Thursday, January 28, 2010

Prehistoric Rivers of Gold (Part 3)


(Hydraulicking Tertiary gravels at the Malakoff Diggings, California.)

Here are more edited excerpts from Waldemar Lindgren’s classic geological treatise, “Tertiary Gravels of the Sierra Nevada of California.” Once again I’ve emphasized what I consider to be key points in bold type:

River Beds on the Summits of Ridges

“The barren lava flows and the canyon slopes again became clothed by earth and vegetation, this time of the type belonging to a cooler but still temperate climate. During the last brief span of a few thousand years the Sierra Nevada has remained as we now know it, with the pleasing oak groves of the foothills, the somber giant pines of the middle slopes, and the storm-scarred hemlocks of the summit ridges.”

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“The peace of this pristine wilderness was interrupted in 1849. An army of gold seekers invaded the mountains; at first they attacked the auriferous gravels of the present streams, but gradually the precious metal was traced to the old Tertiary river beds on the summits of the ridges and to the quartz veins, the primary source of all the gold in the Sierra Nevada.”

Rich but Difficult to Mine

“The Tertiary stream beds, or the 'channels,' as they are sometimes called, proved rich but difficult to mine. New methods were devised; by hydraulic mining the gravel banks were washed down by the aid of powerful streams of water, and by drift mining the bottoms of the old streams beds were followed by tunnels underneath the heavy volcanic covering.”

Treasure Hunting
Gold Concentrators
Metal Detectors

“Millions of dollars in gold were recovered each year from these Tertiary channels but the heyday of this industry fell in the 1870s. Since then, owing to the prohibition of hydraulic mining and the gradual exhaustion of the richer channels suitable for drift mining, the industry has slowly decayed until in the year 1908, the total production of the drift, hydraulic, and surface mines of the range fell below $1,000,000 for the first time since 1848.”

Gold Still Contained in Tertiary Channels

“Indeed, this figure also includes the value of the gold washed from Quaternary gravels along the rivers. (Note: Quaternary gravels are best described as those resulting from the so-called “Ice Ages” where a great deal of glaciation took place. Although Quaternary gravels are not always auriferous many are in California, and in other states and regions where glaciation occurred. J.R.) Gold is still contained in the Tertiary channels; miles of them are still unworked; but the problems are how to extract it without damage to other property from the debris and how to reduce the cost of drift mining so as to permit the exploitation of the less remunerative deep gravels.”

In my next post on this topic I’ll discuss some key points concerning these prehistoric rivers of gold. Until then be safe and keep smiling!

If you liked this post, you may want to read: “Prehistoric Rivers of Gold (Part 2)”

© J.R. 2010

Questions? E-mail me at jr872vt90@yahoo.com

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