Chile A Story of Gold and Quicksilver
By Dr. Ralph E. Pray

My mind is racing. Can it be true? Standing atop this huge artificial mountain the big question I have is: "what values remain in this vast heap?" The man operating the trapiche is also the mine owner. He is leasing the plant to treat his ore. I climb back down to the plant and put the question to him.

A Trapiche, Operating In Chile

"How much gold is in the ore you bring in here?" "It assays eighteen grams." That's almost six-tenths of an ounce per ton. "What is your recovery?"
"About half. The relave gets the other nine grams. But there's nothing we can do about it. It's the same old problem with every trapiche."
"Some of your gold is in the pyrite?" "Yes, that's the part we can't get. The mercury can't pick it up."
My mind is racing. Can it be true? I do the math; with gold selling for $270 per ounce, nine grams is worth $75. That's gold sitting here going to waste. Taking just half of that value for the whole pile would be 11.25 million dollars for the first 300,000 tons. Methods of recovering this gold might be new in Chile, but not up north where I come from.

Five minutes later I've climbed back on top of the relave with four sample bags. I take one sample where the pipeline spits out the slurry An assay of this material will tell the story - if nine grams of gold per ton is realistic or just wild talk. I take three more samples of dry sand at different points, digging down just a few inches. If the surface samples assay as claimed, we can follow up later with auger samples taken through the thirty-foot depth of the mound.

Just as I finish sampling, an associate of the trapiche owner shows up all agitated and wringing his hands. He's worried about the samples I've taken.

"Is there a problem with mercury?" I ask, realizing that this artificial mountain situated above the city, and above the river, is probably laced with mercury made even more toxic by reacting with sulfides in the ore.

"It's a serious business," he says, frowning deeply. "I didn't know. I'm sorry. I'll dump the bags out." "No," he says kindly. "It's okay to keep them."

Just back in L.A.after a thirteen-hour flight I rush to the lab and heat the furnace up to 2000 degrees for the twenty-eight step fire assay procedure. I then get to work on the high-priority four samples. The first sample assays just over 8 grams of gold per ton. All four samples together average 5 grams per ton. This makes it worth going back with an auger to take deep samples.

It may also be a good idea to look at other relaves. From the information I've been able to gather, there are literally hundreds of trapiche plants formerly or currently operating in Chile. Buying gold at each trapiche plant for cash, at a small discount, is something to consider. Mining Professor Claudio Canut de Bon, from the University of La Serena, knows much about trapiches and kindly furnishes me with many technical papers of value. I immediately send off letters to fellow members of the American Institute of Mining Engineers in Chile, and to fellow graduates of the Colorado School of Mines working in Chile. All this correspondence produces little of value. Mining engineers trained in the U.S. deem the trapiche too primitive to be useful.

With equipment I've tracked down across the U.S. I come up with a project to recover the mercury and gold in Chile's relaves. First I design a plant to retort the mercury and roast the sulfides in the relave sands. This is followed by fine-grinding and agitation in cyanide to extract gold.

With funding for the project provided by a New York syndicate, I return to Chile with a detailed agenda. Our group is large enough to require a minibus. First we visit the U.S. embassy, assorted banks, and meet with attorneys, government functionaries, mine owners, mine coop presidents, engineers, geologists, and business leaders. Then, additional meetings at university and analytical laboratories, and private research firms in Santiago. The travel and meetings take weeks. Business is conducted at a slower pace in Chile.

Gold selling is a secretive business.

In the meantime additional samples secured with an auger are sent to first-rate Chilean laboratories with a one day turn-around. While this is going on I charter a Cessna to fly below the Andes escarpment. I'm looking for old relaves from long ago. Back on the ground I rent a four wheel drive and head off to visit and sample each of the sites I've mapped from the air. Taken together the total quantity of relave material available to the project amounts to over five million tons.

To More of "Chile, A Story of Gold and Quicksilver" 

Published in the South American Explorer,
June, 2001.
Reprinted with permission of the author. Dr. Ralph Pray, Mining & Metallurgy 805 S Shamrock Ave
Monrovia, CA 91016
Telephone: 626-357-6511 Fax: 626-358-8386