Summary:
Mineralogical, structural, and geochemical features of the Reliquias Mine vein system fit with the ‘Cordilleran polymetallic’ deposit type as described by Sawkins (1972), Einaudi (1982) and Bendezú et al (2008) and referred to as ‘Intermediate-sulfidation epithermal deposit’ by Wang et al. (2009). In Peru, Cordilleran polymetallic deposits represent the main source of lead-zinc and a significant source of silver, and are found only in the high Andes between 3,500 and 5,000 meters m.a.s.l.
Examples from northern and central Peru display a broad variety of mineral associations which form a continuum between the following two end-member styles (Bendezú, 2009):
1. Strongly zoned deposits consisting of cores dominated by enargite, pyrite, quartz ± (tennantite, wolframite, chalcopyrite, covellite, chalcocite, alunite, dickite, kaolinite) and external parts by sphalerite, galena ± (sericite, kaolinite, dickite, hematite, Mn-Fe carbonates). Examples include most of Smelter-Colquijirca, parts of Cerro de Pasco, Hualgayoc, Quiruvilca, Yauricocha, Morococha, San Cristobal, Huarón, and Julcani.
2. Weakly zoned deposits consisting of internal zones with pyrrhotite, pyrite, quartz ± (chalcopyrite, arsenopyrite, tetrahedrite, carbonates, sericite, chlorite, quartz) and external zones with Fe-rich sphalerite, galena, pyrrhotite ± (MnFe carbonates, sericite, chlorite, quartz). Examples include Huanzalá, Uchucchacua, Mallay, Iscaycruz, and parts of Cerro de Pasco and Morococha.
Mineralization found on the Reliquias property most closely matches the first style of strongly zoned deposits.
Reliquias mineralization represents characteristics of the intermediate-sulfidation subtype based on its high silver and base metal content relative to gold content, an alteration mineral suite of pyrite, sericite, and manganese carbonates, and ore minerals of galena, chalcopyrite, Fe-poor sphalerite and tetrahedrite/tennantite. Zones of high-sulfidation alteration and mineralization have also been noted as indicated by the presence of enargite and advanced argillic alteration minerals.
Geology
The Reliquias Mine area is underlain by sequences of volcanic rocks of the Miocene Caudalosa Formation (500 m thickness) that are intercalations of breccias of andesitic flows, pyroclastic breccias and lava flows of andesitic to trachytic andesite composition, porphyry andesites and basaltic andesites, with minor tuffaceous sandstone. The upper units of the Caudalosa Fm. consist of lava flows, domes, and dome flows of andesitic composition with pyrite dissemination predominate. A feldspar porphyry (andesite) stock is exposed in the northeastern corner of the Reliquias Block in the Carmelas and Poetas zones.
Mineralization
The mineralization is polymetallic with high silver content including silver sulfosalts (proustit- epyrargyrite or ruby silver), silver-rich galena, sphalerite, chalcopyrite, pyrite, and enargite. Gangue minerals include quartz, barite, stibnite, and rhodochrosite. Manganese oxide is common in fractures and halos of altered mineralized veins. In the upper levels of the veins, common minerals are silver sulfosalts (proustite-pyrargyrite), grey copper (tetrahedrite), galena, quartz, barite, and pyrite. At depth, veins carry base metal ore minerals such as: galena, sphalerite, and chalcopyrite with pyrite, quartz, and carbonate gangue minerals. Gold occurs as late-stage inclusions in galena and chalcopyrite.
The mineralized structures identified during previous mining activity have crustiform, cockade, and banded textures with two main trends (northwest-southeast and east-west). The main veins of the Reliquias Mine are described below.
Matacaballo Vein (MTC)
The MTC vein has a recognized length of 2 kilometers with an azimuth ranging from 265° to EW and dips from 70° to 80°NE. Vein widths vary between 0.50 and 5.00 meters. Primary sulphides in the vein are sphalerite, galena, polybasite, pyrargyrite, chalcopyrite, and tetrahedrite distributed in gangue pyrite, quartz, rhodochrosite, and calcite.
Meteysaca Vein (MTS)
The MTS vein is a fault-zone-related structure recognized on different levels (Lv 415, 480 and 520) for about 810 meters by mine development. MTS has an azimuth of 300° with a dip of 80°NE to 85°NE. Below Level 415, MTS consists of milky quartz, grey quartz with widths ranging from 0.10 to 0.80 meters, and disseminated fine sulphide mineralization, galena, and sphalerite.
Sacasipuedes Vein (SCS)
The SCS vein has an azimuth of 305° with dips of 80°NE to 85°NE. This structure is recognized as having 1,200 meters of strike length based on the most recent drilling campaign. SCS is characterized by massive white and grey quartz with patchy sulphide mineralization. SCS is associated with faulting that has resulted in the development of fault gouge and brecciation. Patches of rhodochrosite may be present as gangue.
Ayayay Vein (AYA)
The Ayayay vein is a mineralized structure with brecciated hyaline quartz, grey quartz, and patches of sulphides. Mineralization consists mainly of galena, sphalerite, and lead and silver sulfosalts. The azimuth is 295° with dip of 80°NE to 85°NE and vein widths that vary between 0.10 to 0.50 meters. Its average strike length is 500 meters. To the southeast, the structure is limited by the Matacaballo vein and to the northwest, the limit of this structure has not been defined. To the south and subparallel to the Ayayay vein is the Tomaycalla structure.
Perseguida Vein (PER)
The Perseguida vein outcrops along a strike length of approximately 2 km with azimuths ranging from 115° to 125° and dips between 70°-80°SW. Vein widths range from 0.30 to 5.00 meters. PER was located along 300 meters of strike length with the most recent drilling campaign. Results from levels 4475 to 4725 in the most recent drill campaign showed evidence that the middle segment of this vein is possibly offset by an east-west trending fault.
Sorpresa Vein (SOR)
SOR has an azimuth of 285° with a dip 85°NE and widths ranging from 0.10 to 0.50 meters. The mineralization consists of fine sulphides, galena, and sphalerite. Drilling has confirmed a strike length of 400 meters.
Beatita Vein (BEA)
BET has an azimuth of 300°, dipping of 80°NE, with an average width of 0.80 m. BET has strike length of approximately 500 meters and has been recognized in levels 670, 537, 523, 494, 454 and 404. The vein mineralogy consists of galena, sphalerite (marmatitic), argentiferous galena, pyrite, and quartz. BET forms sigmoidal structures at its intersection with the Matacaballo and Pasteur veins.
Natividad Vein (NAT)
NAT has a 265° azimuth with subvertical dips and widths ranging from 0.50 to 1.75 meters. The structure has a brecciated texture with white and grey quartz. Mineralization consists of patchy and massive galena, sphalerite, and chalcopyrite with fine grey sulphides in traces and pyrite gangue.
Pasteur Vein (PAS)
PAS has an average azimuth of 105° vein with dips between 75° and 80°SW and vein widths that vary from 0.20 to 2.25 meters. PAS strike length has been measured as 600 to 650 meters, with one zone of fault offset. PAS contains brecciated hyaline quartz with patches of galena, sphalerite, chalcopyrite, and fine grey sulphides with a gangue of pyrite, rhodochrosite, and calcite filling fractures.