Tuesday, January 26, 2010

Prehistoric Rivers of Gold (Part 2)

(Waldemar Lindgren.)

A Founder of Modern Geology

German-born Waldemar Lindgren is generally considered as one of the founders of modern geology, particularly in the areas of minerals, naturally occurring metals, and what is now known as “economic” geology. Before moving to the United States in the mid-1880s Lindgren studied geology at the Freiberg Mining Academy.

MagazineDiscountCenter

Although Lindgren wrote numerous books, journal articles, and papers he is perhaps best known for his break-through scientific textbook titled “Mineral Deposits” and the treatise that is the central topic of this series of posts, “Tertiary Gravels of the Sierra Nevada of California.” Also known as Professional Paper 73, “Tertiary Gravels of the Sierra Nevada of California” was written under the auspices of the United States Geological Survey (USGS) and published in 1911.

The Ultimate Source

This classic work has never been surpassed as the ultimate source of information on the geological formation, characteristics, and economic implications of California’s prehistoric rivers of gold. To many gold miner’s of the day Professional Paper 73 was the “bible” for learning about what some still call the Great Blue Lead.

I myself have owned a hard-bound copy of Lindgren’s “Tertiary Gravels of the Sierra Nevada of California” for nearly 30 years now and I still refer to it on occasion. One thing I really like about Professional Paper 73 is the fact that it shows that Lindgren was an excellent writer as well as a scientist and researcher. In my opinion, all of his written works stand head and shoulders above most geological papers and bulletins which tend to be very “dry,” boring reading at best.

Here are some edited excerpts from Lindgren’s classic work on the gravels of these prehistoric rivers of gold (I’ve used bold type to emphasize certain passages):

“One of the Treasure Houses of the World”

This report presents an account of the Tertiary formations of the Sierra Nevada range and deals especially with the origin and distribution of the gold-bearing gravels, which made these mountains one of the treasure houses of the world. Toward the close of the Mesozoic era the sediments from ancient seas were compressed in heavy folds, and the intrusion of granitic magmas forced them upward to lofty summits.

After this intrusion, the fissures and joints of granitic rocks and altered sediments became filled with veins and seams of gold-bearing quartz. A long period of erosion in the early Cretaceous planed down the newborn mountains and the concentration of the gold from the veins began in countless streams.

“The Gold Became Concentrated”

Pauses in the erosion, when the topography had been reduced to gentle outlines, permitted deep rock decay and promoted the liberation of gold from its matrix. Renewed uplift quickened erosion and facilitated the further concentration of gold. Long-quiescent volcanic forces asserted themselves toward the end of Tertiary time and rhyolite flows filled the valleys, covered the auriferous gravels and outlined new stream courses.

Gold Concentrates
Gold Pans
Gold Concentrators

Volcanic eruptions in enormous volume effectually buried a large number of these ancient streams, filling their valleys to the rims. At the close of the Tertiary period a steaming, desolate expanse of volcanic mud covered almost the whole of the northern Sierra. But wherever the canyon-cutting streams destroyed the old river channels, the gold in those channels became concentrated and thousands of disintegrated quartz veins added to the previous concentrates.

I’ll have more from Lindgren’s classic treatise in subsequent posts. Good luck out there!

If you liked this post, you may want to read: “Prehistoric Rivers of Gold (Part 1)”

http://goldbedrockgold.blogspot.com/2010/01/prehistoric-rivers-of-gold-part-1.html

© J.R. 2010

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

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