Porphyry-Related Deposits of Nevada

Welcome to the Geological Society of Nevada’s 2015 Symposium Field Trip, Porphyry-Related
Deposits of Nevada. When explorationists and miners convene in Nevada, gold deposits and
production dominate conversations, but copper should not be considered a deserted step-child. For
example, 19th century prospectors began mining high-grade copper from skarn deposits in the
Yerington district shortly after discovery of the bonanza Au-Ag discoveries at the Comstock Lode.
Copper mining began in earnest during the early 1900’s with the advent of and financial benefit
from bulk-tonnage open pit mining in the Ruth mine at Ely, now part of KGHM’s Robinson copper
mine, which operated nearly continuously over a 100+ year history. Major copper production
continued during the mid-1950’s when the Anaconda Company commissioned their Yerington mine
in Lyon County followed by, in late 1970’s, another porphyry-hosted deposit, Anaconda’s Hall mine
in Nye County, albeit dominated by molybdenum with minor copper. Modern porphyry exploration
includes General Moly’s Mount Hope property in Eureka County, representing another
molybdenum-dominated porphyry deposit.
Our field trip will take us to the Robinson mine at Ely and on to the Yerington district, sharing
similarities of porphyry-derived copper mineralization dismembered by Tertiary extensional faulting.
Both districts include skarn deposits (current mining at Robinson, planned 2016 mining in the
Yerington district) hosted in upper Paleozoic and Mesozoic carbonates and calcareous siltstones,
respectively. Copper mineralization at Robinson derives from mid-Cretaceous monzonite / quartz
monzonite intruded into an upper Paleozoic section that is also credited with gold production from
deposits peripheral to the copper pits. The Yerington district is currently being explored by three
companies with mining planned by Nevada Copper in 2016 on copper-magnetite skarn
mineralization hosted in mid-Triassic / early Jurassic carbonates and calcareous siltstones. Copper is
hosted mid-Jurassic granodiorite and quartz monzonite and, significantly, in related dikes which host
major copper mineralization at Entrée Gold’s Ann Mason deposit and at Singatse Peak Services’
Bear sulfide deposit, MacArthur oxide – sulfide copper deposit, and unmined sulfide mineralization
remaining in the Yerington pit.
The three-day field trip will depart Reno on Thursday, May 21, arriving in Ely that evening for
dinner and a presentation of Robinson mine geology by KGHM geologists who will tour us through
several of the pits at Robinson on Friday morning. Departing Friday afternoon from Ely will take us
back along US Highway 50 to Fernley, then south to overnight in Yerington. Friday’s dinner
discussion in Yerington will feature Singatse Peak Services’ (SPS) geologists describing the Bear,
Yerington mine, and MacArthur deposits. Saturday morning will begin with visits to SPS’s Yerington
mine, Bear overlook, and MacArthur 4680 bench which will also include Entrée Gold geologists
presenting a core shack examination and discussion of their Ann Mason deposit. The Yerington tour
will conclude with an overview of Nevada Copper’s Pumpkin Hollow deposit at the East / E-2