gold mines nickel mine and antimony mining in colombia

ranked: worlds top ten biggest nickel mines - canadian mining journal

Tesla CEO Elon Musk put nickel in news headlines last year when he called on theworlds miners to produce more, and arecent report by Roskillfound nickel demand from the EV sector alone is expected to grow by 2.6 million tonnes to 2040. The global nickel market is currently running at a surplus, but a supply deficit is expected to form in 2027 and remain as demand accelerates.

Russias Norilsk Nickels (Nornickel) Kola division, which includes five operating mines, takes first place. Located on the Kola Peninsula near the Norwegian and Finnish borders, the companys nickel refining hub is a complex fed through the Severny and Kaula-Kotselvaara mines. Kola led global nickel production by far in 2020, with 172,000 tonnes.Under scrutiny for its environmental footprint, Nornickel has pledged to invest about $5 billion over the next decade to clean up lines on the Kola Peninsula.

BHPs Nickel West operations, with three producing mines, takes second place. Low grade sulphide ore is mined from Mt. Keith, a large open pit operation, while high grade nickel sulphide ore is mined at the Cliffs and Leinster underground mines and Rockys Reward open pit mine. BHP is expanding its exposure to nickel bybuying nickel tenementsin Western Australia. Production last year was 75,000 tonnes.

In third place is Sorowako, where PT Vale produces nickel in matte from lateritic ores at its mining and processing facilities near Sorowako on the island of Sulawesi since 1968. Production is sold under long term contracts for refining. The total area is 190,509 hectares, and production for 2020 was 72,000 tonnes.

Nickel Asias Rio Tuba minein the province of Palawan in the Philippines takes 4th place, producing 65,000 tonnes in 2020. The open pit operation exports saprolite and limonite ore and provides limonite ore and non-mining services to the adjacent Coral Bay HPAL plant.

In 5th place is Glencores Sudbury Integrated Nickel Operations, comprised of the Fraser mine, Nickel Rim South mine, Strathcona mill and Sudbury smelter.The global miner has been mining nickel-copper ores in the Sudbury area since 1928. The facilities are spread throughout the 60-km-long geological formation known as the Sudbury Basin.

Rounding out the rest of top 10 areEramets New Caledoniaferronickel operations with five operating mines, Vales century-old Sudbury operations with five mines, the Murrin Murrin operations in Australia held by Glencore, the Cerro Matoso open pit in Colombia, and Vales Voiseys Bay mine in Canada.

ranked: world's top ten biggest nickel mines

Tesla CEO Elon Musk put nickel in news headlines last year when he called on theworlds miners to produce more, and a recent report by Roskill found nickel demand from the EV sector alone is expected to grow by 2.6Mt to 2040. The global nickel market is currently running at a surplus, but a supply deficit is expected to form in 2027 and remain as demand accelerates.

Russias Norilsk Nickels (Nornickel) Kola division, which includes five operating mines, takes first place. Located on the Kola Peninsula near the Norwegian and Finnish borders, the companys nickel refining hub is a complex fed through the Severny and Kaula-Kotselvaara mines. Kola led global nickel production by far in 2020, with 172Kt (kilotonnes). Under scrutiny for its environmental footprint, Nornickel has pledged to invest about $5 billion over the next decade to clean up lines on the Kola Peninsula.

BHPs Nickel West operations, with three producing mines, takes second place. Low-grade sulphide ore is mined from Mt. Keith, a large open-pit operation, while high-grade nickel sulphide ore is mined at the Cliffs and Leinster underground mines and Rockys Reward open-pit mine. BHP is expanding its exposure to nickel by buying nickel tenements in Western Australia. Production last year was 75Kt.

In third place is Sorowako, where PT Vale produces nickel in matte from lateritic ores at its mining and processing facilities near Sorowako on the island of Sulawesi since 1968. Production is sold under long-term contracts for refining. The total area is 190,509 hectares, and production for 2020 was 72Kt.

Nickel Asias Rio Tuba minein the province of Palawan in the Philippines takes 4th place, producing 65Kt in 2020. The open-pit operation exports saprolite and limonite ore and provides limonite ore and non-mining services to the adjacent Coral Bay HPAL plant.

In 5th place is Glencores Sudbury Integrated Nickel Operations, comprised of the Fraser mine, Nickel Rim South mine, Strathcona mill and Sudbury smelter.The global miner has been mining nickel-copper ores in the Sudbury area since 1928. The facilities are spread throughout the 60 kilometer-long geological formation known as the Sudbury basin.

Rounding out the rest of top 10 are Eramets New Caledonia ferronickel operations with five operating mines, Vales century-old Sudbury operations with five mines, the Murrin Murrin operations in Australia held by Glencore, the Cerro Matoso open-pit in Colombia, Vales Voiseys Bay mine in Canada.

stibnite gold project by midas gold, yellow pine, idaho, usa

The Stibnite gold project being developed by Midas Gold in central Idaho is expected to be one of the biggest and highest-grade open-pit gold mines in the US. It will also be the only primary producer of antimony in the country. The project is located in a historical mining district that had seen mining operations since 1894 with a sluice box operation by Caswell brothers in the Thunder Mountain mining district, east of Stibnite. A pre-feasibility study for the project was released in 2014 while the completion of a feasibility study was announced in December 2020. The project is estimated to require an investment of approximately 1.17bn ($1.6bn) for an estimated mine life of 14.3 years. Project location and geology The Stibnite gold project is located approximately 245km north-east of Boise and approximately 16km east of Yellow Pine, in Idaho, US. The project covers a total area of approximately 27,104 acres.

The project is located in a historical mining district that had seen mining operations since 1894 with a sluice box operation by Caswell brothers in the Thunder Mountain mining district, east of Stibnite. A pre-feasibility study for the project was released in 2014 while the completion of a feasibility study was announced in December 2020. The project is estimated to require an investment of approximately 1.17bn ($1.6bn) for an estimated mine life of 14.3 years. Project location and geology The Stibnite gold project is located approximately 245km north-east of Boise and approximately 16km east of Yellow Pine, in Idaho, US. The project covers a total area of approximately 27,104 acres.

A pre-feasibility study for the project was released in 2014 while the completion of a feasibility study was announced in December 2020. The project is estimated to require an investment of approximately 1.17bn ($1.6bn) for an estimated mine life of 14.3 years. Project location and geology The Stibnite gold project is located approximately 245km north-east of Boise and approximately 16km east of Yellow Pine, in Idaho, US. The project covers a total area of approximately 27,104 acres.

The Stibnite gold project is located approximately 245km north-east of Boise and approximately 16km east of Yellow Pine, in Idaho, US. The project covers a total area of approximately 27,104 acres.

The Stibnite ore body is underlain by pre-Cretaceous basement sediments of the Idaho Batholith, Tertiary intermediate to felsic intrusions and volcanics including younger unconsolidated sediments. The central and eastern portions of the property are bound by large, north-south striking, steeply dipping to vertical pronounced gouge and staged breccia. Mineralisation and reserves The mineralisation and alteration within the Stibnite property occurs in structurally prepared zones in association with very fine grained disseminated arsenical pyrite in lesser extent as arsenopyrite, while gold occurs in almost solid solution. The antimony mineralisation is primarily associated with stibnite while additional gold mineralization occurs in epithermal quartz-adularia-carbonate veins towards the roof of the stibnite. The proven and probable mineral reserves at the Stibnite gold project as of December 2020 were estimated to be 104 million tonnes (Mt) grading 1.43g/t gold, 1.91g/t silver, and 0.064% antimony. The project was estimated to contain 4.8 million ounces (Moz) of gold, 1.2Moz of silver, as well as 148.6 million pounds (Mlbs) of antimony. Mining methods The Stibnite Gold Project will utilise the conventional open pit mining method involving drill, blast, load, and haul operations. The mining operations will progress from the highest-grade Yellow Pine deposit to the Hangar Flats and the West End deposits. The first four years of the mining operations will also involve the removal of the historic tailings stockpile along with the mining at the Yellow Pine open-pit. The mining fleet will comprise up to four 23.5t front end loaders and up to eighteen 200t haul trucks, and an auxiliary fleet comprising dozers and motor graders. Mineral processing The processing plant for the Stibnite gold project will be designed to process the sulphide and oxide ore materials as well as the historical tailings at an average rate of 20,000 tonnes per day (tpd). The finished products will be gold/silver dor bars, and the filtered antimonysilver concentrate. The run-of-the-mine (ROM) ore will undergo crushing in a primary jaw crusher followed by grinding in a semi autogenous grinding (SAG) ball mill. The pulp from the grinding mill will be introduced into a two-stage flotation circuit with the first stage producing an antimony-rich concentrate while the gold-rich concentrate will be produced in the second stage. The gold and antimony-rich concentrates will undergo the pressure oxidation, oxidised concentrate neutralization, and the carbon in leach (CIL) processes before the final carbon handling and refining process. The loaded carbon from the CIL process will be screened, washed, and transferred to the elution vessel for stripping the precious metals by the pressure Zadra method. Infrastructure facilities The Stibnite gold project is accessible via a 114.2km-long road from the intersection of Highway 55 and Warm Lake Road. The power supply requirement for the project operations is expected to be sourced from the Idaho Power Companys power grid. It will require the upgrading of approximately 100km of existing transmission lines and the installation of approximately 14.8km of new 138kV line. Contractors involved M3 Engineering & Technologywas engaged by Midas Gold to prepare the feasibility study for the project. Stantec was engaged to carry out the environmental DNA (eDNA) sampling program for the project.

The mineralisation and alteration within the Stibnite property occurs in structurally prepared zones in association with very fine grained disseminated arsenical pyrite in lesser extent as arsenopyrite, while gold occurs in almost solid solution. The antimony mineralisation is primarily associated with stibnite while additional gold mineralization occurs in epithermal quartz-adularia-carbonate veins towards the roof of the stibnite. The proven and probable mineral reserves at the Stibnite gold project as of December 2020 were estimated to be 104 million tonnes (Mt) grading 1.43g/t gold, 1.91g/t silver, and 0.064% antimony. The project was estimated to contain 4.8 million ounces (Moz) of gold, 1.2Moz of silver, as well as 148.6 million pounds (Mlbs) of antimony. Mining methods The Stibnite Gold Project will utilise the conventional open pit mining method involving drill, blast, load, and haul operations. The mining operations will progress from the highest-grade Yellow Pine deposit to the Hangar Flats and the West End deposits. The first four years of the mining operations will also involve the removal of the historic tailings stockpile along with the mining at the Yellow Pine open-pit. The mining fleet will comprise up to four 23.5t front end loaders and up to eighteen 200t haul trucks, and an auxiliary fleet comprising dozers and motor graders. Mineral processing The processing plant for the Stibnite gold project will be designed to process the sulphide and oxide ore materials as well as the historical tailings at an average rate of 20,000 tonnes per day (tpd). The finished products will be gold/silver dor bars, and the filtered antimonysilver concentrate. The run-of-the-mine (ROM) ore will undergo crushing in a primary jaw crusher followed by grinding in a semi autogenous grinding (SAG) ball mill. The pulp from the grinding mill will be introduced into a two-stage flotation circuit with the first stage producing an antimony-rich concentrate while the gold-rich concentrate will be produced in the second stage. The gold and antimony-rich concentrates will undergo the pressure oxidation, oxidised concentrate neutralization, and the carbon in leach (CIL) processes before the final carbon handling and refining process. The loaded carbon from the CIL process will be screened, washed, and transferred to the elution vessel for stripping the precious metals by the pressure Zadra method. Infrastructure facilities The Stibnite gold project is accessible via a 114.2km-long road from the intersection of Highway 55 and Warm Lake Road. The power supply requirement for the project operations is expected to be sourced from the Idaho Power Companys power grid. It will require the upgrading of approximately 100km of existing transmission lines and the installation of approximately 14.8km of new 138kV line. Contractors involved M3 Engineering & Technologywas engaged by Midas Gold to prepare the feasibility study for the project. Stantec was engaged to carry out the environmental DNA (eDNA) sampling program for the project.

The proven and probable mineral reserves at the Stibnite gold project as of December 2020 were estimated to be 104 million tonnes (Mt) grading 1.43g/t gold, 1.91g/t silver, and 0.064% antimony. The project was estimated to contain 4.8 million ounces (Moz) of gold, 1.2Moz of silver, as well as 148.6 million pounds (Mlbs) of antimony. Mining methods The Stibnite Gold Project will utilise the conventional open pit mining method involving drill, blast, load, and haul operations. The mining operations will progress from the highest-grade Yellow Pine deposit to the Hangar Flats and the West End deposits. The first four years of the mining operations will also involve the removal of the historic tailings stockpile along with the mining at the Yellow Pine open-pit. The mining fleet will comprise up to four 23.5t front end loaders and up to eighteen 200t haul trucks, and an auxiliary fleet comprising dozers and motor graders. Mineral processing The processing plant for the Stibnite gold project will be designed to process the sulphide and oxide ore materials as well as the historical tailings at an average rate of 20,000 tonnes per day (tpd). The finished products will be gold/silver dor bars, and the filtered antimonysilver concentrate. The run-of-the-mine (ROM) ore will undergo crushing in a primary jaw crusher followed by grinding in a semi autogenous grinding (SAG) ball mill. The pulp from the grinding mill will be introduced into a two-stage flotation circuit with the first stage producing an antimony-rich concentrate while the gold-rich concentrate will be produced in the second stage. The gold and antimony-rich concentrates will undergo the pressure oxidation, oxidised concentrate neutralization, and the carbon in leach (CIL) processes before the final carbon handling and refining process. The loaded carbon from the CIL process will be screened, washed, and transferred to the elution vessel for stripping the precious metals by the pressure Zadra method. Infrastructure facilities The Stibnite gold project is accessible via a 114.2km-long road from the intersection of Highway 55 and Warm Lake Road. The power supply requirement for the project operations is expected to be sourced from the Idaho Power Companys power grid. It will require the upgrading of approximately 100km of existing transmission lines and the installation of approximately 14.8km of new 138kV line. Contractors involved M3 Engineering & Technologywas engaged by Midas Gold to prepare the feasibility study for the project. Stantec was engaged to carry out the environmental DNA (eDNA) sampling program for the project.

The project was estimated to contain 4.8 million ounces (Moz) of gold, 1.2Moz of silver, as well as 148.6 million pounds (Mlbs) of antimony. Mining methods The Stibnite Gold Project will utilise the conventional open pit mining method involving drill, blast, load, and haul operations. The mining operations will progress from the highest-grade Yellow Pine deposit to the Hangar Flats and the West End deposits. The first four years of the mining operations will also involve the removal of the historic tailings stockpile along with the mining at the Yellow Pine open-pit. The mining fleet will comprise up to four 23.5t front end loaders and up to eighteen 200t haul trucks, and an auxiliary fleet comprising dozers and motor graders. Mineral processing The processing plant for the Stibnite gold project will be designed to process the sulphide and oxide ore materials as well as the historical tailings at an average rate of 20,000 tonnes per day (tpd). The finished products will be gold/silver dor bars, and the filtered antimonysilver concentrate. The run-of-the-mine (ROM) ore will undergo crushing in a primary jaw crusher followed by grinding in a semi autogenous grinding (SAG) ball mill. The pulp from the grinding mill will be introduced into a two-stage flotation circuit with the first stage producing an antimony-rich concentrate while the gold-rich concentrate will be produced in the second stage. The gold and antimony-rich concentrates will undergo the pressure oxidation, oxidised concentrate neutralization, and the carbon in leach (CIL) processes before the final carbon handling and refining process. The loaded carbon from the CIL process will be screened, washed, and transferred to the elution vessel for stripping the precious metals by the pressure Zadra method. Infrastructure facilities The Stibnite gold project is accessible via a 114.2km-long road from the intersection of Highway 55 and Warm Lake Road. The power supply requirement for the project operations is expected to be sourced from the Idaho Power Companys power grid. It will require the upgrading of approximately 100km of existing transmission lines and the installation of approximately 14.8km of new 138kV line. Contractors involved M3 Engineering & Technologywas engaged by Midas Gold to prepare the feasibility study for the project. Stantec was engaged to carry out the environmental DNA (eDNA) sampling program for the project.

The Stibnite Gold Project will utilise the conventional open pit mining method involving drill, blast, load, and haul operations. The mining operations will progress from the highest-grade Yellow Pine deposit to the Hangar Flats and the West End deposits. The first four years of the mining operations will also involve the removal of the historic tailings stockpile along with the mining at the Yellow Pine open-pit. The mining fleet will comprise up to four 23.5t front end loaders and up to eighteen 200t haul trucks, and an auxiliary fleet comprising dozers and motor graders. Mineral processing The processing plant for the Stibnite gold project will be designed to process the sulphide and oxide ore materials as well as the historical tailings at an average rate of 20,000 tonnes per day (tpd). The finished products will be gold/silver dor bars, and the filtered antimonysilver concentrate. The run-of-the-mine (ROM) ore will undergo crushing in a primary jaw crusher followed by grinding in a semi autogenous grinding (SAG) ball mill. The pulp from the grinding mill will be introduced into a two-stage flotation circuit with the first stage producing an antimony-rich concentrate while the gold-rich concentrate will be produced in the second stage. The gold and antimony-rich concentrates will undergo the pressure oxidation, oxidised concentrate neutralization, and the carbon in leach (CIL) processes before the final carbon handling and refining process. The loaded carbon from the CIL process will be screened, washed, and transferred to the elution vessel for stripping the precious metals by the pressure Zadra method. Infrastructure facilities The Stibnite gold project is accessible via a 114.2km-long road from the intersection of Highway 55 and Warm Lake Road. The power supply requirement for the project operations is expected to be sourced from the Idaho Power Companys power grid. It will require the upgrading of approximately 100km of existing transmission lines and the installation of approximately 14.8km of new 138kV line. Contractors involved M3 Engineering & Technologywas engaged by Midas Gold to prepare the feasibility study for the project. Stantec was engaged to carry out the environmental DNA (eDNA) sampling program for the project.

The first four years of the mining operations will also involve the removal of the historic tailings stockpile along with the mining at the Yellow Pine open-pit. The mining fleet will comprise up to four 23.5t front end loaders and up to eighteen 200t haul trucks, and an auxiliary fleet comprising dozers and motor graders. Mineral processing The processing plant for the Stibnite gold project will be designed to process the sulphide and oxide ore materials as well as the historical tailings at an average rate of 20,000 tonnes per day (tpd). The finished products will be gold/silver dor bars, and the filtered antimonysilver concentrate. The run-of-the-mine (ROM) ore will undergo crushing in a primary jaw crusher followed by grinding in a semi autogenous grinding (SAG) ball mill. The pulp from the grinding mill will be introduced into a two-stage flotation circuit with the first stage producing an antimony-rich concentrate while the gold-rich concentrate will be produced in the second stage. The gold and antimony-rich concentrates will undergo the pressure oxidation, oxidised concentrate neutralization, and the carbon in leach (CIL) processes before the final carbon handling and refining process. The loaded carbon from the CIL process will be screened, washed, and transferred to the elution vessel for stripping the precious metals by the pressure Zadra method. Infrastructure facilities The Stibnite gold project is accessible via a 114.2km-long road from the intersection of Highway 55 and Warm Lake Road. The power supply requirement for the project operations is expected to be sourced from the Idaho Power Companys power grid. It will require the upgrading of approximately 100km of existing transmission lines and the installation of approximately 14.8km of new 138kV line. Contractors involved M3 Engineering & Technologywas engaged by Midas Gold to prepare the feasibility study for the project. Stantec was engaged to carry out the environmental DNA (eDNA) sampling program for the project.

The mining fleet will comprise up to four 23.5t front end loaders and up to eighteen 200t haul trucks, and an auxiliary fleet comprising dozers and motor graders. Mineral processing The processing plant for the Stibnite gold project will be designed to process the sulphide and oxide ore materials as well as the historical tailings at an average rate of 20,000 tonnes per day (tpd). The finished products will be gold/silver dor bars, and the filtered antimonysilver concentrate. The run-of-the-mine (ROM) ore will undergo crushing in a primary jaw crusher followed by grinding in a semi autogenous grinding (SAG) ball mill. The pulp from the grinding mill will be introduced into a two-stage flotation circuit with the first stage producing an antimony-rich concentrate while the gold-rich concentrate will be produced in the second stage. The gold and antimony-rich concentrates will undergo the pressure oxidation, oxidised concentrate neutralization, and the carbon in leach (CIL) processes before the final carbon handling and refining process. The loaded carbon from the CIL process will be screened, washed, and transferred to the elution vessel for stripping the precious metals by the pressure Zadra method. Infrastructure facilities The Stibnite gold project is accessible via a 114.2km-long road from the intersection of Highway 55 and Warm Lake Road. The power supply requirement for the project operations is expected to be sourced from the Idaho Power Companys power grid. It will require the upgrading of approximately 100km of existing transmission lines and the installation of approximately 14.8km of new 138kV line. Contractors involved M3 Engineering & Technologywas engaged by Midas Gold to prepare the feasibility study for the project. Stantec was engaged to carry out the environmental DNA (eDNA) sampling program for the project.

The processing plant for the Stibnite gold project will be designed to process the sulphide and oxide ore materials as well as the historical tailings at an average rate of 20,000 tonnes per day (tpd). The finished products will be gold/silver dor bars, and the filtered antimonysilver concentrate. The run-of-the-mine (ROM) ore will undergo crushing in a primary jaw crusher followed by grinding in a semi autogenous grinding (SAG) ball mill. The pulp from the grinding mill will be introduced into a two-stage flotation circuit with the first stage producing an antimony-rich concentrate while the gold-rich concentrate will be produced in the second stage. The gold and antimony-rich concentrates will undergo the pressure oxidation, oxidised concentrate neutralization, and the carbon in leach (CIL) processes before the final carbon handling and refining process. The loaded carbon from the CIL process will be screened, washed, and transferred to the elution vessel for stripping the precious metals by the pressure Zadra method. Infrastructure facilities The Stibnite gold project is accessible via a 114.2km-long road from the intersection of Highway 55 and Warm Lake Road. The power supply requirement for the project operations is expected to be sourced from the Idaho Power Companys power grid. It will require the upgrading of approximately 100km of existing transmission lines and the installation of approximately 14.8km of new 138kV line. Contractors involved M3 Engineering & Technologywas engaged by Midas Gold to prepare the feasibility study for the project. Stantec was engaged to carry out the environmental DNA (eDNA) sampling program for the project.

The run-of-the-mine (ROM) ore will undergo crushing in a primary jaw crusher followed by grinding in a semi autogenous grinding (SAG) ball mill. The pulp from the grinding mill will be introduced into a two-stage flotation circuit with the first stage producing an antimony-rich concentrate while the gold-rich concentrate will be produced in the second stage. The gold and antimony-rich concentrates will undergo the pressure oxidation, oxidised concentrate neutralization, and the carbon in leach (CIL) processes before the final carbon handling and refining process. The loaded carbon from the CIL process will be screened, washed, and transferred to the elution vessel for stripping the precious metals by the pressure Zadra method. Infrastructure facilities The Stibnite gold project is accessible via a 114.2km-long road from the intersection of Highway 55 and Warm Lake Road. The power supply requirement for the project operations is expected to be sourced from the Idaho Power Companys power grid. It will require the upgrading of approximately 100km of existing transmission lines and the installation of approximately 14.8km of new 138kV line. Contractors involved M3 Engineering & Technologywas engaged by Midas Gold to prepare the feasibility study for the project. Stantec was engaged to carry out the environmental DNA (eDNA) sampling program for the project.

The gold and antimony-rich concentrates will undergo the pressure oxidation, oxidised concentrate neutralization, and the carbon in leach (CIL) processes before the final carbon handling and refining process. The loaded carbon from the CIL process will be screened, washed, and transferred to the elution vessel for stripping the precious metals by the pressure Zadra method. Infrastructure facilities The Stibnite gold project is accessible via a 114.2km-long road from the intersection of Highway 55 and Warm Lake Road. The power supply requirement for the project operations is expected to be sourced from the Idaho Power Companys power grid. It will require the upgrading of approximately 100km of existing transmission lines and the installation of approximately 14.8km of new 138kV line. Contractors involved M3 Engineering & Technologywas engaged by Midas Gold to prepare the feasibility study for the project. Stantec was engaged to carry out the environmental DNA (eDNA) sampling program for the project.

The loaded carbon from the CIL process will be screened, washed, and transferred to the elution vessel for stripping the precious metals by the pressure Zadra method. Infrastructure facilities The Stibnite gold project is accessible via a 114.2km-long road from the intersection of Highway 55 and Warm Lake Road. The power supply requirement for the project operations is expected to be sourced from the Idaho Power Companys power grid. It will require the upgrading of approximately 100km of existing transmission lines and the installation of approximately 14.8km of new 138kV line. Contractors involved M3 Engineering & Technologywas engaged by Midas Gold to prepare the feasibility study for the project. Stantec was engaged to carry out the environmental DNA (eDNA) sampling program for the project.

The Stibnite gold project is accessible via a 114.2km-long road from the intersection of Highway 55 and Warm Lake Road. The power supply requirement for the project operations is expected to be sourced from the Idaho Power Companys power grid. It will require the upgrading of approximately 100km of existing transmission lines and the installation of approximately 14.8km of new 138kV line. Contractors involved M3 Engineering & Technologywas engaged by Midas Gold to prepare the feasibility study for the project. Stantec was engaged to carry out the environmental DNA (eDNA) sampling program for the project.

The power supply requirement for the project operations is expected to be sourced from the Idaho Power Companys power grid. It will require the upgrading of approximately 100km of existing transmission lines and the installation of approximately 14.8km of new 138kV line. Contractors involved M3 Engineering & Technologywas engaged by Midas Gold to prepare the feasibility study for the project. Stantec was engaged to carry out the environmental DNA (eDNA) sampling program for the project.

M3 Engineering & Technologywas engaged by Midas Gold to prepare the feasibility study for the project. Stantec was engaged to carry out the environmental DNA (eDNA) sampling program for the project.

cerro matoso nickel mine, colombia - mining technology | mining news and views updated daily

BHP Billitons Cerro Matoso nickel operation is situated in Columbia and combines a lateritic nickel ore deposit with a low-cost ferronickel smelter. It is the worlds second-largest producer of ferronickel and boasts some of the lowest costs. Mining commenced in 1980 and nickel production started in 1982 under the Colombian Government, BHP Billiton and Hanna Mining ownership.

In 1999, an expansion project to double installed capacity was started, and in January 2001 the first metal was tapped from this second line. The smelter produces high-purity, low-carbon ferronickel granules. Production in FY2008 was 41,800t of contained nickel, some 9,000t lower than FY2007s production principally due to an industrial stoppage during FY2008.

Cerro Matoso has an estimated reserve life of 42 years, based on current production levels, however BHP has identified opportunities to expand this significantly, notably building a third and fourth processing line and a heap leaching operation.

The deposit is developed over a peridotitic protolith that is exposed in the form of an elongated hill. The deposits weathering profile is variable both vertically and laterally, and ten distinct lithostratigraphic units have been characterised.

Two typical sections through the weathering profile were sampled from an area of the mine with high (pit 1) and lower (pit 2) Ni grades. Bench mapping has shown that pits 1 and 2 have distinctly different weathering profiles. From bottom to top, the profile in pit 1 is weakly serpentinized peridotitic protolith, saprolitized peridotite, green saprolite (main ore horizon), tachylite (used by mine geologists to describe an enigmatic Fe oxide horizon), black saprolite, yellow laterite, red laterite.

The sequence is then capped by a magnetic to nonmagnetic ferricrete known locally as canga. The succession in pit 2 is from serpentinized peridotite, saprolitized peridotite, brown saprolite, yellow laterite, red laterite and lacks the green saprolite ore horizon. All the units in pit 2 have currently uneconomic Ni grades.

The thickness of the units is highly variable, but most of the major horizons have maximum thicknesses of the order of tens of meters. Both pits contain abundant fault- and joint-related silicate veins, sometimes in stockworks, in the lower part of the sequence. These veins contain the distinctive green mineral known as garnierite (actually pimelite, a form of nickeliferous talc) as well as quartz and chalcedony, and they can have a Ni content of up to 30% to 40%

The ore reserve has increased as a result of revised price forecasts, reducing the Laterite ore cut-off grade used in the reserve estimation from 1.0%Ni to 0.6%Ni. In addition, revised metallurgical recovery parameters have also resulted in an increase to the reserve.

The ore mined from the open pits is sent to Cerro Matosos smelter for processing. High-purity and low-carbon ferronickel granules are produced by the smelter. These ferronickel granules are used exclusively in stainless steel production.

Conceptual studies were undertaken for expanding production at Cerro Matoso. This includes building a third and fourth processing line and a heap leaching operation. All these measures aim at doubling Cerro Matosos capacity within ten years.

The Cerro Matoso mine has the highest-grade lateritic nickel deposits in the world. With exploration rights over 77,000ha in the main part of the Colombian nickel belt, Cerro Matoso has mining concessions containing reserves capable of sustaining the current level of production for at least 20 years.

The ferronickel smelter and refinery are integrated with the mine. Beneficiation plant for the mine consists of a primary and secondary crusher, which is sent to a stacker for ore stockpiling and blending. Process design capacity is 50,000t per annum. Actual capacity depends on nickel grade from the mine.

Costs were higher due to increased electricity and gas costs. The mine has an estimated reserve life of 42 years, based on current production levels, however BHP has identified opportunities to expand this significantly, notably building a third and fourth processing line and a heap leaching operation. Pending board approval, BHP envisages that these projects could see capacity more than doubling over the next ten years.

mining in colombia | the diggings

Colombia has 817 identified mines listed in The Diggings. The most commonly listed primary commodities in Colombia mines are Gold , Silver , and Copper . At the time these mines were surveyed, 197 mines in Colombia were observed to have ore mineralization in an outcrop, shallow pit, or isolated drill holeknown as an occurance mine.1 Colombia has 60 prospect mines.2 559 mines were in production at the time the data was entered into USGS records. Tolima, Antioquia, and Caldas are the with the most mines.

Information hosted on The Diggings is based on publicly available data through the Bureau of Land Management. The Diggings accepts no liability for the content of this data, or for the consequences of any actions taken on the basis of the information provided.

The Diggings makes no warranty, expressed or implied, including the warranties of merchantability and fitness for a particular purpose, nor assumes any legal liability or responsibility for the accuracy, reliability, completeness or utility of these geospatial data, or for the improper or incorrect use of these geospatial data. These geospatial data and related maps or graphics are not legal documents and are not intended to be used as such. The data and maps may not be used to determine title, ownership, legal descriptions or boundaries, legal jurisdiction, or restrictions that may be in place on either public or private land. Natural hazards may or may not be depicted on the data and maps, and land users should exercise due caution. The data are dynamic and may change over time. The user is responsible to verify the limitations of the geospatial data and to use the data accordingly.

colombia's mining industry and the upper miocene belt | inn

The global economys reaction to the COVID-19 pandemic has caused governments around the world to take unprecedented measures in order to balance economies and avoid longterm damage. In North America, economic measures including significant instances of quantitative easing by the US Federal Reserve have helped to drive the economy forward in the face of widespread unemployment and economic uncertainty. Despite this economic turmoil across the world, the precious metals markets have responded strongly in the face of this turmoil, with the price of gold reaching a seven year high in early July. In pursuit of the strong gold price, a number of junior mining companies are beginning to target known mining jurisdictions across the world with a history of production.

A number of financial analysts have pointed to the recent economic measures put into place as one of the many forces driving the gold price in 2020. According to Bank of China International analyst Xiao Fu, quantitative easing and the uncertainty regarding the future of the global economy have combined to help maintain the latest highs. Central bank easing policies and uncertainty surrounding the second wave (of COVID-19) are sustaining gold prices, he told Reuters. Gold is commonly recognized as a safe investment during times of economic uncertainty, which OANDA senior market analyst Jeffrey Halley believes has helped to contribute to the commoditys latest rise as well. Some haven-directed buying of gold is definitely evident, said Halley.

In conversation with the Investing News Network, Sprott (TSX:SII,NYSE:SII) CEO and President Rick Rule echoed the sentiment of his fellow analysts, suggesting that a collection of economic conditions could combine to drive the price of gold moving forward. If the combination of quantitative easing, artificially low-interest rates, debt and deficits did in fact put some wind in golds sails, which I believe they will, the base from which we expand is very low, said Rule. As the gold price continues to improve the economics of gold exploration and production around the world, a number of resource companies are beginning to target proven jurisdictions with potential exploration upside.

For example, junior explorer FenixOro Gold(CSE:FENX) is working to develop its Abriaqui gold project in Colombias Upper Miocene Belt, which the company believes offers potential upside. Relative to the rest of Latin America, Colombia is historically underexplored and boasts some of the highest-grade exploration potential in the world, said FenixOro Gold CEO John Carlesso.

Colombias Upper Miocene Belt has been home to approximately 80 million ounces of new gold discoveries made since 2007. The Upper Miocene, which is a rich stretch of mineralization located approximately 150 kilometers northwest of Medellin, is also home to Continental Minings Buritica gold project, which includes measured and indicated mineral resources of 5.67 million gold equivalent ounces. In March 2020 Zijin Mining Group acquired Continental Goldalong with the Buritica project for C$1.4 billion. Zijin intends to put the Buritica mine into production in 2020, targeting an annual production rate of approximately 250,000 ounces of gold per year.

Like Zijin, gold explorer FenixOro Goldis exploring opportunities in Colombias Upper Miocene Belt, including the Abriaqui gold project. Based on initial exploration on the property, FenixOro believes the Abriaqui project has a number of similarities to the Buritica project, which is the closest nearby mine located only 15 kilometers away. The geological setting has many similarities the age, the host, mineralogy, mineralization style and similarities of the vein system, particularly the vertical continuity and depth, all point to the probability that Abriaqui has the potential to be very similar to Buritica, said Carlesso. Importantly, the individual making these determinations on the comparison, FenixOro VP Exploration Stuart Moller, is responsible for the discovery of the Buritica deposit while at Continental Gold.

FenixOro Gold Corp recently began the preliminary portion of Phase 1 of a US2.9 million exploration program at the Abriaqui project. The company is following up on the discovery of Buritica-style mineralization found on the property in June 2020, which included high-grade gold veins, some of which assayed greater than 20 g/t gold.

The emergence of the COVID-19 pandemic and golds role as a common economic save haven in times of uncertainty have put the spotlight on gold production across the world. Resource exploration companies of all sizes have reacted to these market trends, working to develop future gold supplies by targeting proven jurisdictions with exploration upside. In Colombias Upper Miocene Belt, a number of gold exploration companies are working to develop projects in the region, targeting areas of mineralization that have revealed previous gold discoveries thanks to modern exploration.

This INNSpired article is sponsored by FenixOro Gold (CSE:FENX). This INNSpired article provides information that was sourced by the Investing News Network (INN) and approved by FenixOro Goldin order to help investors learn more about the company. FenixOro Goldis a client of INN. The companys campaign fees pay for INN to create and update this INNSpired article.

INN does not provide investment advice and the information on this profile should not be considered a recommendation to buy or sell any security. INN does not endorse or recommend the business, products, services, or securities of any company profiled.

The information contained here is for information purposes only and is not to be construed as an offer or solicitation for the sale or purchase of securities. Readers should conduct their own research for all information publicly available concerning the company. Prior to making any investment decision, it is recommended that readers consult directly with FenixOro Goldand seek advice from a qualified investment advisor. Request an Investor Kit: FenixOro Gold Corp Include me in the Accredited Investor email list Some investment opportunities are limited to accredited investors. Whether you are an accredited investor or not depends on where you live and other criteria. For full details go to https://investingnews.com/accredited-investor-definition/ or search for "accredited investor" in the search bar above. By completing this form, you are giving consent to receive communication from FenixOro Gold Corp using the contact information you provide. And remember you can unsubscribe at any time.

Please remember that by requesting an investor kit, you are giving permission for those companies to contact you using whatever contact information you provide. If you want more than 20 investor kits, you need to make multiple requests. Select 20, complete the request and then select again.

building colombia's next gold mine: caldas gold's (tsx-v: cgc, otcqx: allxf) marmato project - miningfeeds

On July 29, 2020, the company announced a $50-million (USD) financing led by Canaccord and Scotiabank followed by a $110-million (USD) stream financing with Wheaton Precious Metals (TSX: WPM). Finally, the company closed an $83-million (USD) private placement.

With execution of the Wheaton stream anticipated in the next couple of weeks, Caldas Gold will be fully funded to expand Caldas mining operations into the Marmato Deep Zone MDZ, massively increasing the gold and silver production profile of the Marmato mine.

The Marmato mine has been in operation since 1991 and has produced an average of ~24,000 ounces of gold annually over the last 10 years with 25,750 ounces of gold in 2019. However, exploration revealed there is more at depth to continue mining at depth to dramatically increase gold and silver production.

Acquired in 2011 with Gran Colombias merger with Medoro, the Marmato Project now will stand on its own as a spin-out of Gran Colombia Gold (TSX: GCM) in February 2020. Gran Colombia maintains a 57.5% equity interest in the company. In a telephone call, Serafino Iacono, president of Caldas, commented on the logic behind the new company.

We decided to create a new company, mostly because of the history of Gran Colombia, we managed to have a large debt and bring it down. what we did not want to do was load Gran Colombia with a debt of $265 million to build out Marmato. I would rather own 60% of the project, then to go back to a company with debt. We now have a nice clean company, still own the project but without the debt, by losing 40% equity.

According to the companys most recent resource estai, Marmato hosts 6.6 million ounces of gold defined in the Zona Baja and exploration drilling is continuing to upgrade and expand the Deep Zone mineralization. The bulk of the resource estimate, 4,086,000 ounces, lies in the measured and indicated category with 2,172,000 ounces of gold in the inferred.

A Prefeasibility Study PFS confirmed the economic viability of the underground expansion of the Marmato project. At a gold price of $1,400 (USD) per ounce, total life-of-mine LoM undiscounted after-tax free cash flow from mining operations amounts to $770-million (USD).

At a 5-per-cent discount rate, the net present value of the total life of mine after-tax project cash flow amounts to $263.9-million (USD). Before financing, the project has a 20.1-per-cent after-tax internal rate of return and payback by 2026.

The company is looking to optimize mining in the Upper Zone and increase production from 1,200 tpd to 1,500 tpd. A total of 5.1 million tonnes to be processed over 13-year life with average LoM Au grade of 4.2 g/t resulting in 600,000 ounces of gold (32% of total) from the upper zone.

The remaining 68% of mined material will come from the MDZ. A Total of 14.6M tonnes processed over 10.5 years starting in mid-2023 at an average LoM Au grade of 2.9 g/t resulting in 1.3M ounces of gold.

The spin-out from Gran Colombia created a new company to give Marmato its own sparkle as its own company. Management is looking to further develop under appreciated assets that shine in their own right.

The private company has an agreement to acquire the project from a Pan American Silver (TSX: PAAS; NYSE: PAAS) subsidiary Lake Shore Gold. Also part of the deal is a 25-per-cent interest in the Knight Joint Venture with Lake Shore, adjacent to Juby.

SARC will receive 20 million Caldas shares, and Caldas will also make the final payments on the projects to Lake Shore. Lake Shore is owed US$9.5 million to secure the 100-per-cent interest in Juby, with another US$500,000 required to close the Knight JV interest.

Juby is an advanced exploration-stage gold project, with 1.1 million indicated oz. gold contained in 26.6 million tonnes at 1.28 grams gold per tonne. Inferred resources add 2.9 million oz. gold in 96.2 million tonnes grading 0.94 gram gold.

We were orphans for years, Marmato was an orphan project, we started looking at the Juby project because it was an orphan, we convinced them instead of a publicly listed company, still in Canada, Ontario, 8 hours from Toronto, Ontario. It is all about location, location, we believe that is has big potential, it is one of these projects, it is the last project on the last, it is a progression of a companies that own it, it never got the right attention, this is the perfect project, we are very knowledgeable about the project and hope to upgrade it to a development project by 2021.

Caldas Gold also owns 100% of the Juby Project, an advanced exploration-stage gold project located within the Shining Tree area in the southern part of the Abitibi greenstone belt about 100 kilometres south-southeast of the Timmins gold camp.

The company currently has 77.5 million shares outstanding with a market capitalization of $230.2 million (CDN) as of Sept. 8, 2020. Shares in the company were trading at 2.97 on sept 8 with a 52-week high of $3 and a 52-week low of $1.30.

the impact of artisanal gold mining, ore processing and mineralization on water quality in marmato, colombia | springerlink

Marmato, Colombia, has been an important centre of gold mining since before the first Spanish colonizers arrived in 1536. The Marmato deposit is hosted in a dacite and andesite porphyry stock as sheeted sulphide-rich veinlet systems. The district is currently experiencing a surge in both major mining projects and artisanal mining, driven by sustained high gold prices. Ore from small-scale and artisanal gold mining is processed in numerous small mills (entables) around Marmato, which impact surface water quality through the discharge of milled waste rock slurry, highly alkaline cyanide-treated effluent, and high dissolved metal loads. To investigate the impact of artisanal mining and ore processing, water samples were collected in January 2012 from streams around Marmato. The average dissolved metal concentrations in impacted streams were Zn, 78mgL1; Pb, 0.43mgL1; Cu, 403gL1 Cd, 255gL1; As, 235gL1; Ni, 67gL1; Co, 55gL1; Sb, 7gL1; and Hg, 42ngL1, exceeding World Health Organization drinking water guidelines. In addition, arsenic speciation was conducted in-situ and indicated that 9195% of inorganic arsenic species is in the form of As(V). Spatial analysis of the data suggests that entables processing ore for artisanal miners are the main contributor to water pollution, with high sediment loads, alkalinity and elevated concentrations of dissolved arsenic, cadmium, mercury and lead, caused by the processing of gold-bearing sulphides in the entables. Geochemical data from surface water were compared to a comprehensive data set of whole rock analyses from drill core and channel samples from the deposit, indicating that the deposit is significantly enriched in gold, silver, lead, zinc, arsenic, antimony, and cadmium compared to crustal averages, which is reflected in the surface water geochemistry. However, elevated mercury levels in surface water cannot be explained by enrichment of mercury in the deposit and strongly suggest that mercury is being added to concentrates during ore processing to amalgamate fine gold.

Colombia has a long and rich history of gold mining, dating back to the pre-Colonial era (Brooks et al., 2016). Gold mining is an important economic driver in the impoverished rural regions in Colombia, with around 300,000 miners working in the artisanal and small-scale gold mining (ASGM) sector on a mainly subsistence basis, producing an estimated 54 metric tonnes (Mt) of gold annually (Cordy et al., 2011). Many of these mines operate illegally under Colombian law, without valid mining claims, property title or environmental permits. However, as these mines represent one of the few sources of employment in rural areas, they are generally tolerated by the authorities. The improved security situation in Colombia has made it an active exploration target for foreign mining companies.

It is known that water quality in the Marmato district is impacted by mining; Prieto analysed waters in the Marmato District (G. Prieto, 1998) and reported appreciable quantities of dissolved metals, including Zn, Cd, Cu, and As, with concentrations of dissolved solids up to 39,000mg L1. The purpose of this study was to document the geochemistry of surface water around Marmato, to determine the types of metal pollutants present, and to define their spatial relationship to artisanal mining and ore processing.

The town of Marmato (5.47N, 75.60W) is in the Caldas Department of Colombia, about 80km south of Medellin (Fig.1). Marmato has been a centre of hard rock gold mining since its founding by the Spanish conquistadors in 1532, although gold in the area was exploited in pre-Colonial times by the Quimbaya people (Redwood, 2011). In 2012, approximately 2000 residents were directly employed in mining and ore processing out of a total municipal population of 10,000, with numerous small-scale mines and adits around the town and further up Marmato Mountain. There is one large-scale modern underground mine at an elevation of 1180m, operated by Mineros Nacionales S.A., a subsidiary of Caldas Gold Corporation. An estimated 1.752.25 million ounces (Moz.) of gold was recovered from the Marmato district by 2011 (Redwood, 2011), but the district contains additional large, low-grade ore bodies that could be economically mined by bulk methods.

Marmato is situated at a mean elevation of 1,300m on a steep hillside above the valley of the Rio Cauca, which flows northward towards the Caribbean. The district is readily accessible by road, being connected to the Pan-American Highway by a short length of mostly paved road. The terrain is exceptionally steep, rising over 600m in 2km, so landslides are a frequent problem after heavy rain, blocking roads and damaging property within the town. Marmato has an equatorial climate, described as moist tropical climate, Am by the Kppen and Geiger classification (Peel et al., 2007). Temperatures are warm year-round, with maximum temperatures ranging from 28.7 to 31.6C, and minimum temperatures in the range of 17.418.7C (Knight Pisold Consulting, 2012). The average annual rainfall is 1889mm per year, with drier periods in January, when sampling was carried out, and July (Knight Pisold Consulting, 2012). Wetter periods are in typically in spring and fall.

Marmato Mountain has been an exploration target of Gran Colombia Gold Corporation who originally defined open pit resources in the measured and indicated categories estimated at 11.8 Moz Au and 80.3 Moz Ag in 409.7 Mt of ore grading 0.90g/t Au and 6.1g/t Ag (Parsons & Armitage, 2012). Gran Colombia Gold originally proposed developing an open pit mine, but in 2017, their focus switched to evaluate underground bulk mining potential following discovery of the Marmato Deeps deposit. The current combined underground resource comprises 39.40 Mt at 3.20g/t Au and 8.7g/t Ag in the measured and indicated categories (4.09 Moz Au and 11.05 Moz Ag) plus 26.40 Mt at 2.60g/t Au and 4.4g/t Ag inferred (2.17 Moz Au and 3.73 Moz Ag) in veins, underground porphyry (veinlets) and Deeps deposits (Parsons et al., 2020).

ASGM and ore processing are the most visible sources of water pollution around Marmato. There several hundred artisanal mines around Marmato, exploiting gold-rich pyrite veins in the upper portion (Zona Alta) of Marmato Mountain. A typical small-scale mine consists of a single narrow adit tunnelled into the hillside to a length of 100m or less, following a gold-rich pyrite vein. As most mines lack basic ventilation, these adits do not extend very deep into the hillside. The sulphide-rich ore is manually mined from adits and loaded into ore carts, which are pushed to the mine entrance for loading on to trucks or buckets on aerial cable-ways for transport to the ninety or so local processing mills, called entables, as shown in Fig.2.

a Gold ore processing in an entable in Marmato. b Ore is first crushed by jaw crusher and then (b) ground in small ball mills called cocos. c Gold and auriferous pyrite are separated by gravity using a Wilfley table to concentrate the denser gold and pyrite grains. d Tailings are further concentrated in cyclones, then treated with cyanide to dissolve the remaining gold

At the entables, the ore is crushed, then finely ground using small ball mills, known as cocos, to separate free gold and gold-bearing pyrite from the rock gangue. Denser gold flakes and sulphides are concentrated by gravimetry using cyclones and Wilfley tables (Fig.2c). Gold is recovered from the concentrate by physical processes and by mercury amalgamation. Tailings from the enrichment processes are subsequently treated with sodium cyanide solution, which forms a complex with any remaining gold in the ore according to the Elsner equation (Eq.1), allowing additional recovery.

The addition of sodium cyanide to the milled ore creates an effluent that is highly alkaline; sodium hydroxide is also added to maintain a high pH to favour cyanide complexation and suppress toxic hydrogen cyanide generation. Effluent from processing is discharged directly to drainage channels without basic treatment or settling ponds. This is the most visible source of pollution entering the streams that flow down the mountain into the Rio Cauca. Downgradient of each entable is a distinctive Prussian blue stain caused by the formation of ferrocyanide complexes as the waste effluent is discarded (Fig.3).

A small entable near Marmato, Colombia, built on a precarious slope to process gold ore. Note the distinctive blue ferrocyanide staining from cyanide discharges from the mill. A small adit is visible in the right foreground

By-products from the milling and recovery process are discharged as a grey slurry (Fig.4). A suspended sediment load of 40g of sediment per liter was measured in one sample, downstream of the entables. In addition to the adit mines, small numbers of artisanal miners (barequeros) work the streams using pans, sluice boxes and riffle boards to recover any gold overlooked during processing (Fig.4).

With an improving security situation, the Marmato district has attracted the attention of international mineral exploration companies looking to employ large-scale modern bulk mining methods with efficient gold recovery technologies. Gran Colombia Gold Corporation is exploring and developing the Marmato deposit and filed a NI 43101 with the Toronto Stock Exchange in 2012 (Parsons & Armitage, 2012), which included an outline plan for a large open pit mine. This filing included preliminary environmental baseline studies. In October 2017, Gran Colombia Gold (Gran Colombia Gold Corp. press release, 4 October 2017) announced that they plan to develop the Marmato deposit as an expansion of their existing underground mine and released a preliminary economic assessment in 2019 (Parsons et al., 2019) and a pre-feasibility study in 2020 (Parsons et al., 2020), as well as spinning out the project into a new company, Caldas Gold Corporation. A consequence of this decision is that Marmato will not have to relocate as originally proposed and that artisanal gold mining within the previously planned open pit boundary will continue.

Marmato lies within the Romeral Terrane, an oceanic terrane of probable Late Jurassic to Early Cretaceous age that was accreted to the continental margin along the N-S trending Romeral Fault in the Aptian. This is partly covered by Neogene sediments and volcanic rocks, into which the composite Marmato stock was intruded. Gold mineralization is hosted by a composite andesite to dacite porphyry and is late stage, post-intrusion. Five porphyry pulses have been identified, named P1 to P5 from oldest to youngest. The age of the porphyry intrusions is bracketed by laser ablation ICP-MS 206Pb/238U zircon dates of the P1 dacite stock of 6.5760.075 million years (Ma) and P5 dacite dikes of 5.750.11Ma (Santacruz et al., ). The age of mineralization was dated by 40Ar/39Ar analyses of adularia in veins with plateau ages between 6.950.02Ma and 5.960.02Ma (Santacruz et al., 2018). Mineralization is structurally controlled with dominant NW and WNW trends, which developed from reactivated basement structures and as Riedel shears under WNW-ESE compression in a sinistral transpressional shear system. Mineralization extends over 1400m vertically and is open at depth. Two main zones of mineralization have been identified. The Upper Zone (Fig.5) between 1600 and 900m above sea level (m.a.s.l.), mainly comprises massive, sulphide-rich, relatively quartz-poor, gold-bearing base metal veins and veinlets with sericite-illitesmectite-ankerite-pyrite wall-rock alteration which overprints pervasive propylitic alteration. This zone has a mineral assemblage of pyrite-arsenopyrite-Fe rich sphalerite (marmatite)-pyrrhotite-chalcopyrite and electrum (average 65% Au, 35% Ag). The Lower Zone, below 900m.a.s.l. and is still open at depth below 200m.a.s.l., comprises sulphide and quartz-rich veinlets and minor veins, with a mineral assemblage characterized by pyrrhotite-chalcopyrite-bismuth minerals and free gold (average 94% Au, 6% Ag).

Cross section of the Marmato deposit. Adapted from (Santacruz et al., 2018), showing the different mining zone. Abbreviations: Pypyrite; Ccpchalcopyrite; Popyrrhotite; Apyarsenopyrite; Sphsphalerite (marmatite); Mrcmarcasite; Bibismuth; BiXbismuth minerals; Augold

For this study, twenty sample sites in streams were selected across the district based on their proximity to active mines and entables, as shown in Fig.6. Streams originate as springs and seeps at higher elevations, flowing from west to east into the Rio Cauca, but are largely fed by precipitation with minimal baseflow during dry seasons (JBR Environmental Consultants Inc., 2011). Water samples were collected over two days in January 2012, and their locations were determined using a Garmin Model Oregon 450 global positioning unit.

Field data are presented in Appendix, Table 2. Surface water samples were collected at each sampling point (Fig.6), following the protocols previously described (Torrance et al., 2012a). Water parameters, including temperature, pH, conductivity, and oxygen reduction potential (ORP), were measured at each location using a Hanna HI9828 multi-parameter meter. Alkalinity was measured in the field using a KI-9810 CHEMetrics Titrets titration kit.

The Marmato deposit has characteristics of an intermediate sulfidation epithermal system (Santacruz et al., 2014), which usually has a spatially wide arsenic signature. An additional goal of this investigation was to characterize arsenic speciation in surface water which may control its mobility. A simple field technique was used to separate arsenite species, [As(III)], and arsenate species, [As(V)], as first proposed and qualified by Ficklin (Ficklin, 1983), using a strong anion-exchange resin. An updated method (Wilkie & Hering, 1998) was developed with further modifications (Haque & Johannesson, 2006; Munk et al. 2011; Torrance et al., 2012a). Organic arsenic compounds may elute with As(III) and potentially skew the speciation (Miller, 2000), but is unlikely to be a concern with mineral-derived arsenic sources. Other authors (Issa et al., 2010) recommended pre-concentration of As(III) after separation in samples where As(V) dominates, but this was not found to be an issue at Marmato, where As(III) is always present above detectable limits.

In the field, a 50-mL sample for As speciation was filtered from the bulk sample into a pre-cleaned 50-mL HDPE tube, containing 100L of ultra-pure nitric acid. This was immediately passed through a Poly-Prep anion-exchange column, prepared in 10mL, 0.84cm Poly-Prep columns, purchased from Bio-Rad Laboratories (Hercules, CA). The columns were filled with an analytical grade anion-exchange resin Bio-Rad AG 1-X8 (50100 mesh, chloride form), which had been converted in bulk to the acetate form, replacing the Cl function group with an acetate group. Conversion of the 1-X8 resin from the chloride form to the acetate form was accomplished in the laboratory by washing 50g resin with 150mL of 1M NaOH solution (J. T. Baker, Phillipsburg, NJ), rinsing with NANOpure water and repeating two times until the pH of the rinse was neutral. The resin was then washed with approximately 150mL of 1M acetic acid (BDH Aristar Ultra) a total of four times and rinsed with NANOpure water until neutral after each step. This quantity was sufficient to pack approximately twenty-five 0.84cm Bio-Rad Poly-Prep ion exchange columns, at 2mL per column, which were stored at 4 C before use.

An aliquot, at a pH of less than 3, was passed through the column in increments of 5mL until all the sub-sample had passed through and collected in a 60mL HDPE bottle. As the sample passed through the column, oxy-anionic As(V) species, such as H2AsO4, were exchanged with the acetate functional group in the resin, while neutral-charged As(III) species passed through the column. This allowed the quantities of both As species present in the sample to be determined by comparison of the total dissolved As analysis of both aliquots by ICP-MS. Samples were stored at 4C in the dark until analysis. Duplicate samples were taken to verify the quality of the data. A field blank (KT-419) was processed with the samples in the field and showed no elevated metals, except for Cu (~3.7g L1).

Anions were measured using a Dionex BioIC ion chromatography instrument. Total metal concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS), using an Agilent 7700instrument. Total Hg was determined using a PS Analytical Millennium Merlin Atomic Fluorescence Spectrometer (AFS).

Concentrations of selected dissolved metals in surface water are presented in Appendix (Table 3). The average dissolved metal concentrationsFootnote 1 from streams impacted by ore processing discharges were: Zn, 78mgL1; Pb, 0.43mgL1; Cu, 403gL1 Cd, 255gL1; As, 235gL1; Ni, 67gL1; Co, 55gL1; Sb, 7gL1; and Hg, 42 ngL1. For those metals that the World Health Organization (WHO) has established drinking water guidance (WHO, 2011), average dissolved Cd concentrations are 80 times the WHO guidance value of 3gL1; average dissolved Pb concentrations are 43 times the WHO guidance value of 10gL1, and average dissolved As concentrations are 23 times the WHO guidance value of 10gL1. These represents a significant impairment of water quality rendering it unsuitable for drinking water and livestock watering.

Latin America has well documented occurrences of arsenic exposure including previous studies from Marmato (Bundschuh et al., 2012). Total dissolved As in surface water ranged from 6 to 3521gL1, with higher values in water that was visibly affected by run-off from ore processing. XRD analysis of solid particulates filtered from stream water indicates a high proportion of pyrite (Fig.7), and it seems likely that As enters the watershed from the dissolution of pyrite and arsenopyrite during ore concentration. The upper zone of the deposit, Zona Alta, which is worked exclusively by small-scale miners, containsmore arsenopyrite than the lower Zona Baja (Santacruz et al., 2018).

Dissolved arsenic concentrations in the unpolluted Quebrada (Qda.) Los Indios are also elevated at 90140g L1 which suggests that background As concentration is naturally elevated in the region. This is confirmed by whole rock assays determined during the exploration program, which had an average As concentration of 65ppm.

Arsenic concentrations exceed the WHOs guidance value for drinking water of 10g L1 at all but one sampling point. Figure8a shows total As concentrations around Marmato. Colombia has additional maximum thresholds for arsenic in irrigation water (100g L1) and for livestock water supply of 200g L1 (Alonso et al., 2014). Five of the water samples collected exceeded the higher threshold for livestock water.

Dissolved arsenic is stable under normal Eh and pH conditions in streams as either arsenite, As(III), or arsenate species, As(V) (Cullen & Reimer, 1989). It has been noted that there are no published arsenic speciation results published from sites in Colombia (Alonso et al., 2014). In this study, field separation of arsenic species in water was conducted as previously described by passing a separate aliquot through disposable chromatographic columns to separate inorganic As(III) species, with later analysis by ICP-MS. Anionic arsenate species, having a negative charge, were retained in the resin, while neutral arsenite species passed through the column unimpeded.

The results, which are shown in Table 1, indicated that 91 to 95% of the arsenic species is in the form of As(V), with little spatial variation (Fig.8b). This is consistent with the measured pH and Eh values, which predict the dominance of the more oxidized As(V) form. It is also further evidence that there is minimal groundwater interaction with the streams, which would have an As(III) signature due to reducing conditions within the subsurface.

Qda. Cascabel has some of the highest concentrations of dissolved total arsenic and is fed by smaller tributaries, e.g., Canalon de la Iglesia, into which discharges from entables in Marmato are most severe.

Cadmium is an extremely toxic metal even at low concentrations, attacking the kidney and causing itai-itai disease, an osteomalacia with various grades of osteoporosis accompanied by severe renal tubular disease from chronic exposure (WHO, 2011). Total dissolved Cd in the Marmato samples ranged from 0.2 to 833g L1. For comparison, the WHO guidance value for drinking water is 3g L1. Cd concentrations are below 1g L1 in Qda. Los Indios and the Rio Cauca, indicating background levels that are near normal. Cd is enriched within the deposit by a factor of 100 compared to crustal averages (Table 4). It seems likely that Cd is released from the mineral sphalerite (ZnS) which is abundant in the ore veins and is crushed with the ore; dissolved Cd and Zn concentrations show a strong correlation (R2=0.887). Figure9a shows Cd aqueous concentrations in the vicinity of Marmato. Other trace metals, such as gallium and indium, were present at detectable levels which may also originate the minerals sphalerite (ZnS) and marmatite ((Fe)ZnS), which are abundant in the mineralized zones within Marmato Mountain.

Dissolved lead (Pb) concentrations ranged from 4.4 to 4,880g L1, compared to the WHO guidance of 10g L1. The highest Pb concentrations corresponded to streams with the highest levels of observed suspended sediment, such as Canalon de la Iglesia (KT-415). Figure9b shows Pb levels in stream water around Marmato. Lead in surface water probably originates from the dissolution of the mineral galena (PbS), which is concentrated during ore processing. Concentrations of lead are higher in streams that have a pH of>5.5 and<7.5.

Mercury (Hg) was detected in several samples from Qda. Cascabel (Fig.9d), with concentrations up to 142ng L1, which is well above background levels, which are below detection limits (10ng L1). WHO has set a guideline of 6g L1 for inorganic mercury in drinking water (WHO, 2011), but this is rarely exceeded as inorganic mercury compounds are poorly soluble. Ingestion of methyl mercury is a more potent exposure pathway; analysis of fish tissue is a more appropriate matrix for assessing mercury impacts in a watershed. Nevertheless, the concentrations of Hg at Marmato are comparable to dissolved concentrations reported from a stream traversing an abandoned mercury mine in Alaska (Torrance et al., 2012b).

Leaching studies of representative mining waste carried out to determine the acid rock drainage (ARD) potential at Marmato indicated a maximum dissolved Hg concentration of 10ng L1 in the leachate from a single sample out of 20 tested (Knight Pisold Consulting, 2012). It seems therefore unlikely that dissolved Hg in the streams around Marmato originates from naturally occurring minerals in the ore and that Hg is more likely to have been added during ore processing to enhance gold recovery. This is corroborated by the lack of enrichment of Hg in the deposit as shown by multi-element analyses of drill core samples with a mean value of 0.886ppm and a range of<0.005ppm (lower limit of detection) to 373ppm (n=16,783), compared with a crustal average of 0.5ppm (Fig.10). Less than 10% of samples analysed had mercury concentrations above the crustal average.

The locations of the anomalous Hg sample points, shown in Fig.9d, are not directly related to the position of the entables. This may indicate isolated mercury use by artisanal miners at some mining locations, perhaps to enhance recoveries from gold panning. No attempt was made to determine whether the Hg is present as inorganic mercury or as more toxic organo-mercury compounds.

Entables in the mining districts of the State of Antioquia of Colombia, north of Medellin, are known to make extensive use mercury to extract gold from ore through amalgamation (Hentschel et al., 2002; Prieto & Gonzalez, 1998). High levels of atmospheric mercury have been recorded in Segovia, Zaragoza, and other towns in the district (Cordy et al., 2011) where the raw ore is processed, and gold refined from dor. The United Nations Environmental Program (UNEP) estimates that artisanal gold mining accounts for the release of over 1,000 metric tons of Hg into the environment worldwide every year (Telmer & Veiga, 2009). Further, the monopolistic supply of mercury by gold buyers to the miners is viewed as an agent of poverty (Hilson & Pardie, 2006). An inventory of mercury in Colombia for 2011 estimated that 140 metric tons of mercury are released into the environment each year from artisanal and small-scale mining (Brooks, 2012).

Not only are non-mercury gold extraction processes more environmentally friendly; gold recovery is potentially much higher (Garca et al., 2015). At Marmato, although there was no visible evidence of mercury use in the entables that were visited, it is understood that mercury is frequently used in the final process to extract gold from the concentrate. As confirmation, mercury was detected in some water samples at levels up to 142ng L1.

Antimony (Sb) concentrations in surface water ranged from below the level of detection to a maximum of 30.2g L1, as compared to the WHO drinking water guidance on antimony of 20g L1 (WHO, 2011). Other regulatory agencies, such as the United States Environmental Protection Agency, have set a lower Maximum Contaminant Level (MCL) for Sb of 6g L1. In comparison with other dissolved metals in the streams, Sb is not at especially elevated levels, although it is present in mineralized zones within the deposit. Figure9c shows Sb concentrations in streams around Marmato.

Dissolved gold is present in some water samples up to 108g L1. Their sampling location downstream of the entables suggests that these high values are losses from cyanide processing of crushed gold ore. It highlights the inefficiency of the gold recovery process in the entables and the associated loss of income to the miners. Concentrations of gallium and indium were also elevated; however, indium levels may be an artefact of ICP-MS analysis, which uses indium as an internal standard. Indium and gallium most likely occur as chemical substitutions in the mineral sphalerite, which is an abundant sulphide in the deposit.

Water samples from Qda. Cascabel showed elevated rare earth elements (REEs) including Nd, Eu, Gd, and Er. As there are no observed pegmatite veins in the complex, which are often elevated in REEs, their origin is unknown. For all samples, dissolved arsenic concentration was observed to correlate with zinc (R2=0.68), cadmium (R2=0.65), lead (R2=0.54), and iron (R2=0.43) dissolved concentrations, arsenic concentrations correlated less strongly with selenium (R2=0.35), cobalt (R2=0.34) and nickel (R2=0.26). There was no correlation (R2<0.07) of dissolved arsenic concentrations with antimony, copper, manganese, or barium. Dissolved mercury concentrations also showed no correlation with dissolved arsenic concentration, with reported concentrations of mercury above the detection limit confined to Qda. Cascabel, Qda. Pantanos, and their tributaries. Our interpretation of the spatial data is that dissolved mercury concentrations are related to clandestine mercury amalgamation within entables that discharge into these creeks.

Elemental analysis of drill cores through the mountain is presented as box and whisker diagrams in Fig.10 and as Appendix, Table 4. Distributions for most potentially toxic metals, including As, Cd, Pb, and Sb, are positively skewed, reflecting the elevated concentrations of these metals within the mineralized areas and their association with sulphides such as arsenopyrite, sphalerite, galena and tennantite-tetrahedrite that occur in the low to intermediate sulphidation epithermal veins. Based on average crustal abundances, metals are enriched within the mineralized zone as follows: Cd>Au>As>Ag>Sb>Zn>Hg>Pb. Cu, Mo, Cr, and Sn are enriched within the deposit by a factor of less than 2 and have neither economic value nor environmental concerns.

The disposal of milled ore slurry from the mine workings and entables visibly impacts the clarity of surface water due to very high suspended sediment loads. This renders surface water unsuitable either as a drinking water source or for agriculture.

Water exiting mine adits is acidic due to the oxidation of pyrite and sphalerite, with a minimum pH of 3.85 observed. Surface water downgradient of the entables has elevated pH (maximum pH 10.3) due to the addition of caustic sodium hydroxide pellets during cyanide treatment of crushed ore to extract gold.

Cadmium, lead, and arsenic are present in elevated concentrations within the mineralized zone of the Marmato deposit. The naturally occurring concentrations of these toxic metals in surface waters are exacerbated by mining and ore processing. Further, mining spoil that is dumped on the steep hillside further-enhances frequent mass wasting events, such as landslides and mud flows. These impacts limit evaluation of the natural, pre-mining metal concentrations in surface waters.

Lead, arsenic and cadmium are present in surface water at concentrations that greatly exceed WHO guidance (WHO, 2011) for drinking water quality. Other factors, such as sediment load and alkalinity, render water from these sources unsuitable for human consumption or for irrigation.

The source of elevated mercury concentrations in surface water is most likely from amalgamation of ore concentrates by artisanal miners, as Hg is not significantly elevated in the Marmato deposit. It has been estimated that 3050% of mercury is not recovered during amalgamation in the entables (Garca et al., 2015).

Detection of dissolved gold up to 108g L1suggests that the existing extraction methods do not recover all of the gold present in the ore. More efficient extraction technology could be introduced in Marmato that would be both environmentally friendly and more profitable for the miners.

The human health risks, both chronic and acute, related to ingestion of arsenic, cadmium and lead via drinking water are well documented and associated with mining districts (Candeias et al., 2019). Potable water for the use of Marmato residents is piped in from more distant sources unaffected by mining. In this study, a sampling location at Qda. Los Indios (KT-417) was considered as representative of background water quality, as Marmato residents use this stream as an alternative source of clean water. However, the polluted streams around Marmato discharge into the Rio Cauca, which is the main source of drinking water for several downstream communities and is further impacted by other mining and industrial activities in the region. Human health impacts from exposure to mercury from small-scale mining are linked to inhalation of mercury vapour (Gibb & OLeary, 2014), and to the ingestion of methyl mercury in fish and other food sources (Palacios-Torres et al., 2018; Selin, 2009), rather than ingestion via drinking water. Impacts of artisanal gold mining in similar mining communities in western Colombia are well documented (Gutierrez-Mosquera et al., 2018; Marrugo-Negrete et al., 2017).

It has been estimated that ASGM accounts for around 87% of the gold produced in Colombia (Veiga & Marshall, 2019), which operates under a complex regulatory regime. The socio-technical interactions between large-scale and artisanal miners in Marmato have been discussed in depth (Holley et al., 2020). Gran Colombia Gold Corporations original proposal to develop a large-scale open pit mine at Marmato caused conflict in part because the excavation of the open pit would require the relocation of the town of Marmato. Further, the removal of most of the Zona Alta to create the open pit would greatly restrict ASGM in the district. Although much of this mining is illegal under Colombian law, it is the main source of employment in Marmato.

A modern gold mine operating under a robust permitting regime with appropriate environmental controls would avoid the extreme water quality impacts observed at Marmato. If it is accepted that restriction of ASGM is neither feasible nor socio-economically desirable, there are multiple obstacles to addressing water pollution arising from artisanal mining. The implementation of the Minamata Convention on Mercury in 2017, which was ratified by Colombia in 2019 (UN Environmental Programme, 2020), has formalized restrictions on mercury use but is unlikely to completely eliminate the practice and barriers still remain for the implementation of alternative extraction retort technologies (Bosse Jnsson et al., 2013; Clifford, 2014). A more realistic approach might be to encourage ore processing at a central facility (Veiga et al., 2014), instead of at the numerous small entables in the region. This would permit better environmental controls to be implemented, and the quality of the discharges to the River Cauca to be controlled and monitored.

Analytical results from Canalon de la Iglesia (KT-409) were excluded from the calculated average as dissolved metal concentrations are almost an order of magnitude higher than from other sampling points.

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The authors wish to thank Gran Colombia Gold Corp. and Caldas Gold Corp. for permission to use the assay data from their Marmato exploration program and for covering travel costs to Marmato for Keith Torrance. Analytical results have been previously reported in a PhD thesis (Torrance 2012).

Keith Torrance collected the field samples and performed the analytical analysis of the surface water samples and field arsenic speciation. Dr. Stewart Redwood authored the section on the geology of Marmato, based on his own field studies. Dr. Alessandro Cecchi logged and analysed drill core from Marmato and provided descriptions of the mineralization within the deposit.

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Torrance, K.W., Redwood, S.D. & Cecchi, A. The impact of artisanal gold mining, ore processing and mineralization on water quality in Marmato, Colombia. Environ Geochem Health (2021). https://doi.org/10.1007/s10653-021-00898-y