Located in the El Callao Mining District (Bolivar State), Choco 10 is one of the most important gold deposits in Venezuela. The deposit occurs in the greenstone belt of the Pastora Supergroup, a lithostratigraphic Province of the South American Guyana Shield.The Choco 10 lithostratigraphy is composed of two different formations. The lower El Callao Formation is composed of a Metabasalt Unit, mostly made of tholeiitic basalts, overlain by a Mafic Volcano-Sedimentary Unit, which represents its primary cover. The tholeiitic rocks show a flat, unfractionated REE pattern which is typical of greenstone belt basalts worldwide; the incompatible elements and REE distributions suggest a mid-ocean ridge or back-arc basin setting. Within the tholeiitic series, a transition to more evolved terms is suggested by the occurrence of rocks of andesitic composition mostly in the upper part of the same formation. The overlying Felsic Volcano-Sedimentary Unit, probably pertaining to the Cicapra Formation, is a relatively heterogeneous rock series largely composed of volcaniclastic rocks deriving from an acidic calc-alkaline source, as confirmed by the geochemical data. SHRIMP analyses on zircons from these rocks show consistent magmatic ages of 2143. ±. 6 to 2145. ±. 5. Ma. This unit contains a gabbroic sill-like body (Metagabbro Unit), composed of medium-grained amphibole gabbro, which yields an age (2142. ±. 2. Ma) that is undistinguishable from that of the main body.Both formations are affected by a greenschist-facies metamorphic overprint and different deformation phases. At 2117. ±. 3. Ma, the formations have been intruded by a trondhjemite that displays fractionated REE and incompatible elements patterns typical of calc-alkaline rocks.Gold has been introduced into the rock sequence in different stages; the main mineralization is related to highly focused flow of H2O-CO2, low salinity fluids to give quartz+ankerite±albite±pyrite veins, surrounded by strong sericite+carbonate+pyrite+quartz alteration. Gold concentrations are controlled by both structural setting and fluid-rock interaction processes.The gold metallogeny at El Callao is related to the world-scale metallogenic event of Paleoproterozoic age, which is responsible of important orogenic gold ores formation in the once adjacent Amazonian and West Africa cratons. Even in absence of direct dating of the hydrothermal phases, our precise geochronological dating - together with the geological and petrographic data - constrains the onset of deformation (i.e., the beginning of the Trans-Amazonian deformation) and the subsequent main mineralization phase to the time span comprised between 2142 and 2144. Ma (age of gabbro and calc-alkaline tuffs) and 2117. Ma (emplacement of the trondhjemite). On a regional scale these data suggest eastward younging of deformation and mineralization within the context of the Trans-Amazonian tectonism. © 2014 Elsevier B.V.
Padoan, M., Rossetti, P., Rubatto, D. (2014). The Choco 10 gold deposit (El Callao, Bolivar State, Venezuela): Petrography, geochemistry and U-Pb geochronology. PRECAMBRIAN RESEARCH, 252, 22-38 [10.1016/j.precamres.2014.06.024].
The Choco 10 gold deposit (El Callao, Bolivar State, Venezuela): Petrography, geochemistry and U-Pb geochronology
PADOAN, MARTA
;
2014
Abstract
Located in the El Callao Mining District (Bolivar State), Choco 10 is one of the most important gold deposits in Venezuela. The deposit occurs in the greenstone belt of the Pastora Supergroup, a lithostratigraphic Province of the South American Guyana Shield.The Choco 10 lithostratigraphy is composed of two different formations. The lower El Callao Formation is composed of a Metabasalt Unit, mostly made of tholeiitic basalts, overlain by a Mafic Volcano-Sedimentary Unit, which represents its primary cover. The tholeiitic rocks show a flat, unfractionated REE pattern which is typical of greenstone belt basalts worldwide; the incompatible elements and REE distributions suggest a mid-ocean ridge or back-arc basin setting. Within the tholeiitic series, a transition to more evolved terms is suggested by the occurrence of rocks of andesitic composition mostly in the upper part of the same formation. The overlying Felsic Volcano-Sedimentary Unit, probably pertaining to the Cicapra Formation, is a relatively heterogeneous rock series largely composed of volcaniclastic rocks deriving from an acidic calc-alkaline source, as confirmed by the geochemical data. SHRIMP analyses on zircons from these rocks show consistent magmatic ages of 2143. ±. 6 to 2145. ±. 5. Ma. This unit contains a gabbroic sill-like body (Metagabbro Unit), composed of medium-grained amphibole gabbro, which yields an age (2142. ±. 2. Ma) that is undistinguishable from that of the main body.Both formations are affected by a greenschist-facies metamorphic overprint and different deformation phases. At 2117. ±. 3. Ma, the formations have been intruded by a trondhjemite that displays fractionated REE and incompatible elements patterns typical of calc-alkaline rocks.Gold has been introduced into the rock sequence in different stages; the main mineralization is related to highly focused flow of H2O-CO2, low salinity fluids to give quartz+ankerite±albite±pyrite veins, surrounded by strong sericite+carbonate+pyrite+quartz alteration. Gold concentrations are controlled by both structural setting and fluid-rock interaction processes.The gold metallogeny at El Callao is related to the world-scale metallogenic event of Paleoproterozoic age, which is responsible of important orogenic gold ores formation in the once adjacent Amazonian and West Africa cratons. Even in absence of direct dating of the hydrothermal phases, our precise geochronological dating - together with the geological and petrographic data - constrains the onset of deformation (i.e., the beginning of the Trans-Amazonian deformation) and the subsequent main mineralization phase to the time span comprised between 2142 and 2144. Ma (age of gabbro and calc-alkaline tuffs) and 2117. Ma (emplacement of the trondhjemite). On a regional scale these data suggest eastward younging of deformation and mineralization within the context of the Trans-Amazonian tectonism. © 2014 Elsevier B.V.
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