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Huarón is an underground silver mine located in the Cordillera Occidental of the Peruvian Andes, 37 km SSW of Cerro de Pasco and 320 km NE of Lima in the province of Pasco, Peru (#Location: 11° 0' 15"S, 76° 24' 46"W).
The Huarón mine, mill, and supporting villages were originally built in 1912 by a subsidiary of the French Penarroya Company. In 1987, the mine was sold to Mauricio Hochschild and Cia Ltda, but in April, 1998 was closed after a portion of the bed of the nearby Lake Naticocha collapsed and flooded the neighbouring Animon underground mine and then via connecting workings, entered the Huaron mine. The mine was subsequently reclaimed after the lake level was lowered. A majority interest in the Huaron mine was acquired from Hochschild by Pan American Silver Corp. in 2000 and full-scale operations recommenced in 2001.
For details of the regional setting, see the separate Peruvian Andes Cu-Au Province record.
The district geology is dominated by the massive marine limestones of the Upper Cretaceous Machay Group, which overlies the mid to Lower Cretaceous Goyllarisquisga Group, and by the unconformably overlying Tertiary Pocobamba Formation continental red-bed sedimentary rocks. These units have been strongly folded into the Huaron anticline, the dominant structural feature of the area, and intruded by North-south trending sub-vertical porphyritic quartz monzonite dykes. Following the intrusion of the dykes, the sedimentary rocks were further deformed and fractured, and the fractures were subsequently mineralised by hydrothermal fluids.
The lowest member within the deposit area comprises the Barnabe quartzite conglomerate at the base of the red-bed sequence. These are succeeded by thinly bedded marls and sandstones, known as the lower red beds, which are found in the central part of the mine and at lower elevations. The upper redbeds occur on the eastern side of the mine, and comprise calcareous chert overlying sandstone and marls. On the western side of the mine, the stratigraphy consists of a series of interbedded conglomerates and sandstones.
The axis of the Huarón anticline strikes approximately north-south and plunges gently to the north, and is cut by two main fault systems. The first comprises north-south striking thrust faults, paralleling the axis of the anticline, whilst the second is represented by east-west striking tensional faults.
Huarón is a hydrothermal polymetallic deposit of silver, lead, zinc, and copper mineralisation hosted within structures that are principally located within the Huaron anticline. Mineralisation occurs as veins parallel to the main fault systems, in manto replacement bodies associated with the calcareous sections of the conglomerates and other favourable stratigraphic horizons, and as dissemination in the monzonitic intrusions at vein intersections.
Mineralised veins vary from a few centimetres to up to 10 m in width, and may extend along strike for up to 1800 m. Mineralization within most of the structures is open m at depth and along strike. Vein orientations vary but generally trend east-west or north-south. The current mineral reserves are based on ~100 different structures which have been grouped into 13 families of mineralised trends according to location and orientation.
The most important economic minerals are tennantite-tetrahedrite (containing most of the silver), sphalerite and galena, although more than 90 other minerals have been identified. The principal gangue minerals are pyrite, quartz, calcite and rhodochrosite. Enargite and pyrrhotite are common in the central copper core of the mine and zinc oxides and silicates are encountered in structures with deep weathering. Silver is also found in pyrargyrite, proustite, polybasite and pearceite.
Remaining ore reserves and mineral resources as at 31 December, 2015 (Pan American Silver, 2015) were:
Proved + probable reserves - 9.8 Mt @ 170 g/t Ag, 3.06% Zn, 1.47% Pb, 0.36% Cu;
Measured + indicated resources - 3.1 Mt @ 166 g/t Ag, 2.94% Zn, 1.62% Pb, 0.45% Cu;
Inferred resources - 7.3 Mt @ 153 g/t Ag, 2.75% Zn, 1.48% Pb, 0.32% Cu.
Note: reserves are additional to resources.
Information is also taken from "Annual Information Form by Pan American Silver Corp, Report Year Ended December, 31, 2002."
The most recent source geological information used to prepare this summary was dated: 2015.
This description is a summary from published sources, the chief of which are listed below.
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