As part of its Candelaria segment, the Company owns 80% of Compañia Contractual Minera Candelaria S.A. and Compañia Contractual Minera Ojos del Salado S.A.’s copper mining operations and supporting infrastructure in Chile. The remaining 20% ownership stake is held by Sumitomo Metal Mining Co., Ltd. and Sumitomo Corporation.
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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
Mineralization at the Candelaria Mine
The main mineralized body at the Candelaria mine is hosted in rocks of the Punta del Cobre Formation. Specifically, the host rocks are massive andesite and andesite breccias of the Lower Andesite, and volcanic tuffs and volcaniclastic rocks comprising the base of the Upper Andesite. In the metasedimentary rock unit, the mineralization is confined to a few isolated layers (mantos).
The mineralized body is up to 400 metres thick in its central part and thins towards the edges. In east-west sections, the mineralization has a lenticular, downward concave shape with a steep eastern limb and a moderately steep dipping western limb. The shape of the mineralized body in north-south section is irregular. In plan view, the extent of the mineralization is approximately 1,400 metres by 2,400 metres. The mineralized body was folded after its formation. The northnortheast-trending fold axis corresponds to the Tierra Amarilla Anticline.
The mineralization assemblage in the Candelaria mine consists of chalcopyrite, magnetite, pyrite, pyrrhotite, and sphalerite. Biotite, calc-silicate minerals, and potassium feldspar constitute the gangue minerals. Pervasive potassic alteration is associated with the mineralization.
Dominant copper mineralization styles are mantos, veins, breccia bodies, and veinlets along foliation planes. Gold occurs within chalcopyrite grains and along fractures surface in pyrite. Chalcopyrite and pyrite also occur in secondary northwest and north-northwest-striking faults.