Saturday, January 23, 2010

Prehistoric Rivers of Gold (Part 1)


 (Idealized portrait of a '49er.)

A Misnomer?

I must admit that the title of this post is somewhat of a misnomer. Why do I say this? Simply because nearly all the gold that has ever been mined, recovered, or awaiting discovery dates back millenia....that is, well before the advent of recorded history.

How far back does the formation of gold go? Well, as an example, here in Northern New Mexico (my neck of the woods) the gold found in the historic "Old Placers" District dates back some 20-22 million years. I'd call that prehistoric, wouldn't you?

Rivers of Gold

However when I use the term prehistoric rivers of gold I am, in fact, speaking about the ancient Tertiary geologic period. Tertiary Channels can be found in a number of locations throughout the world, the most famous of these being located in California's Motherlode Region. The gravels of these ancient channels were once part of gold-bearing prehistoric rivers that were eventually disrupted, shaken from their courses, and eventually buried under lava flows or by tectonic activity on a grand scale.

Over time, some of these prehistoric rivers were buried under overburden reaching hundreds of feet or were uplifted and dispersed as terraces and hillsides. Here they remained in place, resting for millions of years until their accidental discovery by some of the more enterprising miners of the California Gold Rush.

 (Tertiary Channels in California's Motherlode Region.)

It didn't take long for the '49ers (and those who followed in their footsteps) to realize the immense wealth in placer gold hidden within the gravels of these ancient rivers. However, the work of mining that wealth proved to be a formidable task since these prehistoric riverbeds were deeply buried or strung out along steep hillsides.

Two Distinct Mining Methods

Not to be dissuaded, California miners (and mining companies) devised two distinct methods for getting at all that ancient gold. The first was by tunneling (similar to what is commonly seen in hard-rock mining) and the second was hydraulicking.

Gold Prospecting Books
Gold Pans
Gold Concentrators

The first method was laborious, time consuming, and often very dangerous since the prehistoric gravels were often loosely consolidated and prone to collapse. The second method, using immense "jets" of high-pressure water shot from cast-iron nozzles to wash down entire hillsides containing Tertiary Channels, was not only imminently successful but also horribly damaging to the environment and waterways downstream. So damaging, in fact, that California lawmakers had banned its use by the 1870s.

One Man and One Man Alone

This bit of historical background only scratches the surface in terms of understanding what these prehistoric rivers of gold were, how they were formed, and what sort of gold potential they hold for enterprising miners, even those operating on a small scale. One man, and one man alone would do more to advance our knowledge of Tertiary Channels than anyone else before or since.

Who was that man? A geologist named Waldemar Lindgren.

If you liked this post, you may want to read: "All About Gold Mineralization (Part 3)"

(c)  Jim Rocha (J.R.) 2010

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

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