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Tuesday, May 10, 2011

Gold Occurrences in Nevada

The Goldstrike Mine in the Carlin Trend of Nevada   USGS



Placer gold has been found in 14 of the 17 counties in Nevada in the form of either commercially viable deposits, or deposits that are potentially viable. Most of these deposits are located in the northern and western part of the state. Many of these deposits were worked out by early prospectors, but there are many areas in the state were overlooked that can still afford a working wage if they are developed. It is especially important to hunt out areas where virgin gold can be found that were never mined in the past.

Much of Nevada is so arid that the early prospectors had several different methods of dry washing their gold bearing gravel. One of the biggest problems they had in processing placer gold was the presence of lots of caliche, a type of hardened sub-soil that attains the hardness of concrete. 

It is felt by many that the discovery of gold is an ongoing process with much of the gold still waiting to be discovered.  By drilling in the basin and range province of the United States exploration geologists are finding even richer deposits of gold then there are in the Carlin Trend.  It is claimed that prospecting in the state is exciting because there is so much undiscovered mineral wealth present, and it isn't all gold.

Placer Gold
Photo by Nienetwiler


Nevada is also the home of unique deposits of finely disseminated gold that was discovered in the 1960s by Newmont Mining Company who developed a method for extracting the gold. For the most part these cool deposits are found in an argillaceous limestone that has been subject to enter thermal alteration. This is the famous Carlin trend of cool deposits where the gold is so fine it can only be seen with electron microscope, and at times goals of the limestone was represented by a single ion.

Gold of this sort is mined using the heap leaching method of recovering the gold values. He teaching consists of piling up a heap of crushed stone about a quarter inch in diameter and treating it with a weak solution of an alkali salt of cyanide. The heap is piled up on a watertight floor that slightly slopes towards the center and all the pregnant liquor from the gold leaching process is directed to a sump where it is collected for treatment to recover the gold.

Although there are several different techniques used on the ore one of the most common is treating the pregnant liquor with powdered zinc. The gold in the liquor chemically replaces the sink it is collected as a black powder that is further refined into pure gold.

Nevada also produces many gemstones including precious opal and turquoise. The precious opal comes mainly from the Virgin Valley, and the author used to buy some really beautiful turquoise from the area around Crescent Valley.

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