CATHODOLUMINESCENCE IN QUARTZ: CLUES TO ORE PARAGENESIS AND ORE FLUID PROPERTIES AT THE GOLDSTRIKE CARLIN-TYPE GOLD DEPOSIT, NORTHERN NEVADA

Microanalyses are being conducted to improve our knowledge of ore fluid components and sources, and conditions of ore deposition at the Goldstrike deposit, the largest Carlin-type gold system in the world. To distinguish ore-stage minerals from pre-ore and post-ore minerals, and to determine the relative timing between various minerals, cathodoluminescence (CL) studies were integrated with chemical, textural, isotopic, and fluid inclusion studies. CL proved to be critical in confirming a paragenetic framework based on petrographic observations, and in identifying various stages of silicification in samples collected from across the Goldstrike system. Results improve our ability to distinguish different generations of quartz and recognize ore quartz, and provide a new exploration tool for these systems.

An Oxford/Gatan Mini-CL detector, mounted to a JEOL JXA 8900 electron microprobe, was used to collect gray-scale CL images that discriminate various generations of quartz based on their relative luminosity's. Ore stage jasperoid quartz, identified by its spatial association with gold-bearing pyrite grains, displays CL-dark luminescence. This jasperoid was overgrown by drusy quartz that also displays CL-dark luminescence, and which appears to be late-ore stage owing to a strong concentration of ore-stage pyrite in the base of the quartz crystals. Multiple generations of post-ore drusy quartz overgrow ore and late-ore quartz and exhibit luminescence of varying intensities (CL-bright & CL-multiple).

In addition to providing paragenetic control, CL analyses provide insight into ore precipitation. The occurrence of both ore-stage jasperoid and drusy quartz indicate that ore deposition accompanied fluid-rock reaction and, locally, fluid cooling. Preliminary electron microprobe analyses indicate that increasing trace Al in quartz corresponds with decreasing intensity of luminosity. The presence of trace Al in ore quartz is consistent with the presence of kaolinite as an alteration mineral and trace Al in ore pyrite. The well-constrained paragenetic framework has allowed us to apply several microanalytical techniques to different generations of quartz including ion probe oxygen isotope analysis, electron microprobe trace element analysis, LA-ICP-MS, and fluid inclusion microthermometry.