GSN Elko Chapter Meeting – February 20, 2020 (3rd Thursday)

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Contact: dianehcheung@gmail.com

GSN Elko Chapter Meeting – February 20, 2020 (Every third Thursday)

The GSN Elko monthly meeting will be held at the Western Folklife Center, 501 Railroad St., Elko, NV.  Refreshments begin at 6 p.m. and talk starts at 7 p.m.  Speaker, Mike Ressel, NBMG. Title: “The Great Basin is bipolar: A case for contrasting metal distribution in the mid-Tertiary and where Carlin-type deposits reside on this spectrum.”

Food & Drinks sponsored by:  MAJOR DRILLING!

For more information please contact Elko Chapter President, Diane Cheung-Harris at dianehcheung@gmail.com.

ABSTRACT:

The Great Basin is bipolar: A case for contrasting metal distribution in the mid-Tertiary and where Carlin-type deposits reside on this spectrum

Mike Ressel, Curtis Johnson, and Philipp Ruprecht (University of Nevada, Reno)

Did you know, Eocene (~42-34 Ma) ore deposits have contributed a majority of the Great Basin’s precious- and base-metal production? Eocene production includes about 6,438 tonnes Au (207 million oz), 38,879 tonnes Ag (1.25 billion oz), 21.7 Mt Cu, and 0.74 Mt Mo. Combined, these four metals would have a cumulative 2019 end-of-year value of about $489 billion (US), about 64% of which is attributable to gold, and 28% to copper. In terms of precious metals, Eocene deposits have contributed about 75% of the 274 million ounces of total recorded Au produced in the Great Basin and about 65% of the 1.93 billion ounces of recorded Ag produced. Gold production from Eocene deposits of the Great Basin, which largely reflects the time since the Carlin mine began producing in 1965, represents one third of the total U.S. gold production since 1835 and an estimated 4% of all of the gold ever produced in the world.

Did you know, metal production from Eocene deposits is strikingly polarized, with 81% of Au production derived from mines in north-central Nevada, and 99% of Cu and 81% of Ag derived from mines in north-central Utah? Most Eocene Au production in Nevada is from three major mineral belts that host giant sedimentary rock-hosted Carlin-type Au deposits: Carlin, Battle Mountain-Eureka, and Getchell. Three major districts produced the bulk of Utah’s Cu, Mo, Au, and Ag production: Oquirrh, Park City, and Tintic, with the vast majority of Cu, Mo, and Au coming from the supergiant Bingham Canyon porphyry Cu-Mo-Au mine.

Did you know, Eocene deposit types are as diverse as the metals they produce, and like metals, vary from west-to-east? Deposits that host primarily gold in Nevada’s famous trends are nearly all replacement-style and are contained in Paleozoic sedimentary rocks, but deposits range from high-temperature gold skarns to low-temperature Carlin-types. In contrast, Eocene deposits in Utah, although forming at the same time as Nevada deposits, are broadly porphyry Cu-related: porphyry Cu-Mo-Au, Cu skarns, Pb-Zn-Ag carbonate replacement deposits, and yes, distal Carlinesque gold. What’s happened to explain this dichotomy in metals and deposit styles across the northern Great Basin, and how might it be important for exploration? We offer one explanation for this $489 billion question.