A series of surface mapping and drilling exploration programmes have located skarn type Pb-Zn mineralization in the Pallca area of the Cordillera Huayhuash in the north-central Andes of Peru. Pb-Zn mineralization consists of sphalerite, galena, pyrrhotite, pyrite, magnetite and minor chalcopyrite hosted in clinopyroxene and garnet skarnized zones of the Cretaceous Santa and Pariahuanca Formation limestones.
Outcrops of portions of the mineralization in the Santa Formation limestone (Berlin zone) have already been reported, however, mineralization zones in the Pariahuanca Formation (Culebra zone) were newly discovered by an investigation programme for skarn-associated intrusive rocks and mineral zoning.
Mineralization is associated with 16.6 m.y. granodiorite porphyry and slightly older quartz porphyry stocks. Skarn and marble contact (marble line) zones are especially important for the Pb-Zn mineralization. Pyrrhotite and pyrite rich man-tos and lenses with Pb-Zn mineralization occur in the outer portions of the skarn zone. Au mineralization is locally encountered in the skarn zones. Mo stockwork type mineralization occurs in the quartz porphyry stock.
Analysis of geochemical composition of the stocks indicates that the granodiorite porphyry stock may have more close association with the Pb-Zn mineralization than the quartz porphyry. Also mineralization surrounding the granodiorite stock is zoned with respect to metals and style of mineralization. Pb increases and Zn and Cu decrease outward from the stock. Sulfide dissemination in skarn is dominant near the stock, sulphide replacement mantos and lenses form outer portions of skarn, while veins are most distal to the stock. Au skarns are characterized in showing rather high contents in As, Sb and Bi. Also the Au skarns show positive Eu anomaly on chondrite-normalized REE pattern, while most of the Pb-Zn skams show negative Eu anomaly.
The mineralized zones are still open in strike and depth. A total of approximately 15 million tonnes of potential ore reserve in-situ at around 10 % Zn is expected in the zones. An extensive exploration programme designed under consideration of metal zoning is being carried out.