Geology Excelsior Stockpile
The low-grade Zn, Pb, Ag mineralisation within the Excelsior stockpile was derived from the extraction of mineral from the Cerro de Pasco Mine (underground and Raul Rojas open pit). The Cerro de Pasco deposit can be considered a complex epithermal polymetallic deposit with base and precious metal mineralization, mainly silver, characterized by vein, breccia-hosted, and carbonate-replacement mineralization. This deposit type has also been referred to as a “Cordilleran base-metal deposit” type (Baumgartner et al., 2008) and Butte-type vein deposits (Meyer et al., 1968) with the Cerro de Pasco mine considered as one of the largest known deposits of this type.
The excelsior stockpile consists of material mined from different areas of the open pit from between approximately 1970 to 1996 and is made of rock fragments presenting an average size of 10 cm, which can reach up to 2.5 m in diameter. The stockpile consists of three terraces constructed by the release of fractured rocks at the slopes of the different terraces representing a mix of various rock types constituted mainly of three different assemblages:
- carbonate (dolomitic) rocks from the host rock formation with Zn, Pb, Ag replacement mineralisation.
- sulfide-rich rocks from the quartz–pyrite ore body accompanied by Fe-oxide-rich oxidation products near the surface, and,
- sericitized monzonites/volcanic rocks,
Metal-bearing minerals consist of sphalerite, tennantite, cerussite, enargite, galena (Ag-rich) and sphalerite.