UNRAVELING THE STRUCTURAL HISTORY OF OROGENIC GOLD DEPOSITS IN THE CORONA DE ORO GOLD BELT, NORTHWESTERN NICARAGUA

The northwestern region of Nicaragua preserves a protracted history of deformation, magmatism, and tectonism spanning multiple Phanerozoic events. Recent exploration work conducted by Mako Mining Corp. has defined a broad, >30 km trend of gold mineralization termed the Corona de Oro Gold Belt. This trend is host to the San Albino mine, which is the highest-grade open pit mine in the world. However, the timing, structural setting, and deposit style are poorly understood within the complex framework of Central American tectonics. This study integrates petrographic observations, fluid inclusion analysis, drill core observations, and pit wall mapping to investigate the tectonic setting and processes related to deposit formation. Deposits and occurrences are represented by quartz (±ankerite) vein sets that yield high gold grades (>100 g/t) over relatively narrow (1-2 m) intervals. Furthermore, the vein sets are hosted by regionally extensive, multiply deformed carbonaceous schist units, occurring as banded sets that are stacked and shallowly to moderately NW-dipping. Ore assemblages contain ankerite, pyrite, arsenopyrite, and galena with native gold. Alteration halos and disseminations are rare with sulfides assemblages being restricted to the vein margins or internal domains. Preliminary fluid inclusion analysis indicates that fluids related to mineralization contain high CO2 contents consistent with vein formation at the brittle-ductile transition zone of the upper crust. Pit mapping and drill core observations indicate that shear and extensional vein arrays formed by episodic emplacement with the gold being paragenetically late. While largely forming flat-lying arrays, shear within the host schist is localized along vein margins and, locally, the veins are folded and thrust stacked. Lastly, late, NNE- and NNW-trending strike-slip faults form vertical zones of gouge and breccia that crosscut the mineralized veins producing locally complex structural domains. These new observations indicate that the vein sets represent orogenic gold mineralization, which likely occurred coeval with oblique collision of portions of Nicaragua with Mexico in the Cretaceous. Ongoing work will seek to constrain the absolute age of mineralization by isotopic analysis of sulfide and/or hydrothermal phosphates phases.