By Thomas Guengerich
SOCORRO, N.M., Oct. 2, 2008 – A New Mexico Tech graduate student is contributing significant geological research into development of the second largest gold and copper deposit in the world.
Melissa Lindholm (right), a master’s student in geology, recently worked on her second summer research season at the Pebble Deposit in remote southwest Alaska. She presented her research into the geology of the untapped deposit at a recent mining conference in Grants.
Landing this summer internship was like striking gold for Lindholm. She has worked on the Western Hemisphere’s second largest untapped deposit of copper and gold for two summers, enjoying the temperate climate and getting hands-on experience in geology and mining.
The Pebble Deposit was first discovered in 1988. Extensive drilling in 2005 confirmed a resource of 42.1 million ounces of gold, 24.7 billion pounds of copper, 1.35 billion pounds of molybdenum and additional silver. In 2007, a second deposit was found – Pebble East – that contains an additional 49 billion pounds of copper, 45 million ounces of gold and 2.8 billion pounds of molybdenum.
“They are in advanced exploration phase, but it’s not totally defined. It’s still open in some directions,” she said.
In her abstract, Lindholm wrote that Pebble is near two small native villages and straddles two important watersheds. Development in the area presents environmental challenges for clean mining.
“Nevertheless, Pebble’s spectacular size and potential make any investigation of this system interesting to exploration geologists as well as ore genesis researchers,” she wrote.
Lindholm landed the job through Dr. William Chavez, professor of mineral engineering at Tech. A colleague of Chavez at Pebble asked him if he knew of a graduate student who could work on advanced exploration on site. Lindholm jumped at the chance to work and learn on such a vast project in an exotic locale.
During the summer, Lindholm did what she called typical junior geologist duties – visually estimating mineral grade and describing textures, inspecting drill rigs and describing drill core samples. The two seasons in Alaska involved mostly work, but Lindholm had her share of fun.
“We get to fly in helicopters and see grizzly bears,” she said. “The area is so beautiful.”
The site of the deposit is about 40 miles inland from Cook Inlet on the southwest tip of Alaska. The site is accessible only by helicopter.
During the summer months, about 100 staff members work at the headquarters and at the site, with as many as 100 outside contractors filtering in and out of the area.
The company funded her research, so Lindholm was allowed to bring core samples back to Socorro for testing.
Her tests involve two main objectives: studying the sulfur isotopes in the samples and petrography, which means giving a detailed chemical and geological description of the rocks.
For her petrography study, she sliced thin sections of rock, which allowed her to examine and analyze the mineral composition. That study has no direct mining application, but could potentially be useful as a metallurgical analysis and provide a geological framework for the deposit, she said.
Lindholm anticipates publishing one of the first – if not the first ever – research papers about the Pebble East deposit.
“It’s fascinating for us to be involved, because we’re getting involved on the ground floor,” said her co-advisor Dr. Andrew Campbell. “Hopefully, Melissa’s work will be some of the good, early work. As this prospect develops into a mine, they’ll be referring back to her work for years to come.”
Lindholm said recent research in Australia and the Canadian west have identified sulfur isotope patterns that appear to correlate with copper and gold grades. She is comparing cores from Pebble East to the other sulfur isotope research papers.
“Most copper and gold is found in alkalic rock, meaning the have more sodium and potassium, as opposed to other deposits that have more sulfur and are acidic,” she said.
Lindholm is studying the sulfur isotopes from various core samples from the Pebble East deposit in an attempt to make a connection between sulfur isotopes and recoverable minerals – mainly copper and gold. For the sulfur isotope study, Lindholm used Dr. Campbell’s mass spectrometer to determine the isotopic composition of the sulfide minerals.
“No one has ever done this sort of study at Pebble,” she said. “I am testing to see if I get the same pattern that was found in Australia and British Columbia.”
A native of Fergus Falls, Minn., Lindholm completed her bachelor’s in geology at Bryn Mawr College in Pennsylvania. After finishing her master’s in geology later this year at New Mexico Tech, she hopes to return to Alaska to start her career working on the Pebble deposits as a full-time geologist.
“It’s pretty unusual to work on a deposit starting with exploration and continue through feasibility and into mining,” she said. “That would be amazing.”
– NMT –