stable isotope and / or radioactive isotope of elements constituting a part of a tracer molecule, dyes, halogenated benzoates, DNA based tracer, halogenated hydrocarbons, metal oxides, perfluorinated compounds, perfluoroethers, organofluorine compound with hydrogen replaced by fluorine, partly fluorinated compounds, perfluoro butane (PB), fluorobenzoates, perfluoro methyl cyclopentane (PMCP), perfluoro methyl cyclohexane (PMCH), organofluorine, sulphonic acid, polyaromatic sulfonate, sulfonates, naphthalene, naphthalene sulphonic acid, crown ether, 12-crown-4, 14-crown-4, organophosphorus compounds, Di-(2-ethylhexyl) phosphoric acid, mono-2-ethylhexyl phosphoric acid, phenylphosphonic acid, polymeric tracer such as chain end functionalized (co)polymers based on poly(N-vinyl pyrrolidone), poly(ethylene oxide), poly(styrene sulfonates), poly(vinyl acetate), poly(vinyl alcohol), nanoparticle and / or quantum dot The at least one tracer may be a water, oil or gas tracer. The at least one tracer may be a solid, liquid or gas. The at least one tracer may be applied in solution. The at least one tracer may be in a semi-crystalline or crystalline form. The at least one tracer may be configured to be soluble and / or dissolve in water. The at least one tracer may comprise a reactive tracer. The method may comprise injecting at least one reactive tracer. The at least one tracer may comprise an interactive tracer. The method may comprise injecting at least one interactive tracer. The at least one reactive tracer and / or at least one interactive tracer may be configured to react and / or interact under reservoir or formation conditions. The at least one reactive tracer may be configured to react under reservoir or formation conditions. The at least one interactive tracer may be configured to interact under reservoir or formation conditions. The at least one reactive tracer may be designed to react in a chemical reaction with the target material. The at least one reactive tracer may be configured to react, partially react, degrade or at least partially degrade on exposure to the target material in the reservoir or formation. The at least one reactive tracer may be configured to react, partially react, degrade or at least partially degrade on exposure to the target material in an injection well and / or a production well. The at least one reactive tracer may be a chemical tracer. The at least one reactive tracer may be a non-radioactive tracer. The at least one interactive tracer may be a chemical tracer. The at least one interactive tracer may be a non-radioactive tracer. The at least one reactive tracer may be configured to degrade or react at a known rate under known conditions. The at least one reactive tracer may be configured to react with the target material to form a distinctive chemical product. The method may comprise measuring the concentration of reacted tracer or chemical product. The method may comprise measuring the concentration of unreacted tracer. The method may comprise estimating a concentration or amount of target material based on the measured concentration of unreacted tracer and / or based on the measured concentration of reacted tracer or chemical product. The method may comprise measuring the concentration of interactive tracer as a function of time. The method may comprise estimating a concentration or amount of target material based on the measured concentration of interactive tracer as a function of time. The at least one reactive tracer may be sulphonic acid, naphthalene sulphonic acid, crown ethers, 12-crown-4, 14-crown-4, organophosphorus compounds, Di-(2-ethylhexyl)phosphoric acid, mono-2-ethylhexyl phosphoric acid or phenylphosphonic acid and / or their derivatives. The at least one reactive tracer may be configured to react with subterranean minerals and / or rocks. The at least one interactive tracer may be configured to interact with subterranean minerals and / or rocks. The at least one reactive tracer may be configured to react with the target material. The at least one interactive tracer may be configured to interact with the target material. The at least one reactive tracer may be configured to react with an ore of the target material. The at least one interactive tracer may be configured to interact with an ore of the target material. The at least one reactive tracer may be configured to be attracted to or repelled by subterranean minerals and / or rocks. The at least one interactive tracer may be configured to be attracted to or repelled by subterranean minerals and / or rocks. The at least one interactive and / or reactive tracer may be configured to be attracted to or repelled by subterranean target material or target material ore. The at least one interactive tracer may be designed to be affected or influenced by the target material. The at least one interactive tracer may be configured to exhibit intermolecular forces of attraction or repulsion with subterranean minerals and / or rocks. The at least one interactive tracer may be configured to exhibit intermolecular forces of attraction or repulsion with target material or target material ore. The affinity and / or specificity of the at least one interactive tracer for the target material may be adjustable based on the structure or structural groups of the at least one interactive tracer. The at least one interactive tracer may be a polymeric tracer. The polymeric tracer may comprise oligomers. The chain length of the oligomers may be adjusted, designed or selected to select a preferred affinity and / or specificity for the target material. The at least one tracer may comprise a passive tracer. The method may comprise injecting at least one passive tracer. The at least one passive tracer may be a stable chemical tracer. The at least one passive tracer may be configured to be stable in subterranean formation or reservoir conditions. The at least one passive tracer may be configured to be stable in geothermal reservoir conditions, supercritical geothermal reservoir conditions, hydrocarbon reservoir conditions, aquifer conditions and / or mining well conditions. The at least one passive tracer may be configured to resist degradation and / or resist full degradation on exposure to a condition in the formation, reservoir injection well and / or production well. The at least one passive tracer may be chemically, physically and / or biologically stable in formation or reservoir conditions. The at least one passive tracer may be configured to behave as closely as possible to the traced fluid or phase. The at least one passive tracer may be configured to not adsorb to any surface or in other ways be chemically affected by the target material, reservoir rocks, minerals and / or chemicals. The at least one passive tracer may be configured to resist interaction with subterranean minerals and / or rocks. The at least one passive tracer may be configured to not be attracted to or repelled to the target material or subterranean minerals and / or rocks. The at least one passive tracer may be configured to exhibit no intermolecular forces of attraction or repulsion with the target material, subterranean minerals and / or rocks. The at least one passive tracer may be a thermally stable tracer and / or chemical stable tracer. The method may comprise injecting two or more tracers. The two or more tracers may comprise at least one passive tracer. The two or more tracers may comprise at least one reactive tracer. The two or more tracers may comprise at least one interactive tracer. The two or more tracers may comprise at least one passive tracer and at least one reactive tracer. The two or more tracers may comprise at least one passive tracer and at least one interactive tracer. The two or more tracers may comprise at least one passive tracer, at least one interactive tracer and / or at least one reactive tracer. The method may comprise injecting a different extraction fluid and at least one different tracer into the subterranean formation. The method may comprise measuring and / or detecting a concentration of the target material extracted in the produced fluids for the different extraction fluid. The method may comprise measuring and / or detecting a variation in the concentration of target material extracted for each extraction fluid type. The extraction fluid type may be identified based on the tracer type in the produced fluid. The method may comprise optimising the extraction operation. The method may comprise optimising the extraction fluid. The method may comprise optimising the extraction conditions. The method may comprise identifying an optimum injection location. The method may comprise identifying an optimum production location. The method may comprise identifying an optimum extraction fluid composition. The method may comprise controlling and / or optimising the rate of injection and / or rate of fluid produced from the subterranean formation based on a measured concentration of the at least one tracer in the produced fluid. The extraction fluid may be a leaching fluid. The extraction fluid may be a liquid, a gas and / or a supercritical fluid. The extraction fluid may comprise water, wastewater, brine (saltwater), steam, acid, organic acid, a leaching fluid and / or water mixed with chemicals. The extraction fluid may be carbon dioxide, nitrogen and / or hydrocarbon gas. The extraction fluid may be a lixiviant. The extraction fluid may be configured to extract the target material from its ore. The extraction fluid may be a geothermal fluid. The extraction fluid may be an injection fluid. The extraction fluid may be a fracturing fluid. The extraction fluid may be selected based on the target material, formation type and / or conditions of the formation. The at least one tracer may be released or injected into the extraction fluid via a tracer injection device. The tracer injection device may be permanently installed in a well or injection site. The method may comprise adjusting and / or controlling the duration and / or frequency of the injection or release of tracer into the extraction fluid. The method may comprise controlling and / or adjusting the release of tracer into at least one extraction fluid for a desired duration and / or frequency. The method may comprise injecting or releasing tracer continuously. The method may comprise injecting or releasing tracer continuously for a sustained period of time. The method may comprise actuating a tracer injection device to allow continuous release of tracer. The method may comprise injecting the at least one tracer and the at least one extraction fluid at the same time. The method may comprise releasing or injecting the at least one tracer on command. The method may comprise releasing or injecting the at least one tracer in response to a timer and / or a control signal. The method may comprise releasing or injecting the at least one tracer in response to a pre-set programme and / or timer. The method may comprise releasing or injecting tracer in response to a trigger event. The tracer release device may be controlled to selectively release at least one tracer into the injection well to facilitate characteristics of the flow of extraction fluid through the subterranean formation to be monitored. Flow measurement, flow paths and / or transport paths of the extraction fluid through the subterranean formation may be identified, calculated and / or monitored. The tracer release device may be configured to release at least one tracer. The tracer release device may comprise a premixed tracer and extraction fluid. The extraction fluid and the at least one tracer may be premixed before injection in to a well. The extraction fluid and the at least one tracer may be mixed during injection into a well. The at least one tracer may be located, arranged or installed as a tracer source in a well in a flow path of the extraction fluid. The at least one tracer may be configured to be released or tracer molecules released from at least one tracer source on command or on contact with the extraction fluid. The tracer source may comprise a tracer material. The tracer material may comprise a tracer and a carrier. The carrier may be a matrix material. The matrix material may be a polymeric material. The tracer may be chemically immobilized within and / or to the carrier. The tracer material may be chemically immobilized configured to release tracer molecules or particles in the presence of a chemical trigger or specific fluid. The carrier may be a polymer. The tracer may be physically dispersed and / or physically encapsulated in the carrier. The tracer material may release tracer molecules into fluid by dissolution or degradation of the carrier and / or the tracer into the extraction fluid. The carrier may be selected to controllable degrade on contact with the extraction fluid. The carrier may be selected to degrade by hydrolysis of the carrier. The tracer and / or the carrier may be fluid specific such that the tracer molecules will be released from the tracer material as a response to contact with a target liquid such as the extraction fluid. The tracers and / or the carrier may be chemically intelligent such that tracer molecules will be released from the tracer material as a response the exposure of the tracer material to a target fluid. The tracer release device may be configured to release two or more tracers. The method may comprise releasing two or more tracers in a known combination or ratio. The at least one tracer may be a liquid, solid or gas. The at least one tracer may be a powdered solid. The method may comprise detecting the presence of tracer in the produced fluid. The method may comprise collecting the at least one sample at one or more sampling times. The at least one sample may be collected for later analysis onsite or offsite. The sample be measured in real time. Samples may be collected and / or measured downstream of a production influx zone at known sampling times. The method may comprise collecting at least one sample at a pre-determined time sequence or pre-determined profile. The method may comprise detecting the presence of tracer in the produced fluid and / or extraction fluid in real time. The method may comprise detecting the presence of tracer in the produced fluid and / or extraction fluid using an online analyser. The method may comprise measuring a concentration of at least one tracer in the produced fluid and / or extraction fluid. The method may comprise measuring a concentration of at least one tracer in the samples. The method may comprise analysing the presence and / or concentration of at least one tracer as a function of time. The method may comprise measuring a concentration of at least one tracer in the produced fluid in real time. The method may comprise measuring a concentration of at least one tracer in the produced fluid using an online analyser. The method may comprise real-time sampling, manual sampling, automated sampling, inline sampling, online sampling, at-line sampling and / or offline sampling. The method may comprise collecting samples at known times. The produced fluids may be sampled at a pre-determined time sequence or pre-determined profile. The method may comprise adjusting the sample volume and / or sampling time. The sampling sequence, duration and / or frequency may be modified during the sampling operation. The sampling sequence, duration and / or frequency may be modified based on measured tracer data. The sampling sequence, duration and / or frequency may be modified based on a model. The method may comprise analysing the at least one sample to measure the presence and / or concentration of the two or more tracers in the sample. The method may comprise analysing the at least one sample for type and / or concentration of the two or more tracers as a function of sampling time. The method may comprise measuring an arrival time of the at least one tracer. The method may comprise measuring an arrival time of the at least one passive tracer, at least one reactive tracer and / or at least one interactive tracer. The method may comprise measuring a ratio of reacted and unreacted tracer. The method may comprise detecting and / or measuring the concentration of the two or more tracers in the at least one sample in real time. The method may comprise detecting and / or measuring the concentration of the two or more tracers in the at least one sample using an online analyser. The method may comprise detecting and / or measuring the concentration of the plurality of tracers in at least one sample. The method may comprise measuring a tracer concentration signature of the two or more tracers in the at least one sample. The method may comprise measuring a tracer concentration signature of the at least one reactive tracer and the at least one passive tracer in the at least one sample. The method may comprise measuring a tracer concentration signature of the at least one interactive tracer and the at least one passive tracer in the at least one sample. The method may comprise comparing the measuring tracer concentration signatures of the at least one reactive tracer and the at least one passive tracer in the at least one sample with the tracer concentration signatures of the at least one reactive tracer and the at least one passive tracer injected in the well. The method may comprise comparing the measuring tracer concentration signatures of the at least one interactive tracer and the at least one passive tracer in the at least one sample with the tracer concentration signatures of the at least one interactive tracer and the at least one passive tracer injected in the well. The method may comprise detecting and / or measuring the at least one tracer using a techniques selected from the group comprising optical detection, optical fibers, polymerase chain reaction (PCR), spectrophotometric methods, spectrometric methods, chromatographic methods, gas chromatography (GC), high performance liquid chromatography (HPLC), liquid chromatography fluorescence detector (LC-FLD), liquid chromatography-ultraviolet (LC-UV), mass spectrometry (MS), multidimensional MS, liquid chromatography-mass spectrometry (LCMS), Liquid Chromatography with tandem mass spectrometry (LCMSMS), Gas chromatography mass spectrometry (GCMS), Gas chromatography with tandem mass spectrometry (GCMSMS), inductively coupled plasma mass spectrometry (ICP-MS), inductively coupled plasma with tandem mass spectrometry (ICP-MSMS) and / or radioactivity analysis such as scintillation counting. The method may comprise comparing the ratio of each of the injected two or more tracers with the ratio of each of the two or more tracers in the at least one sample. The method may comprise using the tracer concentration signatures of the at least one passive tracer as reference data. The method may comprise comparing the tracer concentrations signatures of the two or more tracers in the at least one sample with the tracer concentration signature of the two or more tracers injected into the subterranean formation or injection well. The method may comprise interpretating differences or changes between injected tracer concentrations signatures and produced tracer concentrations signatures to determine and / or monitor characteristics of the subterranean formation, the concentration of target material in the reservoir, the location of target material in the subterranean formation and / or the surface area of the target material in the subterranean formation. The method may comprise extracting and / or separating the target material from the extraction fluid. The method may comprise modelling the subterranean formation, extraction fluid type, injected tracer concentration, injection location, transport time, injection flow rate, production location, tracer concentration in produced fluids, target material concentration in produced fluid and / or production rates in a model. The parameters of the model may be adjusted until calculated concentrations of model tracers compare or substantially match with the measured concentrations of at least one tracer in the samples to estimate flow of tracer and injected extraction fluid. The model may be used to optimise and / or control the flow of extraction fluid into, through and from the subterranean formation to improve the extraction of the target material. The model may comprise parameters selected from the group including: the number of injection wells, temperature, temperature of fluid at each injection well, temperature of fluid produced, number of production wells, temperature of fluid at each production well, transport time, transport time of tracer-containing fluid from injection to production for one or more injection wells, transport time of tracer-containing fluid from injection to production for one or more production wells, transport time of tracercontaining fluid through the formation / reservoir, tracer type; tracer combination, ratio of reacted to unreacted tracer, ratio of at least one passive tracer to at least one reactive tracer, ratio of at least one passive tracer to at least one interactive tracer, formation type, extraction fluid type, extraction fluid composition, concentration of tracer, concentration of tracer as a function of time, fluid flow path from one or more injection well to one or more production wells in communication to the formation, injection rate, production rate, rock mechanics, rock chemistry, gravity, density, viscosity; reservoir permeability, reservoir heterogeneities, solubility, fluid chemistry, porosity, fluid saturation, injection amount, injection volumes and / or migration path of the at least one tracer in and / or through the formation. The method may be a computer-implemented method. The method may be a computer-implemented history matching method. The method may comprise storing the measurement data to a database. The method may comprise storing the model data to a database. The target material may be selected from the group comprising lithium, zinc, manganese, copper, potassium, gold, boron, cobalt, cesium, barium, rubidium and silica. The target material is preferably lithium. The target material may be a non-radioactive material. The method may comprise extracting lithium from a subterranean formation. The method may comprise extracting lithium from a geothermal reservoir. The method may comprise extracting lithium from an enhanced geothermal system. According to a second aspect of the invention, there is provided a method of monitoring flow characteristics of an extraction fluid through a subterranean formation to extract a target material, the method comprising: injecting at least one extraction fluid into the subterranean formation; injecting at least one tracer into the subterranean formation; collecting samples of fluid produced from the subterranean formation; analysing the samples to detect the presence or absence of the at least one tracer; and based on the measured tracer data monitoring at least one flow characteristic of the extraction fluid. The method may comprise monitoring the least one flow characteristic of the extraction fluid based on the presence and / or a concentration of the at least one tracer in the samples. The method may comprise tracing and / or mapping flow of at least one extraction fluid through the subterranean formation. The method may comprise using the measured tracer data to trace and / or map flow between at least one injection well and at least one production well. The method may comprise using the measured tracer data to determine which injection well is a source of fluid produced at a production well. The method may comprise using the measured tracer data to determine which production well is producing fluid injected in an injection well. The method may comprise tracing and / or mapping flow paths of high concentrations of target material extraction. The method may comprise identifying the location of a breakthrough into a producing well. The method may comprise identifying, calculating and / or monitoring flow rates, flow paths and / or transport paths. The method may comprise measuring a concentration of the at least one tracer in the samples. Embodiments of the second aspect of the invention may include one or more features of the first aspect of the invention or its embodiments, or vice versa. According to a third aspect of the invention, there is provided a method of estimating an amount of a target material in a subterranean formation, the method comprising: injecting at least one extraction fluid into the subterranean formation; injecting at least one tracer into the subterranean formation; collecting samples of fluid produced from the subterranean formation; analysing the samples to detect the presence or absence of the at least one tracer; and based on the measured tracer data estimating an amount of a target material in a subterranean formation. The method may comprise estimating an amount of a target material in a subterranean formation based on the presence and / or a concentration of the at least one tracer in the samples. The method may comprise measuring a concentration of the at least one tracer in the samples. The method may comprise injecting at least one tracer into a well in fluid communication with the subterranean formation and collecting or taking the samples from the same well and / or at least one different well. The method may comprise injecting two or more distinct tracers into a well in fluid communication with the subterranean formation and collecting or taking the samples from the same well and / or at least one different well. The at least one tracer may comprise a passive tracer. The method may comprise injecting at least one passive tracer. The at least one passive tracer may be configured to exhibit no intermolecular forces of attraction or repulsion with the target material, subterranean minerals and / or rocks. The at least one passive tracer may be configured to behave as closely as possible to the traced fluid or phase. The at least one tracer may comprise a reactive tracer. The method may comprise injecting at least one reactive tracer. The at least one tracer may comprise an interactive tracer. The method may comprise injecting at least one interactive tracer. The at least one reactive tracer may be configured to react, partially react, degrade or at least partially degrade on exposure to the target material in the reservoir or formation. The at least one interactive tracer may be configured to be attracted to or repelled by subterranean minerals and / or rocks. The at least one interactive tracer may be configured to be attracted to or repelled by subterranean target material or target material ore. The at least one interactive tracer may be configured to exhibit intermolecular forces of attraction or repulsion with subterranean minerals and / or rocks. The at least one interactive tracer may be configured to exhibit intermolecular forces of attraction or repulsion with target material or target material ore The transport time of the at least one reactive tracer and / or the at least one interactive tracer through the subterranean formation may be affected by the presence of the target material in the subterranean formation. The method may comprise comparing the arrival time of a passive tracer and the reactive tracer to assess a delayed arrival time of the reactive tracer. The method may comprise comparing the arrival time of a passive tracer and the interactive tracer to assess a delayed arrival time of the interactive tracer. The method may comprise comparing the arrival time of a passive tracer with the reactive tracer and / or interactive tracer to assess the arrival time of the reactive tracer and / or interactive tracer. The measure may comprise measuring or calculating an arrival time of the at least one tracer in a production well. The measure may comprise measuring or calculating an arrival time of the at least one tracer in samples. The method may comprise estimating an amount or surface area of target material based on the transport time and / or arrival time of the at least one reactive tracer in the production well. The method may comprise estimating an amount or surface area of target material based on the transport time and / or arrival time of the at least one interactive tracer in at least one well. The method may comprise analysing the at least one sample to measure the presence and / or concentration of the two or more tracers in the sample. The method may comprise analysing the at least one sample for type and / or concentration of the two or more tracers as a function of sampling time. The method may comprise measuring or calculating an arrival time of the at least one tracer. The method may comprise measuring a ratio of reacted and unreacted tracer. Embodiments of the third aspect of the invention may include one or more features of the first or second aspects of the invention or its embodiments, or vice versa. According to a fourth aspect of the invention, there is provided a method for monitoring the efficiency of an extraction fluid for extracting a target material from a subterranean formation, the method comprising: injecting at least one extraction fluid into at least part of the subterranean formation; injecting at least one tracer into at least part of the subterranean formation; collecting samples of fluid produced from the subterranean formation; analysing the samples to detect the presence or absence of the at least one tracer; and based on the measured tracer data monitoring the efficiency of the extraction and / or extraction fluid. The method may comprise monitoring the efficiency of the extraction operation and / or extraction fluid based on the presence and / or concentration of the at least one tracer in the samples. The method may comprise measuring a concentration of the at least one tracer in the samples. The method may comprise injecting at least one tracer into a well in fluid communication with the subterranean formation and collecting or taking the samples from the same well and / or at least one different well. The method may comprise back producing fluid in the injection well. The method may comprise injecting two or more distinct tracers into a well in fluid communication with the subterranean formation and collecting or taking the samples from the same well and / or at least one different well. The at least one tracer may comprise a passive tracer. The method may comprise injecting at least one passive tracer. The at least one passive tracer may be chemically, physically and / or biologically stable in the subterranean formation and / or in the presence of target material. The at least one passive tracer may be configured to exhibit no intermolecular forces of attraction or repulsion with the target material, subterranean minerals and / or rocks. The at least one passive tracer may be configured to behave as closely as possible to the traced fluid or phase. The at least one tracer may comprise a reactive tracer. The method may comprise injecting at least one reactive tracer. The at least one tracer may comprise an interactive tracer. The method may comprise injecting at least one interactive tracer. The at least one reactive tracer and / or at least one interactive tracer may be configured to react and / or interact with the target material in the subterranean formation. The at least one reactive tracer may be configured to react with the target material in the subterranean formation. The at least one interactive tracer may be configured to interact with the target material in the subterranean formation. The at least one reactive tracer may be configured to react with target material to form a reacted tracer. The at least one reactive tracer may be configured to react with target material to form a distinctive chemical product. The method may comprise measuring the concentration of reacted tracer or chemical product. The method may comprise measuring the concentration of unreacted tracer. The method may comprise estimating a concentration of target material, an amount of target material, a surface area of target material and / or a position of target material based on the measured concentration of unreacted reactive tracer and / or based on the measured concentration of reacted tracer or chemical product. The at least one reactive tracer and / or at least one interactive tracer may be configured to react or interact with subterranean minerals and / or rocks. The at least one reactive tracer may be configured to react with subterranean minerals and / or rocks. The at least one interactive tracer may be configured interact with subterranean minerals and / or rocks. The at least one reactive tracer may be configured to react with target material. The at least one interactive tracer may be configured to interact with target material. The at least one reactive tracer may be configured to react with an ore of target material. The at least one interactive tracer may be configured to interact with an ore of target material. The at least one reactive tracer and / or at least one interactive tracer may be configured to be attracted to or repelled by subterranean minerals and / or rocks. The at least one reactive tracer and / or at least one interactive tracer may be configured to be attracted to or repelled by subterranean target material. The at least one reactive tracer and / or at least one interactive tracer may be configured to exhibit intermolecular forces of attraction or repulsion with target material. The transport time of the at least one reactive tracer and / or at least one interactive tracer from or through the at least part of the subterranean formation may be affected by the presence of the target material in the subterranean formation. The method may comprise comparing the arrival time of a passive tracer and the reactive tracer to assess a delayed arrival time of the reactive tracer. The method may comprise comparing the arrival time of a passive tracer and the interactive tracer to assess a delayed arrival time of the interactive tracer. The method may comprise estimating a concentration of target material, an amount of target material, a surface area of target material and / or a position of target material based on the transport time and / or arrival time of the at least one reactive tracer in the samples. The method may comprise estimating a concentration of target material, an amount of target material, a surface area of target material and / or a position of target material based on the transport time and / or arrival time of the at least one interactive tracer in the samples. The method may comprise analysing the at least one sample to measure the presence and / or concentration of the two or more tracers in the sample. The method may comprise analysing the at least one sample for type and / or concentration of the two or more tracers as a function of sampling time. The method may comprise measuring an arrival time of the at least one tracer. The method may comprise measuring a ratio of reacted and unreacted tracer. The method may comprise injecting two or more different extraction fluids each with at least one distinct tracer into the subterranean formation. The method may comprise measuring a concentration of the at least one tracer, the at least one reactive tracer, the at least one interactive tracer, the at least one passive tracer and / or the target material in the produced fluids for each of the different extraction fluid types. The method may comprise measuring and / or detecting a variation in the concentration of the at least one tracer, the at least one reactive tracer, the at least one interactive tracer, the at least one passive tracer and / or the target material in the produced fluids for each extraction fluid type. The extraction fluid type may be identified based on the tracer type in the produced fluid. The method may comprise using passive tracer data may also be used to assess the amount of injected extraction fluid which is produced in the well. The method may comprise injecting a first extraction fluid with at least one tracer into the subterranean formation. The method may comprise injecting a first extraction fluid with at least one reactive tracer and at least one passive tracer into the subterranean formation. The method may comprise injecting a first extraction fluid with at least one interactive tracer and at least one passive tracer into the subterranean formation. The method may comprise injecting a second or further extraction fluid with at least one distinct tracer into the subterranean formation. The method may comprise injecting a second or further extraction fluid with at least one distinct reactive tracer and at least one distinct passive tracer into the subterranean formation. The method may comprise injecting a second or further extraction fluid with at least one distinct interactive tracer and at least one distinct passive tracer into the subterranean formation. The method may comprise determining a ratio reacted to unreacted reactive tracer. The method may comprise comparing the passive tracer concentration data with the reactive tracer concentration data. The method may comprise comparing the passive tracer concentration data with the interactive tracer concentration data. The method may comprise comparing the passive tracer concentration data with the reactive tracer concentration data to distinguish between dilution effects and mineral reactions. The method may comprise comparing the passive tracer concentration data with the interactive tracer concentration data to distinguish between dilution effects and mineral reactions. The method may comprise comparing the arrival time of the passive tracer data with the arrival time of reactive tracer data. The method may comprise comparing the arrival time of the passive tracer data with the arrival time of interactive tracer data. The method may comprise assessing the extraction efficiency of each extraction fluid compositions and / or optimise an extraction fluid composition. Embodiments of the fourth aspect of the invention may include one or more features of the first to third aspects of the invention or their embodiments, or vice versa According to a fifth aspect of the invention, there is provided a method of monitoring the extraction of lithium from a subterranean formation, the method comprising: injecting at least one extraction fluid into the subterranean formation; injecting at least one tracer into the subterranean formation; collecting samples of fluid produced from the subterranean formation; analysing the samples to detect the presence or absence of the at least one tracer; and based on the measured tracer data monitoring at least one characteristic of the extraction. The method may comprise monitoring at least one characteristic of the extraction operation based on the presence and / or a concentration of the at least one tracer in the samples. The method may comprise measuring a concentration of the at least one tracer in the samples. The method may comprise extracting lithium by leaching, dissolving or partially dissolving lithium from the subterranean formation. The method may comprise extracting lithium by mobilising lithium from the subterranean formation. The subterranean formation may be selected from the group comprising geothermal reservoir, a supercritical geothermal reservoir, an enhanced geothermal system, an aquifer, a hydrocarbon reservoir; a well, a mining well, a mining reservoir, a water reservoir and / or a shale reservoir. Preferably the subterranean formation is a geothermal reservoir. The at least one characteristic of the extraction operation may be selected from the group comprising identifying and / or characterising a flow path of the extraction fluid in, through or from the subterranean formation, estimating an amount of lithium in the subterranean formation, estimating a surface area of lithium in the subterranean formation; estimating a location of high concentrations of lithium in the subterranean formation and / or flow characteristics of the extraction fluid through the subterranean formation. The at least one characteristic of the extraction operation may be determining or monitoring the efficiency of the extraction operation. The at least one characteristic of the extraction operation may be determining or monitoring the efficiency of one or more extraction fluid to extract lithium. The method may comprise measuring a concentration of lithium in the fluid produced from the subterranean formation. The method may comprise injecting the at least one tracer into a well in fluid communication with the subterranean formation. The method may comprise injecting the at least one tracer into at least one well in fluid communication with the subterranean formation. The method may comprise injecting two or more distinct tracers into a well in fluid communication with the subterranean formation. The method may comprise injecting two or more distinct tracers into two or more wells. The method may comprise injecting a plurality of distinct tracers into a well. The method may comprise injecting a plurality of distinct tracers wherein each tracer is injected into a different well. The well may be an injection well. The method may comprise collecting or taking the samples from a well. The method may comprise collecting or taking the samples from a production well and / or an injection well. The method may comprise collecting or taking the samples from more than one well. The method may comprise collecting or taking the samples from more than one production well. The method may comprise injecting at least one tracer into a well in fluid communication with the subterranean formation and collecting or taking the samples from the same well. The method may comprise injecting two or more distinct tracers into a well in fluid communication with the subterranean formation and collecting or taking the samples from the same well and / or at least one different well. The method may comprise injecting at least one distinct tracer into a first well and at least one distinct tracer into a second well. The method may comprise injecting a first distinct tracer into a first well and a second distinct tracer into a second well. The method may comprise tracing and / or mapping flow of at least one extraction fluid through the subterranean formation . The method may comprise using the at least one tracer to trace and / or map flow between at least one injection well and at least one production well. The method may comprise using the at least one tracer to determine which injection well is the source of fluid produced at a production well. The method may comprise using the at least one tracer to determine which production well is producing fluid injected into an injection well. The method may comprise identifying the location of a breakthrough into a producing well. The method may comprise identifying, calculating and / or monitoring flow rates, flow paths and / or transport paths of the at least one tracer and / or at least one extraction fluid. The at least one tracer may be selected from the group comprising chemical, fluorescent, phosphorescent, radioactive compounds isotope, isotope signature, stable isotope and / or radioactive isotope of elements constituting a part of a tracer molecule, dyes, halogenated benzoates, DNA based tracer, halogenated hydrocarbons, metal oxides, perfluorinated compounds, perfluoroethers, organofluorine compound with hydrogen replaced by fluorine, partly fluorinated compounds, perfluoro butane (PB), perfluoro methyl cyclopentane (PMCP), perfluoro methyl cyclohexane (PMCH), fluorobenzoates, organofluorine, sulphonic acid, polyaromatic sulfonate, sulfonates, naphthalene, naphthalene sulphonic acid, crown ether, 12-crown-4, 14-crown-4, organophosphorus compounds, Di-(2-ethylhexyl)phosphoric acid, mono-2-ethylhexyl phosphoric acid, phenylphosphonic acid, polymeric tracer such as chain end functionalized (co)polymers based on poly(N-vinyl pyrrolidone), poly(ethylene oxide), poly(styrene sulfonates), poly(vinyl acetate), poly(vinyl alcohol), nanoparticle and / or quantum dot. The at least one tracer may be a water, oil or gas tracer. The at least one tracer may be a solid, liquid or gas. The at least one tracer may be applied in solution. The at least one tracer may be in a semi-crystal line or crystalline form. The at least one tracer may be configured to be soluble and / or dissolve in water. The at least one tracer may comprise at least one reactive tracer. The at least one tracer may comprise at least one interactive tracer. The method may comprise injecting at least one reactive tracer. The method may comprise injecting at least one interactive tracer. The at least one reactive tracer may be configured to react and / or interact with lithium in the subterranean formation. The at least one interactive tracer may be configured to interact with lithium in the subterranean formation. The at least one reactive tracer may be configured to react with lithium in the subterranean formation. The at least one reactive tracer may be configured to react with lithium to form a lithiated tracer. The at least one reactive tracer may be configured to react with lithium to form a distinctive chemical product. The method may comprise measuring the concentration of reacted lithiated tracer or chemical product. The method may comprise measuring the concentration of unreacted non-lithiated tracer. The method may comprise estimating a concentration or amount of lithium based on the measured concentration of unreacted non-lithiated tracer and / or based on the measured concentration of reacted lithiated tracer or chemical product. The at least one reactive tracer may be sulphonic acid, naphthalene sulphonic acid, crown ethers, 12-crown-4, 14-crown-4, organophosphorus compounds, Di-(2-ethylhexyl)phosphoric acid, mono-2-ethylhexyl phosphoric acid or phenylphosphonic acid and / or their derivatives. The at least one reactive tracer and / or the at least one interactive tracer may be configured to react or interact with subterranean minerals and / or rocks. The at least one reactive tracer may be configured to react with subterranean minerals and / or rocks. The at least one interactive tracer may be configured to interact with subterranean minerals and / or rocks. The at least one reactive tracer and / or at least one interactive tracer may be configured to react or interact with lithium. The at least one reactive tracer may be configured to react with lithium. The at least one interactive tracer may be configured to react or interact with lithium. The at least one reactive tracer and / or at least one interactive tracer may be configured to react or interact with an ore of lithium. The at least one reactive tracer may be configured to react with an ore of lithium. The at least one interactive tracer may be configured to interact with an ore of lithium. The at least one interactive tracer may be configured to be attracted to or repelled by subterranean minerals and / or rocks. The at least one reactive tracer and / or at least one interactive tracer may be configured to be attracted to or repelled by subterranean lithium or lithium ore. The at least one reactive tracer and / or at least one interactive tracer may be configured to exhibit intermolecular forces of attraction or repulsion with subterranean minerals and / or rocks. The at least one reactive tracer and / or at least one interactive tracer may be configured to exhibit intermolecular forces of attraction or repulsion with lithium or lithium ore. The transport time of the at least one reactive tracer and / or at least one interactive tracer through the subterranean formation may be affected by the presence of the lithium or lithium ore in the subterranean formation. The method may comprise estimating an amount and / or surface area of lithium or lithium ore based on the transport time and / or arrival time of the at least one reactive tracer in the production well. The method may comprise estimating an amount and / or surface area of lithium or lithium ore based on the transport time and / or arrival time of the at least one interactive tracer in the production well. The affinity and / or specificity of the at least one tracer for lithium may be adjustable based on the structure or structural groups of the at least one tracer. The at least one interactive tracer may be a polymeric tracer. The polymeric tracer may be chain end functionalized (co)polymers based on poly (N-vinyl pyrrolidone), poly (ethylene oxide), poly (styrene sulfonates), poly (vinyl acetate) and / or poly (vinyl alcohol). The molecular weight of the polymeric tracer may be less than 20000MW. The molecular weight of the polymeric tracer may be less than 10000MW. The molecular weight of the polymeric tracer may be less than 5000MW. The polymeric tracer may comprise oligomers. The chain length of the oligomers may be selected or designed to select a preferred affinity and / or specificity for lithium. The at least one tracer may comprise a passive tracer. The method may comprise injecting at least one passive tracer. The at least one passive tracer may be a stable chemical tracer. The at least one passive tracer may be configured to be stable in subterranean formation conditions. The at least one passive tracer may be configured to be stable in geothermal reservoir and / or supercritical geothermal reservoir conditions. The at least one passive tracer may be configured to resist degradation and / or resist full degradation on exposure to a condition in the subterranean formation. The at least one passive tracer may be configured to behave as closely as possible to the traced fluid or phase. The at least one passive tracer may be configured to not be attracted to or repelled to lithium or subterranean minerals and / or rocks. The at least one passive tracer may be configured to resist reaction or degradation with lithium or subterranean minerals and / or rocks. The at least one passive tracer may be chemically, physically and / or biologically stable in subterranean formation and / or in the presence of lithium. The at least one passive tracer may be configured to exhibit no intermolecular forces of attraction or repulsion with lithium, subterranean minerals and / or rocks. The at least one passive or stable chemical tracer may be a thermally stable tracer and / or chemical stable tracer. The method may comprise injecting the at least one tracer and the at least one extraction fluid at the same time. The method may comprise injecting two or more tracers. The two or more tracers may comprise at least one passive tracer. The two or more tracers may comprise at least one reactive tracer. The two or more tracers may comprise at least one interactive tracer. The two or more tracers may comprise at least one passive tracer and at least one reactive tracer. The two or more tracers may comprise at least one passive tracer and at least one interactive tracer. The two or more tracers may comprise at least one passive tracer, at least one reactive tracer and / or at least one interactive tracer. The extraction fluid may be a liquid, a gas and / or a supercritical fluid. The extraction fluid may comprise water, wastewater, brine (saltwater), steam, acid, organic acid, a leaching fluid and / or water mixed with chemicals. The extraction fluid may be a lixiviant. The extraction fluid may be configured to extract lithium from its ore. The extraction fluid may be a geothermal fluid. The extraction fluid may be an injection fluid. The at least one tracer may be released or injected into the extraction fluid via a tracer injection device. The tracer release device may be controlled to selectively release at least one tracer into the injection well to allow characteristics of the flow of extraction fluid through the subterranean formation to be monitored. Flow measurement, flow paths and / or transport paths extraction fluid through the subterranean formation may be identified, calculated and / or monitored. The method may comprise comparing tracer concentrations signature of two or more tracers in the at least one sample with the tracer concentration signature of the two or more tracers injected into the subterranean formation or injection well. The method may comprise interpretating differences or changes between injected tracer concentrations signatures and produced tracer concentrations signatures to determine and / or monitor characteristics of the subterranean formation, the concentration of lithium in the reservoir, the location of lithium in the subterranean formation and / or the surface area of lithium in the subterranean formation. The method may comprise modelling the subterranean formation, extraction fluid type, injected tracer concentration, tracer type, injection location, transport time, injection flow rate, production location, temperature, tracer concentration in produced fluids, lithium concentration in produced fluids and / or production rates in a model. The parameters of the model may be adjusted until calculated concentrations of model tracers compare or substantially match with the measured concentrations of identified tracers to optimise and / or control the extraction operation. The model data may estimate flow of tracer and injected extraction fluid. The model may be used to optimise and / or control the flow of extraction fluid into, through and from the subterranean formation to improve the extraction of lithium. The model data may estimate a concentration of lithium in the reservoir, the location of high concentrations of lithium or lithium ores in the subterranean formation and / or the surface area of lithium in the subterranean formation. The model may comprise parameters selected from the group including: the number of injection wells, temperature, temperature of fluid at each injection well, temperature of fluid produced, number of production wells, temperature of fluid at each production well, transport time, transport time of tracer-containing fluid from injection to production for one or more injection wells, transport time of tracer-containing fluid from injection to production for one or more production wells, transport time of tracer-containing fluid through the reservoir, tracer type; tracer combination, extraction fluid type, extraction fluid composition, concentration of tracer, concentration of tracer as a function of time, fluid flow path from one or more injection well to one or more production wells in communication to the subterranean formation, injection rate, production rate, mixing capacity of cold injected fluid with hot fluid in the formation, heat equilibrium rate of the reservoir, rock mechanics, rock chemistry, gravity, density, viscosity; reservoir permeability, formation heterogeneities, solubility, fluid chemistry, porosity, fluid saturation, injection amount, injection volumes and / or migration path of the at least one tracer in and / or through the subterranean formation. Embodiments of the fifth aspect of the invention may include one or more features of the first to fourth aspects of the invention or their embodiments, or vice versa. According to a sixth aspect of the invention, there is provided a method of monitoring flow characteristics of an extraction fluid through a subterranean formation to extract lithium, the method comprising: injecting at least one extraction fluid into the subterranean formation; injecting at least one tracer into a subterranean formation; collecting samples of fluid produced from the subterranean formation; analysing the samples to detect the presence or absence of the at least one tracer; and based on measured tracer data monitoring at least one flow characteristic of the extraction fluid. The method may comprise monitoring at least one flow characteristic of the extraction fluid based on the presence and / or a concentration of the at least one tracer in the samples. The method may comprise measuring a concentration of the at least one tracer in the samples. The method may comprise tracing and / or mapping flow of at least one extraction fluid through the geothermal reservoir. The method may comprise using the at least one tracer to trace and / or map flow between at least one injection well and at least one production well. The method may comprise using the at least one tracer to determine which injection well is the source of fluid produced at a production well. The method may comprise using the at least one tracer to determine which production well is producing fluid injected in an injection well. The method may comprise tracing and / or mapping flow paths of high concentrations of lithium extraction. The method may comprise identifying the location of a breakthrough into a producing well. The method may comprise identifying, calculating and / or monitoring flow rates, flow paths and / or transport paths of the at least one tracer and / or at least one extraction fluid. The subterranean formation may be selected from the group comprising a geothermal reservoir, a supercritical geothermal reservoir, an enhanced geothermal system, an aquifer, a hydrocarbon reservoir; a well, a mining well, a mining reservoir, a water reservoir and / or a shale reservoir. Embodiments of the sixth aspect of the invention may include one or more features of the first to fifth aspects of the invention or their embodiments, or vice versa. According to a seventh aspect of the invention, there is provided a method of estimating an amount of lithium in a subterranean formation, the method comprising: injecting at least one extraction fluid into the subterranean formation injecting at least one tracer into a subterranean formation; collecting samples of fluid produced from the subterranean formation; analysing the samples to detect the presence or absence of the at least one tracer; and based on measured tracer data estimating an amount of a target material in the subterranean formation. The method may comprise estimating an amount of a target material in the subterranean formation based on concentration of the at least one tracer in the samples. The method may comprise measuring a concentration of the at least one tracer in the samples. The method may comprise injecting at least one tracer into a well in fluid communication with the subterranean formation and collecting or taking the samples from the same well and / or at least one different well. The method may comprise injecting two or more distinct tracers into a well in fluid communication with the subterranean formation and collecting or taking the samples from the same well and / or at least one different well. The at least one tracer may comprise a passive tracer. The method may comprise injecting at least one passive tracer. The at least one passive tracer may be configured to exhibit no intermolecular forces of attraction or repulsion with lithium, subterranean minerals and / or rocks. The at least one passive tracer may be configured to behave as closely as possible to the traced fluid or phase. The at least one tracer may comprise a reactive tracer. The method may comprise injecting at least one reactive tracer. The at least one tracer may comprise an interactive tracer. The method may comprise injecting at least one interactive tracer. The at least one reactive tracer and / or at least one interactive tracer may be configured to react and / or interact with lithium in the subterranean formation. The at least one reactive tracer may be configured to react with lithium in the subterranean formation. The at least one interactive tracer may be configured to interact with lithium in the subterranean formation. The at least one reactive tracer may be configured to react with lithium to form a lithiated tracer. The method may comprise measuring the concentration of reacted lithiated tracer or chemical product. The method may comprise measuring the concentration of unreacted non-lithiated tracer. The method may comprise estimating a concentration or amount of lithium based on the measured concentration of unreacted non-lithiated tracer and / or based on the measured concentration of reacted lithiated tracer or chemical product. The at least one reactive tracer and / or at least one interactive tracer may be configured to react or interact with subterranean minerals and / or rocks. The at least one reactive tracer may be configured to react with subterranean minerals and / or rocks. The at least one interactive tracer may be configured to interact with subterranean minerals and / or rocks. The at least one reactive tracer may be configured to react with lithium and / or a lithium ore. The at least one interactive tracer may be configured to interact with lithium and / or a lithium ore. The at least one reactive tracer may be configured to be attracted to or repelled by subterranean minerals and / or rocks. The at least one interactive tracer may be configured to be attracted to or repelled by subterranean minerals and / or rocks. The at least one reactive tracer may be configured to be attracted to or repelled by subterranean lithium or lithium ore. The at least one interactive tracer may be configured to be attracted to or repelled by subterranean lithium or lithium ore. The at least one reactive tracer may be configured to exhibit intermolecular forces of attraction or repulsion with subterranean minerals and / or rocks. The at least one interactive tracer may be configured to exhibit intermolecular forces of attraction or repulsion with subterranean minerals and / or rocks. The at least one reactive tracer may be configured to exhibit intermolecular forces of attraction or repulsion with lithium or lithium ore. The at least one interactive tracer may be configured to exhibit intermolecular forces of attraction or repulsion with lithium or lithium ore. The transport time of the at least one reactive tracer and / or at least one interactive tracer through the subterranean formation may be affected by the presence of the lithium or lithium ore in the subterranean formation. The method may comprise comparing the arrival time of a passive tracer and the reactive tracer to assess a delayed arrival time of the reactive tracer. The method may comprise comparing the arrival time of a passive tracer and the interactive tracer to assess a delayed arrival time of the interactive tracer. The method may comprise estimating an amount and / or surface area of lithium or lithium ore based on the transport time and / or arrival time of the at least one reactive tracer in at least one well. The at least one well may be a production well. The method may comprise estimating an amount and / or surface area of lithium or lithium ore based on the transport time and / or arrival time of the at least one interactive tracer in the production well. The method may comprise analysing the at least one sample to measure the presence and / or concentration of the two or more tracers in the sample. The method may comprise analysing the at least one sample for type and / or concentration of the two or more tracers as a function of sampling time. The method may comprise measuring or calculating an arrival time of the at least one tracer. The method may comprise measuring or calculating an arrival time of the at least one tracer in at least one well. The method may comprise measuring or calculating an arrival time of the at least one tracer in at least one well. The at least one well may be a production well. The method may comprise measuring a ratio of reacted and unreacted tracer. The subterranean formation may be selected from the group comprising a geothermal reservoir, a supercritical geothermal reservoir, an enhanced geothermal system, an aquifer, a hydrocarbon reservoir; a well, a mining well, a mining reservoir, a water reservoir and / or a shale reservoir. Embodiments of the seventh aspect of the invention may include one or more features of the first to sixth aspects of the invention or their embodiments, or vice versa. According to an eighth aspect of the invention, there is provided a method for monitoring the efficiency of an extraction fluid for extracting lithium from a subterranean formation, the method comprising: injecting at least one extraction fluid into at least part of the subterranean formation; injecting at least one tracer into at least part of the subterranean formation; collecting samples of fluid produced from the subterranean formation; analysing the samples to detect the presence or absence of the at least one tracer; and based on the measured tracer data monitoring the efficiency of the extraction operation and / or extraction fluid. The method may comprise monitoring the efficiency of the extraction operation and / or extraction fluid based on concentration of the at least one tracer in the samples. The method may comprise measuring a concentration of the at least one tracer in the samples. The method may comprise injecting at least one tracer into a well in fluid communication with the subterranean formation and collecting or taking the samples from the same well and / or at least one different well. The method may comprise back producing fluid in the injection well. The method may comprise injecting two or more distinct tracers into a well in fluid communication with the subterranean formation and collecting or taking the samples from the same well and / or at least one different well. The at least one tracer may comprise a passive tracer. The method may comprise injecting at least one passive tracer. The at least one passive tracer may be chemically, physically and / or biologically stable in subterranean formation and / or in the presence of lithium. The at least one passive tracer may be configured to exhibit no intermolecular forces of attraction or repulsion with lithium, subterranean minerals and / or rocks. The at least one passive tracer may be configured to behave as closely as possible to the traced fluid or phase. The at least one tracer may comprise a reactive tracer. The method may comprise injecting at least one reactive tracer. The at least one tracer may comprise an interactive tracer. The method may comprise injecting at least one interactive tracer. The at least one reactive tracer and / or at least one interactive tracer may be configured to react and / or interact with lithium in the subterranean formation. The at least one interactive tracer may be configured to interact with lithium in the subterranean formation. The at least one reactive tracer may be configured to react with lithium in the subterranean formation. The at least one reactive tracer may be configured to react with lithium to form a lithiated tracer. The at least one reactive tracer may be configured to react with lithium to form a distinctive chemical product. The method may comprise measuring the concentration of reacted lithiated tracer or chemical product. The method may comprise measuring the concentration of unreacted non-lithiated tracer. The method may comprise estimating a concentration of lithium, an amount of lithium, a surface area of lithium and / or a position of lithium based on the measured concentration of unreacted reactive (non-lithiated) tracer and / or based on the measured concentration of reacted lithiated tracer or chemical product. The at least one reactive tracer and / or the at least one interactive tracer may be configured to react or interact with subterranean minerals and / or rocks. The at least one reactive tracer may be configured to react with subterranean minerals and / or rocks. The at least one interactive tracer may be configured to interact with subterranean minerals and / or rocks. The at least one reactive tracer and / or at least one interactive tracer may be configured to react or interact with lithium or a lithium ore. The at least one reactive tracer may be configured to react with lithium or a lithium ore. The at least one interactive tracer may be configured to interact with lithium or a lithium ore. The at least one reactive tracer may be configured to be attracted to or repelled by subterranean minerals and / or rocks. The at least one interactive tracer may be configured to be attracted to or repelled by subterranean minerals and / or rocks. The at least one reactive tracer may be configured to be attracted to or repelled by subterranean lithium or lithium ore. The at least one interactive tracer may be configured to be attracted to or repelled by subterranean lithium or lithium ore. The at least one reactive tracer may be configured to exhibit intermolecular forces of attraction or repulsion with lithium or lithium ore. The at least one interactive tracer may be configured to exhibit intermolecular forces of attraction or repulsion with lithium or lithium ore. The transport time of the at least one reactive tracer and / or at least one interactive tracer from or through at least a part of the subterranean formation may be affected by the presence of the lithium or lithium ore in the subterranean formation. The method may comprise comparing the arrival time of a passive tracer and the reactive tracer to assess a delayed arrival time of the reactive tracer. The method may comprise comparing the arrival time of a passive tracer and the interactive tracer to assess a delayed arrival time of the interactive tracer. The method may comprise estimating a concentration of lithium, an amount of lithium, a surface area of lithium and / or a position of lithium based on the transport time and / or arrival time of the at least one reactive tracer in the samples. The method may comprise estimating a concentration of lithium, an amount of lithium, a surface area of lithium and / or a position of lithium based on the transport time and / or arrival time of the at least one interactive tracer in the samples. The at least one interactive tracer may be configured to exhibit intermolecular forces of attraction or repulsion with lithium and estimating a concentration of lithium, an amount of lithium, a surface area of lithium and / or a position of lithium based on the transport time and / or arrival time of the at least one interactive tracer in at least one well. The at least one well may be a fluid produced from an injection well. The at least one well may be a production well. The method may comprise analysing the at least one sample to measure the presence and / or concentration of the two or more tracers in the sample. The method may comprise analysing the at least one sample for type and / or concentration of the two or more tracers as a function of sampling time. The method may comprise measuring an arrival time of the at least one tracer. The method may comprise measuring a ratio of reacted and unreacted tracer. The method may comprise injecting two or more different extraction fluids each with at least one distinct tracer into the subterranean formation. The method may comprise measuring a concentration of the at least one tracer, the at least one reactive tracer, the at least one interactive tracer, the at least one passive tracer and / or lithium in the produced fluids for each of different extraction fluid types. The method may comprise measuring or detecting a variation in the concentration of the at least one tracer, the at least one reactive tracer, the at least one interactive tracer, the at least one passive tracer and / or lithium in the produced fluids for each extraction fluid type. The extraction fluid type may be identified based on the tracer type in the produced fluid. The method may comprise using passive tracer data may also be used to assess the amount of injected extraction fluid which is produced in the well. The method may comprise injecting a first extraction fluid with at least one tracer into the subterranean formation. The method may comprise injecting a first extraction fluid with at least one reactive tracer and at least one passive tracer into the subterranean formation. The method may comprise injecting a first extraction fluid with at least one interactive tracer and at least one passive tracer into the subterranean formation. The method may comprise injecting a second or further extraction fluid with at least one distinct tracer into the subterranean formation. The method may comprise injecting a second or further extraction fluid with at least one distinct reactive tracer and at least one distinct passive tracer into the subterranean formation. The method may comprise injecting a second or further extraction fluid with at least one distinct interactive tracer and at least one distinct passive tracer into the subterranean formation. The method may comprise determining a ratio reacted to unreacted reactive tracer. The method may comprise comparing the passive tracer concentration data with the reactive tracer concentration data. The method may comprise comparing the passive tracer concentration data with the interactive tracer concentration data. The method may comprise comparing the passive tracer concentration data with the reactive tracer concentration data to distinguish between dilution effects and mineral reactions. The method may comprise comparing the passive tracer concentration data with the interactive tracer concentration data to distinguish between dilution effects and mineral reactions. The method may comprise comparing the arrival time of the passive tracer data with the arrival time of reactive tracer data. The method may comprise comparing the arrival time of the passive tracer data with the arrival time of interactive tracer data. The method may comprise assessing the extraction efficiency of each extraction fluid compositions and / or optimise an extraction fluid composition. The subterranean formation may be selected from the group comprising a geothermal reservoir, a supercritical geothermal reservoir, an enhanced geothermal system, an aquifer, a hydrocarbon reservoir; a well, a mining well, a mining reservoir, a water reservoir and / or a shale reservoir. Embodiments of the eighth aspect of the invention may include one or more features of the first to seventh aspects of the invention or their embodiments, or vice versa. According to a ninth aspect of the invention, there is provided a system for monitoring the extraction of a target material from a subterranean formation comprising: a tracer release device configured to release at least one tracer into an injection well; at least one pump configured to pump an extraction fluid and the at least tracer into at least a portion of the formation; and a sampling system configured to sample fluid produced from the formation. The at least one pump may be configured to inject the extraction fluid and the at least tracer into at least a portion of the subterranean formation. The sampling system may be configured to collect samples of fluid produced from the subterranean formation. The tracer release device may be configured to release two or more tracers into the injection well. The two or more tracers comprise at least one reactive tracer and at least one passive tracer. The two or more tracers comprise at least one interactive tracer and at least one passive tracer. The at least one reactive tracer may be configured to react in the presence of the target material under reservoir conditions. The at least one interactive tracer may be configured to interact in the presence of the target material under reservoir conditions. The system may comprise at least one tracer analyser device configured to detect the concentration of the two or more tracers in fluid produced from the reservoir. The sampling system may comprise a collection device. The sampling system may comprise a sampler device. The collection device or sampler device may be configured for downhole sampling of produced fluid. The collection device or sampler device may be configured for sampling of produced fluid at surface. The sampling system may comprise at least one probe. The at least one probe may be configured to detect the concentration of the at least one tracer in fluid produced from the subterranean formation. The at least one probe may be configured to detect the concentration of the target material in fluid produced from the subterranean formation. The at least one probe may be a sample collection probe, a detector probe and / or a real time detector probe. The system may comprise a tracer analyser for analysing presence, type and / or concentration of the at least one tracer. The at least one probe may be configured to measure a concentration of the target material in the produced fluids. The system may comprise a processor. The processor may be configured to compare a tracer concentration of the injected at least one tracer with a tracer concentration of the at least one tracer in a produced fluid sample. The processor may be configured to determine and / or monitor a characteristic of the extraction, an amount of target material and / or a surface area of target material in the subterranean formation based on the presence and / or concentration of the at least one tracer in the samples. Embodiments of the ninth aspect of the invention may include one or more features of the first to eighth aspects of the invention or their embodiments, or vice versa. According to a tenth aspect of the invention, there is provided a system for monitoring the extraction of lithium from a subterranean formation comprising: a tracer release device configured to release at least one tracer into an injection well; at least one pump configured to pump an extraction fluid and the at least tracer into at least a portion of the subterranean formation; and a sampling system configured to sample fluid produced from the subterranean formation. The tracer release device may be configured to release two or more tracers into the injection well. The two or more tracers comprise at least one reactive tracer and at least one passive tracer. The two or more tracers comprise at least one interactive tracer and at least one passive tracer. The at least one reactive tracer may be configured to react in the presence of lithium under subterranean formation conditions. The at least one interactive tracer may be configured to interact in the presence of lithium under subterranean formation conditions. The sampling system may comprise at least one tracer analyser device configured to detect the concentration of the at least one tracer in fluid produced from the subterranean formation. The system may comprise at least one probe. The at least one probe may be configured to detect the concentration of the at least one tracer in fluid produced from the subterranean formation. The at least one probe may be configured to detect the concentration of lithium in fluid produced from the subterranean formation. The at least one probe may be a sample collection probe, a detector probe and / or a real time detector probe. The system may comprise a tracer analyser for analysing presence, type and / or concentration of the at least one tracer. The at least one probe may be configured to measure a concentration of lithium in the produced fluids. The system may comprise a processor. The processor may be a computer processor. The processor may be configured to compare a tracer concentration of the injected at least one tracer with a tracer concentration of the at least one tracer in a produced fluid sample. The processor may be configured to determine and / or monitor a characteristic of the extraction of lithium, an amount of lithium and / or a surface area of lithium in the subterranean formation based on the presence and / or concentration of the at least one tracer in the samples. The subterranean formation may be selected from the group comprising a geothermal reservoir, a supercritical geothermal reservoir, an enhanced geothermal system, a hydrocarbon reservoir; a well, an aquifer, a mining well, a mining reservoir, a water reservoir and / or a shale reservoir. Embodiments of the tenth aspect of the invention may include one or more features of the first to ninth aspects of the invention or their embodiments, or vice versa. According to an eleventh aspect of the invention, there is provided a method of collecting samples for analysis in monitoring the extraction of a target material from a subterranean formation, wherein the subterranean formation at least one tracer injected into the subterranean formation with an extraction fluid; producing fluid from the reservoir; and collecting at least one sample from the produced fluid. The subterranean formation may comprise two or more tracers injected into the subterranean formation with at least one extraction fluid. The two or more tracers may comprise at least one reactive tracer and at least one passive tracer. The two or more tracers may comprise at least one interactive tracer and at least one passive tracer. The subterranean formation may comprise two or more tracers injected into the subterranean formation with two or more extraction fluids. The at least one reactive tracer may be configured or selected to react with the target material. The at least one interactive tracer may be configured or selected to interact with the target material. Embodiments of the eleventh aspect of the invention may include one or more features of the first to tenth aspects of the invention or their embodiments, or vice versa. According to a twelfth aspect of the invention, there is provided an interpretation method for an extraction operation of a target material from a subterranean formation comprising; providing tracer data from a producing well after at least one stage of an extraction operation; wherein the at least one tracer was introduced into a well in fluid connection with the subterranean formation; and analysing the tracer data to estimate at least one characteristic of the extraction. The method may comprise estimating at least one characteristic of the extraction operation based on the presence and / or concentration of the at least one tracer. The tracer data may comprise tracer concentrations over time of at least one tracer in the production flow. The method may comprise estimating at least one flow path of the extraction fluid. The method may comprise identifying a producing well of the injected extraction fluid. The method may comprise estimating an amount of a target material in the subterranean formation. The method may comprise estimating at least one location of an ore of a target material in the subterranean formation. Embodiments of the twelfth aspect of the invention may include one or more features of the first to eleventh aspects of the invention or their embodiments, or vice versa. According to a thirteenth aspect of the invention, there is provided an interpretation method for an extraction operation of lithium from a subterranean formation comprising; providing tracer data from a producing well after at least one stage of a lithium extraction operation; wherein the at least one tracer was introduced into a well in fluid connection with the subterranean formation; and analysing the tracer data to estimate at least one characteristic of the lithium extraction. The method may comprise estimating at least one characteristic of the extraction operation based on the presence and / or concentration of the at least one tracer. The tracer data may comprise tracer concentrations over time of at least one tracer in the production flow. The method may comprise estimating at least one flow path of the extraction fluid. The method may comprise identifying a producing well of the injected extraction fluid. The method may comprise estimating an amount of lithium in the subterranean formation . The method may comprise estimating at least one location of lithium ore in the subterranean formation. The subterranean formation may be selected from the group comprising a geothermal reservoir, a supercritical geothermal reservoir, an enhanced geothermal system, a hydrocarbon reservoir; a well, an aquifer, a mining well, a mining reservoir, a water reservoir and / or a shale reservoir. Embodiments of the thirteenth aspect of the invention may include one or more features of the first to twelfth aspects of the invention or their embodiments, or vice versa. According to a fourteenth aspect of the invention, there is provided a method of collecting samples for analysis in monitoring the extraction of lithium from a subterranean formation, wherein the subterranean formation comprises at least one tracer injected into the subterranean formation with at least one extraction fluid; producing fluid from the subterranean formation; and collecting at least one sample from the produced fluid. The subterranean formation may comprise two or more tracers injected into the subterranean formation with at least one extraction fluid. The two or more tracers comprise at least one reactive tracer and at least one passive tracer. The two or more tracers comprise at least one interactive tracer and at least one passive tracer. The subterranean formation may comprise two or more tracers injected into the subterranean formation with two or more extraction fluids. The at least one reactive tracer may be configured or selected to react with the lithium. The at least one interactive tracer may be configured or selected to interact with the lithium. The subterranean formation may be selected from the group comprising a geothermal reservoir, a supercritical geothermal reservoir, a hydrocarbon reservoir; an enhanced geothermal system, a well, an aquifer, a mining well, a mining reservoir, a water reservoir and / or a shale reservoir. Embodiments of the fourteenth aspect of the invention may include one or more features of the first to thirteenth aspects of the invention or their embodiments, or vice versa. Brief description of the drawings There will now be described, by way of example only, various embodiments of the invention with reference to the drawings, of which: Figure 1 is a simplified section of a geothermal reservoir system with one injection well and one production well showing a lithium recovery method in accordance with an aspect of the invention; Figure 2 is a simplified section of a geothermal reservoir system with two possible injection wells and three possible production wells showing a lithium recovery method in accordance with an aspect of the invention; Figures 3A and 3B are a simplified sections of different reservoirs comprising lithium ores of different surface areas respectively, each showing a lithium recovery method in accordance with an aspect of the invention; Figures 4A and 4B are tracer curves of concentrations over time of tracers measured in the production wells of the systems shown in Figures 3A and 3B respectively; Figure 5A is a simplified section of a geothermal reservoir system with one injection well and one production well where three passive tracers and three lithium reactive tracers are injected in accordance with an aspect of the invention; Figure 5B is a tracer curve of concentration over time of the six tracers measured in the production wells of the systems shown in Figure 5A; Figure 6 is a flow chart showing steps for creating and optimising a model to estimate characteristics of a subterranean target material in accordance with an aspect of the invention; Figure 7 is a simplified section of a geothermal reservoir system with one injection well and one production well and a reactive tracer configured to be lithiated in the presence of lithium in accordance with an aspect of the invention; Figure 8 is a simplified section of a partial geothermal reservoir system showing a pull and push tracer test of an injection well in accordance with an aspect of the invention, other sections of the geothermal system are not shown for clarity; and Figure 9 is a simplified section of a geothermal reservoir system with two injection wells and one production well and shows a method of estimating a location of a high concentration of lithium in accordance with an aspect of the invention. Detailed description of preferred embodiments Figure 1 is a simplified section of a subterranean formation 10 showing the recovery of a target material. In this example the target material is lithium and the method is designed to extract lithium present in subterranean rock or subterranean fluids. In this example an injection well 14 is drilled which is in fluid communication with a reservoir 13 comprising a large surface area of lithium 12 which in this example is in the form of an ore. For clarity only one area of lithium is shown in the Figure 1. It will be appreciated that lithium may be present in multiple areas in the formation. A fluid 16 in this example a brine solution of NaCI is injected into the injection well with a passive tracer 18 which in this example is a fluorobenzoate. The brine solution reacts with lithium to form soluble lithium chloride. The soluble lithium chloride 20 is carried with the fluid flow and passive tracer to a producer well 22. The fluid 16, soluble lithium chloride 20 and tracer 18 are pumped to surface where the tracer is detected to confirm it is the same fluid 18 which is pumped into the injector well 14. The lithium may be extracted from the extraction fluid at surface. Typically there is more than one injection well and more than one production well. Fluids can pass through a network of fractures and flow paths underground. It is important to understand which injector wells are in fluid communication with producer wells which contain high levels of lithium in order to optimise the extraction of lithium. It is also important to assess whether low concentrations of lithium in a producer well are due to depleted lithium levels in the reservoir, inefficient extraction processes, inefficient extraction fluids or poor connectivity between an injection well and production well. The concentration of lithium in the produced fluid may be affected by dilution and mixing of water or fluids from different sources. By monitoring the flow of injected tracer it may be possible to distinguish and / or compensate for these effects. The method may facilitate the use of tracers to distinguish between dilution effects and lithium extraction inefficiencies. Figure 2 shows a subsurface geothermal reservoir system 100 which contains a large surface area of lithium 112. In this example the system has two injector wells 114a and 114b. The well system also has three producer wells 122a, 122b and 122c. As can be seen in Figure 2, injector well 114b and producer wells 122a and 122c are in fluid communication with the geothermal reservoir 113. A first tracer 130 is injected into injector well 114a with a first brine solution (extraction fluid) 140. A second tracer 132 is injected into injector well 114b with a second brine solution (extraction fluid) 142. In this example both the first tracer 130 and second tracer 132 are passive tracers designed to follow the flow of injected fluids. After the injections into injector wells 114a and 114b samples are collected from fluids produced in the producer wells at known sampling times. In this example high concentrations of lithium are detected in producer 122a, low concentrations of lithium are detected in producer well 122c and negligible concentrations of lithium are detected in producer well 122b. First tracer 130 is not detected in any of producer wells 122a, 122b or 122c indicating that the injected brine solution (extraction fluid) in injector well 114a is following a different flow path in the subsurface and is not produced in any of producer wells 122a, 122b or 122c. The second tracer 132 was also not detected in producer well 122b indicating that producer well 122b is not in fluid communication with the injector well 114b. A high concentration of second tracer 132 is detected in producer 122a and low concentrations of second tracer 132 is detected in producer well 122c. The arrival time of the second tracer 132 in production well 122a is faster than in producer well 122c. This indicates a primary fluid flow path from injector well 114b to producer well 122a via the reservoir. The high concentration of lithium in producer well 122a indicates that a high surface area of lithium is present in this primary flow path which carries a high concentration of released lithium with the flow to producer well 122a. The results also indicates that a secondary fluid flow path is present from injector well 114b through a portion of the reservoir to producer well 122c where a low concentration of lithium is detected at a longer tracer arrival time than producer well 122a. This indicates that fluid flow in the secondary fluid flow path has less contact time with a surface area of lithium and follows a convoluted path to the production well 122c. Using this knowledge lithium recovery via injector well 114a and producer well 122b may be abandoned. The main focus of lithium recovery may be directed to injector well 114b and producer well 122a. Figure 3A and 3B show two different subsurface geothermal reservoir systems 200 and 250 respectively, each containing lithium 212, 262 of different amounts and surface areas. In each example shown in Figures 3A and 3B the system 200, 250 has one injector well 214, 214a and one producer well 222, 222a. As can be seen in Figures 3A and 3B each of the injector wells 214, 214a and producer wells 222, 222a are in fluid communication with the geothermal reservoir 213, 213a. In this example two tracers 230 and 232 are injected into the injection well 214, 214a with an extraction fluid 216 which in this example is a brine solution. The first tracer 230 is a passive tracer, selected to not interact or react with lithium, rocks or minerals present in the flow path through the geothermal system. In this example the passive tracer is a fluorobenzoate. It will be appreciated that other types of passive tracer may be used. The second tracer 232 is an interactive tracer designed to exhibit intermolecular forces of attraction with the subterranean lithium. By monitoring the relative transport times of the interactive second tracer 232 compared with the passive first tracer 230 information on the amount and / or surface area of lithium in the reservoir may be obtained. In this example the interactive tracer is a polymeric tracer such as chain end functionalized (co)polymers based on poly(ethylene oxide). The interactive polymeric tracer has a chain length selected to optimise the degree of intermolecular forces of attraction with the subterranean lithium. It will be appreciated that other types of interactive tracer may be used. The chain length of the interactive polymeric tracer is adjustable to change or tune the degree of affinity and / or specificity to the target type and / or reservoir conditions to exhibit optimal attraction with the subterranean lithium. The affinity should be selected to enable attraction and delayed transport of the interactive tracer through the reservoir in proportion to the amount and / or surface area of lithium. However, the affinity should not be too high to prevent transport of the interactive tracer through the reservoir to the production well. Figures 4A and 4B are corresponding tracer curves 270 and 280 as a function of time of produced tracers in the producer wells 222, 222a corresponding to tracers 230 (first tracer) and 232 (second tracer) injected into the geothermal reservoirs shown in Figures 3A and 3B respectively. In Figure 3A and 4A the passive tracer 230 (first tracer) passes through the reservoir without interacting with the lithium 212 and arrives in the producer wells 214. In contrast some of the interactive polymeric tracer 232 (second tracer) interacts with the lithium 212 resulting in a slight delay in arrival at the producer well 222, this is seen as a slight offset in the tracer response curve in Figure 4A. Figure 4B shows the tracer curve for the passive tracer 230 (first tracer) is similar to the passive tracer curve in Figure 4A as it passes through the reservoir 213a without interacting with the lithium 212a. However, the interactive polymeric tracer 232 (second tracer) interacts with the significantly larger surface area of lithium 212a in the reservoir 213a in Figure 3B. A larger delay of the interactive tracer 232 is observed as it interacts with the lithium 212a as the tracer 232 passes and is attracted to the larger amount of the lithium. The arrival of tracer 232 in the production well 222a is delayed and interactive tracer 232 is produced in the production well 222a over a longer period. As shown in Figure 4B the arrival of the interactive tracer 232 (second tracer) is significantly delayed and the curve is flattened as tracer gradually arrives in the producer over a longer time period. Analysis of the tracer curves may provide information and characteristics of the subterranean lithium in the reservoir such as the amount of lithium and / or the surface area of the lithium. Figure 5A shows an example subsurface geothermal reservoir system 300 containing a target material, in this example lithium 312. The system 300 has one injector well 314 and one producer well 322 which are in fluid communication with the geothermal reservoir 313. In this example three different passive tracers 330 (tracer A), 334 (tracer B) and 336 (tracer F) are injected into the injection well. The passive tracers 330, 334 and 336 are designed not to interact or react with the lithium, rocks or minerals present in the flow path of the geothermal system. In this example the passive tracers are distinct fluorobenzoates. It will be appreciated that other types of passive tracer may be used. Three interactive polymeric tracers 332 (tracer C), 335 (tracer D) and 337 (tracer E) are injected into the injection well. In this example the interactive tracers are polymer tracers with chain end functionalized (co)polymers based on poly(ethylene oxide). Each of the interactive polymeric tracers have a different chain length which affects the degree of affinity to the target material. Tracer 332 (tracer C) has a short chain length, tracer 335 (tracer D) has a medium chain length and tracer 337 (tracer E) has a long chain length. All of the passive and interactive tracers were injected at the same time in the same injection well 314 and samples were taken at known sampling times in the production well 322. By monitoring the relative transport times of the interactive tracers 332, 335 and 337 compared with the passive tracers 330, 334 and 336 information may be obtained on the amount and / or surface area of lithium in the reservoir. Figure 5B shows a corresponding tracer curve 350 of tracer concentrations of the produced tracers in the production well versus sample number. As shown in Figure 5B, passive tracers 330 (tracer A), 334 (tracer B) and 336 (tracer F) arrive in the production well first as they do not interact with the lithium and pass unhindered to the production well. Tracer 332 (tracer C) although being designed as an interactive tracer does not interact with the lithium and behaves as a passive tracer arriving in the producer with a similar arrival time as the passive tracers. This indicates that the affinity of the short chain length polymeric tracer to the lithium in the reservoir conditions was not sufficient to attract the tracer to the lithium and delay its transport through the reservoir. In contrast the medium chain length interactive tracer 335 (tracer D) and long chain length interactive tracer 337 (tracer E) have sufficient affinity to the lithium under reservoir conditions to delay the arrival of these tracers to the production well. However, the level of affinity of both tracers 335 and 337 allowed both to successfully pass through the reservoir. By modelling the transport times of the interactive tracers 332, 335 and 337 and the passive tracers 330, 334 and 336 the amount and / or surface area of lithium in the reservoir may be estimated. Figure 6 provides a flowchart of a process 500 to determine characteristics of lithium in a well or formation. In step 510 a series of experiments are conducted to test tracer responses to different subterranean lithium characteristics such as concentration, amount, surface area, position and / or different reservoir conditions. The experimental data is used to generate a library of tracer responses associated with the conditions or characteristics of the reservoir and / or lithium in the reservoir (Step 512). In this example the parameters tested may be selected from the group comprising tracer type, polymeric tracer chain length, temperature, pressure, fluid type, wetting, rock composition, injection time, injection location, production location, flow rate, arrival time, lithium surface area, lithium amount and / or lithium concentration. Measured tracer data from tracer tests conducted in the field is collected in step 520 and the measured data is compared with the library of tracer responses in step 522. Characteristics or conditions of the lithium in the reservoir may be determined or estimated (step 524) based on the measured tracer data in the production well compared to the library tracer response data. Optionally as shown in dotted box 530 if there is any deviation (step 532) between the library tracer data and observed tracer data, the observed tracer data may be used to optimize or update the library (step 534). Figure 7 is a simplified section of a subterranean formation 600 for recovery of target material. In this example the target material is lithium and the subterranean formation is a geothermal reservoir. In this example the geothermal reservoir system 600 has one injector well 614 and one producer well 622 in fluid communication with the geothermal reservoir 613. In this example two tracers 630 and 632 are injected into the injection well 614 with an extraction solution 616. The first tracer 630 is a passive tracer, selected to not interact or react with the lithium, rocks or minerals present in the flow path of the geothermal system. In this example the passive tracer is a fluorobenzoate . It will be appreciated that other types of passive tracer may be used. The second tracer 632 is a reactive tracer, in this example a sulphonate based tracer, which is configured to react with lithium to form a lithiated tracer compound. The sulphonate group reacts with the lithium as shown in Equation 1. Equation 1 By analysing the levels of lithiated tracer molecules to non-lithiated tracer molecules produced in the production well information may be inferred about the concentration of lithium present in the reservoir, a position of lithium in the reservoir and / or surface area of lithium. The amount of passive tracer injected and produced may be analysed as a reference for determining the percentage of injected tracer which is produced and assess dilution of the injected fluids. Figure 8 is a simplified section of a partial geothermal reservoir 700. As this test only concerns a pull and push tracer test of an injection well other sections of the geothermal reservoir are not shown for clarity. In this example an injection well 714 is in fluid communication with the reservoir 713 via fractures 740. A passive tracer 730 and a reactive tracer 732 is injected with a first extraction fluid type into the reservoir 713 via the injection well 714 and fractures 740. The first fluid type is a fluid designed to extract lithium from the reservoir. The passive tracer in this example a fluorobenzoate tracer is selected to not interact or react with the lithium ore, rocks or minerals present in the flow path of the geothermal system. In this example, the reactive tracer is a sulphonate tracer which is designed to react with lithium to form a lithiated tracer as shown in Equation 1. After a known period of time, the fluid injected into the reservoir is back-produced into the injection well 714. The back produced levels of passive tracer, lithiated reactive tracer molecules, non-lithiated reactive tracer molecules and optionally lithium concentrations are measured in the back produced fluids in the well. Analysing the concentrations of passive tracer, lithiated reactive tracer, non-lithiated reactive tracer molecules and optionally lithium concentrations in the back produced fluid may facilitate the efficiency of the extraction fluid to be assessed. The amount of injected passive tracer can be compared with the back-produced passive tracer amounts to determine the amount of injected extraction fluid recovered and / or to assess dilution effects. The ratio of injected reactive tracer can be compared with the lithiated reactive tracer and non-lithiated reactive concentrations to determine the amount of lithium present in the reservoir section. This may be compared to the concentration of lithium in the back-produced extraction fluid to assess the efficiency of the extraction fluid. The test may also be used to determine if lithium is present near the injection well in the reservoir. The tracer test can be repeated using different extraction fluid compositions and the tracer data may be used to assess the extraction efficiency of each extraction fluid composition and / or to optimise an extraction fluid composition. Figure 9 is a simplified section of a geothermal reservoir system 800. In this example two injection wells 814a and 814b are in fluid communication with a reservoir 813. A passive tracer 830 and a reactive tracer 834 is injected into injection well 814a with an extraction fluid 835. A passive tracer 832 and a reactive tracer 836 is injected into injection well 814b with an extraction fluid 835. The extraction fluid type is designed to extract lithium 812 from the reservoir 813. The passive tracers 830, 832 in this example are fluorobenzoate type tracers and are distinct from one another. They are selected to not interact or react with the lithium, rocks or minerals present in the flow paths in the geothermal system. The reactive tracers 834, 836, in this example are both sulphonate type tracers and are distinct from one another. The reactive tracers 834, 836 are selected to react with lithium to form a lithiated tracer 834a, 836a respectively as shown in Equation 1. The produced fluids from the production well are measured and the concentrations of passive tracers 830, 832, lithiated reactive tracers 834a, 836a, non-lithiated reactive tracers 834, 836 and optionally lithium concentrations are measured in the produced fluids. In this example a high concentration of lithiated tracer 834a was observed compared with a lower concentration of lithiated tracer 836a. This indicates that the flow path between injection well 814a and the production well 822 has a higher concentration of lithium and / or a higher lithium surface area than the flow path between injection well 814b and the production well 822. This indicates that a higher concentration of lithium and / or a higher lithium surface area may be close to the injection well 814a. This may be confirmed by conducting a pull and push tracer test as discussed in relation to Figure 8 at injection well 814a. Additionally and / or alternatively pull and push tracer tests may also be performed at injection well 814b and / or the production well to confirm the location of the high concentration of lithium. In the above examples the target material is lithium and the subterranean formation is a geothermal reservoir. However, it will be appreciated that other target materials may be extracted. It will also be appreciated that target materials such as lithium may be extracted from other types of subterranean formation. Tracers may be used to monitor and optimise the extraction as discussed in the above examples. The invention provides a method of monitoring and / or optimising the extraction of a target material such as target mineral and / or target metal from a subterranean formation. The method may comprise injecting at least one extraction fluid into the subterranean formation, injecting at least one tracer into the subterranean formation and collecting samples of fluid produced from the subterranean formation. The method may comprise analysing the samples to detect the presence and / or absence of the at least one tracer and based on the tracer data monitoring at least one characteristic of the extraction. Throughout the specification, unless the context demands otherwise, the terms 'comprise' or 'include', or variations such as 'comprises' or 'comprising', 'includes' or 'including' will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers. Furthermore, relative terms such as “up”, “down”, “top”, “bottom”, “upper”, “lower”, “upward”, “downward”, “horizontal”, “vertical”, “and the like are used herein to indicate directions and locations as they apply to the appended drawings and will not be construed as limiting the invention and features thereof to particular arrangements or orientations. The foregoing description of the invention has been presented for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. The described embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilise the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, further modifications or improvements may be incorporated without departing from the scope of the invention as defined by the appended claims.

Claims

1. A method of monitoring an extraction of a target mineral and / or target metal from a subterranean formation, the method comprising: injecting at least one extraction fluid into the subterranean formation; injecting at least one tracer into the subterranean formation;collecting samples of fluid produced from the subterranean formation;analysing the samples to detect the presence and / or absence of the at least one tracer; andbased on the measured tracer data monitoring at least one characteristic of the extraction.

2. The method according to claim 1 wherein the at least one characteristic of the extraction is selected from the group comprising: identifying and / or characterising a flow path of the extraction fluid in, through or from the subterranean formation, estimating an amount of target mineral and / or target metal in the subterranean formation, estimating a location of high concentrations of target mineral and / or target metal in the subterranean formation, monitoring efficiency of the extraction operation, monitoring efficiency of the at least one extraction fluid to extract target mineral and / or target metal and / or flow characteristics of the extraction fluid through the subterranean formation.

3. The method according to claim 1 or 2 comprising injecting at least one tracer into a well in fluid communication with the subterranean formation and collecting the samples from the same well and / or at least one different well.

4. The method according to any preceding claim comprising collecting the samples from a production well and / or from back produced fluid in the injection well.

5. The method according to any preceding claim comprising tracing or mapping flow of at least one extraction fluid through the subterranean formation and / or tracing or mapping flow paths of high concentrations of target mineral and / or target metal extraction.

6. The method according to any preceding claim comprising identifying, calculating and / or monitoring flow rates, flow paths and / or transport paths of the at least one tracer and / or at least one extraction fluid.

7. The method according to any preceding claim comprising measuring or calculating an arrival time of the at least one tracer in at least one well.

8. The method according to any preceding claim wherein the at least one tracer comprises a passive tracer.

9. The method according to any preceding claim wherein the at least one tracer comprises a reactive tracer configured to react with the target mineral or target metal in the subterranean formation and / or the at least one tracer comprises an interactive tracer configured to interact with the target mineral or target metal in the subterranean formation.

10. The method according to any preceding claim comprising injecting two or more distinct tracers wherein the two or more tracers comprise at least one passive tracer and at least one reactive tracer and / or at least one interactive tracer.

11. The method according to claim 10 comprising comparing an arrival time of the at least one passive tracer and the at least one reactive tracer and / or an arrival time of the at least one passive tracer and the at least one interactive tracer.

12. The method according to claim 10 or 11 comprising comparing a tracer concentration signature of the at least one reactive tracer and / or at least one interactive tracer and the at least one passive tracer in the samples with a tracer concentration signature of the at least one reactive tracer and / or at least one interactive tracer and the at least one passive tracer injected into the subterranean formation.

13. The method according to any preceding claim wherein the extraction fluid is selected from the group comprising water, wastewater, brine, saltwater, steam, acid, organic acid, a leaching fluid, or water mixed with chemicals.

14. The method according to any preceding claim comprising collecting the at least one sample for later analysis onsite or offsite.

15. The method according to any preceding claim comprising modelling the subterranean formation, extraction fluid type, injected tracer concentration, injection location, transport time, injection flow rate, production location, tracer concentration in produced fluids, concentration of target mineral and / or target metal in produced fluids and / or production rates.

16. The method according to any preceding claim comprising injecting two or more different extraction fluids each with at least one distinct tracer into the subterranean formation and measuring a concentration of the target mineral and / or target metal extracted in the produced fluids for each of the different extraction fluid types.

17. The method according to any preceding claim wherein the target mineral and / or target metal is lithium.

18. The method according to claim 17 wherein the at least one reactive tracer is configured to react with lithium to form a lithiated tracer and estimating a concentration of lithium, an amount of lithium, a surface area of lithium and / or a position of lithium based on the measured concentration of reacted lithiated tracer and / or unreacted reactive tracer in the samples.

19. The method according to claim 17 or 18 wherein the at least one interactive tracer is configured to exhibit intermolecular forces of attraction or repulsion with lithium and estimating a concentration of lithium, an amount of lithium, a surface area of lithium and / or a position of lithium based on the transport time and / or arrival time of the at least one interactive tracer in at least one well.

20. The method according to any preceding claim wherein the subterranean formation is selected from the group comprising geothermal reservoir, a supercritical geothermal reservoir, an enhanced geothermal system, an aquifer, a hydrocarbon reservoir; a well, a mining well, a mining reservoir, a water reservoir and / or a shale reservoir.

21. A method of collecting samples for analysis in monitoring an extraction of a target mineral and / or target metal from a subterranean formation, wherein the subterranean formation comprises at least one tracer injected into the subterranean formation with at least one extraction fluid; producing fluid from the subterranean formation, and collecting at least one sample from the produced fluid.

22. A system for monitoring an extraction of a target mineral and / or target metal from a subterranean formation comprising:a tracer release device configured to release at least one tracer into an injection well;at least one pump configured to inject an extraction fluid and the at least tracer into at least a portion of the subterranean formation; anda sampling system configured to sample fluid produced from the subterranean formation.

23. The system according to claim 22 wherein the tracer release device is configured to release two or more tracers into the injection well wherein the two or more tracers comprise at least one passive tracer and at least one reactive tracer and / or at least one interactive tracer.

24. The system according to claims 22 or 23 wherein the target mineral and / or target metal is lithium.

25. The system according to any of claims 22 to 24 wherein the subterranean formation is selected from the group comprising geothermal reservoir, a supercritical geothermal reservoir, an enhanced geothermal system, an aquifer, a hydrocarbon reservoir; a well, a mining well, a mining reservoir, a water reservoir and / or a shale reservoir.

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