Most
rockhounds probably think of California, Montana, and Alaska when gold is
mentioned, most likely due to the available nuggets and small grains on the
market. However, all 49 states added
together cannot compete with Nevada in the current production of gold. In fact,
according to the US Geological Survey, if Nevada was a country, it would be the
world’s fourth-largest gold producer, behind China, Australia, and Russia. In
2018 Nevada produced 5,581,160 troy ounces, representing 78% of U.S. gold and
5.0% of the world's production. Total gold production recorded from Nevada from
1835 to 2017 totaled 205,931,000 troy ounces, worth ~$322.6 billion at 2020
values (George, 2018). BTW, gold, and
other bullion is sold and traded in troy ounces and there is a difference between
an ounce of salt and a troy ounce of salt, about 10%: 1 troy ounce = 1.097
ounce.
Gold
in Nevada was originally discovered, at least by North Americans of European
descent, when California 49ers were heading west in 1850; however, it was small
amounts of placer gold and the travelers were more interested in heading to the
“bonanzas” in California. Less than a
decade later silver became the main precious metal target and in 1859 the discovery
of the Comstock Lode was made public, the rush was on, and silver became “king.”
But,
as with most precious metal booms, the mines played out and in 15 years many
miners had departed the Mining Camps for supposed “greener pastures.”
Although
Nevada has many gold producing areas, by far the major group of mines is
located in the Carlin Trend in the north central part of the state, a 15-mile-wide
by 40-mile-long belt of gold deposits that has since produced more gold than
any other district in the U.S. While estimates vary, the Carlin Trend is
believed to contain up to 180 million ounces, making it the second-largest gold
resource in the world behind Witwatersrand in South Africa.
The
Newmont Mining Corporation is credited with the discovery of gold in the Carlin
Trend ~1961-62; however, it was slow going at first due to: 1) the gold in the ore
is quite small, <0.1 to 10.0 microns and disseminated throughout the rock;
and 2) the price of gold in the 1960s was established at ~$35 oz. At the $35 oz
price the cost of mining Carlin Trend gold was not very cost effective. In the early 1970s when gold became unhinged
from the U.S. dollar, the price fluctuated, and generally moved upward. Another
trend that made Calin low grade gold profitable was the development of open pit
mining and cyanide heap leaching.
The
other major player in the Carlin Trend was Barack Gold. In 2019 Barrick Gold merged its Nevada mining
operations with Newmont Gold into a company called Nevada Gold Mines LLC.
Barrick Gold owns 61.5 percent of the new entity with Newmont Gold owning the
remainder. Today, Nevada Gold Mines
dominate the production of gold in the Carlin Trend. As best I can determine
from an investment report is that in 2019 Newmont produced ~2,218,000 and
Barack ~1,475,000 troy ounces of gold, and in 2020 Nevada Gold Mines has only
slightly lower production projections. That is a lot of gold!
OK. But I do not have a single gold or silver
specimen from Carlin rocks! What I do have is a nice specimen of dussertite, a complex
barium iron arsenate [BaFe3(AsO4)(AsO3OH)(OH)6]
collected, according to an older looking label, from the “Gold Quarry Mine,
Carlin, Nev.” According to MinDat
dussertite from Elko County, Nevada, is known from the Rain Mine in the Carlin
Trend and the non-Carlin Tecoma (lead over on the Utah line) and Wells (tungsten
east of Carlin) Districts. USGS data
lists barite and dussertite as gangue minerals in these three mines. The Gold
Quarry Mine is one of the largest mines in the Carlin Trend and MinDat lists
111 known minerals collected from the Mine, but no mention of dussertite! In
addition, USGS data also does not list dussertite as a gangue mineral. I am not
quite certain what all of this means except that MinDat photos of dussertite
from the Rain Mine look like my specimen!
Dussertite
is an arsenate and as common in that group, is some sort of a shade of green or
yellow green or yellow and is an oxidized and alteration product of a primary
arsenic mineral, usually arsenopyrite.
In fact, it seems amazing to me how many secondary minerals are produced
from the alteration of arsenopyrite! The
crystals of dussertite are tiny, flattened and often hexagonal shaped, and at
times the plates are formed into rosettes.
Crystals are semi translucent, soft at ~3.5 (Mohs), and with a vitreous
luster. With that said, I remain a little confused with the specimen from
Nevada! Evidently, according to MinDat, dussertite may be “aggregated into
crusts.” I have found few photos of a
crust of this type, or a least close: 1) MinDat RQE-FR3 from France, Christian
Auer; 2) MinDat 595-WUL from the Rain Mine, Carlin Mining District, Elko
County, Nevada; 3) two specimens from Dakota Matrix, one from Algeria and one
from Rhyolite Prospect, Nevada. The
Carlin specimen I have is a crust compose of numerous, submillimeter, prismatic
and acicular yellow to yellow-green crystals—there are no flat tabs.
So,
in my mind there are two questions: 1) was my specimen collected from the Rain
Mine or the Gold Quarry Mine; 2 is the crust “really” dussertite? Those are some of life’s persistent questions. I will continue to investigate and maybe even
get an answer from Tom up at Dakota Matrix.
REFERENCES CITED
George,
M. W., 31 January 2018, Mineral Commodity Summaries 2018: U.S. Geological
Survey.