Summary:
The Diablillos deposits are examples of high-sulphidation epithermal silver-gold mineralization driven by hydrothermal fluid activity at shallow depth. The principal mineralizing process is by convective flow of meteoric waters driven by remnant heat from intrusive activity at depth and often related to copper porphyry systems. The term “highsulphidation” refers to the dissociation of magmatic SO2 in aqueous solution into H2SO4 and H2S resulting in a highly acidic environment responsible for the diagnostic assemblage of alteration facies. Mineral occurrences are structurally and hydrostatically controlled. Deposition occurs as open space filling at or near the level at which boiling occurs or where hydrothermal fluids mix with meteoric waters. They characteristically subtend a limited vertical range, except where cyclical healing and failure of fractures results in up and down migration of the boiling zone.
High-sulphidation epithermal mineral deposits form in subaerial volcanic complexes of intermediate to felsic composition. Often associated with shallow porphyry intrusions in island arc, back arc, or trans tensional tectonic regimes. Volcanic host rocks are typically andesitic to rhyodacitic flows, pyroclastic rocks and their subvolcanic intrusive equivalents. The age of many deposits is close to that of the volcanic rocks and typically ranges from Tertiary to Quaternary, although older examples are known.
Principal economic minerals include native gold, acanthite, electrum, chalcocite, covellite, bornite, and enargite/luzonite. Accessory minerals include pyrite, chalcopyrite, sphalerite, tetrahedrite/tennantite, galena, marcasite, arsenopyrite, silver sulphosalts, and tellurides. Dominant gangue minerals are quartz and pyrite, occasionally with barite. Alteration is characterized by lateral and vertical zonation of silicic, advanced argillic, argillic, sericitic, and phyllitic facies. Rocks typically have a bleached appearance owing to the acidity of the mineralizing solutions. These deposits can encompass a wide range of geometries from large, low-grade variants to smaller, higher-grade narrow vein types.
Following hydrothermal mineralization, the upper 200-300 meters was oxidized by meteoric weathering. Cu and Ag sulphides may be partially remobilized to form a thin silver enriched oxide layer. An enriched copper sulphide layer forms at the base of oxidation, with secondary chalcocite coating and replacing primary pyrite and chalcopyrite mineralization.
Mineralization
There are several mesothermal, and epithermal precious and base metal occurrences situated along the trend of the Diablillos-Cerro Galán Fault zone. Within the northern and central Puna, including Diablillos, Incahuasi, Cóndor Yacu, Inca Viejo, and Centenario. Many of the mineral occurrences are spatially, and probably genetically, related to small Tertiary stocks and extrusive domes. They can be hydrothermally altered with disseminated and vein - hosted lead, zinc, silver, and gold (± tin, antimony, copper, and molybdenum) mineralization.
There are several known mineralized zones on the Diablillos property. Oculto, JAC, JAC North, Fantasma, Laderas and Alpaca zones are the most important known to date (see Figure 7-5). The known mineralized zones are:
1. Oculto (including the Oculto NE and Deep)
2. JAC and JAC North
3. Fantasma
4. Laderas
5. Alpaca
6. Pedernales including the Pedernales Sur subzone (including Truchas and Saddle showings) and Pedernales Norte subzone (including Vicuña, Corderos, Suri, and Guanaco showings).
7. Cerro Bayo
8. Cerro del Medio
9. Cerro Viejo
10. Cerro Viejo Este
The majority of the mineral resources on the Property are hosted by the Oculto and JAC deposits. are the main known deposits on the property and contain most of the present Mineral Resource. They are components of These were formed as high-sulphidation epithermal silver-gold deposits following Tertiary-age local magmatic and volcanic activity. At surface there is a broad zone of intense acid leaching on the flank of Cerro Bayo. However economic mineralization notably does not appear in outcrop. Host rocks at surface are hornblende porphyritic andesite, intruded by a dacite porphyry.
The deposits are strongly oxidized to approximately 300 m to 400 m below surface. In the oxide zone, precious metal mineralization consists of native gold and chlorargyrite. Less common is iodargyrite, and locally common bismuthinite. These minerals can be found as fine-grained fracture fillings and vugh linings associated with quartz, jarosite, plumbojarosite, hematite, and goethite. Other accessory minerals include alunite, barite, native sulphur, and bismoclite.
Local geology
The Diablillos deposit lies close to the eastern margin of the Puna and close to the intersection of the north-south trending Diablillos-Cerro Galán fault zone with the north-westerly trending Cerro Ratones lineament. The Diablillos-Cerro Galán fault structure is one of several major north south brittles to ductile shear zones in the Puna. These were formed during neoproterozoic and lower Palaeozoic tectonism and then reactivated during the Mesozoic and Cenozoic.
Disseminated and vein occurrences of northern and central Puna are characterized by base metal, gold, silver, tin, and antimony mineralization. They are commonly associated with small, potassic-rich, Tertiary stocks and extrusive domes. These intrusive/extrusive features have been dated at 15 ± 2 Ma. Elsewhere, the salars (salt flats) in the vicinity of Diablillos host borate and lithium.