Prehistoric Rivers of Gold (Part 5)

(Tertiary Channel placer gold from California's historic Ruby Mine. This gold was recovered by tunnelling or "drift mining.")

A Vast Storehouse of Information

As I stated at the close of my previous post on this subject, I wanted to discuss Waldemar Lindgren’s take on the general amounts and relative size(s) of placer gold contained in California’s prehistoric rivers of gold. In this post I'll begin that process and eventually complete it with a final post on the subject.

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There is a vast storehouse of information on this subject in Lindgren’s landmark work, “The Tertiary Gravels of the Sierra Nevada of California.” I highly recommend it to one and all, no matter where you are located or where you do your placer mining.

Gold Distribution

A major point that Lindgren makes in “The Tertiary Gravels of the Sierra Nevada of California” is that assuming that the best gold values will be found on bedrock in these prehistoric rivers may prove a disappointment. In other words, the gold deposition characteristics of a modern running stream are not the same as those found in Tertiary Channels.

This is due to a number of reasons, with the primary causal factor being the fact that these ancient rivers were abruptly “capped” by lava flows or other volcanic/seismic activity, much of this occurring on a vast and intense scale. Because of this placer gold values tended to be “entrained” or frozen in place when these cataclysmic events occurred.

Paystreaks with "Eccentricities"

Although many rich pockets of placer gold were mined on or just above bedrock in Tertiary Channels in the old days, just as many rich paystreaks were found in various layers of Tertiary gravels where, once again, they’d been locked in place millennia ago.

According to Lindgren these Tertiary paystreaks were of “irregular width” and were not always found at the deepest points of a given Tertiary Channel. Lindgren also stated that these paystreaks exhibited many “eccentricities” when it came to their deposition, their richness, and their location within the gravels themselves.

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Over and above all other considerations, Lindgren believed that Tertiary paystreaks were highly dependent on the depositional characteristics of the ancient rivers themselves and, more importantly, the geological processes that froze them in place and eventually buried them.

That’s it for this round. I’ll continue with more of Lindgren’s theories concerning Tertiary gravels in a future post.

Until then, good luck to one and all.

If you liked this post, you may want to read: “A Basic Mining Plan of Attack”

© J.R. 2010

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