The Lost Arch Gold Diggings

A Natural Arch similar to that found in the Turtle's Range of California.
Photo by Library of Congress Prints

We first became familiar with the story of the Lost Arch Gold Diggings by reading an account of the story in the Earth Science Digest a publication that has been long out of print that coupled with tales of my great grandfather’s gold prospecting and mining in eastern Canada in the 1860 fired my imagination for the lure of gold that remains to this day.

The story begins in the northern part of the Turtle Range that lies east and south of a range called the Old Woman’s Mountain on the Colorado River in California.  The Lost Arch Diggings have the distinction of being twice found and twice lost because some strange acts of Providence.

Jim Fish and a prospector that had arrived in California with the first gold rush in 1848 were on their way from Nevada to California in an old-fashioned buckboard drawn by a team of stringy bay horses.  While crossing the Colorado River they had filled their water barrel from the river.  From there they continued to make their slow search for hidden wealth.  They had been looking for gold for months already with little luck.

Two days after crossing the river Fish discovered their barrel was leaking, and when they turned the barrel so the bung-hole was pointing downwards barely two canteens of water flowed out.  Although Fish’s discovery was un-nerving it was a situation that was only to familiar to anyone that was used to traveling through the mountains.  When his partner returned, it is said his name was Crocker, he told him the bad news, so it was decided they would spend a day looking for water in the vegetation covered gulches they saw in the mountains.  

After spending a restless night early the next morning they set off on their search.  “Crocker went up one canyon while I took another, the one to the right,” recounted Fish to some friends from San Bernardino, California some months later.  He went on, “The main canyon deployed into a gulch on the right and I decided to follow this through the hot sun and down among the rocks so far that not a breath of air seemed to pass through the cleft. On and on I went, over stones larger than a house, around smooth and slippery boulders where water had certainly been at one time, but where then not a trace showed.

“My feet were lagging; my shins were barked and aching, for in the rush I had neglected to be careful. Turning a sudden corner in the gulch, I came upon a natural bridge that spanned the canyon. It was so odd, so regular in the outline of an arch that I could only stand and admire it. Beneath its shade, the most cooling place in the hell-hole, I found a large sandy area and there sank down to rest.

“While idly scratching the sand, its peculiarity attracted my closer attention. I got down on my knees and started to blow the dust away, and before me I had a great pocket of precious metal, gold that averaged the size of wheat grains. I filled several pockets with the heavy grains and, with all thought of thirst forgotten, hurried excitedly down the canyon to impart the news of the find to Crocker.”

After arriving at the buckboard Fish had to wait for several hours before Crocker showed up again.  Crocker finally showed up hours later despairing that he hadn’t found any water where he went.  At that moment gold was the last thing on their minds because all their thoughts were their quest for water, and the nearest water was in the Colorado River two days distant.

After a harrowing trip to the river they finally reached it only to have Crocker die a few days later and left Fish in a state of shock that took three months of recovery before Fish could set out for the Turtle’s again.  After expending all his money on a fruitless search Fish gave up the quest.

In 1900 a German prospector whose name was probably Peter Kohler came back from the Turtle’s came back from them with a tale of rediscovering the Lost Arch, but because he had been a naturalist in the Old Country he didn’t have a thought about any gold there, he was completely lost in the beauty and strangeness of the setting.  He had never hears Fish’s story of the gold so he missed the chance of a lifetime.

Later a prospector named John Packer searched in vain for ten years without finding a trace of the Lost Arch Diggings.  The desert is a strange place that has the capability of changing its face in the blink of an eye; perhaps a flash flood destroyed the arch and its usefulness as a landmark.

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.

The Carlin Trend in Nevada has invisible gold

One of the premier gold producing areas in the United States is the Carlin Trend of northern Nevada. This small area covering 6 by 35 kilometers produces more gold then any other area in the US. The gold here is found associated with pyrite crystals in sizes ranging from single ions to masses containing only a few atoms of gold. This kind of gold is invisible to the naked eye and is not detectable to an ordinary microscope but becomes visible under an electron microscope.

This was country that was heavily prospected during the nineteenth century by typical prospectors with a gold pan and donkey. Although some small amount of placer gold was found these prospectors had no idea of what they were walking over since they couldn’t see much gold there. The Carlin type gold deposit is a recent phenomenon that was discovered during the 1960s by Newmont Mining although gold deposits like this were just becoming to be known during the late 1920s.

Gold in this kind of deposit is found in limestone deposits disseminated throughout the whole deposit. The gold itself is actually found as single ions or small aggregates of gold atoms that can be seen only by the use of an electron microscope. When this type of deposit is mined it involves tearing down whole mountains. It is in a mine like this that are the home of giant machines like trucks capable of holding 350 tons of ore at once and shovels that can fill one of these trucks with three shovels full.

Getting the ore out of the mine is only the beginning of a long and arduous job because the next step in the process of producing gold is crushing all the ore into pieces that do not exceed one-quarter inch in size that is then trucked to an asphalt pad covering several acres that slopes in to the center to a drain that removes any gold charged liquid. This is called the heap leaching process.

The heap leaching process works on a simple principle that gold is dissolved in a solution of alkaline cyanide. It is this solution that drains into the center of the asphalt pad for recycling onto the heap of stone once again. The cyanide solution is sprinkled onto the top of the heap using sprinklers similar to lawn sprinklers. This solution makes several circuits through the heap dissolving a small amount of gold during each circuit.

After several months the cyanide solution is finally drawn off when it is charged with dissolved gold. The gold is usually recovered from the solution by being precipitated using powdered zinc. The precipitate falls out of solution collecting on the bottom of the vat as a black powder where it is removed for further processing. The cost of recovering gold using the heap leaching process is about $320 per ounce.

References:

Carlin type gold deposits, Steve Castor, Nevada ureau of mines and geology, http://www.smedg.org.au/oct01.html

Heap Leaching, Wikipedia, http://en.wikipedia.org/wiki/Heap_leaching