Bolivia

Porco Mine

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Overview

Mine TypeUnderground
StatusActive
Commodities
  • Silver
  • Zinc
  • Lead
  • Silver Equivalent
Mining Method
  • Longhole stoping
  • Shrinkage stoping
  • Cut & Fill
Backfill type ... Lock
Production Start... Lock
SnapshotPorco Mine Complex consists of: an underground mine, 1,400 tonnes per day process plant, a water treatment plant, a tailings storage facility, camp and support buildings, and produces zinc and lead concentrates. The Porco Mine has been active for nearly 500 years.

The focus for 2023 at Porco is to send higher-grade feed to the plant by using more selective mining techniques to minimize dilution.

Owners

SourceSource
CompanyInterestOwnership
Santacruz Silver Mining Ltd. (operator) 45 % Indirect
Corporación Minera de Bolivia (COMIBOL) 55 % Indirect
On March 18, 2022, Santacruz Silver Mining Ltd. acquired 100% ownership of Sociedad Minera Illapa S.A. (“Illapa”) from Glencore plc. The producing Porco mine held under an association agreement with Corporación Minera de Bolivia (“COMIBOL”) a Bolivian state-owned (Illapa holds a 45% interest, and COMIBOL – 55%).

Santacruz Silver Mining Ltd. is the operator of the Illapa Business.

Deposit type

  • Epithermal
  • Vein / narrow vein

Summary:

The Porco silver-zinc-tin deposit is located 35 km southwest of the Cerro Rico de Potosí deposit on the southeastern edge of the Los Frailes volcanic field. It was the first silver deposit discovered in Bolivia, with exploitation dating to pre-colonial times. The geology has been described by Sugaki et al. (1983), Cunningham et al. (1993, 1994a, b) and Jiménez et al. (1998).

The deposit is hosted by a north-south-elongated caldera that is 5.0 km x 3.0 km and formed at 12.0 ± 0.4 Ma with the eruption of the crystal-rich dacitic Porco Tuff. Well defined topographic walls of the caldera cut Ordovician phyllites and Cretaceous sandstones. The 12.1 ± 0.4 Ma Apo Porco stock (4,886 masl) occurs on the southern margin of the caldera. Mineralization is associated with the younger 8.6 ± 0.3 Ma Huayna Porco stock (4,528 masl) in the center of the caldera. Radial dykes, alteration and metals are zoned around the stock. To the north, the Porco Tuff is overlain by the ignimbrites of the Los Frailes Formation dated at 6 to 9 Ma.

Mineralization occurs in NNE to NE-trending veins that cut the Porco Tuff about 1 km east of the Huayna Porco stock. The deposit is zoned around the stock with cassiterite proximal to the stock and base metals, mainly sphalerite and galena, further away. The upper parts of the veins are silver-rich with pyrargyrite, acanthite and stephanite. The main structure is the San Antonio vein which strikes N10º - 30ºE and dips between 70º and 85º to the east. It is 300 m in vertical extent and 1.2 m to 2.0 m in width. To the south, the vein branches into the Oriente, Misericordia, and Santos veins, whose lengths vary between 500 m to 1,500 m. The main ore minerals are pyrite, sphalerite, galena, argentiferous galena, native silver, chalcopyrite, and arsenopyrite in a gangue of quartz. Other important structures are the Muestra Grande vein on Huayna Porco Hill, where the grade reached 2,300 g/t Ag (Sugaki et al., 1983), and the Rajo Zúñiga vein, which strikes N30ºE and dips 75º-80ºE. The latter vein, with widths between 1.0 m and 1.5 m, was exploited in a 100 m x 20 m open pit. This altered dacite-hosted vein is accompanied by associated veinlets and disseminations in the wall rock and consists of cassiterite, wolframite, galena, silver sulphosalts, and pyrite.

The characterization of the mineralization at the Porco site 8 may be summarized as follows:
• Hydrothermal reservoir;
• Epithermal phase, which allows the uptake of base metals (Zn, Pb, Cu) and (Au-Ag) of low sulphidation;
• Vein type;
• Temperature range, 50°C - 300°C;
• Deposit depth, between 50 m-500 m depth from the surface;
• Mineralization can be internally heterogeneous, with low to high-strength sectors and sterile sectors;
• Filled in fractures or zones of weakness;
• Vein systems can be parallel, reticular, convergent and or conjugate;
• Plutonic rocks of intermediate to acidic composition are favorable;
• Epithermal deposits are generally associated with Tertiary volcanism and very few older deposits;
• Alteration is predominantly sericitization, hydration, carbonatization, pyritization and propylitization; and
• The Porco deposit is typical Philonian type deposit, the mineralization to refill the fractures within the superjacent Ordovician slate north of the deposit.

The mineralized zones or veins are polymetallic, monoclinal banded structures but may also be crustiform or in geodes presenting in rosary form. Thicknesses range from between 0.01 m to 4.0 m but can reach widths of ~10.0 m usually in rameada form interspersed with country rock or mineral gangue.

Veta San Antonio Principal
The San Antonio structure is located in the main corridor striking N 10° - 30°E with dips ranging between 60°-75° and is developed from the Santacruz level to the -330 level. The mineralogy of the San Antonio Principal vein, located in the central sector of the deposit), consists of sphalerite, pyrite, galena, marcasite, which correspond to the intermediate phase of the mineralization this is changing towards depth enriching in marmatite, pyrite.

Elena Vein
The structure is located in a fault oriented N 10° - 50°E and dipping between 40°-62° which is developed from the San Cayetano level to the -330 level. The mineralogy of the vein consists of sphalerite, pyrite, galena, siderite kaolin, which corresponds to the intermediate phase of the mineralization this changing at depth enriching in marmatite and pyrite.

Vein Ramo Elena
The structure is located between the main San Antonio and Elena veins in direction and diving ranging from N 70° - 80°W/50°-75° in vertical longitude is developed from level 105 to level -195. The mineralogy of the vein consists of marmatite pyrite galena, and they correspond to the late phase of mineralization.

Vein Rosario
The Rosario structure is located between the Elena and Ramo Elena veins oriented N 10° - 30° W and dipping 55°-65° which developed from level 60 to level -195. The mineralogy of the vein consists of sphalerite, pyrite, galena, siderite kaolin, which corresponds to the intermediate phase of mineralization.

Vein RH6
The RH6 structure is located at the intersection of the Huayna Porco stock and Apo Porco becoming part of the Pamela, Crucera II, Larga 3, Crucera IV, Crucera Pamela, Ramo Pamela and H-6 vein system. This corridor has high concentrations of silver sulfosalts compared to the rest of the corridors. All the structures that are contained in this vein system oriented N 10°W - N 40°E and dipping 60°SW- 70°SE which has been developed from the Huayna Porco level to the -240 level. The mineralogy of the vein consists of sphalerite, marmatite, pyrite, galena, sulfosalts, siderite, and hat correspond to the intermediate phase of the mineralization.

Veta Colorada Uno
The Veta Colorada Uno is located along a corridor north of the Huayna Porco stock that emerges from the main Hundimiento vein, with an orientation of N 5°E. Located in Tertiary age dacitic rocks the vein has approximate length of 500 m in length with thicknesses that average 2 m and occur in the form of massive veins. The mineralogical content consists of ~70% sphalerite, ~10% pyrite, ~10% galena and ~10% marmatite. However, at deeper levels the percentages are reversed reducing to 45% sphalerite and 5% galena, with the marmatite and pyrite proportionally increases at depth.

Veta Hundimiento
The Hundimiento zone corridor intersects the Huayna Porco stock at an orientation of N 15°E. It is hosted in Tertiary age dacitic rocks extending ~1,000 m in length with average widths of 3 m in the form of massive veins. The mineralogical content consists of ~30% sphalerite, ~50% pyrite, ~10% galena, ~5% marmatite and ~5% siderite. However, the percentages are decrease at depth to ~25% sphalerite and ~2% galena; while pyrite proportionally increases at depth but marmatite and siderite remain at depth.

Vein California
Veta California is located in the Hundimiento zone corridor where it intersects the Huayna Porco stock parallel to the Hundimiento vein at an orientation of N 15-20° E. Veta California is hosted in Tertiary age dacitic rocks extending approximately 1,000 m with average widths of 1.5 m in the form of gaped veins. The mineralogical content consists of ~60% sphalerite, ~10% pyrite, ~5% galena and ~25% marmatite. However, as the vein deepens the percentages decrease to ~45% sphalerite and ~20% marmatite; while pyrite increases proportionally, and siderite begins to appear.

Reserves

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Mining Methods

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Comminution

Crushers and Mills

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Processing

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Production

Similar to Bolivar, the process plant is also fed by the mine (approximately 55%), and toll feed from the San Lucas Business (45%).
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Operational metrics

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Production Costs

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Financials

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Heavy Mobile Equipment

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Personnel

Mine Management

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Aerial view:

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