CHARACTERIZATION OF CARLIN-TYPE GOLD ASSEMBLAGES FROM NORTHEASTERN NEVADA

The Carlin and Cortez deposits of Northeastern Nevada are among the most prolific gold producers in North America and follow a trend about 50 miles long and 40 miles wide, with the majority of the area currently controlled by Barrick Goldstrike Company. Host rocks for the deposits are mostly Paleozoic sedimentary rocks, calcsilicate hornfels, argillic rocks, and intrusive igneous rocks of Jurassic through Miocene age. Models for the generation of the deposits range from entirely amagmatic to strictly magmatic, and are still debated after decades of study. The purposes of this study are to: gain experience and knowledge of Carlin-type deposits; evaluate styles of mineralization; and to model types of analyses and mineralogical characterizations of samples commonly used by exploration geologists in the minerals industry. Samples for this project range in composition from altered shales, carbonates, and sandstone to lamprophyre and dacitic dikes, and were obtained from different subsurface locations. Samples were photographed using a high-resolution digital camera using photomontage software to identify mineral phases in reflected light, and provide maps for further analysis. Splits were crushed and powdered in an alumina shatterbox for analysis by powder X-Ray Diffraction (XRD) and fused into glass disks for X-Ray Fluorescence (XRF). XRD analyses showed some expected minerals such as pyrite, orpiment, and barite, whereas Raman Microscopy analysis identified less common accessory minerals like violarite and aleksite. Slabs were also analyzed using reflected light microscopy and Raman spectroscopy to identify mineral associations, which include barite and gold rimmed pyrite. Commercial chemical assays were obtained from most samples for gold concentrations, and ranged from approximately 0.02 ounces per ton to seven ounces per ton. Mineral assemblages and assays were then compared with broader results from the different sample areas for consistency.