Genesis and structure of the San Albino orogenic gold deposit, NW Nicaragua with implications for Mesozoic tectonic and metallogenic processes
Understanding the genesis and tectonic framework for orogenic gold deposits is critical for guiding exploration vectoring and understanding the geometry of ore zones within these systems. Thus, structural investigations are needed to establish a holistic deformational framework encompassing the entirety of the geological history for a host region. The San Albino orogenic gold deposit of NW Nicaragua represents a poorly constrained mineral system. In part, uncertainty around the genesis and structural modification arises from a paucity of academic work in Nicaragua, which is further exacerbated by the fact that the host region has experienced a protracted, nearly continuous, history of tectonism since the Jurassic. Active open pit mining of the deposit provides a unique opportunity to conduct new detailed investigations. To better understand the San Albino deposit and related tectonic framework this study synthesizes varied perspectives derived from drill core logging and open pit mapping, petrographic analysis, statistical and kinematic analysis of structural orientations, and U-Pb zircon geochronology of dike samples. Drill core logging and open pit mapping provided key observational constraints, helping to delineate pre- to syn-mineralization structure, such as isoclinal folds and mylonitic textures in schistose host rocks, as well as a post-mineral, multi-episode history of fault formation. Characterization of the mineralized vein sets reveals four distinct stages of vein development: early shear vein emplacement (stage 1), episodic reactivation and progressive deposition of sulfides with minor gold deposition (stage 2), localized recrystallization and deposition of galena and most of the free gold (stage 3), and a retrograde phase (stage 4). Subvertical dike sets cross-cut the primary ore zones and are themselves cut by younger faults. Thus, the emplacement age of these dikes places an absolute timing constraint on mineralization and later structure. U-Pb dating of zircon grains from these dikes by LA-ICP-MS yields an emplacement age of ~96 Ma, meaning mineralization likely occurred in the Early Cretaceous. It is interpreted here that mineralization likely occurred between ~115–100 Ma, perhaps triggered by large-scale tectonic reconfigurations. Post-mineralization fault and fold activity includes at least one Laramide (~70-55 Ma) phase of shortening, with a younger, Tertiary to present-day, phase of extension.
Nicaragua, orogenic gold, San Albino, structural geology, tectonics
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Colorado School of Mines. Arthur Lakes Library