Systems and methods for monitoring a leaching heap with a movable sensor

Abstract

A system, apparatus, and method for mapping a three dimensional density distribution including placing a first muon detector within a trench, borehole, tunnel, or pipe that is located within a first portion of a heap, measuring an incidence of atmospheric muons on the first muon detector, determining a density distribution of the first portion of the heap, moving the first muon detector to a second portion of the heap, measuring a second incidence of atmospheric muons on the first muon detector; and determining a density distribution of the second portion of the heap. This may include comparing the incidence of atmospheric muons detected by the first muon detector to a muon attenuation of a material in the heap and a surface flux measurement. This also may include comparing an initial muon attenuation for an initial density from an initial sample of the materials of the heap with the muon attenuation in the heap, comparing a prior time interval muon attenuation in the heap as measured during a prior time interval with the muon attenuation in the heap, comparing a fluid muon attenuation of process fluids with the measured incidence of atmospheric muons on the muon detector, or comparing the muon attenuation in the heap to a surface flux measurement. This may also include placing a second muon detector within a trench, borehole, tunnel, or pipe that is located within a third portion of the heap.

Description

Priority

[001] This application claims priority to United States Provisional Patent Application Serial Number 63 / 564,491 filed on March 12, 2024 with the same title and inventors. The application is incorporated by reference in its entirety herein. Field

[002] This disclosure relates to monitoring and assessing the mechanical stability and fluid accumulation in natural or man-made slopes primarily including unconsolidated material, such as mining ore and tailings, embankments, dams, roads, and waste dumps using muon sensor measurements from more than one location. Background

[003] The monitoring of unconsolidated materials for mechanical stability and fluid accumulation is a significant challenge. Slope failures and landslides of unconsolidated materials, soft soils, and sediments generally occur when the static stress due to the weight of the accumulation of material exceeds the shear strength of the material itself. Different failure modes such as translation failure, rotational failure, or wedge failure exist. Monitoring is critical in the mining industry, where personnel are frequently in close proximity to large quantities of unconsolidated materials posing an occupational hazard.

[004] A mix of granular or pebbly materials may arise from a variety of industrial activities. In some instances, mining ore is oxidized or calcined, sometimes at high temperatures, before being stockpiled in a heap for further processing. Unconsolidated materials may also be found in tunnels, including mining tunnels, and in general during the excavation of large pits, channels, roadways, and a variety of other earthworks. Stockpiles of unconsolidated materials are also found when transporting, storing, and shipping (for example, by boats such as bulk carriers) valuable materials such as ores, coal, and bauxite.

[005] Also within the mining industry, large accumulations of unconsolidated materials are encountered in “heap leaching,” which is a commonly used production technique for one or more base and precious metals including copper, gold, silver, nickel, lithium, and uranium. During heap leaching, large accumulations of unconsolidated materials are irrigated with a leaching solution. The unconsolidated materials may exist at heights of 3 to 10 meters and exceed 10 meters. Some can exceed 100 meters in height. The leaching solution is selected to cause the valuable minerals to leach from the ore.

[006] The heap leaching process is a chemical extraction process. Generally all leaching operations start with the grading of the soil and the installation of an impermeable membrane or liner, which is then typically followed by ~30 - 150 cm thick drainage layer (the overliner layer). The ore, i.e. the unconsolidated material, is then deposited on top of the liner or overliner. Finally, an irrigation system is placed on top of the ore stack in order to inject the leaching agent or solution (i.e. the lixiviant) into the pile. Commonly used irrigation systems include drip-line systems and sprinklers. The ore may be deposited by a variety of methods, including trucks, conveyor belts, radial stackers, excavators etc.. Typically the ore in a leaching heap has been crushed to a small uniform size (e.g. ~lmm to 10cm) prior to deposition in order to maximize the contact surface between ore and the lixiviant. In certain operations, the heap is charged with ore, which is then processed and removed prior to the deposition of fresh ore (i.e., a dynamic or on / off leaching heap). In certain other operations, fresh ore is deposited on top of previously process materials (i.e. a static or multi-lift leaching heap).

[007] In some instances, the heap is built on a sloped surface or conforming to the local topography. This type of operations are referred to as valley-fills. In some other instances leaching operations use run of mine material (ROM) which is deposited in situ essentially right off a mining truck and does not undergo any pre-processing in a crusher. This type of leaching is sometimes called dump leaching, to differentiate its lower value from the more engineered heap leaching. Also, the feed material in a leaching operation could come from a stockpile, previous waste dump and from reclaimed (i.e. dewatered) tailings. Some heap leaching operations use an unconsolidated material that includes mining ore that has been crushed, premixed and agglomerated (possibly binding it with cement), or otherwise mechanically prepared to improve its overall permeability or to pre-mix it with a suitable chemical solution. Chemical extraction of metals by aqueous solution containing acids, salts, and other agents is generally referred to as hydrometallurgy.

[008] Heap leaching involves accumulations of unconsolidated materials which can exceed 10 meters or even 100 meters in height. Slope failures of leaching pads and heaps can severely damage valuable mining and material handling equipment and are hazardous to any person nearby, as well as posing a significant threat to the local environment and watershed. For leaching pads that are generally built above a lined surface, -a common stability failure mechanism is a block or translational type failure along the interface with the lowest shear strength parameters which is typically the liner. More complex compound failure modes are also possible, including slope liquefaction.

[009] In certain mining operations, sludges and fluids from a variety of chemical refining or hydrometallurgical processes may accumulate overtime in large tailing ponds. It is commonplace in the industry to build the retaining walls for such tailing ponds from excavated and potentially poorly consolidated material. The material contained in the tailing pond generally contains a large amount of water. Frequently, mine operators recover the water contained in tailing ponds and recycle it back to the mining process. At the conclusion of mine operations, water contained in a tailing pond such as the supernatant (floating) water or the water remaining in the materials undergoing sedimentation should be removed to enable soil reclamation and proper abandonment of the area according to environmental best practices. In many instances, tailing ponds and associated retaining walls remain after the conclusion of mining operations.

[010] In most cases, slope failure occurs within an accumulation of unconsolidated material and depends strongly on the amount of fluids within the pore space of the material itself. The amount of fluids may change as a result of man-made irrigation, rain and snow accumulation, permafrost melt, or changing phreatic levels of the underlying water table. Excessive fluid accumulations lead to build up of pore pressure within the material, which in turn results in reduced frictional and cohesive strengths, for example, a loss of overall shear strength. Under these conditions, the slope of unconsolidated material will ultimately fail under its own weight. In the case of a mining heap, where fluid may be trapped in varying concentration due to complex fluid percolation patterns and flow barriers (such as the presence of clays or fines, which effectively plug the permeability and hinder uniform fluid flow in the material), slope failure may also occur at the toe or at the top of the heap. In general, slope failure may also depend on the heterogeneity and size distribution of the unconsolidated material and the geomorphology of the terrain. [Oil] Sudden slope failure is also referred to as slope collapse or liquefaction and poses an ongoing risk for the mining, construction, and cargo industries as well as whenever stockpiling of large quantities of materials occurs. It is also a natural risk, which may result for instance in landslide and soil movement across a variety of terrains and environments. These risks are often compounded by events such as heavy rains, snow melt, and the occurrence of seismic events. Seismic events can trigger slope liquefaction by allowing sudden surge of excess pore water pressure or water build-up leading to a reduction in shear strength of the slope. Slope failure may lead to tragic loss of life, environmental damage, damage to specialized equipment or infrastructure, and significant loss of productive time.

[012] In addition, for a given set of characteristics of the unconsolidated material (including its permeability, porosity, and / or coarseness) the optimal geometry and aspect ratio of a stockpile, retaining wall, or slope, including a man-made slope as a result of construction and engineering work, may be determined based on the actual volume of fluids present or expected to be present within the stockpile and on the availability of means of monitoring such volumes over large scales. An optimal stockpile or slope design may lead to preferred outcomes such as increased metal extraction from leaching heaps, longer asset lifetimes, continuity of operations, or increased safety of operations.

[013] Dewatering is often used as a mitigation strategy against slope liquefaction or failure in, for example, open pit mining operations or to mitigate the settling or sinking of heavy structures such as buildings, bridges, or foundations during construction or excavations. In mining, dewatering strategies are also used to allow the safe movement of heavy equipment and machinery, including surface equipment that must travel over areas that have been previously flooded, for instance by seasonal rains. However, dewatering can be a complex and expensive process with a wide range of techniques and equipment available. Improper deployment of dewatering strategies will not only result in excess costs, but it can also fail to prevent slope failure as intended.

[014] Dewatering of active or previously abandoned mine tunnels and shafts is an ongoing concern for mine safety, particularly when these areas are difficult to access. Drilling or breaking through an abandoned mine tunnel filled with water can pose considerably risk of loss of equipment, asset value or even human lives. Many underground mines can only operate with pumps actively removing water that seeps from the subsurface into tunnels and other structures.

[015] The risk of changing fluid levels is present in rocky but highly porous materials such as limestones or karst. Indeed, seasonal flooding can be a recurring problem in such areas and being able to monitor underground water tables can help in developing mitigating or dewatering strategies. A common associated phenomenon is the appearance of a sinkhole, which could occur in densely populated areas. For example, a sinkhole can occur when a rock surface gives way as it is being eroded from below by a rising water table.

[016] Based on all of the above, there is continued need for monitoring and localizing (mapping) changing fluid levels deep within a large volume of earth, including a heap, a stockpile, a slope, a tunnel, or a shaft or a karst formation. Such monitoring is of interest not only to prevent slope failure, but also for planning and operating one or more of dewatering, construction, water reclamation, soil reclamation, or spill mitigation. For example, knowledge of the amount of fluid present within the sludge and unconsolidated sediments contained in a tailing pond can inform the operator regarding the effectiveness and residual value left of any water reclamation and densification operations and the optimal location of pumps or drainage channels as well as how to plan the water reclamation and densification operations, including forecasting future water output from such operations. In soil reclamation activities, densification is a primary objective where the desire is to return a wet soil to a state with enough shear strength to sustain the weight of people, vehicles, buildings, reforestation, or the like without sinking or shifting. Densification requires eliminating most of the water that is trapped within the grains of the soil as a result of industrial processes such as mining operations. For these and other applications, having a way to directly monitor the density of soil is a critical need. Summary

[017] Embodiments herein relate to a system, apparatus, and method for mapping a threedimensional density distribution including placing a first muon detector within a trench, borehole, tunnel, or pipe that is located within a first portion of a heap, measuring an incidence of atmospheric muons on the first muon detector, determining a density distribution of the first portion of the heap, moving the first muon detector to a second portion of the heap, measuring a second incidence of atmospheric muons on the first muon detector; and determining a density distribution of the second portion of the heap.

[018] In some embodiments, determining the density distribution of the first portion of the heap includes comparing the incidence of atmospheric muons detected by the first muon detector to a muon attenuation of a material in the heap and a surface flux measurement. In some embodiments, determining the density distribution of the second portion of the heap comprises comparing the second incidence of atmospheric muons detected by the first muon detector to a second muon attenuation of a material in the heap and a surface flux measurement.

[019] Determining the density distributions of the first and second portions of the heap may include comparing an initial muon attenuation for an initial density from an initial sample of the materials of the heap with the muon attenuation in the heap, comparing a prior time interval muon attenuation in the heap as measured during a prior time interval with the muon attenuation in the heap, comparing a fluid muon attenuation of process fluids with the measured incidence of atmospheric muons on the muon detector, or comparing the muon attenuation in the heap to a surface measurement of the atmospheric muon flux. The surface measurement of the atmospheric muon flux may include an independent reference flux measurement at the surface or at a depth. In some embodiments, the moving is horizontal or vertical or both to the earth’s surface.

[020] Some embodiments may further include placing and moving a second muon detector within a trench, borehole, tunnel, or pipe. In some embodiments, the spacing between the first and second muon detectors is fixed as they both move. In some other embodiments, the spacing between the first and second muon detectors is controlled as one of them moves. The second muon detector may have movement that is parallel or perpendicular to the movement of the first muon detector.

[021] Embodiments herein relate to a system, apparatus, and method for mapping a three dimensional density distribution including placing a first muon detector within a trench, borehole, tunnel, or pipe that is located within a first portion of a heap, measuring an incidence of atmospheric muons on the first muon detector, moving the first muon detector to a second portion of the heap, measuring a second incidence of atmospheric muons on the first muon detector, placing a second muon detector within a trench, borehole, tunnel, or pipe that is located within a third portion of the heap, and measuring a third incidence of atmospheric muons on the second muon detector.

[022] Some embodiments may further include moving the second muon detector to a fourth portion of the heap and measuring a fourth incidence of atmospheric muons on the second muon detector. In some embodiments, the trench, borehole, tunnel, or pipe of the first muon detector is parallel to the trench, borehole, tunnel, or pipe of the second muon detector.

[023] Some embodiments further include determining the density of the first, second, and third portions of the heap.

[024] In some embodiments, the first muon detector further comprises an armored multiconductor cable. Detailed Description of the Figures

[025] Figure lisa graphical representation of sensitivity across a plane within leaching heap.

[026] Figure 2 is a graphical representation of sensitivity across a plane within a leaching heap in a series over time.

[027] Figure 3 is a graphical representation of sensitivity across a traverse YY-Z plane within a leaching heap.

[028] Figure 4 is a graphical representation the sensitivity from three sensors across a plane within a leaching heap.

[029] Figure 5 is a graphical representation of the sensitivity from three sensors across a plane within a leaching heap.

[030] Figure 6 is a graphical representation of the sensitivity from five sensors across a plane within a leaching heap.

[031] Figure 7 is a graphical representation of the sensitivity from three sensors across a plane within a leaching heap.

[032] Figure 8 is a sectional view of two pipes with three sensors.

[033] Figure 9 is a three-dimensional view of an anomaly inside a heap volume as observed by two sensors in multiple positions.

[034] Figure 10 is a graphical representation of the sensitivity from seven sensors across a plane within a leaching heap.

[035] Figure 11 is a sectional view of a leaching heap with aeration pipes, an inspection well, overliner material, drainage pipes, and a lined surface.

[036] Figure 12 is a sectional view of an installation pipe with a sensor with conveyance cables and a pulley.

[037] Figure 13 is a sectional view of a detector traveling in a casing pipe.

[038] Figure 14 is a dimensional view of two detectors configured to travel or to communicate or both with each other. Detailed Description

[039] This disclosure relates to monitoring and assessing the mechanical stability and fluid accumulation in natural or man-made slopes primarily including unconsolidated material, such as embankments, dams, roads, and waste dumps. This disclosure also relates to monitoring and assessing the mechanical stability and fluid accumulation in man-made heaps of bulk materials that may occur in the stockpiling of grains, gravel, stones, sand, coal, cement, fly ash, salts, chemicals, clays, and crushed limestone. This disclosure further relates to monitoring and assessing the mechanical stability and fluid accumulation in heaps of mining ores, including crushed, milled and / or agglomerated ore. This disclosure also relates to monitoring and assessing the mechanical stability and fluid accumulation in run-of-mine materials. Throughout this disclosure, the word “heap” may be used generally to include any combination of these physical and mechanical features of unconsolidated material. That is, the word “heap” may encompass unconsolidated material, a tailing dam, a stockpile, dry-stacked tailings (i.e. tailing materials that have undergone a previous dewatering step), wet tailings, mining ore, ore in storage, a berm, a levee, a buttress, a dump or ROM heap, a valley fill or leaching heap, or a combination thereof.

[040] Embodiments herein relate to various systems and methods for inserting, positioning, and moving a muon radiography sensor under unconsolidated material, such as embarkments, earthen dams, waste dumps, as well as man-made heaps of bulk materials that may occur in the stockpiling of grains, gravel, stones, sand, coal, cement, fly ash, salts, chemicals, clays, and crushed limestone as well as heaps of mining ores, including crushed, milled, and agglomerated ore, and run-of-mine materials. Stockpiles of unconsolidated materials are also found when transporting, storing, and shipping (e g. by boat) valuable materials such as ores, coal, and bauxite.

[041] Large accumulations of unconsolidated materials, in some cases well exceeding 10 m in height, are also encountered in heap leaching, a primary production method for many base and precious metals such as copper, gold, silver, nickel, uranium, and others. The heap leaching process is a chemical extraction process that consist in irrigating with an appropriate chemical solution large man-made stacks and accumulations of mining ore that have been crushed or otherwise prepared before the chemical extraction step. Chemical extraction of metals by means of aqueous solution containing acids, salts, and other agents is generally referred to as hydrometallurgy.

[042] In other mining operations, sludges and fluids such as from a variety of chemical refining or hydro-metallurgical processes are accumulated in large tailing ponds. It is commonplace in the industry to build the retaining walls of such tailing ponds from excavated and potentially poorly consolidated material. The material contained in the tailing pond generally contains a large amount of water. Often, operators are interested in recovering water from a tailing pond so as to recycle it back to the mining process. Generally, at the end of its economic life, water contained in a tailing pond must be removed to enable soil reclamation and proper abandonment of the area according to environmental best practices.

[043] Muon radiography is a well-established technique for determining the bulk density of materials over large distance scales. Muon radiography can be utilized to assess the stability of a large pile of unconsolidated material generally using individual, static sensors. The sensor, or muon detector, observes an incidence of atmospheric muons. The range of effective muon directions is limited to angles up to 9 ~ 70-80 degrees from the vertical. Thus, for a fixed detector positioned at a depth h, the areal coverage at the surface of the heap is a circle with a radius r = h * tan(0). Large leaching heaps can have areas of up to a few km2, and may be just a few meters thick (h = 5-10m for an on / off or dynamic heap). As such, the area coverage from a single sensor is insufficient to cover the full leaching surface. In addition, within such areal coverage, i.e. the natural muon radiography acceptance cone, the sensitivity of the measurement (i.e. the error with which bulk density is determined for a given installation geometry, sensor configuration and cumulative measurement time) is non-uniform and is mostly concentrated around the vertical direction which is the direction of maximum available muon flux. Indeed, the muon flux peaks in the vertical direction (6 =0) and monotonically decreases for increasing angles away from the vertical. The resulting non-uniform coverage is illustrated in Figure 1, where the expected sensitivity of the measurement (i.e. the statistical error for the density determination from the observed muon flux, Ap, in g / cc) is projected on top of a 15 m tall heap.

[044] Figure 1 is a graphical representation of a sensor’s feedback 102, 103 across a plane within a leaching heap. That is, a “sensor’s feedback” is used in this application as shorthand. The embodiments herein are mapping the sensitivity to density, expressed as the error delta-rho due to the statistical precision of the measurement for density determination from a given sensor in a given geometry. In other words, such sensitivity is always different case by case. Embodiments herein are mapping a density distribution based on the given sensor’s given geometry. In some embodiments, this density distribution is in three dimensions. Here, the figure is adjusted in the direction of motion. It shows a single sensor advancing in an X-direction which offers un-equal coverage and sensitivity to fluid content or density changes or both, as seen projected on top of a heap. A surface flux measurement may eventually become a necessary condition for an improved absolute measurement normalization. Here one sensor is placed at position A and then moved through installation pipe 101 to a position B after a certain station time. In Figure 1, the heap is a trapezoid with a top surface area of 120x180 m2 and the results are given for a detector with an effective surface area of ~0.2m2 placed at the base of the heap and after 30 days of data collection. Thus, a single measurement position is insufficient to characterize the full heap. Further, that the area with a sensitivity < 0.1 g / cc is restricted to a circular area with just a 30 m radius.

[045] The bulk density measured via the muon radiography method is a proxy for fluid content inside the heap as the two are related by the basic volumetric equation Pheap Pm^ 1 ¢0 T (p * S * Pfluid   Pdry T (p * S * Pfluid

[046] wherein pheap is the bulk density of the heap, consisting of an unconsolidated material with a matrix or grain density pm and a porosity (p, to which a fluid (i.e. the lixiviant fluid) with density Pfiuid is added up to a partial saturation S (5 6 [0,1]).

[047] The reagent or fluid content distribution inside the heap is a key parameter of any leaching operations as not having enough fluid leads to dry or underexposed zones and thus a lower metal recovery, whereas volumes containing too much fluid may lead to slope instability and landslides. Further, the fluid content provides information about compaction, migration, and clays. The fluid content helps infer where metal is produced or how much volume of liquid to introduce or insert into the heap.

[048] During operations, it is important to detect anomalies in the volumetric fluid content along the full extent of (e.g.) leaching heap, both in the longitudinal (X axis) and transverse (Y axis) directions as soon as possible to be able to avoid “imprinting” on the heap unwanted preferential flow channels and to maximize the effectiveness of remedial actions such re-adjustment to fluid flow in certain areas of the heap.

[049] For a given available muon flux (i.e. a location on the earth) the speed for density anomaly (i.e. fluid content anomaly) detection depends on many factors such as the size of the detector (diameter, length), the required spatial sensitivity (binning), the measurement time and the desired confidence level for anomaly detection (i.e. the “amplitude” of useful density anomalies). In some cases, such density anomalies or differences can be inferred relatively to or as a deviation from an average density. This relies only on assuming uniformity rather than a specific knowledge of the local muon flux (particles / m2 / second) and distribution. The muon flux is not expected to change significantly across the areal extent of the muography scan. Some embodiments may compare a muon flux at the earth surface including compared to an independent reference flux measurement at the surface or at a depth (i.e.. a depth comparable with the application.).

[050] As an aside, both saturation and porosity are expressed as a volume percentage but they are different. A pile of sand or rigid packed spheres in a container would have ~36% porosity has that is the fraction / amount of empty space between individual grains / spheres. Note that porous space is filled with air (essentially ~0 density). Fluid saturation is also expressed in percentage, but relative to porosity. Thus, 100 percent saturation means all of the pore space is filled by the fluid. Here, 10 percent water saturation means that 10 percent of the pore space (itself a fraction of the total volume) is filled with water. So if the porosity was 30 percent, only 3 percent of the total volume consists of water.

[051] For a material with a grain density of 2.5g / cc, and 30% porosity, the bulk density is 2.5 *0.7 = 1,75g / cc under dry conditions. When irrigation is started and the porosity of this material is filled with 10% fluid saturation, the leaching fluid having a 1.05g / cc density, the resulting bulk density of the material is the dry density + fluid contribution i.e. 1.75 + 0.3*(10%)*(1.05g / cc) = 1.785 g / cc, a + 0.035 g / cc (+1.8%) increase over its dry density. If the fluid saturation of 20%, the resulting bulk density would have been 1.75 + 0.3*(20%)*(1.05g / cc) = 1.813 g / cc, a + 0.063 g / cc (+3.6%) increase over the dry density and a +0.028 g / cc (+1.6%) density increase (over the 10% saturated material. Compaction in the material is often inevitable and generally leads to a reduction of the available porosity over time.. In some instances, this may introduce additional uncertainty.

[052] Figure 2 is a graphical representation of a sensor’s feedback 201, 202, 203 across a plane within a leaching heap in a series over time. Figure 2 shows that even at a fixed sensor position 204, the measurement sensitivity for a single sensor 205 (shown as a dot in the center of the graphs) increases if we increase the measurement (or station) time. The optimal measurement time at each position will thus be an optimization taking into account the amount of total area that needs to be scanned, in how much time, with how many sensors and to what level of statistical precision or sensitivity, as well as the heigh of the heap (which determines the available muon flux in the first place).

[053] Figure 3 is a graphical representation of a sensor’s feedback 302across a traverse YY-Z plane within a leaching heap. Figure 3 shows what typical coverage and sensitivity looks like in the transverse YY-Z plane. The distance from and angle to the Y center have varied shading in this figure to imply reliability of the measurement of sensor 301.

[054] Figure 4 is a graphical representation of the feedback 402 from three sensors, A, B, and C, across a plane within a leaching heap including multiple positions 4A, 4B, 4C for each sensor 42A, 42B, 42C in installation or infill pipes 401. Figure 4 shows multiple sensors, A, B, C, in parallel to increase measurement coverage. The optimal pipe spacing is determined based on the requirements for scanning speed, density sensitivity, area to covered, spatial sensitivity, detector size (diam, length), detector depth, or a combination thereof.

[055] Figure 5 is a graphical representation of three sensors’ feedback 502 across a plane within a leaching heap. Figure 5 is similar to Figure 4, but also shows that the sensors (A, B, C) may not all be moved at same speed or distance through installation pipes 501. There are many reasons to move sensors differentially, for instance to better focus onto a certain region of the heap by providing a more precise measurement (i.e. statistics) via a longer station time or by providing more view angles for an improved 3D, three-dimensional, analysis of the data.

[056] Figure 6 is a graphical representation of five sensors’ feedback 602 across a plane within a leaching heap. Figure 6 shows additional sensors (D, E) in optional or additional installation or infill pipes 601 may also help focus more and provide more information about the material in a specific area such as area 62D and area 62E.

[057] Figure 7 is a graphical representation of three sensors’ D, E, F feedback 701, 702 across a plane within a leaching heap in a series over time when the sensors are moved at different speeds. Figure 1 shows how the scanning speed affects measurement sensitivity. The left figure in the series has sensors DEF advancing at 20 m / month and the right figure advancing at 40 m / month. The faster we move the less time we have for collecting muons at any given position. In other words, there is a tradeoff for the statistical sensitivity with which we can resolve density anomalies.

[058] Thus, when radiographically inspecting an active leaching heap with cosmic ray muons, we are seeking a measurement with a sensitivity on the density measurement of - 0.05g / cc or better per station time of the sensor, which is equivalent to a sensitivity to fluid saturation content of-20% for accumulation of materials with standard porosities (<[) = 20-40%). In some other cases one may seek more sensitivity, therefore more counts at any given positions. This can be obtained with longer station times or with sensors with a larger surface area for muon detection.

[059] This level of performance must generally be extended over the full area of the leaching heap. To achieve this, it is advantageous to use multiple sensors in parallel. Indeed, the optimal spacing between sensors in the transverse direction, i..e. the separation between parallel scan lines (installation pipes), as well as the speed with which the scan can proceed longitudinally is determined by the desired level of performance and statistical accuracy (i.e. the sensitivity to density changes) in the region between the parallel sensors. This is illustrated in Figure 8.

[060] Figure 8 is a sectional view of two installation pipes 801, 802 with three sensors 1, 2, 3. Figure 8 compares two ways to space sensors across an installation pipe, fixed sensor spacing 803 or adjustable sensor spacing 804, 805.

[061] At the same time, one needs to maximize coverage also in the longitudinal direction (i.e. the X direction). When a faster scan of the heap is required, some embodiments use multiple sensors acting in parallel within the same installation pipe. The optimal spacing between these sensors is also determined by the requirements for scanning speed, density sensitivity, and spatial resolution, within the measurement time allowed. There will be cases, however, wherein this spacing needs to be adjusted based on findings obtained during an initial scan of the measurement campaign. This could be the case when an anomaly is detected during an initial longitudinal scan, and the sensor positions are then adjusted to optimize the statistical accuracy with which this density anomaly can be further resolved, quantified, and located, including in the 3D sense, after a 3D tomographic reconstruction. Practical 3D tomographic reconstructions typically require at least 2 sensors but more sensors and more view angles quickly improve the leverage with which the physical extent and the size of the anomaly (in terms of density contrast) is resolved in 3D. While multiple sensors systems take data simultaneously, sequential 3D tomographic reconstructions can also be realized with a single sensor, considering that this will be placed at different longitudinal positions along the scan direction which results in viewing the same volume from multiple angles. Single sensor 3D reconstruction are generally less accurate than surveys involving multiple sensors simultaneously.

[062] Figure 9 is a three-dimensional view of an anomaly 901inside a heap volume 902 as observed by two sensors 903, 904 in multiple positions 905, 906, 907, 908. Figure 2 illustrates that the nearer plot shows that sensors 903, 904 may advance at a different rate or that their positions 905, 906, 907, 908 need not be aligned in paralel or perpendicular to each other. Generally, horizontally oriented sensors 903, 904 move longitudinally, ie parallel to the surface of the earth, along their installation pipes 909, 910, which may be at a slant in some instances. If a sensor is installed vertically, it will only move up and down along the borehole, which may also be slanted in some instances.

[063] A 3D localization of any potential density or fluid content anomaly is important from the practical point of view, as it determines what type of intervention can be taken in response. For instance, if the 3D analysis identifies a dry zone in the middle of the heap, this could be a shadowing effect from a lens of impermeable materials such as clays or a failure of the irrigation system directly above it. In this case, an operator seeking to remediate this may decide to drill into the heap to deliver the fluid at depth, i.e. past the impermeable layer. If the density anomaly is such that the excessive fluid is accumulating at the bottom of the heap, then this may pose slope stability risks (requiring a different type of intervention, such as the insertion of a drainage wick) or it may be an indication that the heap has a very high permeability and the fluid flow must be adjusted accordingly in order to optimally recover metal from the heap.

[064] Thus, an adjustable spacing between the sensors allows the user to collect data from a wide range of angles and with more flexibility, which generally results in a much-improved tomographic reconstruction and definition of the anomaly in 3D. Herein, embodiments benefit from configurations that allow one to do just that. For instance, a system with one or more movable or retractable sensors such as that in Figure 9, including when the spacing between sensors is adjustable, can be realized in a number of ways.

[065] Multiple sensor systems are advantageous. Generally, for the purpose of conducting a radiographic muon survey, two Im long sensors at a spacing of 10m may perform better than a single 2m long sensor, especially for providing distinct view angles required for a 3D tomographic reconstruction.

[066] For the same reasons, it may be advantageous to prepare the leaching heap such that a number of additional or infill pipes are made available for sensor locations. These infill pipes may be utilized from time to time and depending on initial survey results, to better measure, define and reconstruct volumes of particular interest. Such an approach would allow one to minimize the number of installed sensors overall. For instance, pipes or a borehole may be installed at intervals of 10m whereas sensors will be initially installed ever 20 m. After providing an initial fast scan of the heap, these sensors may be relocated in pipes with a closer spacing to better investigate areas of interest.

[067] We refer to those initial configurations that allow for an initial scan of the heap “scan configurations” whereas those configurations around volumes of interest featuring closer spacing (longitudinally or transversely) between sensors, for the purpose or providing additional view angles, “spotlight mode”.

[068] Figure 10 is a graphical representation of seven sensors’ G, H, I, J, K, L, M feedback 1001, 1002 across a plane within a leaching heap. Figure 10 shows having a system with multiple infill pipes 1003 pre-installed near installation pipes 1004would allow one to relocate sensors to better image anomalies with more resolution and faster. The user may refer to this as spotlight mode.

[069] Figure 11 is a sectional view of a leaching heap 1101 with aeration pipes 1102, an inspection well 1103, overliner material 1104, drainage pipes 1105, and a lined surface 1106. Figure 3 shows that while using sensors installed in horizontal pipes in the overliner material may be effective for some embodiments, additional information aiding a 3D reconstruction can be had by deploying sensors in additional horizontal pipes (e.g. similar to aeration pipes) or vertical wells. The pipes may be drainage pipes or one may install similar pipes with no fluid present. The pipe may exist in the heap at a slant to the earth’s surface, S-shaped, or curved. In some embodiments, the pipes could be at a slant angle to each other or one may have a long, curved trajectory. In some other embodiments the pipes may be placed in trench previously realized under the unconsolidated material, including below any liner placed to prevent fluid infdtration into the subsurface. In yet other embodiments, the pipes are replaced with borehole drilled at some safe distance below the unconsolidated material, including boreholes drilled under a protective liner.

[070] To inspect a large pile or object with muon radiography sensors, one may be able to move the sensor at various locations under the heap in order to extend the area of investigation while, at the same time, minimizing the number of boreholes required. In some cases, such as with mining leaching heaps, it is also necessary to protect the sensors from corrosive fluid such as dilute solution of sulphuric acid employed for the extraction of copper and other metals or cyanide for use with gold. In such cases, a protective casing must be used, such as corrosion resistant HDPE pipes that are used in leaching heaps for the purpose of distributing or collecting process fluids. In some other cases, similar pipe networks may also be in place and used to convey warm air deep or inject reagents or catalysts inside the heap in order to facilitate the leaching process. A properly optimized and ruggedized sensor (e.g against corrosion, high temperature) could also be advantageously operated in a pre-existing infdl pipe such as a hot air pipe or a fluid collection pipe. Any of these pipe systems could be installed at the bottom of a leaching heap (i.e. in the drainage or overliner layer) or under or mid-way inside the heap, and at any orientation although horizontal pipe is typically selected for the best coverage in some embodiments.

[071] Other casing materials can be used including drainage or dewatering pipes, ad-hoc pipes, or boreholes dedicated to the insertion of monitoring instrumentation such as muon radiography sensors. Suitable pipe materials are not limited to HDPE. PVC, other plastic, hard rubber, metal, or concrete pipes may also be utilized, as the thickness of any such pipes does not significantly introduce additional muon attenuation, at least compared to the attenuation due to the heap or stockpile itself. At any rate, the effects due to the presence of any such pipe can be accurately accounted for in the analysis of the muon radiography data In certain cases, the pipe may be replaced entirely by a borehole or a tunnel directionally drilled under the mining asset, including under any impermeable geomembrane or layer utilized to segregate process fluids from the environment. In certain other cases, a simple trench may be drilled and appropriately prepared for accommodating one or more movable muon radiography sensors, prior to the mine operation levelling or grading the soil, installing the protective geomembrane and accumulating material on the leaching pad.

[072] Finally, it is also desirable to be able to send external power to the system of sensors, as well as to maintain an open data communication channel for the purpose of reading-out the sensor data as well as change various configuration parameters in near real time (as compared to memory mode). Batteries may be selected for some embodiments. Conventional wireless communications are greatly hampered when communicating with a device that could be buried under several tens of meters of unconsolidated material such as soils or a crushed mining ore. Data transmission is not limited to the muon track data. Useful data from the sensors also includes health monitoring data (e.g. temperature, humidity, health of electronics components and support system) as well as sensor orientation data such as sensor pitch, yaw, and roll angle inside the installation pipe.

[073] Some embodiments may employ an armored, multi-conductor cable that serves both the purpose of enabling movement of the tool string, or in the cases of vertical installation also supporting its weight and provide data and power connection.

[074] Embodiments herein relate to methods with which to move one or more muon radiography sensors inside a pipe, conduit, or hole that is inserted inside or under a leaching heap, stockpile or other accumulation of materials, in a way that is robust, low cost, and able to maintain reliable power and data connection with the sensors, while providing an optimal and adjustable range of viewpoints and angles for the purpose of performing a 3D density reconstruction of the in situ bulk density of the material, including when such bulk density changes over time due to the addition (or removal) of water or processing fluids.

[075] Without loss of generality, a muon sensor may be installed under stockpile of materials, in or near a dam, or in unconsolidated (non-hard-rock) soil. The casing pipe could be made of many materials. HDPE pipe is commonly used in leaching and other mining operations

[076] In some cases, the casing pipe may be placed on top of an existing heap lift and then be buried by a fresh accumulation of ore to be processed in next phase of a leaching heap. In other cases, the casing pipe may be inserted or left inside a borehole, including a directionally drilled borehole, a horizontal borehole, a sonically drilled borehole, or boreholes prepared by augers, micro tunnel boring machines or other equipment. Generally, of course, open holes are undesirable in unconsolidated materials. In yet other cases, the casing pipe may be positioned at the bottom of a trench and then be covered by new material, or in an ad-hoc borehole drilled under the leach pad.

[077] The casing pipe may be inserted into the borehole with a variety of techniques, or it may be dragged by the boring or drilling equipment or it may be inserted with the help of a cable plough. The casing pipe may also be a dual-purpose pipe that is inserted inside of the accumulation of materials - e.g. - for the purpose of delivering or collecting processing fluids such as leaching solutions, extracting water or other water management activities, or aerating a heap of materials, such as with hot air injection that is commonly used in several bioleaching applications for the purpose of accelerating leaching reactions.

[078] The casing pipe could be a corrosion resistant pipe such as a high-density polyethylene (HDPE) pipe, or any other plastic (e.g., solid wall, ABS, PVC), metal (e.g., steel, iron) or concrete pipes. Generally, the casing pipe is realized by joining multiple sections either mechanically or by fusing together different pipe sections during its installation, thus it may have features where these joints are made including flanges, inward bulges, excess materials and generally rugose profdes. The casing pipe could also be a perforated pipe for the purpose of collecting or distributing fluids or gases. In certain implementations the casing pipe could be replaced by any other existing pipe including municipal pipes, electrical conduits, sewers, water pipes, pipes or conduits that are inside a dam, or other infrastructure.

[079] A muon radiography sensor includes a sealed housing of primarily a cylindrical shape. Generally, a muon radiography sensor also has a data and power interface to the outside world. Some embodiments may also include sensors that are battery powered or operated in memory mode (without a continuous data connection to the outside world). Generally, a borehole muon radiography sensor may have a diameter ranging from 5 to 500 cm, and a length in the range of 10 cm to 10 m.

[080] In order to advance a sensor longitudinally, one could use a variety of methods. Figures 12 and 13 show a movable muon sensor that is inserted inside a casing pipe positioned at the bottom of a leaching heap. The sensor is attached to two conveyance cables. One of these cables is attached to a back face of the sensor, whereas the other passes through the sensor housing all the way to the end of the installation pipe where it is returned via a pulley or a rod to be rigidly attached to a front face of the sensors. In this way, pulling the first cable attached to the back face moves the sensors closer to a near end or entrance of the pipe, whereas pulling on the second cable moves the sensor (via the return pulley) towards the far end or exit of the pipe.

[081] To allow moving the sensor as well as maintain it centered inside the casing pipe above defined, while overcoming possible small deformations of the casing pipe, including bumps or ridges that may be present when two sections of pipe are joined, the sensor housing may be furnished with a set of spring-loaded wheels, rollers, skids (including wearable skids), motorized wheels or externally facing bearings. The sensor may also be moved along one or more rigid tracks, ridges, or guides or with a motorized high traction rubber track, installed inside the casing pipe.

[082] In some implementations, the front face of the muon sensors may be furnished with cones, plows or other structures that facilitate moving the sensor inside the casing pipe in the presence of material residues or fluids.

[083] In some embodiments, the return pulley may be hosted in a pipe section including a sealed pipe section that is anchored to the ground. Such a pipe section may be thermally sealed or flanged onto the main casing pipe. In other cases, the casing pipe emerges on the side the heap and the pulley systems may be anchored outside of the pipe or the heap itself.

[084] Figure 12 is a sectional view of an installation pipe 1201 with a sensor 1202 with conveyance cables 1203 and a pulley 1204. The sensor 1202 may have wheels 1205, fixed anchors on its back side 1206 and front side 1207, and aligned surfaces to engage with the conveyance cables. The wheels may engage with the installation pipe surfaces, and spring-loaded wheels also offer the advantage of center the sensor relative to the installation pipe. The conveyance or traction cables may be configured to pull the sensor along the installation pipe surface by using a return pulley. The traction cable and pulley system may be actuated manually, with one or more hand cranks, captsans or with manual or motorized winches, including remotely operated winches. The traction cable itself could be any of a natural or synthetic fiber rope, or a steel or an armored multiconductor cable.

[085] The traction cable serves primarily the purpose of transmitting tension and moving the sensor housing. While the traction cable is stiff, it is generally important that the data and power connections do not witness excessive tension. This is particularly so when the communication cable is an optical fiber which is easy to break under tension. It is also important to avoid any tangling or crossing of traction and signal cables.

[086] Armored multi-conductor cables such a wireline cables can support high mechanical tensions while still providing electrical connections for data and power and may be utilized as the first section of the traction cable (i.e., the one attached to the sensor back face). With the design of an appropriate telemetry system, such cables can transmit power and data over very long distances (> 1km). In some instances, the armored cable with sufficient stiffness may have one or more data communication links.

[087] Figure 13 is a sectional view of a detector 1301 traveling in a casing pipe 1302. The detector 1301 may use a pully and cable system 1303 with a winch, capstan, spool, or lever 1304 to control its movement that may be remotely controlled. The detector may further have an ethernet and power secondary cable. A secondary cable may also be used for power and data communication with the sensor, separately from the traction cable. The secondary cable may consist of an assembly of multiple cables or a composite cable, including cables protected by armor or a secondary conduit. Such a secondary cable can be substantially cheaper, lighter, and easier to handle or transport than a wireline cable. It may also feature standard data communication links such as an RG-485 or other standard communication cables, or ethernet cables or optical fibers, which would greatly simplify or eliminate the need for a custom telemetry system. All of these power and data communication cables will be connected to suitable feedthroughs in the sensor housing, such as feedthroughs on a lid, cap, or flange that may seal the housing hermetically, depending on the application.

[088] The secondary cable assembly or the individual cables power and communication cables may be wound around their own winch system, on a rotating drum or other structure, such that its tension cable can be maintained substantially lower than the tension of the traction cable while advancing or retracting the sensor inside the casing pipe. Likewise, the conveyance mechanism may have features to prevent accumulating too much tension that could potentially damage the sensor in the installation pipe or other connections to the sensors.

[089] Multi-sensor installations may be effective for some embodiments, i.e. when more than one radiography sensor is inserted in the casing pipe at some distance from a first sensor. In these instances, additional segments of the traction and the data and power cable are required between sensors and the distance between sensors is generally fixed.

[090] In place of a cable-based conveyance system, one could utilize an externally controlled motorized track, rail, or wheel-based system to advance the one or multiples sensors inside the one or more installation pipes. In other implementations, one may use a pneumatic based conveyance system or suitable tool pushers, including coiled tubing systems, to mechanically advance or retract a sensor assembly or multiple sensor assembly inside the installation pipe. In yet other implementations, suitable tractoring or actuation systems may be built in within a tool section or sections, including additional tool sections attached to the sensor housing.

[091] With a multi-sensor system, the spacing between sensors will be optimized such as to acquire a full scan, i .e. travel the full length of the installation pipe, in the shortest amount of time possible. Changing the relative distance between sensors is important particularly for those muon radiography applications wherein a 3D (tomographic) reconstruction of the density of a given volume or sub-volume under investigation is obtained by comparing data obtained from different angles.

[092] As such, each tool housing must be mechanically connected to that of the next sensor for the purpose of moving the tool string along the installation pipe and, in addition, allow for tool-to-tool connectivity of power and data signals. To be clear, a tool-to-tool power and data bus is convenient but some systems may exist wherein each tool has its own separate conveyance and signal cable. In certain implementations, this may be achieved with a distributed power bus and / or networking system, including a wireless tool-to-tool communication system for short-haul connections. The mechanical connection between multiple sensors in a tool string may also be realized with a rigid pipe or tubing.

[093] When the mechanical connection between the individual elements (sensors) of the overall tool string features one or more remote-controlled motorized winches, e.g. winches hosted inside at least one of the two tool housing, it becomes possible to change the distance between sensors for the purpose of optimizing a radiographic or tomographic survey as described above. In some embodiments, the tools may be at a fixed distance such as pearls on a sparse necklace and they all move at once. In other implementations, the function of the on-board winch may be realized by using remotely retractable or telescoping tubing to allow for a change in the separation between two tools.

[094] Figure 14 is a dimensional view of two sensors 1401, 1402 configured to travel or to communicate or both with each other. The view shows two sensors 1401, 1402 with an intra-tool connection 1403, a remote-controlled winch 1404, a tool extension cartridge 1405, and back and front face conveyance cables 1406, 1407. A return pully 1408may be used to align the cables. In such a multi-sensor configuration, a suitable tool extension cartridge may be attached to the front or the back of each individual sensor housing. This may have wheels to allow for tool conveyance along the pipe as well as remote controlled anchors, packers, clamps, or other mechanisms to fix the position of one sensor in place, while moving the other sensor relative to it. Such cartridges or tool extensions may also have ways to control the tension of the connection between sensors. In certain implementations, each housing must have the appropriate number of passthrough connections to maintain overall conveyance function and feedthroughs to allow for tool-to-tool power and data distribution. In many implementations, these connections will also allow for time synchronization between the different elements of the tool string to a reference clock or timing system, including an external one. To minimize the number of individual data connections, suitable duplexers or data routers may be installed in each of the elements of the tool string.

[095] It is also important to verify the orientation of the sensor relative to the true vertical direction as, in general, the casing pipe may not be perfectly straight or the sensor may rotate azimuthally inside the casing pipe during motion or both. In many implementations, one or more muon radiography sensors may indeed host a combination of inclinometers, accelerometers, inertial or magnetic sensors for the purpose the determining the true orientation of the one or more sensors. In certain implementations, GPS-based systems may be utilized to provide the absolute location of a sensor under the mining asset.

[096] In heap leaching applications, the heap is built in stages, generally by using a movable ore spreader or conveyor moving along a primarily longitudinal section of the leaching field. After the ore material is deposited and the spreader has moved far away enough, irrigations pipe can be installed and thus production commences on a partial section of the heap. In some other cases installation of the irrigation system and the start of production may be delayed until the full heap or heap module is built. With embodiments described herein, it becomes possible to optimize the position of one sensor or more with the location of the spreader and the heap construction schedule so as to optimize the coverage offered by the one or more muon radiography sensors and focus it to those sections of the heap module that are under active irrigation and where density mapping provides the maximum value. Similarly, when multiple strings of muon sensors are placed inside one or more parallel casing pipes, the ability to move each sensor string or an individual sensor within a string becomes advantageous in terms of optimize coverage with a minimum number of sensors.

[097] Further, some embodiments will benefit from having a sensor housing with wheels, rollers, or skids moving inside a casing pipe with a through hole to allow a traction cable to pass though the housing and be returned via a pulley for the primary purpose of advancing the sensor housing inside the casing pipe. Some embodiments have a second (or return) section of the traction cable which is an armored cable. Some embodiments have a distinct secondary cable that is used for data and power connection in place of the armored cable, and such secondary cable is maintained at a substantially lower tension than the traction cable. In some embodiments, the wheels, rollers, or skids on the sensor housing are replaced by a track system. In some embodiments,

[098] the sensor housing has cones to remove debris or fluid along its path. Some other embodiments may use a snowplow cone, an inflatable balloon, or pig.

Claims

1. A method for mapping a three-dimensional density distribution, comprising:placing a first muon detector within a trench, borehole, tunnel, or pipe that is located within a first portion of a heap,measuring an incidence of atmospheric muons on the first muon detector;determining a density distribution of the first portion of the heap;moving the first muon detector to a second portion of the heap;measuring a second incidence of atmospheric muons on the first muon detector; and determining a density distribution of the second portion of the heap.

2. The method of claim 1, wherein determining the density distribution of the first portion of the heap comprises comparing the incidence of atmospheric muons detected by the first muon detector to a muon attenuation of a material in the heap and a surface measurement of the atmospheric muon flux.

3. The method of claim 1, wherein determining the density distribution of the second portion of the heap comprises comparing the second incidence of atmospheric muons detected by the first muon detector to a second muon attenuation of a material in the heap and a surface measurement of the atmospheric muon flux.

4. The method of claim 1, wherein determining the density distributions of the first and second portions of the heap includes:comparing an initial muon attenuation for an initial density from an initial sample of the materials of the heap with the muon attenuation in the heap,comparing a prior time interval muon attenuation in the heap as measured during a prior time interval with the muon attenuation in the heap,comparing a fluid muon attenuation of process fluids with the measured incidence of atmospheric muons on the muon detector, orcomparing the muon attenuation in the heap to a surface measurement of the atmospheric muon flux.

5. The method of claim 4, wherein the surface measurement of the atmospheric muon flux includes an independent reference flux measurement at the surface or at a depth.

5. The method of claim 1, wherein the moving is horizontal to the earth’s surface.

6. The method of claim 1, wherein the moving is vertical to the earth’s surface.

7. The method of claim 1, wherein the moving is both horizontal and vertical to the earth’s surface.

8. The method of claim 1, further comprising placing and moving a second muon detector within a trench, borehole, tunnel, or pipe.

9. The method of claim 8, wherein the spacing between the first and second muon detectors is fixed as they both move.

10. The method of claim 8, wherein the spacing between the first and second muon detectors is controlled as one of them moves.

11. The method of claim 8, wherein the second muon detector has movement that is parallel to the movement of the first muon detector.

12. The method of claim 8, wherein the second muon detector has movement that is perpendicular to the movement of the first muon detector.

13. A method for monitoring a three-dimensional density distribution, comprising:placing a first muon detector within a trench, borehole, tunnel, or pipe that is located within a first portion of a heap,measuring an incidence of atmospheric muons on the first muon detector;moving the first muon detector to a second portion of the heap;measuring a second incidence of atmospheric muons on the first muon detector;placing a second muon detector within a trench, borehole, tunnel, or pipe that is located within a third portion of the heap; andmeasuring a third incidence of atmospheric muons on the second muon detector.

14. The method of claim 13, further comprising moving the second muon detector to a fourth portion of the heap and measuring a fourth incidence of atmospheric muons on the second muon detector.

15. The method of claim 14, wherein the trench, borehole, tunnel, or pipe of the first muon detector is parallel to the trench, borehole, tunnel, or pipe of the second muon detector.

16. The method of claim 13, further comprising determining the density of the first, second, and third portions of the heap.

17. The method of claim 13, wherein the moving is horizontal to the earth’s surface.

18. The method of claim 13, wherein the moving is vertical to the earth’s surface.

19. The method of claim 13, wherein the moving is both horizontal and vertical to the earth’s surface.

20. The method of claim 13, wherein the first muon detector further comprises an armored multiconductor cable.

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