Unidad Minera Americana is 100% owned and operated by Sobreandes S.A.C., which holds the formal mining title. Sobreandes S.A.C. is part of Grupo Minero Alpayana, a 100% privately owned Peruvian mining group founded by the Balarezo family and partners.
Sobreandes S.A.C. is the legal successor of Compañía Minera Casapalca S.A., following a name and brand change completed in 2019, with full continuity of legal registration. Grupo Alpayana manages Unidad Minera Americana through a centralized management team based in Lima, applying group-wide standards for operations, sustainability, and social responsibility.
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Summary:
[Translated from Spanish]
Local Geology
The Casapalca Formation is a folded sequence of Cretaceous continental sediments that includes the rocks hosting both types of mineralization. The lower member of this formation, known as the “Casapalca Red Beds,” is composed of sandstones, siltstones, reddish shales, and some levels of whitish limestone. The upper member, the “Carmen Conglomerate,” consists of reddish, silicified clayey sandstones that have undergone hydrothermal alteration and contain lenticular conglomerate horizons.
Within the conglomerates of the Carmen Conglomerate, very well-rounded clasts are present, mainly composed of fine quartzites from the Goyllarizquisga Group, limestones from the Jumasha Formation, and traces of chert. The mineralized bodies are located within this unit, whereas the veins in the Red Beds occur as mineral-filled fractures.
The Tablachaca Conglomerate, which includes quartzitic clasts, volcanic andesites, and some calcareous clasts, forms the base of the Carlos Francisco Formation, which has a concordant appearance. Its upper portion consists of andesitic subvolcanic intrusions and volcanic flows that crop out in the middle and upper parts of Casapalca. The Taruca and Victoria porphyries are hypabyssal, porphyritic dioritic and granodioritic intrusions associated with mineralized veins that display branching and flaring.
Gray limestones of the Bellavista Formation crop out at the crest of a southern syncline, where fracturing favors the development of economically viable mineralized veins.
Economic Geology
Due to the mesothermal nature of the veins, the Alpayana Mine is a Cordilleran-type polymetallic deposit containing copper, zinc, lead, and silver minerals. The deposit mineralogy varies according to vertical and horizontal zoning and shows significant vertical extent, reaching below 3,900 m above sea level.
Highly irregularly shaped mineralized bodies can be found in sedimentary rocks as a result of hydrothermal solutions replacing the calcareous matrix.
Within the Mining Unit area, a wide variety of outcrops can be observed, ranging from simple carbonate (calcite) fractures to very strong veins filled with carbonates, quartz, and sulfides.
Mineralization and Veins
Mineralization
The most common minerals in the vein zones are silver minerals (tetrahedrite, freibergite), lead (galena), zinc (sphalerite), and traces of copper (chalcopyrite, bornite). The most common gangue minerals are pyrite, calcite, rhodochrosite, rhodonite, and quartz.
Veins
The Sobreandes Mine currently has five main veins: Juanita, Ximena, Don Reynaldo, Oroya, and Esperanza–Mariana–Mercedes. Fractures, loops, different types of cymoids, mantos, breccias, and replacement bodies are also present.