PRELIMINARY STRUCTURAL ANALYSIS OF THE CORONA DE ORO BELT IN NORTHWESTERN NICARAGUA WITH IMPLICATIONS FOR GOLD MINERALIZATION AND LATER STRUCTURAL MODIFICATION

Understanding the tectonic and structural history of deposit hosting regions is critical for elucidating the processes that controlled precious metal deposition as well as for understanding the post-formational geometry – both essential for guiding exploration and mining models. This study is focused on a segment of the Corona de Oro belt in northwest Nicaragua that hosts the San Albino gold deposit. This deposit is defined by a set of NW dipping, fault-fill quartz-carbonate veins that are typically 1-2 meters thick with grades averaging 12 g/t gold and locally over 100 g/t gold. The veins are hosted by carbonaceous schist of the Nueva Segovia formation, and both are cut by multiple generations of faults. Despite active mining and abundant exposure within the open pit, the relative timing and structural history of the mineralized domains are poorly constrained within the regional tectonic framework. Furthermore, the significance of later faulting to grade distribution is unclear. To address these knowledge gaps, new mapping of active pit walls and detailed re-logging of drill core were conducted. Based on these new results, several major episodes of deformation have been recognized. Early deformation was localized along moderate- to low-angle west-dipping thrust faults that largely host the mineralized shear vein sets. Progressive deformation led to further shortening, resulting in anastomosing shear arrays and duplex stacks of the relatively competent banded shear veins. The third faulting event resulted in the formation of a subvertical, NNE-SSW trending, ~50-100-meter-wide zone of steeply dipping strike-slip faults characterized by discrete gouge and breccia zones as well as abundant well-defined, lineated fault surfaces. The youngest faults are moderately WNW-dipping normal faults with a predominately dip-slip component. Based on existing models, the early contractional event likely relates to late Cretaceous orogenesis, while the strike-slip and normal faulting are likely related to Caribbean plate reconfigurations over the last 60 Ma. Therefore, the preliminary results provide a better understanding of the relative evolution of a multiply reactivated fault zone that contains significant gold mineralization, which will help to guide tectonic, gold exploration, and mining models in the region.