Geology of the Cerro de Pasco Area.
At Cerro de Pasco, the magmatic center was emplaced directly west of a major high-angle, N 15° W-striking reverse fault (“the Longitudinal Fault”), mainly intruding weakly metamorphosed shales of the Middle Paleozoic Excelsior Group, the oldest lithological unit in the area, and polymictic conglomerates and sandstones of the Middle-Late Triassic Mitu Group (Spikings et al., 2016). East of the Longitudinal Fault there is a thick sequence (about 1,000 m) of massive carbonate rocks, mainly limestones with locally sandy intercalations, black bituminous limestones, and beds with chert nodules belonging to the Late Triassic Chambará Formation. The latter is part of the Pucará Group that overlies the Excelsior and Mitu groups (Rosas et al., 2007; Angeles, 1999). The sedimentary sequence was folded prior to the Mid-Miocene magmatism, thus creating the main structural feature in the area, the Cerro anticline with a north-south axis and plunging to the north (Baumgartner et al., 2008; Angeles, 1999).

The magmatic core of the Cerro de Pasco district consists of a large diatreme-dome complex, 2.5 km in diameter, which was formed by a succession of phreatomagmatic and magmatic events (Baumgartner et al., 2009; Rogers, 1983). An early phase of explosive activity produced a diatreme-breccia known locally as the Rumiallana agglomerate, which is the most common lithology in the magmatic complex and has been dated at 15.36 ± 0.03 Ma and was followed by emplacement at 15.40 ± 0.07 Ma of dacitic to rhyodacitic lava-dome complexes along the western margin of the diatreme (Baumgartner et al., 2009).

East-west–trending quartz-monzonite porphyry dykes cut the diatreme breccias and the magmatic domes. These dykes do not propagate into the Excelsior shales west of the diatremedome complex; to the east they crosscut locally the carbonate sequence. Two of these dykes have been dated at 15.35 ± 0.05 and 15.16 ± 0.04 Ma (Baumgartner et al., 2009). The end of the phreatomagmatic and magmatic activity at Cerro de Pasco is marked by the emplacement of numerous, 20 cm to 3 m-wide, E-W–trending, milled-matrix fluidized breccia dykes, occurring in various parts of the diatreme-dome complex.

Following this event, epithermal base metal mineralization took place, mainly in carbonate rocks along the eastern margin of the magmatic complex (Baumgartner et al., 2008; Einaudi, 1977). A striking feature of the Cerro de Pasco mineralization is the occurrence of an NS- trending, 1.5 km-long, 250 m-wide, and more than 550 m-deep, funnel-shaped massive pyrite- quartz body that replaced mainly carbonate rocks from the Pucará Group, as well as, subordinately, the diatreme dome complex itself (Baumgartner et al., 2008; Baumgartner, 2007). At least five main pipe-like, up to 150 m-wide, massive pyrrhotite-dominated bodies have been recognized. They grade outward into massive Fe- rich sphalerite (up to 80% in volume) and galena.

Ore production totaled 89,920 metric tons in 2014; 90% of this production came from the María Inés veins and the María Inés branch. At depth these veins are weaker and shorter but they contain higher grades of zinc and lead, although a lower grade of silver.

On December 29, 2014 the Volcan Compania Minera S.A.A. requested the temporary suspension of operations at Vinchos; this request was approved by the Ministry of Energy and Mines in January 2015.

The San Expedito/Paragsha plant treated ore from the Vinchos Mine.

During 2014 the Volcan Compania Minera S.A.A continued using crushing, milling and filtration circuits at the Paragsha plant to increase the treatment capacity of the San Expedito plant. In addition, recovery improved after installation of a flash SK-240 cell and an automatic lime dosing control system, as well as greater flotation time in the lead-zinc circuits with large cells transferred from the Paragsha plant. However metallurgical testing was continued in order to improve recovery and zinc grade, given the higher copper head grade of the ore.