This collaborative study by researchers at the University of Nevada Las Vegas and the University of Nevada Reno aims to develop a time-space geological and geochemical framework of the classic Carlin-type gold deposits of the Getchell district in northern Nevada by utilizing data from more than 12,000 holes drilled by mining companies and sophisticated 3D modeling software to identify samples for state-of-the art in situ micro analytical techniques. With the drill holes and modeling software we will build a comprehensive 3-dimensional model from which we will interpret fluid pathways taken by the gold-bearing hydrothermal fluids. We will then add the fourth dimension, time, to the model by integrating detailed micro analytical studies of various stages of quartz, pyrite, and other sulfide minerals at locations along interpreted fluid pathways. Specifically, the investigators will document how the textures and isotopic and trace element compositions of quartz and pyrite vary with time and at any given point in space, using cathodoluminescence, electron microprobe chemical analyses, laser ablation ICP-MS chemical analyses, and in situ ion probe isotope analyses. The isotopic and trace element composition of the quartz and pyrite are essentially fingerprints of the hydrothermal fluid and analyses of various minerals will allow better tracking of the passage and evolution of the ore fluid. By comparing these "fingerprints" in different samples from different locations along fluid pathways it will be possible to deduce how the composition of the hydrothermal fluid, which formed the gold-bearing pyrite and quartz, varied both in time and space. It is also planned to study samples of the hydrothermal fluid trapped as fluid inclusions in the quartz to deduce how temperatures and compositions of the ore-forming fluid varied in time and space along fluid pathways. From these data the investigators will be able to constrain depositional mechanisms in high-grade portions of the ore bodies by identifying how fluids physically and chemically evolved as they traveled into, through, and out of high-grade ore zones.
Carlin-type gold deposits in Nevada account for about 8% of the annual worldwide gold production, making the United States the second largest gold producer in the world. Despite their importance, several aspects of their origin remain enigmatic. The results of this research will not only lead to better understanding of the origin of Carlin-type deposits, but will also lend insights into broader earth processes. This project will advance our understanding of hydrology and mass transfer involved with hydrothermal circulation in upper crustal rocks that were being heated and extended. Important new knowledge will be generated through a research partnership between the mining industry, Nevada's second most important industry, and the researchers, including a post doctoral fellow and graduate and undergraduate students. This knowledge will improve exploration for similar gold deposits in Nevada and other parts of the world. Project results will also contribute to mineral potential assessment by government agencies and mining companies, and improved land use decisions by government agencies.
