Recovery of metals from sulphide ores

Abstract

20 26 20 10 13 12 F eb 2 02 6 A B S T R A C T 2 0 2 6 2 0 1 0 1 3 1 2 F e b 2 0 2 6 1 / 3 12 10 Crushing 14 Flotation 18 16 44 Classification 46 SO4 bleed 24 20 26 22 53 42 Fe3+ Cu Heap 38 Biox 36 Cu SX / EW Leach 32 48 34 60 40 1 / 3 28 51 Au tank 54 Au Heap Au recovery Leach Leach 56 50 64 58 64 62 NaSCN or thiourea Heap capping / restoration 30 Fig. 1 20 26 20 10 13 12 F eb 2 02 6 2 0 2 6 2 0 1 0 1 3 1 2 F e b 2 0 2 6 C r u s h i n g F l o t a t i o n C l a s s i f i c a t i o n F e 3 + C u H e a p B i o xL e a c h A u t a n k A u H e a p L e a c h L e a c h H e a p c a p p i n g / r e s t o r a t i o n F i g . 1

Description

BACKGROUND OF THE INVENTION The present application claims priority from U.S. patent application No. 63 / 757,420, dated 12 February 2025, the contents of which are incorporated in their entirety. BACKGROUND OF THE INVENTION The recovery of gold from mixed copper and gold sulphide ores usually requires grinding the ore to a p80 of less than 0.2mm, and flotation of a copper concentrate containing some of the gold. This copper concentrate is then transported and smelted, with gold ultimately being recovered from the anode slimes. To meet the smelter requirements, the flotation conditions at the mine are adjusted to reject the pyrite that is present in the ore. Since the gold content of the ore is associated with all sulphides, this pyrite rejection also rejects part of the gold. Typical gold recoveries in the flotation concentrate, depending on the ratio of sulphides between copper and pyrite, is in the range from 50 to 80%. Copper flotation recoveries are typically between 80-90%. Even in ores when gold is partially liberated, rather than locked and hence inaccessible inside the pyrite grains, the copper content and the sulphidic nature of the ore makes cyanidation of gold difficult due to high cyanide consumption. Where gold grades don’t justify further recovery and processing of the pyrite in the ore, the gold is lost into the flotation tailings. Whether the feed originates from the tailings of a copper float, or directly from comminution of a gold ore, the pyrite can also be floated to form a pyrite concentrate containing the gold. This gold is typically present as fine grains 2026201013   12 Feb 2026 locked in the pyrite particle matrix. Recoveries by direct cyanide leaching of this pyrite concentrate are low because much of the gold is inaccessible inside the pyrite grains. Where gold grades in this pyrite concentrate justify the cost of further processing, the gold can be exposed for subsequent extraction by breaking down the pyrite crystal structure to expose the gold. This may be through ultrafine grinding, or roasting, or pressure oxidation, or biological oxidation, albeit at significant cost per tonne of pyrite treated Particularly for low grades of gold in the pyrite concentrate, this limits the gold that can be economically extracted. Where the pyrite is oxidised in solution it forms acid, which must be neutralised. Where economically feasible gold grades exist, the pyrite destruction is followed by cyanidation of the exposed gold. In a very different field of activity, the bioleaching of the copper content of primary copper ores has been claimed by various authors (Filmer - WO 2021 / 234653, Crundwell - US757522B, and Burley - US 11286540). Ore is crushed, preconditioned, and stacked in a heap and an acidic leachant is irrigated on the surface and aerated from the base, dissolving the copper and sulphide content of the rock as the leachant migrates down through the crushed rock. The microbial species in the heap accelerate the oxidation process. High extractions of chalcopyrite are achieved by maintaining the temperature of the heap above 60°C for an extended period. A counter current flow of air from the base of the heap supplies the oxidant in the form of oxygen. With appropriate balancing of aeration and irrigation rates, much of the exothermic heat of reaction can be retained in the heap. The hot, oxidising and acidic conditions for copper dissolution in such heaps are equally well suited for oxidation of pyrite and recovery of uranium, and other base metals such as zinc, which may be present in the ore being heap leached. 2026201013   12 Feb 2026 During the crushing of the ore to prepare it for heap leaching, selective breakage occurs along sulphide grain boundaries, such that even at coarse crush sizes such as 2-10mm, much of the copper sulphide and pyrite mineralisation in the ore is exposed, but not fully liberated. Unlike chalcopyrite, the pyrite fraction can be leached at near ambient temperatures. The pyrite oxidation creates both heat and acid, providing the pH conditions of the heap are such that ferric ion is soluble. The soluble ferric ion oxidises the pyrite more rapidly, and the resultant ferrous ion is re-oxidised by air, assisted by microbial species present in the ore. The oxidation of the exposed pyrite provides the initial thermal energy and acid generation to assist with the initiation and finalisation of the chalcopyrite leaching. Most of the iron ultimately precipitates in the heap predominantly as a jarosite. This iron precipitate is problematic if the ore is to subsequently cyanide leached for recovery of gold. The redissolution of the acidic jarosite occurs as the pH rises, consuming substantive amounts of base over the duration of the leach where cyanidation can take place safely. Gold content of the ore is not dissolved in bioleaching due to a lack of complexant to stabilise the dissolved gold, in addition to the locking in the pyrite for some of the leach duration. The pyrite oxidation in a fully leached copper heap is initially faster than chalcopyrite, but surprisingly the final extraction is often slightly lower than other sulphides. Since pyrite is a source of both heat and acid for the leaching of copper ores, it is possible to precondition the heap not only by the conventional methods of 2026201013   12 Feb 2026 reducing the fines and adding acid to precondition the ore. But also, to add additional pyrite to the primary copper ore to be heap leached. Filmer and Burley teach the generation of a pyrite concentrate and add this back to the stacked ore. Filmer classifies the crushed ore to remove much of the fines and improve heap permeability, recovers the pyrite from a parallel flotation concentrator, and blends this pyrite concentrate either directly or by agglomeration back to the delimed coarse fraction. The prior classification enables a finer crush size without exceeding the permeability limits for a heap leach. The prior classification also increases the quantity of fines that can be introduced. Burley recovers the pyrite from historical tailings and adds this concentrate to the agglomeration stage of the more coarsely crushed ore. In a third field of endeavour, cyanide is the preferred leachant for recovery of gold from most gold ores. HCN gas formed in even mildly acidic cyanide solutions is highly toxic, so the cyanidation leach must operate under basic conditions, typically above pH 10, to ensure the hydrogen cyanide vapour pressure remains very low. The cyanide leaching takes place both in agitated tanks, and in the heap leaching of lower-grade gold deposits which do not justify milling to liberate the gold. The cyanide cannot not leach the gold particles that are fully locked in the pyrite fraction of the ore, where the solution simply cannot access the gold surfaces. Cyanide reaction rates, even in an agitated tank, require an extended leach duration (12-36 hours). Even when safely handled, the dissolved cyanide and complexes of cyanide in the wastewater are toxic to the receiving environment. 2026201013   12 Feb 2026 Because of the many concerns about cyanide use, many alternative leachants have been proposed to replace cyanide in gold extraction. These efforts have focussed almost exclusively on finely ground and well liberated Au ores. One group of alternative leachants are the halogens, chlorine, bromine of iodine. These typically require high pH environments to reduce their vapour pressure. Chlorine and bromine also suffer from high consumption in sulphidic ores as they preferentially oxidise the sulphides. Iodine is a weaker oxidant and only oxidises the sulphides very slowly. Whilst this oxidation by chlorine or bromine can liberate the gold, the oxidant must be regenerated electrolytically, and generation of acid through the oxidation of sulphides causes a high consumption of lime or similar alkali to maintain a safe pH. Applications of the halogens have been limited to recovery of gold from very specific gold containing intermediates. A second grouping of alternative complexants for gold, also operating in basic conditions, comprises thiosulphate, and glycine. These complexants can themselves be oxidised so must be utilised in mildly oxidising conditions. Under these conditions of pH and eH, pyrite is not significantly oxidised. Hence, any gold that is locked in the pyrite remains unleached. The extent of thiosulphate consumption by oxidation is a problem even under mildly oxidising conditions. Glycine is an expensive reagent at the concentrations required. Neither has found widespread commercial applications. A third grouping of complexants operate under acidic conditions at pH around 1.5-2.5 and comprise thiocyanate Azizitorghabeh et. al. A review of thiocyanate gold leaching - Chemistry, thermodynamics, kinetics and processing, Minerals Engineering Volume 160, 1 January 2021, 106689; and thiourea Li et. al A Review of Gold Leaching in Acid Thiourea Solutions Mineral Processing and Extractive Metallurgy Review ; An International Journal; Volume 27, 2006 - Issue 3 pages 177-214. 2026201013   12 Feb 2026 When considering the acidic leaching of gold, the acid consumptions of the ore to reach this low pH can be excessive. Both complexants typically use ferric ion as the oxidant. Pyrite in the ore will react slowly with the ferric ion, reducing the eH, but not substantively dissolving the pyrite. As noted previously, the pyrite must be oxidised to allow leachant access to the locked gold. This requires the use of an additional oxidant which will oxidize the complexants, and very large reactors given the residence time required to oxidise pyrite. Hence leaching of gold in sulphidic ores using thiourea or thiosulphate or thiocyanate is inefficient. With acidic leaching of gold, the presence of dissolved copper in the leach solution can also be problematic, causing the precipitation of thiocyanate, and catalysing the oxidation of thiourea. Azizitorghabeh recognises these issues for thiocyanate leaching, and postulates that prior heap leaching of the base metal sulphides will dissolve copper, expose the gold, allowing subsequent leaching of gold with thiocyanate. But she provides no teachings on crush size and associated heap permeability constraints. In particular, she does not address the issue of iron precipitation in the heap, and its impact on the crush size that can be utilised and the impact of this on consequential gold recovery. With the proposed conventional agglomeration, the smallest crush size in commercial operation for secondary copper ores is a p80 of around 10mm. This limit is due to heap permeability constraints. At this crush size, the secondary copper sulphide heap leaching operations are achieving 75% recovery of copper or less. This recovery is consistent with results of Miller who used tomography 2026201013   12 Feb 2026 to study the liberation of sulphides at different crush sizes. Exposure of pyrite at similar levels can be expected. And most sulphidic gold ores contain higher levels of soluble iron (e.g. pyrite and chalcopyrite) than secondary copper ores (e.g. chalcocite and covellite). The dissolution of pyrite to liberate the gold will result in significantly more iron precipitation in the agglomerated heap. The iron precipitation as fine jarosite blocks the fine pores in the agglomerates reducing micro as well as macropermeability. Heap permeability issues of poorly distributed fluid flows will be substantially greater for heap leaching a sulphidic gold ore than for secondary copper ores. The only option for a proponent of Azizitorghabeh (heap leaching to pre-oxidise the pyrite) is to crush even more coarsely to reduce the quantum of naturally occurring fines in the heap. Gold recoveries will be adversely affected. Because the permeability constraints become significantly worse when considering a preleach of gold ores, bio-leaching to pre-oxidise pyrite is undertaken commercially using finely ground ore in agitated tanks. In summary, despite considerable intellectual effort over many years, sulphidic gold ores remain problematic. They require much higher grades than their oxide equivalents to justify the high-cost processing of a pyrite flotation concentrate to expose the locked gold prior to cyanidation. Cyanide, with its associated toxicity concerns, remains the complexant in common use for gold extraction. For mixed copper and gold sulphide ores, the optimum recovery method remains the grinding and flotation of a copper concentrate, despite low recoveries of gold. The tailings from this copper flotation, mostly do not justify the cost of a 2026201013   12 Feb 2026 sequential flotation of pyrite, and the high-cost processing of the pyrite concentrate prior to cyanidation, so are stored in a tailing’s storage facility. It is the aim of this invention to provide a process for the recovery of gold from mixed copper and gold sulphide ores. Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each of the appended claims. SUMMARY OF THE INVENTION In a first aspect, disclosed herein is a method for recovering metals from a sulphidic gold ore, comprising the steps of: - crushing and stacking the ore in a permeable heap; - heap leaching the stacked ore in a permeable heap in a first stage with an acidic ferric-containing solution to dissolve and recover a pregnant solution containing copper; and - leaching the ore in a second stage with an acidic ferric solution containing a complexant, to dissolve and recover a pregnant solution containing gold. In a second aspect, disclosed herein are recovered metals from a sulphidic gold ore, obtained by the method of the first aspect. Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the 2026201013   12 Feb 2026 exclusion of any other element, integer or step, or group of elements, integers or steps. Disclosed herein is a method for recovering metals from a sulphidic gold ore, including copper and gold containing sulphidic ores, comprising the steps of: 1. crushing and stacking the ore in a permeable heap; 2. heap leaching the stacked ore in a permeable heap in a first stage with an acidic ferric-containing solution to dissolve and recover a pregnant solution containing copper, expose gold in the ore, and prepare the ore for acidic gold leaching; and 3. leaching the ore in a second stage with an acidic ferric solution containing a complexant, to dissolve and recover a pregnant solution containing gold. The acidic ferric-containing solution of the first stage has a pH below 4, typically pH 1.2 to 3, and may contain 0.2 to 0.01M ferric as an oxidant. The first stage heap leach is typically carried out at a pH of 1 to 3, preferably a pH of 1.5-2.5. The acidic ferric-containing solution of the second stage second stage typically has a pH below 2.5, preferably 1 to 2, most preferably about 1.5 and may contain 0.2 to 0.001M ferric, typically 0.1 to 0.01M ferric as an oxidant. The complexant in the acidic ferric containing solution of the second stage may be thiourea or thiocyanate, or a combination thereof. 2026201013   12 Feb 2026 The acidic ferric-containing solution of the second stage may contain 0.025 to 0.3M thiourea, typically about 0.1M thiourea. The acidic ferric-containing solution of the second stage of leaching may contain 0.025 to 1M thiocyanate, typically about 0.5M thiocyanate. The second stage leach is typically carried out at a pH of 1 to 3, preferably a pH of 1.5-2.5. The ore may be crushed to a p80 of between 2-15 mm and preferably 3-7mm and most preferably about 5mm. Preferably, the fines content of the crushed ore is reduced to less than 15%, preferably less than 10%, more preferably less than 5% by subjecting the crushed ore to classification, agglomeration, or classification and agglomeration. Typically, the crushed ore is classified with a cut-point between 0.050 and 0.200 mm. Fines from the classification may be subjected to flotation to obtain a pyrite containing sulphide concentrate and a sulphide-depleted residue. Part or all of the pyrite containing flotation concentrate, or any externally generated pyrite concentrate, may blended with separated oversize crushed ore from classification, which is subsequently stacked and heap leached in the first stage. Part or all of the pyrite containing flotation concentrate, or any externally generated concentrate, may treated in an agitated biological reactor to generate a ferric solution which is supplied to the first stage of leaching. 2026201013   12 Feb 2026 Part or all of the fines from classification may be assigned directly to the agitated biological reactor. The ferric solution generated in an agitated biological reactor, and containing a microbial mix, may utilised in the irrigant including at the initiation of the heap leaching cycle to equilibrate the pH profile of the heap and hence to enhance the extraction of copper and oxidation of pyrite. The ferric solution generated in an agitated biological reactor, and containing a microbial mix, may be utilised in the irrigant in the final 50 days of the first stage heap leaching, to enhance the rate of extraction of the remaining pyrite. Residue from the agitated biological reactor may be further processed in an agitated gold leach reactor to recover the exposed gold, or the residue from the agitated biological reactor may be added to the heap during preconditioning for further sulphide oxidation and a subsequent second leach stage to recover the contained gold. The heap in the first stage of leaching is irrigated with acidic ferric containing leachant, and air is introduced from the base to leach the contained sulphides. Preferably, first stage heap leach conditions are controlled to a temperature between 50-80°C. Dissolved copper may be recovered from the pregnant solution from the first stage heap leach by solvent extraction and electrowinning to yield an acidic raffinate solution for recycle for further leaching or washing of the heap in the first stage leach. The acidic raffinate solution from the solvent extraction and electrowinning may be recycled as solution supplied to the agitated biological reactor. 2026201013   12 Feb 2026 The acidic raffinate solution from solvent extraction and electrowinning may be recycled as solution supplied to the copper heap leach. The second stage leach may be in an agitated vessel or a heap leach, preferably a heap leach. Residue from second stage heap leaching may be stored, and pregnant solution containing gold may be supplied to a gold agitation leach tank. A pregnant solution from the gold agitation leach tank may be supplied to a gold recovery process, for example a precipitation process. Acidic raffinate from the solvent extraction and electrowinning, which is deleted of copper and containing ferric, may be supplied as a ferric solution to the irrigant. A pregnant solution from second stage heap leaching may be supplied to a gold recovery process, for example a precipitation process. A barren thiocyanate / thiourea solution from the gold recovery process may be supplied with the leachant of the second stage heap leaching. Thiourea and thiocyanate may be added to the leachant of the second stage heap leaching. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1      is a block diagram of an embodiment of the invention: Figure 2     is a block diagram of another embodiment of the invention; and 2026201013   12 Feb 2026 Figure 3      is a graph illustrating the distribution of metals by particle size and height profile after column pre-leaching of the sulphides. DESCRIPTION OF EMBODIMENTS According to method of the present invention, a sulphidic gold ore comprising copper and gold containing sulphidic ores, wherein the ore is: crushed, preconditioned, and stacked in a permeable heap; leached in a first stage with an acidic ferric containing solution, wherein microbes enhance the oxidation of the sulphide content, enabling the recovery of copper, and oxidising the sulphides to increase the exposure of gold; leached in a second stage, with an acidic ferric containing solution containing thiocyanate and / or thiourea as a complexant, to dissolve the exposed gold. Preconditioning of the ore may comprise any one or more of: •  reducing the fines content in the ore by size classification •  reducing the fines content in the ore by classification and agglomeration. • mixing the ore with sulphuric acid and / or microbes and / or ferric ion to prepare it for heap leaching, • and blending additional pyrite from any source, together with the ore. The first stage of leaching is a heap leach under acidic and oxidising conditions, to extract most of the copper present in the ore and oxidise the pyrite in the ore, to dissolve and partially reprecipitate the iron. 2026201013   12 Feb 2026 The second stage of leaching of the residue of the first stage of leaching is in either a heap or an agitated vessel, under acidic conditions using a suitable complexant to extract the gold. Crush size of the ore for heap leaching is selected to achieve sufficient liberation of the sulphide fraction, such that a high proportion of the sulphides are exposed and hence subject to dissolution in the initial heap leach. The percentage exposure is preferably greater than 70%, most preferably greater than 85%. The crushed ore, depending on the grain size of the sulphides, may have a p80 in the range of 2-15mm, and preferably around 3-7mm, typically around 5mm. Preparation of the crushed ore for the first stage of heap leaching requires a suitably permeable heap. The ore may be preconditioned through size classification or agglomeration or both, to reduce the fines (<75 micron) content of the stacked heap to less than 15%, and preferably around 5%, and hence generate adequate permeability for fluids to flow uniformly through the heap for the full cycle of leaching. Where size classification is used in preconditioning, the fine fraction may be floated to form a sulphide concentrate containing pyrite. This pyrite concentrate will contain a substantive percentage of gold and copper that is present in the fine fraction of the ore to be floated. This pyrite containing sulphide concentrate, or additional pyrite concentrate from any source may be added to the first stage heap to generate more heat and acid through the oxidation process, hence aiding the heap leaching of the more refractory sulphides. Additional pyrite concentrate, from any source containing gold locked in pyrite, may also be added to the heap for the pyrite to be dissolved and hence expose gold for subsequent recovery. 2026201013   12 Feb 2026 The fines generated from classification may also be directed to an agitated biological leach to dissolve the copper and expose the gold. The stacked heap is leached for a sufficient duration under acidic conditions suitable to oxidise and extract the copper sulphides. The copper is recovered from the pregnant solution recovered from the base of the heap. Much of the iron and sulphate generated from the pyrite are reprecipitated in the heap, or precipitated external to the heap to maintain heap permeability. Under such conditions most of the pyrite present in the ore is also oxidised, exposing any contained gold. This may be more than 50%, and preferably more than 70% of the total contained pyrite. Once the heap leaching of copper and exposure of gold is completed, the heap may be efficiently washed to reduce the copper content, leaving the gold in the form of fine exposed grains suitable for subsequent extraction. The exposed gold in the residual heap is subsequently leached in a second stage of leaching in acidic conditions using ferric as the oxidant and a complexant such as thiocyanate or thiourea in acidic conditions. This extraction of the gold may be undertaken in a second stage of heap leaching, or the heap may be reclaimed with part or all of the residue processed in agitated vessels. This processing may be through agitated leaching of the reclaimed residue, or through further comminution and agitation leaching, or through size classification and agitation leaching of only the finer fraction of the residue. 2026201013   12 Feb 2026 Whilst the acidic condition of the residual heap from the first stage of leaching is a substantive disadvantage for gold cyanidation, the residue is ideally suited for acidic leaching with ferric ion as the oxidant. Much of the acid consuming gangue in the ore has already been consumed in the first stage of heap leaching. The bulk pH of the ore is around 1.5-2.5, minimising the acid consumption required for leaching with ferric ion in combination with thiocyanate or thiourea. The ferric content of the solution in the first stage of heap leaching has already created an equilibrium between the solution and jarosite precipitated in the heap. This jarosite acts as a potential form of soluble ferric ion during the second stage of gold leaching. The eH of the ore has been increased by an extended period of ferric leaching in the first stage, so the high eH required for gold leaching is easily maintained. And finally, the copper present in the ore has already been leached in the first stage of leaching. And residual copper content in the ore is low, avoiding the inadvertent consumption of the thiocyanate or thiourea complexant, either by oxidation catalysed by copper, or as a complex with copper. The first stage of leaching that takes place in the heap may be supplemented in part by an external agitated bioleach of some of the pyrite containing fine ore or flotation concentrate. to generate ferric and a microbial solution suitable for supplementing the irrigant with acid, microbial mix and ferric ion, in the first stage heap leaching. This agitated bio-leach concurrently exposes the gold present in the pyrite concentrate. Such agitation bioleaching is undertaken commercially under the trade name of Biox. The separate agitated bioleaching may take place on the fines generated by size classification, or on an externally generated pyritic concentrate. This external bioleach of a pyrite concentrate provides for the possibility of reducing fines content in the heap in the first stage of leaching, and for 2026201013   12 Feb 2026 processing externally generated gold pyrite concentrates at a greater proportion than the heap permeability constraints could absorb. The addition of the solution generated in the agitated bioleaching can utilise the slowly reacting gangue minerals present in the heap to precipitate some or much of the iron and sulphate within the heap. The separate agitated bioleaching and the consequential warm ferric solution it produces, may provide an opportunity to selectively use this solution in the irrigant. The solution can be used early in the leach cycle to further condition the heap. As the ferric ion buffers at around pH 2.5, it is consumed more slowly than acid alone. Hence it is more efficient than acid alone to dissolve the fast reacting gangue down through the full depth of the heap profile. The solution efficiently equilibrates the pH profile of the heap, into a pH and eH zone where the sulphides are reactive without excess acid consumption. The presence of the ferric ion also accelerates the rate of oxidation of pyrite, thus exposing gold more completely. The ferric solution generated by the separate agitated solution may also be used at the end of a first stage heap leach cycle, to extend the heap leach duration and maximise the extraction of pyrite in the heap. The dissolved copper generated in the pregnant liquor recovered from the first stage of leaching may be further processed by various methods well known to those skilled in the art, including by solvent extraction and electrowinning. The raffinate from solvent extraction can be recycled for further heap leaching, or to the agitated biological leach. The dissolved gold generated in the second stage of leaching may be recovered by various methods well known to those skilled in the art, including by 2026201013   12 Feb 2026 precipitation, such as by cementation with iron or zinc powder, or by ion exchange or by activated carbon, or any other suitable means. The reduction in fines content of the crushed ore prior to being stacked may be achieved by agglomeration of the fines onto the coarser fraction of the crushed ore. The reduction in fines content of the crushed ore prior to being stacked may be achieved by classification at a p50 cut size between 50 and 200 microns to remove the size fraction suited to flotation and reduce the content of the fines remaining in the oversize proportion of the crushed ore that is assigned to be heap leached. This fines fraction from the classification may floated to produce a sulphide concentrate containing most of the gold and base metal values. The sulphide concentrate may be blended back into the coarse ore fraction from classification prior to stacking of the heap. This blending may involve agglomeration or may be simple addition to the coarse stream. The coarse ore fraction from classification is stacked in the heap in the first stage of leaching and irrigated with an acidic ferric containing solution, and aerated, such as to create pH conditions in the range of 1.5-2.5 where pyrite and any other sulphides present are oxidised. This dissolves the copper and iron sulphides to expose the gold, and leaves the residue suitably prepared for the second stage of leaching. Some, or all of, the sulphide concentrate may be separated and oxidised in an agitated bioreactor to generate an acidic ferric sulphate solution for use as an additive to the irrigant in heap leaching. 2026201013   12 Feb 2026 The solution from the bioreactor, which is high in iron and microbial population, may be used as the irrigant or a supplement to the irrigant for the heap. In this duty the contained iron will at least partially precipitate forming acid and a ferric oxide such as jarosite or goethite within the heap. The pyrite oxidation resulting from additional ferric ion in solution will also accelerate the generation of heat and acid within the heap. The solution from the bio-oxidation may be added to the irrigant at selected times during the heap leach cycle, preferably in the initial stages of heap leach to rapidly condition the heap acidity, or in the final stages of the leach cycle to achieve the maximum oxidation of the remaining pyrite in the heap. The residue from the separate bio-oxidation of the sulphide concentrate may be further processed in an agitated reactor to recover the exposed gold, or the residue from the agitated bioreactor may be added to the heap during preconditioning for further oxidation and subsequent gold leaching. In the case of a primary copper containing sulphide ore, the heap temperature in the first stage of leaching may be maintained in an optimum range, typically in the range from 50-80°C, such as to leach the copper present as chalcopyrite, in addition to the pyrite. This exposes the gold present in the chalcopyrite particles. The pregnant solution containing copper from the first stage of leaching may be treated for copper recovery, preferably using solvent extraction and electrowinning, to generate a raffinate which may be used directly in the first stage leachant or used to dissolve iron in the bioreactor prior to being used in the irrigation of the first stage heap leach, or may be used as an acidic ferric containing solution in the second stage of leaching. 2026201013   12 Feb 2026 The iron leached from the pyrite is at least partially reprecipitated in the heap as a jarosite or goethite, or equivalent. The iron in the PLS or raffinate is recycled as raffinate to leach further copper and pyrite. Sulphate may be precipitated from the recirculating solution, for example by precipitation with lime or limestone, to maintain sulphate levels that enable effective population growth of the microbes. The gold that is present in both the copper and iron sulphides is liberated when the surrounding sulphide lattice is oxidised, leaving very finely divided gold particles adhering to the coarser ore residue in the heap. The high reactive surface area of this gold is particularly amenable to subsequent dissolution. The pH within the heap after pyrite oxidation is typically between 1.5 and 2.5 and the fast-reacting gangue present in the ore has been consumed in neutralising the ferric ions. Most of the copper has been dissolved and washed out of the heap, avoiding excessive reagent consumption in the second stage of leaching. As such, the heap is prepared by the first stage of leaching for subsequent second stage leaching of the gold using either thiocyanate or thiourea, with ferric as an oxidant. Once the copper and iron sulphides are adequately leached, the gold that was locked in the sulphides is exposed and hence is accessible to the leachant in subsequent heap or agitation leaching. Preferably the heap previously used to oxidise the sulphides is converted to a gold heap leach by changing the leachant. Ferric ion generated from the sulphide oxidation and contained in the raffinate from which the copper has been extracted, can be utilised as the oxidant in the second stage of leaching, in combination with thiourea or thiocyanate added as the complexant. 2026201013   12 Feb 2026 The finely divided gold is extracted and recovered from the pregnant solution, with recoveries that are higher than can be achieved without the pre-oxidation of the pyrite. Alternatively, the residue from the first stage heap leach may be reclaimed, and all or part of this residue can be agitation leached with ferric thiourea or ferric thiocyanate. With reference to Figure 1, in a process according to an embodiment of the invention, a sulphide ore 10 containing copper and gold is crushed 12 to a size where most of the sulphides are exposed. Due to differential fracture along sulphide grain boundaries, this size may have a p80 in the range of 2-15mm, and preferably in the range from 3-7 mm, typically around 5mm. Crushed ore 14 is prepared for heap leaching by size classification 16 to separate most of the fines 18, leaving the coarse fraction of the ore 20 sufficiently permeable for stacking and subsequent Cu heap leaching 22. The p50 classification cut size may be between 30 and 200 microns and preferably around 100-150 microns to generate the coarse ore fraction 20 for heap leaching and a fine ore fraction 18 for flotation. The fine ore fraction 18 may be floated 24 to generate a sulphide concentrate 26 containing most of the copper and gold, and a fine residue 28 for disposal or use in rehabilitating the heap 30. The flotation process 24 may comprise both conventional flotation and coarse flotation. The sulphide concentrate 26 may be biologically leached in an agitated reactor 32 to dissolve the pyrite and other sulphides to expose the gold in the residue 34 and dissolve the copper to generate an acidic ferric containing solution 36. 2026201013   12 Feb 2026 The ferric solution 36 (acidic (pH 1.2 to 3) ferric (0.01M to 0.2M) may be utilised in the irrigant used for Cu heap leaching 22 either as a mix with raffinate and intermediate leach solutions, or to form most or all of the irrigant at selected times through the leach cycle. The prepared ore with fines removed 20 may be further preconditioned prior to being stacked and Cu heap leached 22 with irrigant and aeration, to dissolve the pyrite and copper sulphides. Acidic ferric sulphate containing raffinate and ferric solution 36 may be added across the upper surface of the heap in the Cu heap leach 22, and air may be introduced from the base of the heap. Iron may be precipitated in the heap as jarosite or goethite. Copper may be recovered from the pregnant leach liquor 38 reporting to the base of the heap in the Cu heap leach 22, preferably by solvent extraction and electrowinning 40, with the acidic raffinate 42 recycled for further leaching. A bleed 44 from this raffinate 42 may be treated with lime or limestone 46 to manage the total sulphate concentrations in the irrigant to the heap leach 22, at levels which are not harmful to the microbial mix in the heap. On the completion of heap leaching to dissolve copper and pyrite and expose the gold the heap may be washed with raffinate 42 to reduce the concentration of copper and drained. The gold present in the washed heap is exposed, often as very finely divided gold particulates that were previously locked in either pyrite or copper sulphides. The residue 48 is now prepared for a second stage of heap leaching for gold recovery 50 using an acidic solution containing ferric as the oxidant, with a complexant for gold such as thiocyanate or thiourea. 2026201013   12 Feb 2026 The ferric solution used in this irrigant may be generated from raffinate 42 from copper solvent extraction 40, or directly from pyrite in a bio-oxidation reactor. Thiosulphate or thiourea, or both 64 may be added to the ferric containing solution to form the irrigant for dissolving gold. The prepared heap in the Au heap leach 50 is then irrigated with the acidic solution containing ferric as the oxidant 51 and a complexant suitable for dissolution of gold in the heap 50 (acidic (pH 1.5) ferric (0.1M) thiocyanate (0.5M solution or thiourea 0.1M, or both). Acidic raffinate 42 from the solvent extraction and electrowinning 40, which is depleted of copper and containing ferric, may be supplied as a ferric solution 53 to the irrigant 51. Pregnant solution 54 from the of the gold containing heap 50 may be used as a leachant in the agitated dissolution of gold in a tank leach 56 from the fine residue 34 in which the gold was previously exposed in the bioleaching 32 of the flotation concentrate. Gold may be recovered 58 by precipitation from a pregnant liquor 60 from the by a less noble metal powder such as iron or zinc, to generate a fine gold product suitable for smelting and further refining. Alternatively gold may be recovered 58 by extraction using ion exchange or activated carbon or cementation, prior to being eluted and recovered. Where gold is recovered 58 by precipitation, barren thiocyanate / thiourea solution 59 from Au recovery may be supplied as irrigant 51 to the heap leach 50. Additional thiocyanate / thiourea 64 may be added to the irrigant 51. A low grade pregnant liquor 54 from gold recovery 50 is used for the tank leach 56, and the pregnant liquor 60 from the tank leach 56 is sent for gold recovery 58. The spent heap 62 from gold leaching 52 can be sealed using the fines from flotation 24 and gold leaching 64 to reduce future mine drainage. 2026201013   12 Feb 2026 Figure 2 illustrates another embodiment of the invention. In this embodiment of the invention, a sulphide ore 10 containing copper and gold is crushed 12 to a size where most of the sulphides are exposed. Due to differential fracture along sulphide grain boundaries, this size may have a p80 in the range of 2-15mm, and preferably in the range from 3-7 mm, typically around 5mm. Crushed ore 14 is prepared for heap leaching by size classification 16 to separate most of the fines 18, leaving the coarse fraction of the ore 20 that is agglomerated 21 for stacking and subsequent Cu heap leaching 22. The p50 classification cut size may be between 30 and 200 microns and preferably around 100-150 microns to generate the coarse ore fraction 20 for heap leaching and a fine ore fraction 18 for flotation. The fine ore fraction 18 may be floated 24 to generate a sulphide concentrate 26 containing most of the copper and gold, and a fine residue 28 for disposal or use in rehabilitating the heap. The flotation process 24 may comprise both conventional flotation and coarse flotation. The pyrite containing concentrate 26 and any additional sulphide concentrates 27 may be agglomerated 21 with the oversize 20 from classification. Acidic, ferric sulphate containing irrigant may be added across the upper surface of the heap in the Cu heap leach 22, and air may be introduced from the base of the heap. Iron may be precipitated in the heap as jarosite or goethite. Copper may be recovered from the pregnant leach liquor 38 reporting to the base of the heap in the Cu heap leach 22, preferably by solvent extraction and electrowinning 40, with the acidic raffinate 42 recycled for further leaching. 2026201013   12 Feb 2026 On the completion of heap leaching to dissolve copper and pyrite and expose the gold the heap may be washed with raffinate 42 to reduce the concentration of copper and drained. The gold present in the washed heap is exposed, often as very finely divided gold particulates that were previously locked in either pyrite or copper sulphides. After the initial heap leach 22, acidic residue 48 with exposed gold is subjected to a second heap leach 50 using an irrigant 51 containing a complexant for gold such as thiocyanate or thiourea, with iron as the oxidant. Acidic raffinate 42 from the solvent extraction and electrowinning 40, which is deleted of copper and containing ferric, may be supplied as a ferric solution 49 to the irrigant 51 Pregnant solution 52 from this heap leach 50 is subjected to gold recovery 58 using techniques such as ion exchange or activated carbon or cementation. The residue 62 from the second heap leach 50 from which most of the sulphides have been oxidised, is appropriately disposed 30. As will be apparent to those skilled in the art, there are many alternative embodiments to the example utilised in Figures 1 and 2. Some examples are described herein The sulphide ore may contain values of copper and gold; or may contain predominantly gold. For ores containing copper, prior oxidation of the copper minerals exposes the gold in chalcopyrite and pyrite for subsequent recovery. Where the ore does not contain copper, the recovery of copper will not be required. Where the ore contains additional values such as uranium and zinc, additional recovery stages will be included. 2026201013   12 Feb 2026 The reduction in fines prior to heap leaching may be achieved by either classification and / or agglomeration. In the embodiments in which agglomeration is used, the fines to be agglomerated may be the whole of the fines fraction generated by crushing or may be the concentrate formed by flotation of the fines after classification. The pyrite containing concentrate generated by flotation of fines, or any additional source of pyrite concentrate may be separately agitation bioleached or added directly to the heap during preconditioning or both. The bioleach may process all or part of the fines directly from classification. The residue from the separate agitated bioleach may be either separately leached for gold recovery, or may be added to the heap, for gold recovery, The residue of the first stage of heap leaching may be heap leached for gold recovery, or may be directly agitation leached, or screened with the resulting fine fraction being enriched in gold content. These fines may be agitation leached, or further comminuted and agitation leached. The flotation of the fines may comprise conventional flotation and coarse flotation. The flotation may produce a single copper and pyrite concentrate or may produce a copper and a pyrite concentrate. Where separate concentrates are produced, the copper concentrates may be sold as a final product or may be further processed. 2026201013   12 Feb 2026 The acidic ferric solution for gold extraction may be generated by the internal oxidation of sulphides, or by the dissolution of precipitated iron in the heap, or by a separate solution of complexant and oxidant suited for gold dissolution The fine residues may be separately stored, or may be admixed with the coarse residue from heap leaching, or may be used to seal the surface of the heap during rehabilitation. By adapting the many possible embodiments to suit the particular ore characteristics, the invention can increase the recovery of both copper and gold relative to prior art, and minimise the reagent costs for leaching of gold in a second stage leach by preconditioning the pH and eH of the ore, and generate the particle size distribution and composition of the residues that enables a reduced environmental footprint of the processing. The invention provides several benefits relative to conventional flotation and subsequent gold exposure and cyanidation technologies. Firstly, the ore does not need to be finely ground to fully liberate the sulphide fraction, thus reducing energy consumption in comminution, and providing a residue which is ideally sized for dry disposal thus reducing overall water consumption. Secondly, the copper and gold can both be recovered in metallic state, eliminating the need for subsequent smelting of concentrates with its associated transportation and processing costs. Thirdly, the gold can be subsequently recovered from an acidic system, eliminating the need for neutralisation of the acid prior to recovery of gold from a basic system, and reducing the reagent costs for acidic gold leaching by 2026201013   12 Feb 2026 preparing the ore at an appropriate pH and providing stable conditions for ferric leaching. Fourthly environmental footprint is much reduced by eliminating the use of cyanide. Also, the oxidation and reprecipitation of the sulphides avoids the future sulphide oxidation and potential for acid mine drainage. And fifthly, the recovery of copper and especially gold is enhanced relative to flotation of a saleable copper concentrate. Sixthly, the costs of gold recovery are much enhanced over the alternative methods of liberating and recovering sulphidic gold. In combination, these factors enable the economic processing of lower grade ores. EXAMPLE EMBODIMENTS The present disclosure may be described by one or more of the following example embodiments. 1. A method for recovering metals from a sulphidic gold ore, comprising the steps of: - crushing and stacking the ore in a permeable heap; - heap leaching the stacked ore in a permeable heap in a first stage with an acidic ferric-containing solution to dissolve and recover a pregnant solution containing copper; and - leaching the ore in a second stage with an acidic ferric solution containing a complexant, to dissolve and recover a pregnant solution containing gold. 2026201013   12 Feb 2026 2. The method of example embodiment 1, wherein the acidic ferric-containing solution of the first stage has a pH below 4. 3. The method of example embodiment 1 or example embodiment 2, wherein, the acidic ferric-containing solution of the first stage has a of pH 1.2 to 3. 4. The method of any one of example embodiments 1 to 3, wherein the acidic ferric-containing solution of the first stage contains 0.2 to 0.01M ferric. 5. The method of any one of example embodiments 1 to 4, wherein the first stage heap leach is carried out at a pH of 1 to 3. 6. The method of any one of example embodiments 1 to 5, wherein the first stage heap leach is carried out at a pH of, optionally a pH of 1.5-2.5. 7. The method of example any one of example embodiments 1 to 6, wherein the acidic ferric-containing solution of the second stage has a pH below 2.5. 8. The method of any one of example embodiments 1 to 7, wherein the acidic ferric-containing solution of the second stage has a pH from 1 to 2. 9. The method of any one of example embodiments 1 to 8, wherein the acidic ferric-containing solution of the second stage has a pH of about 1.5. 2026201013   12 Feb 2026 10. The method of any one of example embodiments 1 to 9, wherein the acidic ferric-containing solution of the second stage contains 0.2 to 0.001M ferric. 11. The method of any one of example embodiments 1 to 10, wherein the acidic ferric-containing solution of the second stage contains 0.1 to 0.01M ferric. 12. The method of any one of example embodiments 1 to 11, wherein the complexant in the acidic ferric containing solution of the second stage contains thiourea or thiocyanate, or a combination thereof. 13. The method of any one of example embodiments 1 to 12, wherein the complexant in the acidic ferric containing solution of the second stage contains thiourea. 14. The method of any one of example embodiments 1 to 13, wherein the acidic ferric-containing solution of the second stage contains 0.01 to 0.3M thiourea. 15. The method of any one of example embodiments 1 to 14, wherein the acidic ferric-containing solution of the second stage contains about 0.1M thiourea. 16. The method of any one of example embodiments 1 to 15, wherein the complexant in the acidic ferric containing solution of the second stage contains thiocyanate. 17. The method of any one of example embodiments 1 to 16, wherein the acidic ferric-containing solution of the second stage contains 0.01 to 1M thiocyanate. 2026201013   12 Feb 2026 18. The method of any one of example embodiments 1 to 14, wherein the acidic ferric-containing solution of the second stage contains about 0.5M thiocyanate. 19. The method of any one of example embodiments 1 to 18, wherein second stage leach is carried out at a pH of 1 to 3. 20. The method of any one of example embodiments 1 to 19, wherein second stage leach is carried out at a pH of 1.5-2.5. 21. The method of any one of example embodiments 1 to 20, wherein the ore is crushed to a p80 of between 2-15 mm. 22. The method of any one of example embodiments 1 to 21, wherein the ore is crushed to a p80 of between 3-7mm. 23. The method of any one of example embodiments 1 to 22, wherein the ore is crushed to a p80 of about 5mm. 24. The method of any one of example embodiments 1 to 23, wherein the fines content of the crushed ore is reduced to less than 15% by subjecting the crushed ore to classification,  agglomeration,  or classification and agglomeration. 25. The method of example embodiment 24, wherein the fines content of the crushed ore is reduced to less than 10%. 26. The method of example embodiment 24 or example embodiment 25, wherein the fines content of the crushed ore is reduced to less than 5%. 2026201013   12 Feb 2026 27. The method of any one of example embodiments 1 to 26, wherein the crushed ore is classified 16 with a cut-point between 0.050 and 0.200 mm. 28. The method of any one of example embodiments 1 to 27, wherein fines from the classification is subjected to flotation to obtain a pyrite containing sulphide concentrate and a sulphide-depleted residue. 29. The method of example embodiment 28, wherein part or all of the pyrite containing flotation concentrate, or any externally generated pyrite concentrate, is blended with separated oversize crushed ore from classification, which is subsequently stacked and heap leached in the first stage. 30. The method of example embodiment 28, wherein part or all of the pyrite containing  flotation concentrate, or any externally generated concentrate, is treated in an agitated biological reactor to generate a ferric solution which is supplied to the first stage of leaching. 31. The method of example embodiment 30, wherein part or all of the fines from classification may be assigned directly to the agitated biological reactor. 32. The method of example embodiment 30, wherein the ferric solution generated in an agitated biological reactor, and containing a microbial mix, is utilised in the irrigant at the initiation of the heap leaching cycle to equilibrate the pH profile of the heap and hence to enhance the extraction of copper and oxidation of pyrite. 2026201013   12 Feb 2026 33. The method of example embodiment 30, wherein the ferric solution generated in an agitated biological reactor, and containing a microbial mix, is utilised in the irrigant in the final 50 days of the first stage heap leaching, to enhance the rate of extraction of the remaining pyrite. 34. The method of example embodiment 30, wherein a residue from the agitated biological reactor is further processed in an agitated gold leach reactor to recover the exposed gold, or the residue from the agitated biological reactor is added to the heap during preconditioning for further sulphide oxidation and a subsequent second leach stage to recover the contained gold. 35. The method of any one of example embodiments 1 to 34, wherein the heap in the first stage of leaching is irrigated with acidic ferric containing leachant and air is introduced from the base to leach the contained sulphides. 36. The method of any one of example embodiments 1 to 35, wherein the first stage heap leach conditions are controlled to a temperature between 50-80°C. 37. The method of any one of example embodiments 1 to 36, wherein dissolved copper is recovered from the pregnant solution from the first stage heap leach by solvent extraction and electrowinning to yield an acidic raffinate solution. 38. The method of example embodiment 37, wherein the acidic raffinate solution from the solvent extraction and electrowinning is recycled as solution supplied to the agitated biological reactor. 2026201013   12 Feb 2026 39. The method of example embodiment 37, wherein acidic raffinate solution from solvent extraction and electrowinning is recycled as solution supplied to the copper heap leach. 40. The method of any one of example embodiments 1 to 39, wherein the second stage leach is in an agitated vessel or a heap leach. 41. The method of example embodiment 40, wherein the second stage leach is a heap leach. 42. The method of any one of example embodiments 1 to 41, the pregnant solution containing gold is supplied to a gold agitation leach tank. 43. The method of example embodiment 42, wherein a pregnant solution from the gold agitation leach tank is supplied to a gold recovery process. 44. The method of example embodiment 43, wherein the gold recovery process is a precipitation process. 45. The method of example embodiment 37, wherein acidic raffinate from the solvent extraction and electrowinning, which is deleted of copper and containing ferric, is supplied as a ferric solution to the irrigant. 46. The method of any one of example embodiments 1 to 45, wherein the pregnant solution from second stage heap leaching is supplied to a gold recovery process. 47. The method of example embodiment 46, wherein a barren thiocyanate / thiourea solution from the gold recovery process is supplied with the leachant of the second stage heap leaching. 2026201013   12 Feb 2026 48. The method of any one of example embodiments 1 to 47, wherein thiourea and thiocyanate is added to the leachant of the second stage heap leaching. 49. Recovered metals from a sulphidic gold ore, obtained according to the method of any one of example embodiments 1 to 48. EXAMPLES The heap leaching of primary copper ores has been extensively investigated in laboratory column and pilot scale experimentation. Extractions of copper at a crush size ranging from 0.15-7mm exceed 80% with some in excess of 90% after around 250 days. Pyrite extractions are marginally lower. At coarser crush sizes 0.15-12mm under comparable conditions, these copper extractions decline to around 70%. Higher copper extractions (>90%) are observed at a smaller crush size (top size 3mm). Higher pyrite extractions (>80%) are observed at 0.15-6.7mm when increasing the ferric content in the leachant to around 3gpl, simulating the recycle of raffinate from solvent extraction, or addition of ferric containing solution from a Biox reactor. To examine the impact of bioheap leaching on the subsequent liberation of gold for extraction, different types of copper gold ores were bio-leached to oxidise the copper minerals and pyrite with the residue subsequently leached for gold recovery. Four different samples from a gold resource, typically containing around 0.15% Cu, with pyrite levels ranging from 2% to 7% were tested. 2026201013   12 Feb 2026 Flotation recoveries of gold into a saleable copper concentrate, generated from the different ore samples ranged from below 50 to 70%. One sample from a copper ore containing 0.15gpt Au and 2% pyrite was also tested. Flotation recovery of gold into a saleable copper concentrate from this ore was 70%. Each ore sample was crushed to a top size of 6.9 mm and then screened at 0.15 mm to remove the fine fraction, to generate a coarse ore fraction with high permeability suitable for heap leaching. The oversize fraction of each sample was preconditioned with 5kgpt sulphuric acid and placed in a column for bio-heap leaching. The temperature of each column was controlled to simulate a large 3-dimensional heap, with irrigant added to the top of the column and aeration from below. Column temperature was ramped commensurate with the expected heat generation in a large heap, calculated from the rate of oxygen uptake by the oxidising ore. After around 250 days at 70°C, the bioleach of copper and pyrite was terminated. For each ore sample, the extraction of copper in the bioleach column was around 85% with no gold reporting to the leach solution. Around 70% of the pyrite was oxidised in the 250 days in each sample. Despite very high pyrite contents in some of the ore samples, and visual evidence of jarosite precipitation within the column, no blocking or channelling of the irrigant was observed in the crushed and classified ore. 2026201013   12 Feb 2026 The residues from each of the 5 column bioleach tests were split, with samples being tested for subsequent gold leaching in both rolling bottle and column heap leaching conditions. The rolling bottle tests were intended to show maximum potential extraction from the 0.15-6.9mm bioleach residues, while the column leaching was designed to illustrate the gold extraction in a heap that contained jarosite which had precipitated, hence might be subject to surface coatings or channelling of leachant. Two alternative acidic leachants were used for both the rolling bottle and column leaching. In the column tests, an acidic (pH 1.5) ferric (0.01M) thiourea (0.1M) solution, an acidic (pH 1.5) ferric (0.1M) thiocyanate (0.5M solution) and a alkaline sodium cyanide solution (pH 10, 0.02M) was used. In rolling bottles, reduced concentrations of the acidic thiourea and thiosulfate reagents were used. In the rolling bottles, extractions of the gold from the column leaching residues ranged from 60-80% depending on ore sample. Comparative testing of each residue with a basic cyanide leachant showed no significant difference in extractions, indicating that the gold that was liberated from the -6.9mm + 0.15mm ore by the prior bio-oxidation was being efficiently extracted by both the acidic thiourea and the thiocyanate leachants. The same residues were carefully repacked in smaller columns and heap leached until the gold in the pregnant solution was no longer detectable. Based on solution analysis, rapid gold dissolution was observed with all leachants, indicating that the gold was present in finely divided and liberated form. Again, no statistical difference in extractions was observed between the acidic and basic leaching solutions. 2026201013   12 Feb 2026 Nor was there any statistical difference between bottle rolled and column leached gold extractions. Data from the second stage of column and roll-bottle leaching of the different ore samples with alternative leachants is illustrated in Table 1. Extractions were calculated by reconciliation of the solution and solids analyses. Table 1 Leachant Test Conc. (M) Durati on (d) Au Extraction % Gold Ore 1 Gold Ore 2 Gold Ore 3 Gold Ore 4 Copper Ore 1 Thiocyanate Column 0.50 45 66 70 79 62 81 Roll-bottle 0.10 8 68 72 75 66 79 Roll-bottle 0.05 8 66 75 75 71 72 Roll-bottle 0.02 8 83 50 53 69 69 Thiourea Column 0.10 36 71 68 83 68 74 Roll-bottle 0.10 7 83 86 78 68 74 Roll-bottle 0.05 7 62 62 65 59 55 Roll-bottle 0.02 7 71 67 71 69 75 Cyanide Column 0.02 11 52 74 76 73 65 These tests illustrate that high recovery of both copper and gold can be achieved in sequential heap leaching under acidic conditions. In summary, the copper recoveries by heap leaching ore crushed to 6.9mm are comparable to flotation at a p80 of 200 microns. The gold extractions by heap leaching are superior to those achievable by fine grinding and flotation into a saleable copper concentrate, especially for the ores containing high pyrite contents. 2026201013   12 Feb 2026 And gold extractions are broadly comparable to those anticipated from grinding, flotation, pressure oxidation, and cyanidation. The residue from the first stage of heap leaching contains coarse gangue together with fine fold that has been exposed by the sulphide dissolution. To test whether all the residue from the first stage of leaching needed to be leached in the second stage, the residue from the column leach of a primary copper ore containing gold was screened at 0.212 mm. Gold was distributed selectively to the fines with the gold centration in the fine fraction being 4 times that in the coarse ore. (Figure 3) Hence potential exists to upgrade the heap leach residue. However, for some ores, the overall recovery of gold to the fines may not justify direct disposal of the coarse fraction. It will be appreciated by persons skilled in the art that numerous variations and / or modifications may be made to the invention as shown in the specific embodiments without departing from the scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

1. A method for recovering metals from a sulphidic gold ore, comprising the steps of:-   crushing and stacking the ore in a permeable heap;-   heap leaching the stacked ore in a permeable heap in a first stagewith an acidic ferric-containing solution to dissolve and recover a pregnant solution containing copper; and- leaching the ore in a second stage with an acidic ferric solution containing a complexant, to dissolve and recover a pregnant solution containing gold.

2. The method claimed in claim 1, wherein the acidic ferric-containing solution of the first stage has a pH below 4, optionally a of pH 1.2 to 3.

3. The method claimed in any one of claim1 or claim 2, wherein the acidic ferric-containing solution of the first stage contains 0.2 to 0.01M ferric.

4. The method claimed in any one of claims 1 to 3, wherein the first stage heap leach is carried out at a pH of 1 to 3, optionally a pH of 1.5-2.5.

5. The method claimed in any one of claims 1 to 4, wherein the acidic ferric-containing solution of the second stage has a pH below 2.5, optionally a pH from 1 to 2 or optionally a pH of about 1.5.

6. The method claimed in any one of claims 1 to 5, wherein the acidic ferric-containing solution of the second stage contains 0.2 to 0.001M ferric, optionally contains 0.1 to 0.01M ferric.2026201013   12 Feb 20267. The method claimed in any one of claims 1 to 6, wherein the complexant in the acidic ferric containing solution of the second stage contains:- thiourea or thiocyanate, or a combination thereof; or - thiourea.

8. The method claimed in any one of claims 1 to 7, wherein the acidic ferric-containing solution of the second stage contains:-   0.01 to 0.3M thiourea; or- about 0.1M thiourea.

9. The method claimed in any one of claims 1 to 7, wherein the complexant in the acidic ferric containing solution of the second stage contains thiocyanate.

10. The method claimed in any one of claims 1 to 7 or 9, wherein the acidic ferric-containing solution of the second stage contains:-   0.01 to 1M thiocyanate; or-  0.5M thiocyanate.

11. The method claimed in any one of claims 1 to 10, wherein second stage leach is carried out at a pH of 1 to 3, optionally at a pH of 1.5-2.5.

12. The method claimed in any one of claims 1 to 11, wherein the ore is crushed to:- a p80 of between 2-15 mm; or- a p80 of between 3-7mm; or- a p80 of about 5mm.

13. The method claimed in claim 12, wherein the fines content of the crushed ore is reduced to less than 15% by subjecting the crushed ore to classification, agglomeration, or classification and agglomeration.2026201013   12 Feb 202614. The method claimed in claim 12 or claim 13, wherein:- the fines content of the crushed ore is reduced to less than 10%; or- the fines content of the crushed ore is reduced to less than 5%.

15. The method claimed in any one of claims 12 to 14, wherein the crushed ore is classified 16 with a cut-point between 0.050 and 0.200 mm, optionally wherein fines from the classification is subjected to flotation to obtain a pyrite containing sulphide concentrate and a sulphide-depleted residue, optionally wherein:- part or all of the pyrite containing flotation concentrate, or any externally generated pyrite concentrate, is blended with separated oversize crushed ore from classification, which is subsequently stacked and heap leached in the first stage; and / or- part or all of the pyrite containing flotation concentrate, or any externally generated concentrate, is treated in an agitated biological reactor to generate a ferric solution which is supplied to the first stage of leaching.

16. The method claimed in claim 15, wherein:- part or all of the fines from classification may be assigned directly to the agitated biological reactor; and / or- the ferric solution generated in an agitated biological reactor, and containing a microbial mix, is utilised in the irrigant at the initiation of the heap leaching cycle to equilibrate the pH profile of the heap and hence to enhance the extraction of copper and oxidation of pyrite; and / or- the ferric solution generated in an agitated biological reactor, and containing a microbial mix, is utilised in the irrigant in the final 50 days of the first stage heap leaching, to enhance the rate of extraction of the remaining pyrite; and / or2026201013   12 Feb 2026- a residue from the agitated biological reactor is further processed in an agitated gold leach reactor to recover the exposed gold, or the residue from the agitated biological reactor is added to the heap during preconditioning for further sulphide oxidation and a subsequent second leach stage to recover the contained gold.

17. The method claimed in any one of claims 1 to 16, wherein the heap in the first stage of leaching is irrigated with acidic ferric containing leachant and air is introduced from the base to leach the contained sulphides.

18. The method claimed in any one of claims 1 to 17, wherein the first stage heap leach conditions are controlled to a temperature between 50-80°C.

19. The method claimed in any one of claims 1 to 18, wherein dissolved copper is recovered from the pregnant solution from the first stage heap leach by solvent extraction and electrowinning to yield an acidic raffinate solution, optionally wherein:- the acidic raffinate solution from the solvent extraction and electrowinning is recycled as solution supplied to the agitated biological reactor; and / or- the acidic raffinate solution from solvent extraction and electrowinning is recycled as solution supplied to the copper heap leach; and / or- the acidic raffinate from the solvent extraction and electrowinning, which is deleted of copper and containing ferric, is supplied as a ferric solution to the irrigant.

20. The method claimed in any one of claims 1 to 19, wherein the second stage leach is in an agitated vessel or a heap leach, optionally wherein the second stage leach is a heap leach.2026201013   12 Feb 202621. The method claimed in any one of claims 1 to 20, the pregnant solution containing gold is supplied to a gold agitation leach tank, optionally wherein a pregnant solution from the gold agitation leach tank is supplied to a gold recovery process, and optionally wherein the gold recovery process is a precipitation process.

22. The method claimed in any one of claims 1 to 21, wherein the pregnant solution from second stage heap leaching is supplied to a gold recovery process, optionally wherein a barren thiocyanate / thiourea solution from the gold recovery process is supplied with the leachant of the second stage heap leaching.

23. The method claimed in any one of claims 1 to 24, wherein thiourea and thiocyanate is added to the leachant of the second stage heap leaching.

24. Recovered metals from a sulphidic gold ore, obtained by the method of any one of claims 1 to 23.

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