PETROGRAPHIC ANALYSIS OF PYRITE MINERALIZATION IN ASSOCIATION WITH GOLD OF THE TYPE 3 GOLD ORE IN ROUND MOUNTAIN MINE, NEVADA

Round Mountain (RM) is an open pit gold mine; one of the largest in Nye County, Nevada at the base of the Toquima Mountains. Owned and operated by Kinross Gold Corporation, the primary resource mined at RM is Au with minor associated Ag. The volcanics of RM were deposited when a series of calderas moving SW throughout the region began to produce several widespread ash-flow tuffs and ignimbrites of andesitic to rhyolitic composition. The RM Tuff was deposited at ~26.9 Ma by the RM Caldera which generated low sulphidation epithermal mineralization (LSEM). This allowed for near surface meteoric fluids to be heated by the RM caldera which were then able to transport elements such as Au, Ag, As, S, and Fe. The heated fluid rose, cooled, mineralized the elements within the porous volcanic tuff of RM, and recirculated. RM mine classifies many rock types within it but this project focuses on the Type 3 (T3) ore host that is a moderately welded tuff with lithics from the previously deposited Paleozoic bedrock termed Type 4 (T4) ore host. Pyrite (Py) is one of the main minerals to be deposited through LSEM and the Au mined is assumed to be associated with the Py and its deposition. One major question is the role of the hydrothermal fluids depositing Py within both the T3 ore host and the T4 Paleozoic bedrock indicative of multiple pulsing’s of fluid depositing within the volcanics of RM. The focus of this project is to characterize and observe the distribution of Py crystals throughout a thin section of T3 ore both within the T3 tuff and T4 bedrock. Assessing the Py crystals in this ore will provide insights into the hydrothermal mineralization associated with the Au. T3 ore was studied in hand sample, with petrographic/reflective microscopy and with SEM as well as EDS, and XRF/XRD on Py grains both within the T4 lithic clasts and the T3 tuff. This project will evaluate the distribution and chemical variability between the Py entrained within the T4 lithic clasts and T3 volcanic tuff in hopes of constraining the role of LSEV within RM and the extent to which it occurred. Analyzing the Py as well as future investigations into the nature of the RM caldera and hydrothermal fluid movement will potentially allow timing and nature of Au mineralization and when it ceased as geochemical evidence will possibly show differences in levels of As and Au between the T4 lithics and T3 tuff.