Summary:
Deposit Types
The copper-gold sulphide mineralization present at the Candelaria Copper Mining Complex is generally referred to as iron oxide copper gold (IOCG). Depending on lithology and the structural setting, the polymetallic sulphide mineralization can occur as veins, hydrothermal breccias, replacement mantos, and calcic skarns (Sillitoe, 2003).
The Candelaria IOCG deposit lies within the metamorphic aureole of the Lower Cretaceous magmatic arc plutonic complex that is located within the Candelaria-Punta del Cobre district, Atacama Region, northern Chile. IOCG deposits are primarily defined by their elevated magnetite and / or hematite with elevated copper and gold contents (Sillitoe, 2003). The IOCG belt located in the Coastal Cordillera of northern Chile and southern Peru is part of a volcano-plutonic arc of Jurassic to Early Cretaceous age. The arc is characterized by voluminous tholeiitic to calc-alkaline plutonic complexes of gabbro to granodiorite composition and primitive, mantle-derived parentage. Major arc-parallel fault systems developed in response to extension and transtension induced by subduction roll-back at the retreating convergent margin.
Most of the sulphide mineralization at Candelaria and Ojos del Salado occurs in breccias, stockwork veinlets, and disseminations in andesite, especially where the rocks are strongly foliated. Highergrade copper mineralization is controlled by stratigraphy in mantos and by faults, trending predominantly northwest. The host rocks are thermally metamorphosed (hornfels and skarn) in the aureole of the Copiapó Batholith, within 1 kilometre from the intrusion. The top of the mineralization system consists of magnetite-amphibole skarn within calcareous meta-tuff mineralized with pyrrhotite, pyrite and chalcopyrite.
Mineralization at the Española Project
In the Española project area, the primary dominant copper sulphide is chalcopyrite found as clusters and in disseminated form commonly associated with brown garnet porphyroblasts. Gangue minerals are pyrite and iron oxides (magnetite-hematite). Near the surface and down to a depth of approximately 70, the mineralization is oxidized, characterized by the presence of chrysocolla, malachite, native copper, diogenite and bornite.
The mineralized bodies are arranged as mantos and are hosted mainly in the brown garnet skarn and in less proportion in silica hornfels. Locally in the south part of the project veins and veinlets of metric thicknesses are observed that were interpreted in parallel to the Española vein-fault.
Mineralization at the Santos Mine
Chalcopyrite is the only primary copper sulphide present in the Santos mine. In addition to copper mineralization, there are economic values of gold. Most frequent gangue minerals are pyrite, magnetite, actinolite, potassic feldspar, chlorite, biotite and hematite.
In the Santos mine, three styles of mineralized bodies are observed: veins, mantos, and breccia bodies. An important vein in the Santos mine is the Isabel Vein, which is oriented northwest-striking, and extends over 1 kilometre in length and between 4 and 30 metres in width. Manto-type mineralization occurs as tabular bodies located at two sedimentary horizons located in the floor and roof of the albitophyre. The manto mineralization is characterized by variable iron contents with magnetite common in the north and deeper areas, and specular hematite in the south. Mineralization occurs within breccia bodies is typically contained with the albitophyre and lower andesite and is formed by steeply west-dipping and north-northwest- to northwest-striking bodies.
Mineralization at the Alcaparrosa Mine
Mineralization at the Alcaparrosa mine principally occurs as mantos that trend to the northeast and dip to the west. Ore mineralogy consists of chalcopyrite, pyrite, and magnetite, with trace pyrrhotite, molybdenite, and arsenopyrite. Mineralization at the Alcaparrosa mine also occurs as veinlets defining dense stockwork, breccias (hydrothermal potassium feldspar and magnetite) as well as fine dissemination in biotite meta-andesites. High-grade bodies are also found in massive veins striking north-northwest, north, and east.