Summary:
The basement at Nueva Recuperada is a thick sequence of Paleozoic-Mesozoic sedimentary rocks including the wellendowed Pucara limestone sequence. Located above these units is a massive Cenozoic volcanic sequence which includes rhyolitic tuffs, andesitic to rhyodacite lavas, breccias and pyroclastic rocks of the Huachocolpa Group. Hydrothermal alteration associated with doming has caused intense argillic alteration in contact with volcanic and sedimentary rocks.
Mineralized structures are prevalent in the Miocene volcano-sedimentary rocks such as the Apacheta unit and Caudalosa formation of the Huachocolpa group which host the Tangana, Positivas, Blenda Rubia, Maria Luz, Huachocolpa Sur, Plata – Rico Antimonio, Esperanza veins and others, and in the carbonate-sedimentary rocks of the Jurassic such as the Pucara group which is the principal Peruvian metallotect for Ag-Pb-Zn deposits.
Sedimentary rocks
There are four Groups of sedimentary rocks: the Pucará, Chunumayo, Goyllarisquizga, and Chonta. The Triassic to lower Jurassic Pucará Group limestones outcrop in the Huachocolpa area represented by three units: the Chambará (between the Pirata and Mauricio mines); Aramachay (San Antonio, Angelica, Luchito and Betty mines); and Condorsinga (Luchito mine).
The middle Jurassic Chunumayo Formation limestone outcrops in the area of Positivas. The Goyllarisquizga Group includes quartzites and red shales and sandstones of the lower Cretaceous which sit below the Chulec unit.
The mid-Cretaceous Chonta Group includes sandstones, shales and limestones. The Permian Mitu Group is located to the west of’ and parallel to the NW-SE striking Chonta fault. It consists of mudstones and siltstones with gastropods and volcanic shales. (María Luz, Hallazgo, and Escopeta mines).
Igneous rocks
The Apacheta y Caudalosa volcano-sedimentary units of the Huachocolpa Group are the main mineralization hosts in the Nueva Recuperada project area. They comprise early sedimentary rocks, volcanics including lavas, breccias, tufts dacitic-rhyolitic domes and other intrusions. Lesser volcanic units include the Yahuarcocha, Sacsaquero, Castrovirreyna and Caudalosa formations.
Mineralization
Mineralization in the Huachocolpa district is typically low to intermediate sulphidation, lower epithermal to mesothermal veins, but also mesothermal Fe and Cu bearing skarns, high sulphidation epithermal disseminated bodies, hot springs deposits and mesothermal porphyries. Ore-shoots in the veins at the Property are generally localized at the junctions of abundant cross-cutting mineralized veins and at preferential changes in strike and dip. Some of the district’s veins are being exploited by Silver X and local subcontractors who allowed the author to have access to their workings and veins. Veins are typically 0.3 – 4.0 m wide, averaging approximately 1.0 m with exposed strike lengths of 0.3 to 3.0 kms and demonstrated vertical extension of over 500 m. Principal vein minerals display classic epithermal and mesothermal-textured, banded and brecciated veins containing argentiferous galena, sphalerite, pyrite, minor chalcopyrite, tetrahedrite/reibergite and native gold. Gangue minerals include chalcedony, subhedral to euhedral quartz, calcite, rhodochrosite, rhodonite and barite.
Intrusive rocks have metasomatically and hydrothermally altered the Pucara Formation limestones to create mineralized exoskarns. Magnetite, pyroxene and (grossular) garnet-rich skarn zones have been mapped adjoining argillic alteration with high trace element values and some minor disseminated chalcopyrite.
High sulphidation epithermal disseminated mineralization is found in different areas at high altitudes exhibiting a solfataric assemblage of clays, alunite, pyrite and silicification typified by opal and chalcedony veins. There is small to very large hot spring deposits of travertine, silica and sometimes gossan, the largest of which is located immediately north of the town of Huachocolpa with a horizontal extent of over three hectares.
Porphyry mineralization in the district displays primary sericite, quartz veinlets, broader silicification, pyrite and chalcopyrite and has been mapped at the Arcopunco and Terciopelo project areas.
Deposit Type
The characteristics and alignments noted above describe the principal deposits at the Property as comprising a group of lower epithermal to mesothermal, low to intermediate sulphidation veins. The majority of veins outcrop for between 1 to 2 km; thickness varies from a few centimeters to more than three meters; veins extend down-dip from 300 to 500 meters. Mineralization continuity is occasionally offset by faulting. High-grade, valuable ore-shoots occur where veins intersect.
Fluid flow, temperature and the relative position of mineral deposits related to a generative porphyry system is demonstrated by Hedenquist’s model of epithermal systems. Vein deposits in the district do contain notable levels typical of intermediate mineralization, with moderate to high copper, high gold and arsenic contents and associated sulfosalts such as tetrahedritetennantite-freibergite. Sphalerites are of moderate to low iron content which are more common in lower temperature sulphidation systems. There appears to be a district-wide zoning with increasing copper and gold tenor towards the north and northwest, approaching known porphyry deposits and the Chonta fault, respectively. The likely interpretation is that the veins are relatively distal horizontally to the fluid source porphyry systems. The relative uniformity of the mineralization over an area of more than 200 square kilometers suggests that fluid flows were interconnected and of substantial size. The main mineralizing events occurred between 8 Ma and 4.6 Ma. Sericite in the Teresa veins give an age estimate of 6.4 Ma, dating it to the Quechua III orogenic phase.
A preliminary interpretation ascribed to Silver X and PAS describes five pulses or phases of mineralization at Nueva Recuperada defined by five zones with clear mineralogy and grade differentiation:
• Zone 1 represented by Plata Project and others contains predominantly Pb (3 to 4 %) / Zn (3 to 7 %) and high grades of Ag and Sb;
• Zone 2 represented by Blenda Rubia – Micaela sector, Caudalosa, Caudalosa Chica and others contain grades of 3 to 5 % Pb/Zn and lower Ag grades;
• Zone 3 in the north represented by the San Antonio, Angélica, Positivas, Tangana, Cauca and other veins hosted in volcanic and sedimentary rocks returns grades averaging >5 % Pb, 3 to 5 % Zn and lower Ag and Au grades;
• Zone 4 in the south is represented by the Maria Luz sector displaying epithermal banding containing higher Ag grades and low Pb and Zn (<1 %) contents;
• Zone 5 in the Pucapunta sector displays intermediate to high sulfidation mineralogy.