Huaron mines, The

LOCATION

Huaron lies 40 km south-southwest of Cerro de Pasco, on the road from Canta, near Huayllay. The district is about 14-15 km due west of the northwest shore of Lake Junin, and lies next to Lake Huaron. The mines are located on the east flank of the Western Cordillera of the Andes, at elevations ranging from 4,300 to 4,800 meters; the district is small, measuring about 3 km by 4 km (Fig. 81).

HISTORY

Pasco Department was originally part of Junin Department; they were divided after 1919 into the current configuration. Initially the Huaron area was known as the Huancavelica District of Junin Department (Miller and Singewald, 1919). This led to confusion as to precise mineral locations. The mine was referred to as the San Jose mine in the 1920's, and is now considered to be in the San Jose de Huayllay district. The Compagnie des Mines de Huaron has been active at Huaron since 1912, and in continuous production since 1914. Ownership of the mines was partially sold off in 1987 to several other companies. Peak output was reached in the 1970's, but fell off in the 1980's as ore grades declined and costs increased. The low price of silver hurt the company also, as it has so many Peruvian mining companies. In 1991 the Compania Minera Huaron S.A., as the company is titled, filed for temporary closure and reduction of personnel. As of April 1991, ore production was 40% of normal (Cavanagh, 1993?). Production today is predominantly lead and zinc (approximately 96%), with lesser copper and minor silver.

GEOLOGY

The Cretaceous Machay Group limestones and Tertiary Pocobamba (Casapalca Red Beds) continental sedimentary rocks are the dominant sedimentarv rocks in the area. The Huaron anticline is the dominant structural feature of the area. The Machay Group limestones and Pocobamba sedimentary rocks are strongly folded, and are intruded by quartz monzonites and quartz monzonite dikes, with accompanying fracturing. This fracturing was followed by alteration and mineral deposition by hydrothermal fluids. Following the intrusion of the dikes, the sedimentary rocks were further compressed and fractured, and the fractures were subsequently mineralized by hydrothermal fluids. These fractures frequently attain considerable width, and persist to great depth. The dikes have undergone extensive hydrothermal alteration, typified by sericitization, kaolinization and pyritization. Post-mineralization Huayllay pyroclastic volcanics have mantled the region.

The area has been glaciated, and surface oxidation is minimal. The ore is described by Petersen (1965) as similar to that found at Morococha. The deposits are composed of veins, shoots and mantos (blanket like orebodies); general zoning occurs from the center of the district outward in an asymmetrical pattern.

Huaron is described as a complex copper-lead-zinc-silver deposit; distinct zonation exists from the center zone where copper ores predominate, to an outer lead-rich zone. Five major east-weststriking lead-zinc ore veins are distributed over 3 or 4 km, along with two northeast striking copper-ore veins. Orebearing veins vary from a few dozen centimeters to 10 meters wide, and may extend, in the larger veins, over 1,800 meters horizontally. Ore veins have been traced to depths exceeding 500 meters.

Three major periods of mineralization occurred in the fracture zones. The initial mineralization consists of relatively high-temperature minerals deposited in the following order: milky quartz, pyrite, enargite, and tetrahedrite. Enargite dominates the mineralization in the central part of the district, while tetrahedrite dominates the outer part of the enargite zone. Reopening of the fractures caused the initial mineralization to be brecciated, and the breccia was subsequently cemented together by the next, second-period generation of medium-temperature minerals: milky quartz, brown sphalerite, and galena. Crystals of large size were deposited during this period, usually on a botryoidal gangue of siderite, dolomite and rhodochrosite. A final, third period re-fracturing, followed by a rapid deposition of hydrothermal minerals, resulted initially in the formation of minerals with colloform and botryoidal textures. This rapid deposition continued with fine-grained crystallization and continuous late precipitation of the carbonates, beginning with siderite and gradually changing to dolomite, rhodochrosite, and calcite. As a final pulse during this late-stage deposition, barite, pale to reddish amber-colored sphalerite, galena, tetrahedrite, polybasite and chalcopyrite were deposited.

Most of the ore being mined today is from veins in the second stage lead-zinc mineralization zones. There are about 20 mines in the Huaron district; in the south and middle part of the district are the Andalucia, Restauradora, Cometa, Elena, Yanamina, Travieso, Alianza, and Yanacreston mines; in the north part of the district are the Shiusha, Mechita, and Patrick mines; and in the western part of the district are the Fastidiosa, San Narcisco, and Constancia mines. The Alimon mine, a source of specimens, is not mentioned in the literature.