Austral Gold's 2025 report for the Casposo mine in Calingasta, San Juan, Argentina, expects the plant to run another seven years. In the refinery, nitric acid dissolves the silver and zinc from the Merrill-Crowe precipitate, gold is smelted from the residue, and silver is recovered as chloride.
The Technical Report on the Casposo Mine, Calingasta Department, San Juan Province, Argentina, was prepared by Austral Gold Limited, with an effective date of June 30, 2025 and a signature date of October 14, 2025. The plant was designed and built for 1,200 t/d. It can handle up to 438,000 t a year over about 8,000 operating hours (93% physical availability), or about 55 t/h. The circuit has crushing, SAG grinding with gravity and an intensive leach reactor, agitated cyanide leaching, two-stage counter-current decantation (CCD) with belt filtration, and clarification and Merrill-Crowe. An on-site refinery and Inco air/SO2 cyanide destruction of barren solution complete the plant.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Report effective date | June 30, 2025 | Not applicable | Austral Gold Limited |
| Design capacity | 1,200 t/d (up to 438,000 t/a) | Not applicable | About 55 t/h; 46 t/h nominal |
| Crusher | 1.22 m x 0.91 m single-toggle jaw | Not applicable | Up to 110 t/h |
| Stockpile | About 3,300 t live, 8,500 t total | Not applicable | Open stockpile |
| SAG mill | 4.9 m x 7.0 m Allis, 1,870 kW VSD | Not applicable | About 76% of critical speed, up to 5% ball charge |
| Classification | Six 250 mm cyclones | Not applicable | P80 106 µm at 43% solids |
| Gravity | Gravity concentrator and intensive leach reactor | Not applicable | Batch ILR with hydrogen peroxide |
| Grinding thickener | To about 55% solids | Not applicable | Hychem AF302 flocculant |
| Leach | Nine tanks, up to 80 h | Not applicable | One 600 m³, six 300 m³, two 1,000 m³ |
| CCD | Two thickeners and two horizontal belt filters | Not applicable | Filter cake below 14% moisture |
| Metal recovery | Merrill-Crowe zinc cementation | Not applicable | Solids below 1 ppm before zinc addition |
| Cyanide destruction | Inco air/SO2 on barren bleed | Not applicable | Zinc removed by sulphide precipitation |
Overview
Front-end loaders feed run-of-mine ore into a ROM bin with a 400 mm static grizzly and rock breaker. An apron feeder feeds a jaw crusher, and the product goes to an open stockpile. Quicklime is added to the mill feed. A grate-discharge SAG mill with a scats crusher and a cyclone cluster grinds to P80 106 µm. A split of the cyclone underflow feeds a gravity concentrator and intensive leach reactor. The ground ore is thickened and leached in nine agitated tanks, then washed in two CCD thickeners and two belt filters. The filter cake is stockpiled and trucked to the waste dump. Pregnant solution is clarified, deaerated and precipitated with zinc dust. The precipitate is retorted for mercury, leached with nitric acid, and refined to separate gold and silver ingots.
Key Process Stages
Crushing. The crushing plant is designed for up to 110 t/h, twice the plant rate, to allow for shorter operating hours and maintenance. A tramp magnet protects the discharge conveyor. An emergency feed hopper with its own apron feeder keeps the mill supplied and is also used to recycle refinery slag.
Grinding and gravity. The SAG mill runs at up to 65% solids. Scats of 12 to 50 mm are crushed and returned. Two Warman 6/4 pumps feed the cyclones at 120 to 130 kPa, usually with four cyclones operating. The intensive leach reactor treats batches of gravity concentrate in a rotating drum with barren solution, hydrogen peroxide, cyanide, caustic and lead nitrate. The pregnant solution goes to clarification.
Leaching. Sodium cyanide pellets are dissolved to a 20% solution. Grinding thickener underflow at a nominal 46 t/h (maximum 55 t/h) flows through nine tanks totalling up to 80 hours of residence.
CCD and filtration. Leached slurry passes two CCD thickeners. The final underflow is filtered on two parallel horizontal belt filters with flocculant and guar gum. The first filtrate returns to CCD Thickener 2 as wash water. The last section of the belt is left unwashed so the cake dries enough for dry handling.
Clarification and Merrill-Crowe. A pre-clarification hopper forms a floc bed to remove fine solids carried over from the thickeners. Clarifying filters then bring solids below 1 ppm. A vacuum deaeration tower removes oxygen. Zinc dust is mixed with lead nitrate, which prevents passivation and helps silver recovery, and the precipitate is collected in filter presses.
Refinery. A refractory-lined electric retort removes mercury, which is caught in a condenser. Dilute nitric acid at 70°C for up to 12 hours dissolves the silver and zinc and leaves gold as a residue. The residue is filtered, dried and smelted with soda ash and borax into gold ingots. Sodium chloride precipitates silver chloride from the filtrate, which is filtered, dried and smelted into silver ingots. A packed-bed scrubber treats the nitrogen oxide and chlorine fumes.
Cyanide destruction. Most barren solution is reused in the grinding circuit. A bleed is detoxified by the Inco air/SO2 process with copper sulphate catalyst and reused as process water, including for belt filter cake washes.
Additional Interesting Data and Summary
Water sprays use process water from which most of the cyanide has been removed, to reduce environmental impact. Refinery slag is broken up, and large prills go back to the gold furnace. The remaining slag is fed to the mill to recover fine gold.
In summary, the 2025 Casposo report describes a small, established SAG, gravity and agitated leach plant with CCD and belt-filter washing and Merrill-Crowe recovery. Its refinery separates gold and silver on site by nitric acid leaching and silver chloride precipitation, and the filtered tailings are trucked as dry cake.
Key Processes
- Jaw crushing and open stockpile
- SAG milling with scats crushing to P80 106 µm
- Gravity concentration and intensive leach reactor
- Pre-leach thickening and agitated cyanide leaching
- Counter-current decantation and horizontal belt filtration
- Clarification, deaeration and Merrill-Crowe zinc cementation
- Mercury retorting, nitric acid leaching and separate gold and silver smelting
- Inco air/SO2 cyanide destruction of barren solution
Source: Technical Report on the Casposo Mine, Calingasta Department, San Juan Province, Argentina, prepared by Austral Gold Limited, effective date June 30, 2025.
Technical report and processing history
The following archived source profiles have been consolidated here to preserve the project’s processing history and study context.
Casposo Mine — 2016 Technical Report
Casposo Mine — 2016 Technical Report
| Company | Austral Gold Limited |
| Date | 2016-09-07 |
| Region | San Juan |
| Commodities | Gold, Silver |
Executive Summary
The Casposo Mine Technical Report outlines the recovery methods for gold and silver doré, which is transported to a refining facility in Brampton, Ontario, Canada. The processing and recovery method involves whole ore cyanide leaching for extraction, counter-current decantation (CCD) and filtration for liquid-solid separation, and Merrill-Crowe for recovery of the metal from the leach solution. The processing plant was designed by Mineral Engineering Technical Services Pty Ltd (METS) and utilizes second-hand equipment from the former McKinnons Gold Project in New South Wales, Australia.
The plant has a nameplate throughput of 400,000 tpa (50 tph), though current underground mine plans deliver approximately 300,000 tpa. The crushing circuit uses a single toggle jaw crusher fed by an apron feeder, with crushed ore stored in an open stockpile before being fed to the semi-autogenous grinding (SAG) mill. The SAG mill operates with a ball charge and discharges pebbles to a pebble crusher or bypass chute.
The grinding circuit includes a SAG mill and a decommissioned ball mill, with a gravity circuit using a Falcon centrifugal gravity concentrator to treat undersize material. Leaching is conducted in nine agitated tanks with an Intensive Leach Reactor (ILR) for high-grade gravity concentrates. Recovery is achieved via Merrill-Crowe zinc cementation after clarification and de-aeration, followed by refining in a mercury retort and smelting furnace to produce silver-gold doré.
Website: https://australgold.com/projects/operations/argentina-casposo-manantiales-mine-complex/
Report Date: 2016-09-07
Region: San Juan
Commodity: Gold, Silver
Casposo Project — Technical Report
Casposo Project — Technical Report
| Company | Troy |
| Date | Not Specified |
| Region | Not Specified |
| Commodities | Gold, Silver |
Executive Summary
The Casposo Project is designed to recover gold and silver dore bullion using the well-established Merrill Crowe process, a method widely used throughout the gold and silver mining industry. The recovered dore is subsequently transported to a refining facility in Brampton, Ontario, Canada, for further processing into high-purity gold and silver.
The processing plant configuration was strategically designed to utilize second-hand equipment from the former McKinnons Gold Project in New South Wales, Australia. This approach was adopted to ensure financial viability and immediate availability of plant components. Mineral Engineering Technical Services Pty Ltd (METS) of Perth, Western Australia, developed the process description for the project.
Detailed information regarding the processing plant configuration and operation is documented in Sections 13.1 through 13.13 of the full report, with the flowsheet included as Figure 13.1. This section focuses on the recovery methods and the strategic equipment sourcing that underpins the project’s economic model.
Website: https://www.mining.com/troy%E2%80%99s-casposo-gold-silver-project-goes-into-production/
Report Date: Not Specified
Region: Not Specified
Project Status:
Commodity: Gold, Silver
Throughput:
Mine Life:
Mine Type:
Ore type:
Casposo Project — NI 43-101 Technical Report
Casposo Project — NI 43-101 Technical Report
| Company | Troy Resources NL |
| Region | Argentina |
| Commodities | Gold, Silver |
| Status | Development |
Executive Summary
The Casposo Project is a proposed mining development focused on the recovery of gold and silver dore bullion. The recovered dore will be transported to a refining facility located in Brampton, Ontario, Canada, for further processing into high purity gold and silver. The proposed processing and recovery method is described as well known and widespread throughout the gold and silver mining industry.
The processing plant design prioritizes financial viability by utilizing second-hand equipment sourced from the former McKinnons Gold Project in New South Wales, Australia. This approach ensures that equipment is immediately available and reduces capital expenditure. Mineral Engineering Technical Services Pty Ltd (METS) of Perth, Western Australia, developed the process description for the project.
The processing plant is designed to handle up to 438,000 tons per annum (tpa) of ore. At 8,000 working hours per annum, this equates to an average throughput of 55 tons per hour (tph). The crushing section is designed to operate at a higher rate of up to 110 tph to allow for reduced operating hours and equipment maintenance. Detailed configuration and operation are referenced in Sections 13.1 through 13.7 of the full report.
Website: https://www.mining.com/troy%E2%80%99s-casposo-gold-silver-project-goes-into-production/
Report Date:
Region: Argentina
Project Status: Development
Commodity: Gold, Silver
Throughput:
Mine Life:
Mine Type:
Ore type:
