Abstract
The El Callao district, with a total endowment of more than 2000 t Au, is considered to be the most prolific gold resource in Venezuela. Mineralization is hosted by a vein system that is genetically associated with the El Callao transpressional shear zone. This vein system consists of a network of interconnected quartz–albite–ankerite veins enveloping a large number of metabasaltic fragments that host gold-bearing pyrites. Based on detailed mineralogical, microstructural, and fluid inclusion studies, a pressure-temperature pathway was established for the evolution of the mineralizing fluid during shear-zone development and exhumation. This path is characterized by repeated episodes of fluid pressure fluctuation from lithostatic (higher than 1.6 kbar) to near-hydrostatic values (<0.4 kbar), recorded throughout the transition from the quasi-plastic to frictional deformation cortical domains. Each successive pressure drop induced boiling of the hydrothermal fluid, with the resulting fluid phase separation controlling: (i) pyrite and invisible gold crystallization, which occurred during ductile and ductile-brittle transition strain conditions, and (ii) primary gold remobilization with consequent native-refined gold precipitation, occurring mainly under brittle conditions. The metallogenic framework that was proposed for the El Callao shear zone can be used as a vector to explore and characterize other mineralized shear zones in the Guiana Shield and analogous orogenic systems worldwide.
Highlights
Located in the Guiana Shield of South America (Figure 1), the El Callao gold deposit is hosted by the El Callao shear zone, a megatectonic feature extending through the entire Guyana Craton in Venezuela [1,2]
Magmatic history of an evolving orogeny [3,4,5,6]. They are believed to be syn-kinematic with at least one main penetrative deformation stage of the host rocks, based on the widespread observation that the deposits structurally cut across fabrics that were formed during orogenesis, and that most of them are largely unaffected by early orogenic deformation [3,4,5,6]
The El Callao vein system occurs in the exhumed El Callao transpressional shear zone, in which crustal shortening was accommodated along a discrete deformation band, hosted by low-grade metamorphic rocks
Summary
Located in the Guiana Shield of South America (Figure 1), the El Callao gold deposit is hosted by the El Callao shear zone, a megatectonic feature extending through the entire Guyana Craton in Venezuela [1,2]. During the past several decades, orogenic lode gold deposits have been investigated from different points of view, including structural analysis of veins systems, petrological and geochemical. During the pastand several decades, orogenic lode gold deposits investigated studies of alteration ore paragenesis, and fluid inclusion studieshave [6,7], been providing insightsfrom into different points of view, including structural analysis of veins systems, petrological and geochemical the origin of the mineralizing fluids as well as on the pressure-temperature (P-T) evolution within studies of alteration ore paragenesis, fluidstudies inclusion studies [6,7], providing insights into the fault zone systems.andThe majority of and these have documented the involvement of origin of the mineralizing fluids as well as on the pressure-temperature (P-T).
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