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February 4, 2011
By Tiffany Moore
A team of University of Nevada, Reno and University of Nevada, Las Vegas researchers 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 characterized by extremely fine-grained nanometer-sized particles of gold adhered to pyrite over large areas that can extend to great depths. More gold has been mined from Carlin-type deposits in Nevada in the last 50 years – more than $200 billion worth at today’s gold prices – than was ever mined during the California gold rush of the 1800s.
This current Nevada gold boom started in 1961 with the discovery of the Carlin gold mine, near the town of Carlin, at a spot where the early westward-moving prospectors missed the gold because it was too fine-grained to be readily seen. Since the 1960s, geologists have found clusters of these “Carlin-type” deposits throughout northern Nevada. They constitute, after South Africa, the second largest concentration of gold on Earth. Despite their importance, geologists have argued for decades about how they formed.
John Muntean, the lead researcher in the creation of the model, has dedicated much of his life to researching gold deposits throughout the world. He received his Ph.D. in geology from Stanford University in 1998, and for many years immediately following, he worked as an industry geologist exploring for gold in Nevada.
“Carlin-type deposits are unique to Nevada in that they represent a perfect storm of Nevada’s ideal geology – a tectonic trigger and magmatic processes, resulting in extremely efficient transport and deposition of gold,” he said.
Muntean came from a family of steel workers from Indiana. He always had an interest in the history of prospecting in the American west, but thought the hunt for gold was a dead art. His perspective changed at the age of sixteen, when the Public Broadcasting Service aired a television show about modern-day gold exploration. The fact that searching for gold and other minerals was still alive along with the modern technology shown in the episode convinced him that looking for minerals was what he wanted.
In 2010, he had a chance to be the person on television. The History Channel featured him and his work on an episode of a four-part special of “How the Earth was Made: America’s Gold.” He hoped his work with the History Channel would inform and interest others, just as a television show interested him.
“I knew if it wasn’t for that television show, I wouldn’t be doing what I’m doing now,” he said.
While working in industry, he realized the tools he had were limited. He also started wondering why and how the deposits were made. His desire to improve technology, research the Carlin-type deposits’ origin, and continue looking for gold brought him to the Nevada Bureau of Mines and Geology at the University of Nevada.
“One of my career goals has always been to bring together the interests and needs of industry and academia,” he said. “With this job, I can work with industry, do pure and applied research and work at developing tools I wish I had when I was in industry.”
Unfortunately, many of the Carlin-type deposits in Nevada are becoming mined out, forcing industry to seek new ideas and methods to find new gold deposits. The recently published model by Muntean and his colleagues is a step toward helping industry narrow its search.
“Understanding how these deposits formed is important because most of the deposits that cropped out at the surface have likely been found,” he said. “Exploration is increasingly targeting deeper deposits. Such risky deep exploration requires expensive drilling.”
For the model, Muntean collaborated with researchers from the University of Nevada, Las Vegas: Jean Cline, a faculty professor of geology at UNLV and a leading authority on Carlin-type gold deposits; Adam Simon, an assistant professor of geoscience who provided new experimental data and his expertise on the interplay between magmas and ore deposits; and Tony Longo, a post-doctoral fellow who carried out detailed microanalyses of the ore minerals.
“Our model for the formation of Carlin-type deposits may not directly result in new discoveries, but models for gold deposit formation play an important role in how companies explore by mitigating risk,” Muntean said. “Knowing how certain types of gold deposits form allows one to be more predictive by evaluating whether ore-forming processes operated in the right geologic settings. This could lead to identification of potential new areas of discovery.”
The team combined decades of previous studies by research and industry geologists with new data of their own to reach their conclusions, which were written about in the Jan. 23 early online issue of Nature Geosciences magazine and is now in print in the February edition. The team relates formation of the gold deposits to a change in plate tectonics and a major magma event about 40 million years ago. It is the most 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 not necessarily be ore-deposit geologists.”
The work was funded by grants from the National Science Foundation, the United States Geological Survey, Placer Dome Exploration and Barrick Gold Corporation. The article appears in the online edition of the Journal Nature Geosciences.