Pacococha, San Mateo District, Huarochirí Province, Lima, Perui

Regional Level Types
Pacococha	- not defined -
San Mateo District	District
Huarochirí Province	Province
Lima	Region
Peru	Country

The Pacococha District is located four kilometers SW of Millotingo, on the banks of Pacococha lake, nearly due southwest of Casapalca about 20 km, and about 35 km SW of Yauli. Elevations range between 4,600 - 5,000 meters, and the district measures about 4 km by 6 km. Pacococha is situated among the mining districts of Viso-Aruri, Millotingo, Pucacorral, and Chanape (Fig. 18). Millotingo is considered as part of the Pacococha district by Ly and Arce (1965). Petersen (1962) and Ly and Arce (1965) briefly describe the district, and much of the data is abstracted from their reports.

Scattered workings suggest some mining was going on during the Colonial period in the country. Modern development began in 1950 with the building of a 27 km road from the Central Highway to the district. As of the mid-1970's, approximately 42,000 meters of drifts had been completed from 24 veins in the various mines.

The predominant rock types are Cenozoic andesitic volcanic flows with a composite thickness of 700-1000 meters. These flows are interlayered with tuffs and rhyolites. The volcanic rocks have been intruded by several fine-grained diabase or diorite porphyry stocks, which have pyritized, silicified, kaolinized, and otherwise altered the proximal volcanics surrounding them.

Mineralization is by fracture filling, with the larger veins having lengths of 500 to 1000 meters and thicknesses of 1 to 1.5 meters. Outcrops of these veins are composed of quartz with box-works from weathered-out sulfides. Veins are discontinuous and new reserves must be continuously sought.

Vein mineralization is dominantly chalcopyrite, galena, dark sphalerite, and quartz, with lesser pyrite. Tetrahedrite, silver sulfosalts, argentite, marcasite, fluorite, barite, calcite, and rhodochrosite are minor constituents. Pyrite is usually present as stringers in the veins and disseminated in the wall of the veins as small cubes. High grade veins have almost no quartz. Quartz is usually found in the sub-economic portions of the veins or as the veins narrow and pinch-out.

Some veins are located in the upper parts of the diabase stocks and have a more complex mineralogy than do the veins in the tuffs and andesites. Typical minerals in these stocks are pyrite, sphalerite, chalcopyrite, arsenopyrite, galena, bornite, pyrargyrite, tetrahedrite, trace gold, calcite, and quartz.

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