Summary:
The Diablillos Project contains a weathered high-sulphidation epithermal silver-gold system hosted primarily in Tertiary volcanic and sedimentary rocks. Drilling to date has outlined several occurrences of epithermal silver-gold mineralization, the Oculto zone, JAC zone, Laderas zone and Fantasma zone.
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.
Several satellite zones of silver/gold-rich epithermal mineralization have been located within a 500 m to 1.5 km distance surrounding the Oculto/JAC epicentre.
The Diablillos Property hosts several zones of high-sulphidation epithermal alteration and mineralization with a strong supergene overprint. The main zone of mineralization, the Oculto zone, is hosted by a subaerial volcanic sequence, ranging in composition from pyroxene– hornblende to biotite-hornblende andesite. These volcanic rocks have been age dated by Stein (2001) and assigned to the Middle Miocene Tebequincho Formation. Basement rocks comprise Ordovician-age alkali-feldspar, porphyritic granite of the Complejo Eruptivo Oire and Neoproterozoic to Cambrian age metasedimentary rocks of the Complejo Metamorfico Rio Blanco. SmaIl altered dacitic bodies have also intruded the basement and andesitic sequence (Stein, 2001).
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. The known mineralized zones are: Oculto (including the Oculto NE and Deep), JAC and JAC North Fantasma, Laderas, Alpaca, Pedernales including the Pedernales Sur subzone (including Truchas and Saddle showings) and Pedernales Norte subzone (including Vicuña, Corderos, Suri, and Guanaco showings), Cerro Bayo, Cerro del Medio, Cerro Viejo, 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 andesites overlie a basement assemblage of phyllites and granitic rocks. At the contact between the andesite and basement, there is a paleo-surface occupied by a discontinuous breccia unit of widely ranging thickness. Recent drilling review suggests that this unit thickens along a trend corresponding to one of the predominant controlling structures. This zone is coincident with broader lateral extent of mineralization. Tate (2018) suggests that the conglomerate filled a paleo-trough related to that structure. Later reactivating and providing a conduit for ore-forming fluids.
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 (Stein, 2001). 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.
Stein (2001) reported the occurrence of a high-grade zone at Oculto comprised of native gold, native silver, and acanthite. Accessory minerals included chlorargyrite, iodargyrite, and jalpäite in the southwest Oculto extremity. Gangue minerals in this zone included quartz, alunite, jarosite, iron oxide, and intergrowths of barite.
Hypogene mineralization comprises vein or breccia-hosted sulphides underlying the oxide zones. Primary sulphide and sulphosalt minerals include pyrite, galena, enargite, chalcopyrite, sphalerite, tennantite, and matildite. Accessory minerals include barite and alunite. Incipient supergene enrichment was observed by Stein (2001), where covellite partially replaced chalcopyrite and polybasite replaced tennantite. A review of drilling results conducted by Tate (2018) outlined a flat-lying zone of very high silver grades located between 100 and 120 m below surface. This zone has no apparent relationship with any contact or geological unit and is viewed as a possible zone of supergene enrichment.
Gold-silver mineralization is observed to occur in tabular silica veins, disseminations in wall rocks, and siliceous hydrothermal breccias. Mineralization propagated laterally along the trend of the conglomerate and the Tertiary-Ordovician contact. This has imparted a complex geometry, with a broadly north-easterly trend consisting of steeply dipping, structurally hosted zones and horizontal tabular bodies. Mineralization occurs within a vertical range of 3,965 masl and 4,300 masl, predominantly between elevations of 4,050 masl and 4,250 masl.