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Finding Pocket Gold


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Great Topic! Thanks for bringing it up :biggrin:

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  • 3 months later...

I am apparently a little more than confused. When you say "pocket gold" are you including pocket mining? 

In1999 the Tuolumne County Historical Society republished a 1901 edition of the illustrated  historical brochure of "Tuolumne County California" which covered the patent mines and mineral belts through the county.  The brochure has a section on "pocket mining" in the vicinity of Bald Mountain and the Big Bonanza pocket mine. It defines "pockets to mean an agglomeration of gold held by quartz and often solid masses of metal without any quartz. From the text  " Pocket mining is reduced today (1901) to an absolute science... Understanding this class of mining watch for every sign known to the practical miner....Shoots almost invariably come to the surface and continue down on the line of crossing till a pocket is found. There are other things needed besides crossings- the right kind of metallic slate, that cuts the veins obliquely; then there are gold seams, which are small quartz feeders, that the strike into the vein at certain angles. Often they of themselves are rich in gold...

Here is what I gather: a main fissure vein strike is some where around 30 degrees west of north with metallic slates on both the hanging and foot walls. At varying depths where the shoots (quartz stringers?) cross the main fissure vein at an oblique angle gold seams (pockets) can form. Am I correct?

Is this related in anyway to the Gold Hill pocket deposits?

 

 

 

 

 

 

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According to a couple of diagrams of the Bald Mtn pocket deposits. A diorite dyke fissure containing three quartz veins has a  strike of N 30 W cutting across a slate formation with a strike of N 30 E. The dip of the dyke is 30 degrees west with one quartz vein at the hanging wall, one at the foot wall and one middle vein. The multiple gold seams are indicated where narrower quartz feeders that strike the main diorite dyke veins at an angle. Apparently, it was not uncommon for one the dyke veins to be barren at the feeder seams.

The top view diagram indicate four crossings lines running parallel within & along the strike of the diorite dyke. Where these crossings intersect the gold seams of the quartz feeders gold pockets form in one or more of the three dyke quartz veins. 

I am not clear on what the crossings lines are indicating. Where the dyke veins cross the feeder seams? There are several references to shoots which I assume is referring to the combination of diorite dyke vein structure.

 

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Great thread.

Yesterday and today I and about 40 other people, of all flavors, attended a metal detecting outing for hillside pocket/placer gold on a side hill side above the Klamath River just downstream of Happy Camp, Ca. 

The outing was a combined effort of Whites Electronics (metal detectors), Armadillo Mining Supply, Tom and Josh Bohmker, and The New49ers, on whose claim we were detecting. Although rainy, it was good fun and great lessons in metal detecting for gold.

All who put this outing on are very good at what they do. As the topic of this thread is pocket gold hunting, I'd like to give a big shout out to Tom Bohmker and his son Josh as truly knowledgeable people on pocket gold and finding it. It was a pleasure to meet and learn from them. Tom does have quite a few good publications on the subject.

All I found was a lot of old square nails.

Mike

 

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  • 2 weeks later...

"Fists Full of Gold" by Chris Ralph has a good section on "seam deposits" that appears to be related to "pocket deposits" and quartz feeders.

Diorite is a member of the diorite/gabbro family which are a meta-volcanic. Greenstone meta-volcanics are a source for chloride.  I found a old reference to the "crossings" as being partially open and as running within and parallel with the diorite dyke's strike. These crossings are also composed of diorite. The "crossings" refer to the crossing with groups of quartz feeders within the diorite dyke to form pocket gold. The requirement for a metallic slate may be referencing to the requirement iron sulfides.

According to Chris gold may be deposited in three hydrothermal mineral pulses. After the main fissure is full the third pulse fills the seams (feeders?) without closing off the seams completely. This may be how the quartz feeders continue to fill the "pockets" within the diorite dykes.  

I have been working a claim know for pocket gold with the following sequence from west to east: black slates with iron sulfides and narrow quartz stringer, greenstone of either dibase or grabbro with narrow quartz stringers, serpentine, the main fissure quartz lode vein then a igneous feldspar porphyry. Old surface diggings follow the surface stringers to the crossing with the main quartz vein with deeper excavations at these intersections. What gold I have found is rough but not as rough as you would expect from a pocket deposit. 

Merton found a reference to "potash feldspar" in the study of the Shoo Fly Complex.

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  • 5 months later...

"Orogenic Gold Deposits" by geology films 2014 (on YouTube) covers mountain building, high pressure fluids, faults, earthquakes, pulses and gold deposition.

One item of interest was regarding the precipitation of gold after crossing a wall rock containing "carbon". The carbon (C) combined with hydrogen (H) to form methane (CH4). Methane (gas) interacted with the quartz solution causing the gold to drop out of solution is the green schist zone.

The Tuolumne County pocket mines were associated with "diorite dikes" and secondary quartz crossings passed through a "black mineralized slate" wall rock. These crossings were at an acute angle to the the primary NW vein (Sonora Fault). 

The Siskiyou pocket mines are apparently associated with "Andesite" dikes which is the extrusive equalivalent of the intrusive "Diorite".

There are seven short informative videos covering the Orogenic deposits around the Pacific Rim, check them out. 

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  • 5 months later...

Good information Steve.

A slightly different interpretation of pocket gold deposits in the southeastern Klamaths would go like this:  

Hydrothermal waters (hot water) moving upward through the greenstone of the Copely formation tends to lay down some quartz and perhaps other minerals like pyrite and calcite, but does not lay down much gold.  When these waters reach the black shale of the Bragden formation, the carbon causes the gold in solution to precipitate within the pyrite (5% gold by weight might by typical).  This, however, is not yet mineable.

The next phase occurs with oxygen-rich rain water causes the pyrite to oxidize.  In the presence of manganese oxide, the iron in the pyrite completely oxidizes to ferric iron yielding an acid solution rich in sulfate and ferric iron.  Because these black shales were layed down in sea water, there is abundant salt present.  This sodium chloride added to the sulfate and ferric iron in a acid solution forms a complex which dissolves the gold.

The final phase occurs when this descending gold-carrying fluid either: 1) encounters enough calcite to neutralize the acid precipitating the well-known porous gold of pocket deposits or 2) encounters the water table where the low oxygen content of the water table reduces the ferric iron to ferrous iron again precipitating porous gold.

There are two other larger belts of greenstone overlain by black shales in the Klamaths.  Both lie well to the west of the Copely-Bragden belt.  You could spot them easily on a geologic map because they lie  immediately to the west of serpentine belts.  Each should contain pocket gold deposits of this type.

There are other pocket gold deposit models, but I am still learning about them.  I would, in particular, like to hear more about the occurrence of pocket gold deposits adjacent to serpentine/ultra magic rocks.  I'm not necessarily looking for scientific observations.  Miners often have practical knowledge of mineral deposits that exceeds that of those of us who are economic geologists.

Oldmancoyote

 

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  • 1 month later...

Here is the next piece in my posts about the geology of and prospecting for pocket gold in the Klamath Mountains of California.  If this sort of thing interest you, let me know.

You might use this geological info to locate pocket deposits without using the standard method of following a pocket's trace (the debris trail of small gold and associated minerals)leading uphill to the pocket itself.*

Trace the contact between black shale in contact with greenstone looking for quartz veins.  Here is how to recognize a prospect of this sort.

Look at this photo.  Outcrop.thumb.JPG.743ae60a731de6aaa15a8e1ef40f5bd0.JPG It shows Bragden black shale on the left with Copley Greenstone out of view to the left, and off to the right is more black shale.  I took the small outcrop in the center of the photo be be black shale, as well, until I put my hand on it.  It's a wide quartz vein extending beneath the soil to the left and right.

Here is a photo of a piece of this vein.photo.thumb.JPG.af765699dfb6881c0b204d301cdefe77.JPG  The black is manganese oxide (see my first post).  Many of the holes once contained pyrite as shown by the rust-colored stain and perhaps calcite  (again see my first post).  It is highly likely that the pyrite once contained gold, and that gold is located somewhere downhill and close-by.  The coin is a US quarter.

The quartz of the oxidized zone within the Bragden formation in the well-known pocket deposit at the Mad Mule Mine has been described this way:  "The quartz is honeycombed with cavities, many of witch are partially filled with sooty manganese oxide."(Pocket Deposits of the Klamath Mountains California, Ferguson, 1915)

I'm currently looking for that gold using two possible models:  hosted within streaks and pockets of calcite; and plating the bottom of a nearby stream or dry water course.  

Calcite-hosted gold in pocket deposits can "...consist of calcite covered with fine-sized gold and manganese oxides often in cracks and fissures in the calcite." (Canadian Gold Prospector: http://gpex.ca/smf/index.php?topic=11152.20).  I carry a small sniffer bottle containing weak hydrochloric acid to test whitish streaks.  If they fizz, it is calcite.

Downhill from this site is a small stream.  I'll probably have to dig to the bottom of the center of the stream looking for the gold.  Here is a photo878286184_ScreenShot2018-08-31at10_53_41AM.png.5344f59f7a486039553ea213e2adbf26.png   posted by Creekboy here:  https://www.detectorprospector.com/forums/topic/7359-odd-gold/?tab=comments#comment-74991.  of black sand encrusted by gold. It's probably from such a deposit.

Alternatively 100 feet away I have found stream gravels exposed near the edge of a small plateau.  This is probably a paleo-stream bed (geologically old and now dry).  At one time the gold-bearing fluids may have made their way here and formed a pocket in or below the bed.  I may dig some of this looking for the gold.

 

The recent fire here has made the area inaccessible.  So, I sit here twiddling my thumbs.  If folks are interested it this sort of thing, I'll report later on any progress.  I plan to use my Gold Racer to help in the search.

* Jack London's short story The All Gold Canyon http://livros01.livrosgratis.com.br/ln000422.pdf describes the standard method well.  Useful modifications and extension of this technique have been published by many people including [trinityAU https://www.detectorprospector.com/forums/topic/7359-odd-gold/?tab=comments#comment-74991, and by EMF http://gpex.ca/smf/index.php?topic=12499.0, but the basic technique is the same.  Tom Bohmker describes a similar metal detecting approach here Elusive Pocket Gold of Southwest Oregon.

 

Oldmancoyote

 

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