Wednesday, July 30, 2014

Gearing up for gold production

From page A8 | May 14, 2012 |

Getting the gold mine operational has been a lengthy process for Sutter Gold Mining Inc. said Vice President for Environment, Health & Safety David Cochrane. It can take six to 10 years to get the permits to do commercial mining. “There were a lot of public hearings. The project was litigated against in Amador County,” he said, “but the mining companies prevailed. Some people are opposed to mining in general and others to mining in their backyard.

“Some mining operations do leave a big footprint,” he admitted. “But we don’t think that kind of mining is compatible with the land value. The type of mining we are going to do is more compatible than open-pit projects.”

Currently there is a lot of activity at the mine. Above ground, drillers are bringing up core samples that help identify where the richest veins of gold are. The rig has diamond encrusted drill bits that go through, on average, 100 feet of solid rock a day but on a good day can drill up to 200 feet. What comes up are core samples of greenstone that is used afterwards as decorative rock on the site.

Below the drill site is where the new mill will go which they expect to complete by October. It will contain a state of the art assay lab and like the other buildings on the site, is being designed to look like an old mill building from the gold rush era complete with a “rusty” corrugated metal exterior.

Trucks will come to the top of the building and dump their rock loads into the mill. A conveyor belt will take it down and grind it. Then it will go into a rod mill with tumblers that will crush the material into sand. Then a centrifuge is used to separate the gold from the sand. This is followed by a cleaning process to concentrate and clean up the gold. The last step is smelting the gold and turning it into a doré bar, which is a semi-pure alloy of the gold. The concentrated ore is then shipped to Nevada for further processing. Ultimately, most of it ends up in jewelry or electronics.

Cochrane said the ore processing method they use removes up to 96 percent of the gold from the ore without using cyanide on site. It also removes approximately 90 percent of the naturally occurring sulfide minerals. Since there is naturally occurring arsenic in the water from the mines and the gold, chemicals are added to remove the arsenic. The treated water is then used to irrigate neighboring ranch lands.

Up to 65 percent of the tailings from the mill will later be disposed of underground in the mine. The balance of the tailings will be disposed of in a lined waste management unit similar to an earth fill.

The mine itself is a cavernous affair. The main tunnel is large enough to drive a vehicle through with side pockets carved out where promising veins of quartz are visible and marked as having been assayed. Along one wall is a huge duct for expelling air and dust and a ventilation system for pumping in fresh air. Other pipes mounted to the wall bring in fresh water, remove dirty water, and provide electricity and telecommunications. And though it is considered a “dry mine,” Cochrane said the water in the mine is equivalent to a 25 mile long, 8 inch deep well.

“Our mine is actually very small,” said Cochrane.”We plan to take out 200 tons of material a day although we’re permitted to take out 1,000 tons a day. In most open-pit mines, the gold percentage is about 1 or 2 grams per ton. However we expect to take out .56 ounces of gold per ton in the Lincoln Project. It’s a very rich deposit. We are trying to model where the richest deposits are using a high-tech system to find the gold. But the actual mining techniques are not that different from the 1920s to 1930s technologies.”

Cochrane estimated that the gold in the mine is about 120 to 125 million years old and is usually associated with quartz which is highly visible in the mine. Some quartz veins are narrow and spidery while others are several feet wide. “We target veins that assay tests show have at least .22 ounces of gold or more per ton,” he said.

Blasting is done using ANFO which is 94 percent ammonium nitrate. “We do a very controlled blasting” stated Cochrane. “We don’t want to over blast. It reduces the waste that has to be handled.”

In the event of an emergency, the mine has a safe room complete with a fire safe door, water, communication equipment, and first aid gear. Filled with pew like seating, Cochrane said it was also used in the past for tour groups. Hanging from the ceiling is one reminder of how miners worked in the past. Early miners would get their clothes wet while underground so they would hang them from overnight to dry. In the safe room was a hanger complete with a pair of jeans, boots, and a fake canary in a cage.

Preventing theft of the gold has also been considered. Cochrane said in addition to video surveillance and guards, anyone coming to work in the mine will go in one door and change into their work clothes. When their shift is done, they will take off their work clothes, take a shower and put their street clothes back on.

“It’s pretty well controlled. In the old days one of the reasons some of the miners used to have straggly beards was so they could hide nuggets in them.”





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