Carlin Trend Model Advance

I have been exposed to the Carlin trend for over thirty years and most Americans barely know it exists and that it single handedly has make the US an important gold producer.

What is exceptional about Carlintype deposits is that the gold failed to form large crystals as it typicallydoes in other deposits.  Explorers do notknow what to make of all this.

This suggests that these deepmagmas somehow were sufficiently unique in some way for this to occur.  If it had been just chemistry, it would havebeen obvious long ago.  More plausiblythe gold arrived in a chemically bound form and was reduced in contact with thepyrites to produce the small particle size.

Then the next question is to askwhy this only happened in Nevada.

Most likely we are failing tounderstand something that is important and particular to these magmaevents.  Even more likely we are missinga source of gold in many other geological provinces.

New Model For How NevadaGold Deposits FormedMay Help In Gold Exploration

by Staff Writers
Reno NV (SPX) Feb 07, 2011

Barrick Gold Corporation's largeopen pit at its Goldstrike Mine on the Carlin Trend. The mine has Carlin-typegold deposits, the formation of which has been newly modeled by University of Nevada researchers. Credit:Photo by John Mundean, University of Nevada, Reno and it'spublic service department, the NevadaBureau of Mines andGeology.

A team of University of Nevada, Reno and University of Nevada, Las Vegasresearchers have devised a new model for how Nevada's gold deposits formed,which may help in exploration efforts for new gold deposits.

The deposits, known as Carlin-type gold deposits, are characterizedby extremely fine-grained nanometer-sized particles of gold adhered to pyriteover large areas that can extend to great depths. More gold has been minedfrom Carlin-type deposits in Nevada in thelast 50 years - more than $200 billion worth at today's goldprices - than was ever mined from during the California gold rush of the 1800s.

This current Nevada gold boom startedin 1961 with the discovery of the Carlin gold mine, near the town of Carlin, at a spot wherethe early westward-moving prospectors missed the gold because it was toofine-grained to be readily seen.

Since the 1960s, geologists havefound clusters of these "Carlin-type" deposits throughout northern Nevada. Theyconstitute, after South Africa, the second largest concentration ofgold on Earth. Despite their importance, geologists have argued for decadesabout how they formed.

"Carlin-type deposits are unique to Nevada in that they representa perfect storm of Nevada's ideal geology - a tectonic trigger and magmaticprocesses, resulting in extremely efficient transport and deposition ofgold," said John Muntean, a research economic geologist with the NevadaBureau of Mines and Geology at the University of Nevada, Reno and previously anindustry geologist who explored for gold in Nevada for many years.

"Understanding how these deposits formed is important because mostof the deposits that cropped out at the surface have likely been found.Exploration is increasingly targeting deeper deposits. Such risky deepexploration requires expensive drilling.
"Our model for the formation of Carlin-type deposits may notdirectly result in new discoveries, but models for gold deposit formation playan important role in how companies explore by mitigating risk.

Knowing how certain types of gold deposits form allows one to be morepredictive by evaluating whether ore-forming processes operated in the rightgeologic settings. This could lead to identification of potential new areas ofdiscovery."

Muntean collaborated with researchers from the University of Nevada,Las Vegas: Jean Cline, a facultyprofessor of geology at UNLV and a leadingauthority on Carlin-type gold deposits; Adam Simon, an assistant professor ofgeoscience who provided new experimental data and his expertise on the interplaybetween magmas and ore deposits; and Tony Longo, a post-doctoral fellow whocarried out detailed microanalyses of the ore minerals.

The team combined decades of previous studies by research and industrygeologists with new data of their own to reach their conclusions, which werewritten about in the Jan. 23 early online issue of Nature Geoscience magazineand will appear in the February printed edition.

The team relates formation of the gold deposits to a change in platetectonics and a major magma event about 40 million years ago. It is themost complete explanation for Carlin-type gold deposits to date.

"Our model won't be the final word on Carlin-type deposits,"Muntean said. "We hope it spurs new research in Nevada, especially by people who may notnecessarily be ore deposit geologists."

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