At LDM, there is evidence of old trapiches (tra-peach-ee) that were used there. The following is interesting article about their use..near Medinah's old property at the Andacollo.
http://www.mine-engineer.com/mining/chile1.htmPart 1
Chile A Story of Gold and Quicksilver
By Dr. Ralph E. Pray
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Chile can be a very friendly and pleasant country to visit. Some of the biggest Chilean smiles are for mining engineers arriving in Santiago.
For arrivals from the U.S. it's a welcome change. Chile can look back on a long history of mining and has, today, one of the most progressive mineral industries in the Western Hemisphere. Chile was producing gold to finance Spain's wars almost one hundred years before the first pilgrim set foot on Plymouth Rock. Gold production has continued since about 1530.
Coming from the States, where interest in mining is at an all-time low, Chile's rich, old mining culture is like a first date, full of promise. I'm traveling from L.A. to examine a large underground gold mine project for U.S. financial interests. For me, working underground goes back to Pioche, Nevada. There, in 1946, fresh out of New York, I worked as a teenage ore-car trammer.
As we drive to the Chile gold mine one of the Chilean engineers asks if I'd like to see a trapiche operation. It's just off of the highway, processing ore from a small gold mine. This sounds like a good idea. I've seen, designed, or built just about every kind of ore-processing plant around, but never a trapiche. We stop off at Plante, Chile a few klicks out of Illapel, between Santiago and La Serena. A simple open roof covers two large rotating wheel assemblies, shiny wet with brown slurry. The lights are on, the motors humming, Two men running the plant greet us with smiles.
I'm fascinated. One man shovels rock in the large concrete tub while the other squeezes mercury off of the amalgam plates with his fingers. Seeing the operation all its simplicity, makes me wonder how I could missed all this in over fifty years of mining work, travel and study.
Rooted to the spot, I watch for twenty minutes before unlimbering the photographic equipment. My intepreters work double time to satisfy my curiosity The video of the trapiche I shoot this first day has been shown in New York skyscrapers and mansions in Beverly Hills.
On my daily trips to the mine I keep returning to this site as a visitor, or more precisely, as a student, to view my "discovery" one more time. While it's unique to me, it is "old hat" to my hosts, of course, just part of everyday life The plant processes over ten tons of ore every 24 hours.
Pyrite, the glittering iron sulfide, sparkles in the rock. At different times, someone shovels ore into the trapiche bowl and periodically releases the slurry. Once the gold is removed, the slurry containing the finely ground waste is drained out of the trapiche bowl, pumped uphill and discharged beside the plant.
I climb the soft trail to the top and view the flat crown of the tailings with alarm. It is huge! Pacing in off along the built-up wall around the edges, I calculate the mass at several hundred thousand tons. The ground ore must go back many, many years. I've seen a few mills, centuries old, south of Santiago that used mule teams to turn the huge stone wheels. Is this the site of such a mill? I feel like I'm standing on a history book.
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.
That's the upside. At the same time I've been forced to realize that not one relave contains much material that assays at over five grams per ton. Most, in fact, assay at about two grams per ton or less. Given the current low price of gold this does not bode well for the project.
The despondency I encounter among the trapiche operators is, I think, linked to this low price of gold. The Chilean govemment;-out of greed and a lack of good sense, places a heavy tax on the sale of raw gold. The small, gold producers and trapiche operators get around the tax by selling to jewelers' at just below market. My L.A. associates repeatedly try get in on this business in a big way.
Brinks is standing by to transport bullion to a Waiting U.S. refinery. But in Chile, gold selling is a secretive business with its own cultural norms. The gold melts, untaxed into the national economy.
During this second trip to Chile I make a surprising discovery. What I had first taken to be dejection over the low price of gold, is not that at all. It has to do with mercury. After more than 400 years the gold-processing trapiches of Chile are being shut down by government edict. The reason? Mercury! Trapiche amalgamation plants have contaminated the environment with so much mercury that it's now viewed as a national disgrace. The result - Public health agencies, and other social forces, have pressured federal legislators to take action. Throughout Chile mercury poisoning of land and water is all but banned. This development just happens to coincide with my visits.
In all this public and government outcry, no mention is made of air pollution. On any hot day a trapiche gold relave will exhaust toxic fumes of pure mercury into the atmosphere. The concentration is often measured in micrograms per cubic meter. I have brought a state of the art "mercury sniffer" with me, that I rented from Arizona Instrument Company for $1,000 per month. A pump sucks in air across a gold gauze hooked to a resistivity meter. As I walk around a 300,000-ton relave in the Los Negritos District of Andacollo with owner Luis Donoso Garcia, we take readings of the invisible mercury vapor.
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Topic: LDM MINE SHAFT PROJECT (Read 1995 times)