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Geology, geochronology and geochemistry of the El Alacrán Deposit, San Matías District, Cordoba-Colombia

University of British Columbia

The El Alacrán Deposit is located in the San Matías District (SMD) in the Northern Western Cordillera of Colombia and is associated with a Late Cretaceous pre-accretional island arc environment of the Calima Terrane. The El Alacrán Deposit comprises a replacement style of mineralization that trends northerly for about 1 km and has a vertical extent of >200 m. Ore is primarily hosted within a calcareous volcanoclastic sequence (Unit 2), which was intruded by a series of andesitic sills and tonalites (e.g. the El Alacrán Oeste Tonalite). The El Alacrán Deposit contains total resources of 82.15 Mt of 0.73-0.49% CuEq which represents ~ 87% of the total mineral resources of the SMD (94.9 Mt@ 0.71% Eq. Cu, Cordoba Minerals Corp., 2019b). The genesis and evolution of the El Alacrán Deposit had not been properly established, thus making it challenging to explore for similar deposits in the SMD. This thesis presents the results of petrographic, geochronologic (U-Pb, Ar-Ar, Re-Os), and isotopic (Pb, S) characterization of the El Alacrán Deposit ores and related representative units and prospects of the SMD. The hydrothermal alteration assemblages of the El Alacrán Deposit are zoned from early high-temperature calc-silicate alteration to a subsequent calc-potassic, sericitic, and carbonate base metal (CBM) alteration. The mineral paragenesis indicates at least three different gold precipitation events: 1) associated with pyrite – mushketovite in the calc-silicate alteration; 2) precipitation of Au electrum with chalcopyrite, traces of the pyrrhotite and molybdenite in the calc-potassic and sericitic alteration; and 3) as visible grains in the carbonate base metal-related alteration. The mineral paragenesis, Ar-Ar dates, Pb and S isotopic composition (δ34S ~ 11‰) from the El Alacrán Deposit can be explained by two different magmatic fluids with a marked interaction with seawater. The magmatic fluids might have been sourced from the El Alacrán Oeste Tonalite and a concealed intrusion (Px2) that is possibly associated with the Montiel E porphyry event (~68-70 Ma). The results suggest a hybrid model between iron oxide copper gold (IOCG)-style and a carbonate replacement deposit (CRD) that is associated with a porphyry source can best explain the El Alacrán Deposit mineralizations.

Text

2020-05-12

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/74407

Geological Sciences

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/