Location: Elko, NV


GSN Elko Chapter and Co-hosted by the GSN Winnemucca Chapter

Justin Milliard, Elko President 2020-2021

We are excited to announce that we will be hosting a virtual talk series through the fall until circumstances allow us to return to in-person meetings at the Western Folk Life Center.

Speaker: Mr. Christian Thomas, will be giving a presentation on his MS research at the Ralph J. Roberts Center for Research in Economic Geology (CREG) at the University of Nevada, Reno.

September 17, 2020 – 7:00 PM Pacific Time (US and Canada) via Zoom

(see login credentials below abstract)

Title:  “Comparative Fluid Inclusion Geochemistry and Properties of the Buffalo Canyon and Grantsville Intrusion-Related/Epithermal System”

Abstract. The Union district, located in northern Nye County, Nevada, hosts a variety of ore deposit types in strongly deformed and locally altered Triassic and Tertiary metasedimentary and volcanic rocks. Low-sulfidation epithermal Ag-(As-Hg) mineralization at the Grantsville Pit occurs as mm- to cm-scale brecciated zones of µm-mm pyrite, illite, and very fine-grained quartz. The mineralization exploits permeability in folded, brecciated, and intensely silicified carbonates of the Triassic Luning and Grantsville Formations; these units are part of the northern, upright limb of a northwest-trending overturned anticline. The open pit is capped by northwest-trending jasperoid bodies and parallel bull quartz veins. Alteration is centered around a silicified core that zones out into illite-illite/smectite-smectite over ~100 m laterally and vertically, strongly affecting Oligocene volcanics overlying the deposit. Fluid inclusions in quartz associated with the epithermal mineralization are chiefly 2-phase, coexisting liquid- and vapor-rich, and display rounded/equant to negative crystal forms, indicating formation at or above 230 ºC. A Ag-Cu-Pb-Zn-F-W skarn body occurs roughly 50 m beneath the epithermal system, and jasperoid-hosted F-Ag mineralization with massive botryoidal/crystalline fluorite is found on the south side of the anticline. 4 miles to the east, the Grantsville Summit epithermal Au-Ag-Hg-Sb deposit is hosted as coarser quartz veins in variably dolomitized limestones and limestone breccias with bladed calcite, overlain by bleached Oligocene tuffs; the highest grades occur in hematite-bearing dolomites. 2-phase liquid-rich fluid inclusions are highly abundant in the epithermal quartz at Grantsville Summit, commonly following primary growth zones in quartz grains with feathery rims; similar textures and fluid inclusions are also present in comb quartz veins cutting jasperoids at Grantsville Ridge. The proximity of the Grantsville Pit epithermal system to the Oligocene Buffalo Canyon reduced intrusion-related gold (RIRG) deposit makes the Union district well suited for study of the zonation of ore deposits formed at a range of depths and distances from an Oligocene pluton, with estimates of formational temperatures and pressures from fluid inclusion microthermometry. Insights gained from this work will enhance exploration strategies for epithermal mineralization, illuminate the transition between RIRG and epithermal systems, and improve our knowledge of a little-studied potential belt of Oligocene precious metal-fluorite deposits in central Nevada.

Keywords: epithermal, silver, intrusion-related, Nye County, Berlin, low-sulfidation, Oligocene

Topic: Elko GSN – September Talk – Christian Thomas

Time: Sep 17, 2020 7:00 PM Pacific Time (US and Canada)

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Meeting ID: 869 1714 2942

Passcode:  ELKOGSN


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Meeting ID: 869 1714 2942

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09/17/2020 19:00:0009/17/2020 21:00:00America/Los_AngelesGSN Elko Chapter and Winnemucca Chapter Zoom Meeting – Thursday, September 17, 2020 @ 7:00 p.m.Reno, NV
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