The Maricunga gold belt extends over a distance of approximately 150 km from north to south and is approximately 30 km wide, close to the border with Argentina. Mineralization is related to the emplacement of Miocene age calc-alkaline volcanic and sub-volcanic units over basement rocks of Paleozoic to Cenozoic age. The Maricunga belt hosts a number of gold and gold-copper (silver) deposits.
The structural setting of the Volcan property is related to, and associated with, the formation of the Copiapo stratovolcano (Volcán Copiapo) and may also be related to regional northerly-trending high angle reverse faulting. Prior work on the property identified three generally moderate to steeply dipping fault systems, trending northwest-southeast, northeast-southwest and east-west, and considered the northeast-southwest and east-west trending systems to be the more important structural controls on alteration and mineralization.
The principal rock types identified on the Volcan property are:
- Dacite, rhyodacite and andesite lavas.
- Volcanic flow and dome complex rocks.
- Pyroclastic flows.
- Hydrothermal breccias.
- Sub-volcanic porphyry.
Each of these rock types has a number of sub-units.
Alteration is prevalent and has been divided into the following principal categories:
- Acid leaching with silica, alunite, gypsum, pyrophyllite and sulphur.
- Intermediate to advanced argillic alteration represented by a quartz-alunite-illite-smectite-kaolinite-chlorite assemblage.
- Moderate to intense silicification resulting in cryptocrystalline silica with lesser alunite and clay minerals.
- Transitional alteration between potassic, chloritic and argillic alteration most commonly visible affecting feldspars hosted in dacite and andesite.
- Potassic alteration, the presence of remnant secondary biotite and potassium feldspar as halos around quartz veinlets.
- Propylitic alteration which is only present in volcanic flows surrounding the principal alteration zones.
Gold-copper mineralization at Volcan is related to the intensely developed hydrothermal alteration that gave rise to the native sulphur deposits. The hydrothermal system was a consequence of the sub-volcanic intrusion of dacitic to microdioritic porphyry into a complex of domes and lava flows of dacitic composition.