STRUCTURAL ANALYSIS OF GOLD MINERALIZATION IN THE SOUTHERN EUREKA MINING DISTRICT, NEVADA: A PREDICTIVE STRUCTURAL SETTING FOR CARLIN-TYPE GOLD DEPOSITS

Identifying favorable structural settings for Carlin-type gold deposits is crucial for future mineral exploration. To enhance active exploration efforts in the southern Eureka mining district, in eastern Nevada, and to understand the spatial and temporal relationships between structural systems and Carlin-type gold mineralization, new 1:6,000 scale geologic and alteration mapping was performed. The map, along with five retro-deformable cross-sections, illustrates the structural evolution of the district, and aids in identifying structural controls on mineralization.

Bedrock units in the map area consist of Cambrian-Devonian carbonates and Late Eocene volcanics. Four distinct structural systems are defined, including Early Cretaceous folds and thrust faults, and three overprinting sets of normal faults: 1) 1st-order (km-scale offset), N-striking faults; 2) 2nd-order (10’s to 100’s m-offset), N-striking faults, and 3) 3rd-order (m-scale offset), E-striking faults that offset Late Eocene jasperoid bodies. The 1st- and 2nd-order faults are interpreted to be contemporary, cut Late Cretaceous intrusions and an associated contact metamorphic aureole, and are overlapped by a Late Eocene sub-volcanic unconformity.

The 2^nd-order faults form a km-scale accommodation zone that transfers slip between 1st-order faults. Within such accommodation zones, wall-damage zones are predicted to provide hydrothermal fluid pathways and localize mineralization. Carlin-type gold mineralization within Cambrian rocks is spatially-coincident with a set of 2^nd-order, wall-damage zone faults, in the immediate footwall of a 1^st-order fault.

The map area contains several favorable structural conditions for Carlin-type gold mineralization, including: 1) normal fault systems that pre-date or are contemporary with Eocene gold mineralization; 2) complex normal fault interactions in an accommodation fault zone, including zones of dense fault intersections, antithetic normal faults, and fault-damage zones. This structural setting was fundamental for generating a network of open-system fluid pathways, which created an ideal architecture for Carlin-type mineralization, and can be used as a predictive tool for exploration elsewhere.