The Shalipayco Project is a joint venture between Nexa Peru (Nexa Peru – a Peruvian company that is 83.554% directly and indirectly owned by Nexa Resources S.A.), which holds a 75.0% interest and Pan American Silver Perú S.A.C.(a wholly-owned subsidiary of Pan American Silver Corp.), which holds the remaining 25.0%. Compania Minera Shalipayco S.A.C. holds 100.0% of the mineral interests in the Shalipayco Project, with the exception of one mineral concession held directly by Nexa Resources S.A.
Nexa Resources S.A. owns a total of 62.61% in the Project.
- subscription is required.
Summary:
The Shalipayco deposit is interpreted to be a Mississippi Valley-type (MVT) deposit. The following is taken from Leach et al. (1995).
The mineralization at Shalipayco consists of stratabound mantos and lenses subparallel to the stratigraphy. Vein mineralization (Veta Eddy) has also been identified at the Project site, however, it is not considered part of the resources because of insufficient drill hole information and lack of structural interpretation.
The main mantos are the Resurgidora, Intermedio, San Luis, Pucará, and Virgencita mantos. The mantos do not generally display extensive lateral continuity. Length varies between 50 m and 400 m and thickness averages 1.50 m. However, the Intermedio and Resurgidora Mantos can reach up to 3.0 km and 4.0 km in length, respectively, and a thickness of up to 18 m.
Mineralization in the Project consists of sphalerite, galena, and pyrite, with a gangue of marcasite, bravoíte, barite, dolomite, calcite, quartz, and dolo-sparite. Mineralization occurs with varying textures like rhythmites, replacements, collapse breccias, crackle breccias, mosaic breccias, veinlets, and evaporitic textures among others. The zinc and lead content may vary up to 51% Zn (Intermedio Manto) and 17% Pb (Intermedio Manto). The average grades for mineralization are 4.9% Zn and 0.5% Pb, respectively. The Zn/Pb ratio varies from 73.2 in the Resurgidora to 304.6 in the Intermedio Manto.
INTERMEDIO AND RESURGIDORA MANTOS
Mineralization in the Intermedio and Resurgidora mantos appears to be related to lateral variation in the former amount of gypsum in the carbonate mud and to porous dolostone that is interpreted to be a hydrocarbon and reduced sulphur reservoir that precipitated the sulphides. Although both mantos have carbonate host rocks with locally important evaporitic facies, the Intermedio Manto contains considerably more evidence for the presence of former evaporites as well extensive porous dolostone that probably served as a laterally permeable reservoir for hydrocarbon and reduced sulphur gases. Furthermore, a fine-grained dolomite mudstone of a sabkha facies that overlies the Intermedio Manto could have served as an excellent hydrocarbon and gas trap that provided a large source of reduced sulphur and reductants for the mineralized fluid. The Resurgidora Manto appears to lack a comparable seal for hydrocarbons.
THE PUCARÁ AND SAN LUIS MANTOS
Unlike the Intermedio and Resurgidora mantos that have abundant evaporative facies, former evaporites and porous dolostone, these textures have not been identified at the Pucara and San Luis Mantos to date. The mineralization observed is in fractures and organic-rich concentrations within a bituminous limestone. This style of mineralization is common in many MVT deposits in the world, however, it usually represents a minor part of reserves. Generally, mineralization in limestone is lower grade than in dolostone, which can be attributed to the usually lower permeability of limestone. The precipitation of sulphides in organic-rich rocks, limestone or dolostone, is related to the greater reducing capacity of these rocks that are better precipitation sites. However, in the case of the Pucará and San Luis Mantos, the limited lateral permeability of the limestone will probably limit resources in these rocks.
VIRGENCITA MANTO
In the Virgencita Manto, the mineralized host rocks appear to be a poorly sorted sedimentary breccia with mineralization that replaced carbonate fragments and fine-rock matrix of a debris flow from an adjacent fault. Considering the apparent spatial relationship of the mineralization with the debris flow, it seems reasonable to suggest that mineralization will continue to be limited to the fault intersection with the breccia.
EDDY VEIN
The Eddy Vein is a complex structure that played an uncertain role in the Zn-Pb mineralization based on the apparent lack of mineral or element zonation from the fault into the manto. Nevertheless, the fault appears to have been active before and after deposition of Zn-Pb mineralization. The presence of reasonably abundant evaporite tectonic breccia in the fault appears to have been a common site for Zn-Pb mineralization. However, mineralization has been commonly brecciated by later fault movements. Particularly characteristic of the Eddy Fault (and associated fractures) is a late-stage overprinting by a pyrite-rich (Zn-Pb poor) event.