TECHNICAL FIELD

The invention relates to the use of in situ recovery (ISR) technology in hard rock ore bodies.

The invention relates particularly, although by no means exclusively, to the use of ISR technology to recover gold and copper from hard rock ore bodies.

The invention relates particularly, although by no means exclusively, to a method of in situ recovery of a valuable metal such as gold and copper from a hard rock ore body reserve and to an in situ recovery mine.

BACKGROUND ART

Current ISR technology includes (a) injecting a leach liquor into an ore body so that the leach liquor can extract valuable metals into the leach liquor and (b) removing, typically by pumping, leach liquor with metals in solution from the ore body, (c) extracting metals from the leach liquor, and (d) regenerating to the extent possible and returning regenerated and make-up leach liquor to the ore body.

ISR technology has been applied to the recovery of uranium and copper.

Uranium deposits suitable for ISL technology are in permeable sand or sandstone that are confined by adjacent impermeable structures, which facilitate leach liquor injection and leach liquor removal. A leach liquor is pumped into the ore body (below the water table) via a borehole and takes uranium in the ore body into solution. Typically, leach liquors fall into two categories: acids and carbonate reactants. Commonly used reactants include sulfuric acid, nitric acid, hydrochloric acid, sodium bicarbonate, and hydrogen peroxide. Sulfuric acid offers high leach performance at a relatively low cost but produces residues (e.g., gypsum), which degrade performance.

In current uranium ISR operations, uranium is recovered at relatively high recoveries from permeable sands and sandstones.

The applicant is not aware of ISR technology being applied on a commercially viable basis to hard rock ore bodies.

The term “hard rock ore bodies” is understood herein to mean ore bodies that have a low permeability, typically < 0.01 mD, more typically < 0.001 mD. Permeability and porosity are important criteria in the application of ISR.

As defined in Jackson, Kuhar, Esteban, and Dai (2017), although interlinked, key differences between the parameters include: permeability is “the ability of a rock to transmit fluids under differential pressure", and porosity is “the ratio of void space to bulk volume within a rock sample". Furthermore, effective porosity is “the ratio of interconnected pore volume (excluding dead-end or isolated pores)” .

Permeability is considered to be a more important factor in ISR where a fluid must be able to flow through rock from an injection point to a recovery point. High rock porosity will maximize the rock surface area that the fluid will contact during its flow path. However, fluid flow in and out of pores is usually a much slower process that is governed by diffusion.

The inherent permeability and porosity of the target ore body will have a significant impact on the extent to which ore body liberation will be required and therefore the cost of a process. Uranium has generally seen widespread is suitable for use of ISR owing to the natural permeability of many of these deposits. Similarly, examples may be found where copper has been extracted via ISR.

In summary, ISR applications tend to be confined to naturally permeable ore bodies or where the ground has been previously broken intentionally or as part of previous mining activity.

Typically, hard rock ore bodies include ore bodies that contain base metals, precious metals, industrial minerals, and precious or semi-precious gemstones.

Hard rock ore bodies do not usually include coal, oil shale, phosphate, sodium, potassium, or gilsonite deposits.

Challenges for hard rock ISR technology are creating access, leach liquor and redox chemistry, and solution containment.

Another over-arching challenge is to operate on a commercially viable basis in hard rock ore bodies that the applicant believes will only be able to operate at leaching rates that are an order of magnitude slower with lower recoveries than is the case with the use of ISR technology for uranium-containing permeable sands and sandstones.

A concept called “Resource ISR” was presented by the applicant at the 2018 ALTA conference. The concept includes leaching an entire ore body or large parts of the ore body at the same time. This ensures a continuous high metal production rate despite a low rate of metal leaching. This is a very different approach to that adopted in existing ISR operations.

The above description is not an admission of common general knowledge in Australia or elsewhere. SUMMARY OF THE DISCLOSURE

The invention is based on a realization that drill holes that were formed in a resource definition program to establish a hard rock ore body reserve, as described herein, are an opportunity for in situ recovery of a valuable metal from hard rock ore bodies.

The use of these resource definition drilled holes as production holes for in situ recovery of a valuable metal in a hard rock ore body reserve is an advantage because it does not incur additional drilling costs, which are typically substantial costs, and reduces the time required to commence an ISR operation.

The term “resource definition program” is understood herein to mean a drilling program and assessing rock samples collected in the program to establish a reserve in a mineral resource, including establishing boundaries of the resource and the geology and mineralogy of the reserve. Typically, the objective of a resource definition program in any given situation is to match a resource confidence level gained from an exploration drilling program to a short-, medium- and long-term mine design and schedule.

The term “reserve” is understood herein to mean an economically mineable part of an inferred and indicated resource. Reserves are that subgroup of a mineral resource that have been discovered, have a known size, and can be extracted at a profit.

The term “inferred resource” is understood herein to mean that part of a mineral resource for which quantity and grade or quality can be estimated on the basis of geological evidence and limited sampling and reasonably assumed, but not verified, geological and grade continuity.

The term “indicated resource” (also referred to as measured reserve) is understood herein to mean economic mineral occurrences that have been sampled (from locations such as outcrops, trenches, pits, and drill holes) to a point where an estimate has been made, at a reasonable level of confidence, of their contained metal, grade, tonnage, shape, densities, physical characteristics.

The term “valuable metal” is understood herein to mean any precious metal and any base metal that has economic value. Gold is an example of a precious metal and copper is an example of a base metal.

In general terms, the invention is a method and a mine for in situ recovery of a valuable metal from a hard rock ore body reserve. Resource definition holes that were drilled as part of a resource definition program are used as production holes. The resource definition holes are located over all or at least a substantial part of an area of the reserve. The method includes injecting a leach liquor into a plurality of the resource definition holes. The leach liquor penetrates the rock mass surrounding the resource definition holes and dissolves the valuable metal. The depleted leach liquor that contains the valuable metal is removed via the same or another plurality of the resource definition holes for downstream recovery of the valuable metal. As a consequence, there is leaching of at least a substantial part of the rock mass in the reserve at the same time.

The invention provides a method of in situ recovery of a valuable metal from a hard rock ore body reserve, as described herein, that includes:

(a) supplying, for example by injecting, a leach liquor into a plurality of resource definition holes as described herein that were drilled as part of a resource definition program for a hard rock ore body reserve and dissolving a valuable metal in the rock mass into the leach liquor, with the resource definition holes being located over all or at least a substantial part of an area of the reserve and thereby leaching at least a substantial part of the rock mass in the reserve at the same time;

(b) removing depleted leach liquor containing dissolved valuable metal from the resource definition holes, and

(c) processing the discharged depleted leach liquor containing and recovering the valuable metal.

In the above-described method, in effect, the resource definition holes are modified to become production holes.

Simultaneously leaching all or at least a substantial part of the rock mass in the reserve provides an opportunity for an economic mining operation in a hard rock mass, where it is usually only possible to achieve low leach rates because of the low permeability of the rock mass and other factors. The use of existing resource definition holes as production holes minimizes capital costs and the time to start production. Unlike known ISL technology that is used in permeable sand or sandstone deposits and is a small-scale well-field by small wellfield approach, the method of the invention is a comparatively large-scale operation, simultaneously leaching from at least a substantial part of the rock mass of the hard rock reserve and thereby compensating for low leach rates with a large-scale leaching operation, and accepting that full recovery from the rock mass could take a considerable time period, typically years. The method provides an opportunity for a low environmental impact mining operation, with a minimal above ground footprint and land disturbance. Conducting leaching operations in hard rock deposits that tend to be not very permeable makes it possible to mine safely, with leach liquor being contained within the reserve.

The substantial part of the reserve may be at least 85% of the area within a boundary of the reserve.

The substantial part of the reserve may be at least 90% of the area within a boundary of the reserve.

The substantial part of the reserve may be at least 95% of the area within the boundary of the reserve.

The method may include supplying the leach liquor into one group of resource definition holes and removing depleted leach liquor containing dissolved valuable metal from another group of resource definition holes.

The method may include supplying the leach liquor into and removing depleted leach liquor containing dissolved valuable metal from the same resource definition holes.

The method may include continuously supplying the leach liquor to the resource definition holes and continuously removing depleted leach liquor containing dissolved valuable metal from the resource definition holes.

The method may include periodically supplying the leach liquor to the resource definition holes and periodically removing depleted leach liquor containing dissolved valuable metal from the resource definition holes.

The method may include allowing a residence time of at least 2 hours of the leach liquor in the resource definition holes before removing depleted leach liquor containing dissolved valuable metal from the resource definition holes.

The method may include installing at the resource definition holes facilities for supplying leach liquor and recovering depleted leach liquor containing dissolved valuable metal.

In some embodiments, the method may include fracturing the rock mass surrounding at least some of the resource definition holes before supplying the liquor into the resource definition holes.

In other embodiments, fracturing the rock mass may not be required.

The fracturing step may include fracturing at least substantially all of the volume of rock mass in the reserve.

The fracturing step may include fracturing at least 85% by volume of the rock mass in the reserve. The fracturing step may include fracturing at least 90% by volume of the rock mass in the reserve.

The resource definition holes may be any suitable spacing(s).

For example, typical hole spacings are between 50- 100m.

The resource definition holes may be spaced further apart or closer than 50-100m.

The arrangement of holes may be in any suitable two-dimensional grid pattern.

Typically, the resource definition holes are in a 100m xlOOm, typically a 50m x 50m grid pattern.

The resource definition holes may be any depth(s).

The resource definition hole diameters may be any suitable diameter.

By way of example, internal hole diameters may be 40- 100mm, more typically 50- 70mm.

The extent of fracturing required in the fracturing step in any given situation will be a function of a range of factors including, but not limited to the geology of the hard rock ore body, such as permeability and porosity, and the selected recovery step (b).

The fracturing step may be any suitable step.

The fracturing step may be NaturaFrac™ pulsed gas stimulation inducing fractures in the rock mass.

The fracturing step may be NaturaFrac™ dynamic pulsed fluids injection unit inducing fractures in the rock mass.

The fracturing step may include injecting a hydraulic fracturing fluid into the drilled holes and inducing fractures in the rock mas.

The recovery step may be electrokinetic in situ leaching (EK-ISL), i.e. recovering valuable metal from the ore body by using an electric field to induce the migration of a leach liquor through the ore body. In electrokinetics, the generation of a current facilitates flow and transport of solutes through different processes (Acar and Alshawabkeh, 1993; Yeung, 2006).

The method may include drilling additional holes to the existing resource definition holes to cover at least the substantial area of the hard body rock mass in the reserve. For example, it may be found that the spacing and/or depth of the existing resource definition holes are not sufficient for recovering valuable metal from at least the substantial area of the hard rock ore body reserve and additional holes are required to do this.

The method may include designing the resource definition program and any additional holes having regard to requirements for using the holes to recover the valuable metal from the ore body. The method may include regenerating the leach liquor after recovering the valuable metal from the leach liquor/dissolved valuable metal removed from the resource definition holes and returning regenerated leach liquor to the resource definition holes, optionally with make-up leach liquor.

The leach liquor may be any suitable leach liquor in any suitable concentration having regard to the valuable metal and the mineralogy of the ore body and leach liquor injection/removal conditions.

In any given situation, key considerations for the fracturing step may include:

(i) forming fractures that provide pathways for leach liquor to penetrate the ore body including, for example, forming pathways for leach liquor to flow between resource definition holes; and

(ii) forming a network of fractures that facilitates a target recovery rate and recovery from the rock mass in the reserve.

The fracturing step may include casing each resource definition hole.

The fracturing step may include casing and lining each hole.

The fracturing step may include perforating each cased and lined hole so that injected hydraulic fracturing fluid flows through the perforations into the rock mass and induces fractures in the rock mass.

The fracturing step may include perforating the casing of each drilled hole at spaced intervals along a section of the drilled hole.

The fracturing step may include:

(i) lining each resource definition hole with a casing, such as with a metallic casing or a non-metallic casing;

(ii) pumping cement or any other suitable lining material down the cased hole to a lower end, i.e., toe, of the hole and then up into an annular space between a hole wall and the casing to form a lining between the hole wall and the casing;

(iii) positioning a well head on the cased and lined hole that closes the hole;

(iv) perforating the casing and the outer lining at spaced intervals along a section of the drilled hole with a perforating apparatus, such as a perforating gun having spaced explosive charges that is lowered down and raised from the cased and lined hole on a wire line;

(v) injecting a hydraulic fracturing fluid into the cased, lined, and perforated hole via the well head and forcing hydraulic fracturing fluid through the perforations into the rock mass and inducing fractures in the rock mass; and (vi) carrying out the series of steps (i) to (v) for each of a plurality of resource definition holes.

The perforated holes may be in “frac clusters”, with multiple perforated holes at different heights forming a single cluster.

The cased and lined hole may be perforated by any suitable perforating apparatus.

One example of a suitable perforating apparatus is a perforating gun having spaced explosive charges that can be initiated to from a perforate the immediate part of the cased and lined hole.

The hydraulic fracturing fluid may be any suitable hydraulic fracturing fluid. Typically, water is the hydraulic fracturing fluid.

The invention may include selecting hydraulic fracturing fluids that are suitable for forming fractures having different sizes and shapes.

Different hydraulic fracturing fluids may be required in different situations.

One option is forming parallel fractures (preferred by miners) - slower flow rate and more viscous hydraulic fracturing fluids.

Another option is forming complex fractures (preferred by seismologists) - different hydraulic fracturing fluids and higher flow rates.

The method may include positioning sensors in production holes that are outside the boundary of the reserve and assessing whether there is any escape of leach liquor from the reserve.

The invention also provides an in situ recovery mine for recovering a valuable metal from a hard rock ore body reserve, as described herein, that includes:

(a) a plurality of resource definition holes as described herein;

(b) a recovery unit configured for recovering a valuable metal from the hard rock ore body reserve by: i. supplying, for example by injecting, a leach liquor into a plurality of resource definition holes located over all or at least a substantial part of an area of the reserve and thereby leaching at least a substantial part of the rock mass in the reserve at the same time; ii. removing depleted leach liquor containing dissolved valuable metal from the resource definition holes; and iii. processing the removed leach liquor and recovering the valuable metal. In the above-described mine, the resource definition holes are modified to become production holes.

The recovery unit may be configured to supply leach liquor to and remove depleted leach liquor containing the valuable metal from the same resource definition hole.

The recovery unit may be configured to supply leach liquor to a plurality of the resource definition holes and remove depleted leach liquor containing the valuable metal from another plurality of plurality of the resource definition holes.

The recovery unit may include a fracturing unit configured for fracturing the rock mass of the reserve from the resource definition holes.

The fracturing unit may be a NaturaFrac™ pulsed gas stimulation unit for inducing fractures in the rock mass.

The fracturing unit may be a NaturaFrac™ dynamic pulsed fluids injection unit for inducing fractures in the rock mass.

The fracturing unit may be configured for injecting a hydraulic fracturing fluid into the drilled holes and inducing fractures in the rock mas.

The recovery unit may be an electrokinetic in situ leaching (EK-ISL) unit.

The invention provides a method of mining a valuable metal from a hard rock ore body reserve, as described herein, that includes:

(a) conducting a resource definition program to establish a hard rock ore body reserve, the program including drilling a plurality of resource definition holes as described herein and assessing rock samples collected in the program;

(b) the above-described method of in situ recovery of the valuable metal from the hard rock ore body reserve.

BRIEF DESCRIPTION OF THE DRAWING

The invention is described further below by way of example only with reference to the accompanying drawings, of which:

Figure l is a diagram of one embodiment of an in situ recovery mine and a method of in situ recovery in accordance with the invention; and

Figure 2 illustrates a series of resource definition holes in a section of a mine.

It is noted that the Figures are from publicly available sources and have been amended to include reference numerals. By way of example, Figure 2 is from a paper entitled “Geometallurgy - A Route to More Resilient Mine Operations” by Simon C Dominy et al, Minerals 2018, 8, 560, and has been amended to include reference numerals.

DESCRIPTION OF EMBODIMENT

The following description is in the context of in situ recovery of gold and copper from a hard rock ore body.

The invention is not confined to gold and copper recovery and extends to recovering any valuable metal from a hard rock ore body.

The embodiment of the mine and mining method shown in the Figures is based on the use of existing resource definition holes 3 in a hard rock ore body in a mine reserve that have been retrofitted to supply a leach liquor to the hard rock ore body and to remove depleted leach liquor containing valuable metal in solution for above-ground recovery of the valuable metal and regeneration and return of the leach liquor to the hard rock ore body.

The embodiment of the mine and mining method shown in the Figures supplies a leach liquor to a plurality of resource definition holes 3 and removes depleted liquor containing dissolved valuable metal from another plurality of resource definition holes 3.

Other embodiments of the mine and mining method supply leach liquor to a plurality of resource definition holes 3 and remove depleted liquor containing dissolved valuable metal from the same resource definition holes 3.

With reference to the Figures, the existing resource definition drilled holes 3 cover all or substantially the whole area of the reserve, i.e., the economically mineable part of an inferred and indicated resource, and often extend beyond a boundary of the reserve (not shown). The extent of resource definition holes 3 in a typical mine is illustrated in Figure 2. There is a significant number of resource definition holes 3 in the Figure, over a range of depths and drill angles.

In the embodiment, the resource definition holes 3 within the boundary of the reserve are modified to become production holes and the mine is configured to recover valuable metal from large fractions of the ore in a reserve at once rather than via smaller well-field by well-field approach that characterizes known in situ mining operations. In this way, the slow metal recovery in hard rock is at least partially overcome by leaching all or at least a substantial part of a reserve, albeit at potentially increased significant upfront capital, but longer term lower operating costs and minimal environmental impact and remediation costs. In addition, in the embodiment, sensors for assessing whether there is any escape of leach liquor from the reserve are positioned in resource definition holes 3 that are outside the boundary of the reserve.

With reference to Figure 1, the mine includes:

(a) a plurality of resource definition holes 3 that were drilled as part of a resource definition program to establish the hard rock ore body reserve;

(b) a fracturing unit (not shown) configured for fracturing the rock mass of the reserve from the resource definition holes; and

(c) a recovery unit generally identified by the numeral 5 configured for recovering valuable metal from the hard rock ore body reserve by supplying, in this instance, injecting a leach liquor into one group of resource definition holes and removing depleted leach liquor containing dissolved valuable metal from the rock mass from another group of resource definition holes and processing the removed leach liquor and recovering valuable metal.

The mining method includes the following steps:

(a) fracturing the rock mass of the reserve from the resource definition holes 3 that were drilled as part of a resource definition program to establish the hard rock ore body reserve; and

(b) recovering valuable metal from the hard rock ore body reserve by supplying, in this instance, injecting a leach liquor into one group of resource definition holes 3 and removing depleted leach liquor containing dissolved valuable metal from the rock mass from another group of resource definition holes 3 and processing the removed leach liquor and recovering valuable metal, with the resource definition holes 3 covering all or substantially all of the whole area of the reserve.

In the embodiment described in relation to Figure 1, the plurality of resource definition holes 3 have been modified to deliver a hydraulic fluid to the holes 3 to fracture rock mass between the holes 3.

The invention is not confined to the use of hydraulic fluid for fracturing the rock mass and extends to any other suitable options.

Hydraulic fracturing includes positioning well-heads on the resource definition holes 3 and injecting a suitable hydraulic fluid into the holes 3.

International application PCT/AU2021/050932 in the name of the applicant describes a method of hydraulic fracturing a rock mass as part of a method of establishing a block cave mine or extending an existing block cave mine. The hydraulic fracturing steps described in the international application, whilst for a different purpose, are suitable steps for use in the subject mining method. The disclosure in the international application is incorporated herein by cross reference.

After the hydraulic fracturing has been completed, the resource definition holes 3 are divided into a 1 ^st group of holes (the injection holes 3) for injecting a leach liquor and a 2 ^nd group of holes (the discharge holes 3) for discharging the pregnant leach liquor containing a target valuable metal (in this embodiment, gold or copper) in solution. The 1 ^st and 2 ^nd groups of holes 3 are indicated by the arrows in the Figure. The leach liquor is injected continuously into the 1 ^st group of resource definition holes 3 and depleted leach liquor containing dissolved valuable metal is removed continuously from the 2 ^nd group of resource definition holes.

The leach liquor may be any suitable leach liquor depending on the target valuable metal.

The mine includes a holding tank 11 containing pregnant leach liquor and a network of pipes 7 for delivering leach liquor to the injection holes 3 and a network of pipes 9 for transferring pregnant leach liquor from the discharge holes 3 to the recovery unit 5.

The recovery unit 5 includes:

(a) the holding tank 11 containing pregnant leach liquor,

(b) processing units 13, 15 for separating the target valuable metal from the pregnant liquor and regenerating the leach liquor and adding make-up leach liquor (as may be required), and

(c) a final processing unit 17 for producing separate marketable target valuable metal product.

The processing units 13, 15, 17 may be any suitable processing units depending on the target valuable metal.

The above-described embodiment is one embodiment amongst a number of embodiments in accordance with the invention that include fracturing a hard rock ore body of a reserve and recovering valuable metals from the ore body.

The process of assessing the requirements for any mine and mining method in accordance with the invention includes considering a range of factors, including the following factors.

• Natural porosity and permeability of the ore body itself versus the effort required to liberate via artificial means.

• The ore body texture (veins, brecciated, stockwork etc.). • The mineral dissemination across the ore body texture.

• Rock mass stability pre-post access creation.

• Target mineral extraction and recovery: o A good understanding of the mineralogy for both target and gangue minerals as this will dictate what chemistries may be applied. o Maximising target mineral extraction and recovery. o Minimising the time to extraction.

• Containment of the applied chemical fluid and metal-enriched pregnant leach liquor: o The hydrogeology of the target area needs to be well understood, including natural fluid flow through the ore body prior to access creation and location of the water table in relation to the target ISR zone. o Any major or minor faulting that may lead to losses need to be identified and assessed to determine whether barrier technology may be a solution or whether they represent fatal flaws in project execution.

• Well design: o Building on hydrogeological understanding to include potential flow paths and travel time from the injection to recovery wells for the ore target and this is influenced by the level of liberation that may be imparted.

Many modifications may be made to the above-described embodiment of a mine and a mining method without departing from the spirit and scope of the invention.

By way of example, the invention is not confined to fracturing a rock mass before supplying the leach liquor to the resource definition holes 3, as described in the embodiment. The invention extends to embodiments in which it is not necessary to fracture a rock mass.

In addition, the invention is not confined to gold and copper as target valuable metals, as described in the embodiment.

In addition, whilst the embodiment injects the leach liquor for the target valuable metal continuously into the 1 ^st group of resource definition holes 3 and removes depleted leach liquor containing dissolved valuable metal continuously from the 2 ^nd group of resource definition holes, the invention is not so limited. For example, the invention extends to embodiments in which there is periodic supply of leach liquor into the 1 ^st group of resource definition holes 3 and periodic removal of depleted leach liquor containing dissolved valuable metal from the 2 ^nd group of resource definition holes.