Monday, March 26, 2012

The Geology and Dynamics of Beach Gold Placers (Part 2)

 (Bering Sea storm surge at Nome.)

Gold-Bearing Terrace Gravels

In addition to the four gold deposition methods listed in my previous post on this topic, geologists believe that many beach gold placers were formed when elevated sections of coastline overlain with gold-bearing terrace gravels were eroded or broken down over time. Eventually, these auriferous benches, bluffs, or even cliffs were reduced to the level (or nearly so) of existing beaches and the gold they once contained deposited on the beaches themselves (and just offshore).

Gold Concentrates
Gold Pans

Most of the old timers who worked the gold-rich beaches of Nome, Alaska actually believed that the placer gold there came from the sea. Although not true in the strictest sense, the old timers were right in a way because Bering Sea storms with strong winds, very high tides, and large waves both "stripped" gold from Nome's beaches and then re-deposited it...sometimes in very rich pockets or paystreaks.

An Amazing Sight

Although not nearly as rich in gold as Nome, a number of other beach locations farther south also contain decent amounts of the yellow metal. These include Gold Beach in Oregon and stretches of Pacific Coast beaches to South Francisco and even south of the Bay Area.

Placer Gold Locations

I can personally verify the existence of placer gold along some of San Francisco's beaches, including the area near the Cliff House and the long defunct amusement center, Playland at the Beach (shows you how old I am doesn't it?!). At that time in the early 1980s huge Pacific storm surges had ravaged the beaches and stripped most of the overburden off them...the beach sands were completely covered with cobbled rock and heavy, coarse black sands, an amazing sight indeed.

Fossilized Sea Shells and Gold

Unlike the beach gold placers at Nome and elsewhere, however, the majority of Northern California's beach gold was derived from ancient sedimentary gravels of the Upper Cretaceous period. Geologists know this for a fact because of the fossilized sea shells found along with the beach gold.

 (San Francisco's Cliff House in the 1880s. I found beach placer gold here on more than one occasion.)

These gold-bearing gravels on Northern California beaches are tougher to to pull color from than those at Nome or other locations, however. This is simply because larger amounts of sterile overburden sands cover the paystreaks...that is, unless you "mine" these beaches after large Pacific storms strip this overburden off as I once did.

At any rate, the gold is there...both on selected Northern California beaches and just offshore as at Nome. Stay tuned...there's more to come.

If you liked this post, you may want to read: "Learn to Keep Your Mouth Shut"

(c)  Jim Rocha (J.R.)  2012

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


2 comments:

  1. Have you found any lately at the cliffhouse area?

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  2. Mary, I haven't worked those beaches since the early-to-mid 1980s. The only good time to try them is during the late fall, winter, and early spring months when the big Pacific storm surges strip the overburden off. Best of luck, J.R.

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