GSN Membership Meeting Reno – January 17, 2020

Description

Contact: gsn@gsnv.org

GSN MEMBERSHIP MEETING (3rd Fridays) will be held at Great Basin’s Taps & Tanks, 1155 S. Rock Blvd. Reno, NV.  Drinks @ 6:00 pm, DINNER @ 6:30 pm, Talk @ 7:30 pm.

Speaker: Brian May, Elko Mining Group

Title: “Updates to the High-Sulfidation Goldfield District, Esmeralda County, Nevada”

Drinks Sponsored by:  MINE DEVELOPMENT ASSOCIATES, a division of RESPEC

DINNER AGAIN THIS MONTH!  $30/person.  Click here to prepay:  https://www.gsnv.org/dinner-reservations. Email the GSN office to RSVP and pay at the door.  gsn@gsnv.org

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ABSTRACT:

Updates to the High-Sulfidation Goldfield District, Esmeralda County, Nevada

Brian May

The Goldfield District is in northern Esmeralda County, 27 miles south of the city of Tonopah, and is characterized by gold mineralization predominantly hosted in Tertiary intermediate to felsic volcanic units. The district hosts high-sulfidation/acid sulfate epithermal gold deposit types that are the largest of its type in the USA with a gold endowment (production/reserves/resources) of greater than 5.5 million ounces gold. Key geological features observed throughout this prolific gold district include several ore-hosting horizons, stratigraphic and structural controls, a large alteration footprint, and bonanza gold grades.

The district encompasses approximately 300 shafts, 100+ levels, and 4 open pits from historic workings. Underground production between 1904 and 1946 from the district yielded 4.2 million ounces gold from 8.0 million tons (0.5 opt gold average). Open pit production between 1986 and 1997 from the Kendall-Adams, Combination, Red Top, and Jumbo pits yielded 50,000 ounces gold from 0.85 million tons (0.05 opt gold average).

Between 2017 and 2018, Gemfield Resources LLC has completed drilling at the Gemfield, Goldfield Main and McMahon Ridge deposits to support an updated feasibility study. The programs included 60 diamond holes comprising 31,725 feet completed at Goldfield Main and McMahon Ridge. Twenty-five RC holes comprising 5,260 feet were also completed at Gemfield. The purposes of the diamond and RC holes were to improve geological understanding, increase confidence in historic drill data, resource conversion, advance metallurgical testwork, and update geotechnical plus geohydrological parameters.

Gemfield Deposit: Kennecott Exploration Company discovered the Gemfield deposit in 1992 through exploration RC drilling. Historic mining has not been conducted on the Gemfield deposit. Gold mineralization is hosted in weakly to pervasively quartz-alunite-kaolinite-altered Tertiary Sandstorm Rhyolite with the highest grades typically hosted in pervasively quartz-altered units. Mineralization is also interpreted to be controlled by north-northwest and northeast trending faults. The mineralized zones are strongly oxidized and amenable to heap leach processing.

Goldfield Main Deposit: Mineralization at the Goldfield Main deposit was discovered in 1902 through prospecting at Columbia Mountain. Historic mining at the Goldfield Main deposit involved extraction of high-grade oxide and sulfide material from stopes, and more recently from open pit mining of lower grade oxide material. Mineralization is hosted in variably quartz-alunite-kaolinite altered and veined Tertiary dacite located in the hanging wall of the low-angle, north-northwest trending Columbia Mountain Fault. Northeast trending structures are also observed. The mineralized zones are oxidized and sulfidic, both of which are amenable to heap leach processing.

McMahon Ridge Deposit: The McMahon Ridge deposit, discovered in 1907, consists of the Daisy and Great Bend mines. Historic mining at the McMahon Ridge deposit involved extraction of high-grade oxide and sulfide material from stopes. Mineralization is hosted in intensely to pervasively quartz-alunite-kaolinite-altered Tertiary Milltown Andesite that is localized along subvertical, east-west trending faults. Narrow (<20 feet wide) pervasively silica-altered structures are hosted in both the hanging wall and footwall blocks. The mineralized zones are oxidized, mixed, and reduced; all of which are amenable to heap leach processing.

Gemfield Resources LLC is expecting to complete updated resource estimates on Gemfield, Goldfield Main, and McMahon Ridge in early 2020.