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Finding Pocket Gold


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On 7/24/2018 at 1:45 PM, oldmancoyote1 said:

like to hear more about the occurrence of pocket gold deposits adjacent to serpentine/ultra magic rocks

The article “ Pocket Mining” originally published in the Mining and Scientific Press in July/August 1893 under the pseudonym Alex Quartz. The article covers the area from Fresno, California north to Douglas County, Oregon. The chemistry is similar to the description in your first post. This is the only information found in the article regarding crossings at serpentine contacts:

” They (pockets ?) occur on small stringers of quartz not over a half inch in width and often not more than six or eight feet in length, and generally cut through soft, yellow porphyry. The best free pockets are always found in the porphyry or on or near the contact with the porphyry and serpentine. The most of this class of pockets when laid bare are very deceiving to the eye, for the reason that little or no gold is visible, it being coated and concealed by iron oxide, manganese, etc.” 

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More from the same 1893 article “ Pocket Mining”:

” The pocket-belts, or streaks of formation, which are prolific in pockets, are mostly porphyry or of a porphyritic or quartz-porphyry nature running parallel with the slate, granite, lime, etc.”

” …at the point where the pocket occurs, is generally largely composed of lime (calcite), iron, copper or manganese.”

“ …a pocket without lime (calcite), iron, copper, lead and sulfur has not yet been found. They are always present in free or decomposed pockets. They may not always occur in the same form, but they are generally in a chloride or metallic state. These five minerals are the key to the pocket and what cause the pocket to form.”  With gold as the sixth.

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I believe Goldbrick linked the original article “ 1893 Pocket Hunting Treatise” on the DP forum back in 2014 which he found on a Canadian forum.

From experience in the Mother Lode region “surface pockets” are commonly localized shallow deposits at narrow points where smaller east to west trending quartz stringers cross larger north to south trending quartz veins in the proximity of a ferrous rich rock formation. The N/S veins often occur along faults as a result of plate subduction. The E/W stringer veins often occur at along fractures as a result of subsequent earthquakes. The crossings occurred miles below ground under both high temperature and pressure. Millions of years of erosion has exposed the crossings on the surface. The hillside quartz float is indicative of the scale of uplift and erosion. Only a portion of the surface quartz veins may still exist both horizontally and vertically. Rock type contacts with a mafic rock* (silica poor igneous rock with a relative to a high magnesium, iron and calcium content) fit the minerals described in the article including porphyritic. 

* Ophiolite rock sequence: basalt, diabase, gabbro, serpentinite, peridotite; mafic to ultramafic; oceanic crust, igneous, volcanic, intrusive & extrusive. Greenstone=chloritic basalt; feldspar porphyry; Smartville Complex.

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Mining and Scientific Press, May 18, 1893; page 289, California Manganese.

“Manganese is a "pockety" sort of substance to mine, the deposits being irregular and not to be counted on as to extent. It is produced in this State in a small way, mainly for use in the manufacture of chlorine for the chlorination of auriferous sulphurets…”

Manganite: hydrated manganese oxide (MnO(OH)), opaque metallic gray or black, occurs in hydrothermal deposits with calcite; alters to pyrolusite.

Gold is often locked within the matrix of iron sulfides (not chemically bonded). Manganese in proximity to chloritic basalt or schists may actual play a role in concentrating gold in pockets. Check the hillside quartz float for iron oxide rust strains, calcite and dark traces of manganite. 

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Found the original Mining and Scientific Press July-Dec 1893 article on “Pocket Mining”  published July 8, 1893 in the California Historical archives. There was the original article then several following articles published under “ Pocket Mines/ Free or Decomposed Pockets”  on the following pages & dates.

July 8, 1893, page 22, “Pocket Mining’ the original article;

July 15, 1893, page 37, “Pocket Mining Number II”

July 22, 1893, page 53, “Pocket Mining Number III”

July 29, 2893, page 68, “ Pocket Mining Number IV”

August 5, 1893, page 84, “Pocket Mining Number V”


Google: Mining and Scientific Press July-Dec 1893

or

https://archive.org/embed/miningscien67unse

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This link may be a clue to the connection between northern and southern gold pocket regions. It appears the Penon Blanco Formation is a basalt island arc sandwiched within the Sierra Foothill Jurassic terrane slates extending from the area of Coulterville, CA north beyond the confluence of the Klamath & Salmon rivers at Sawyers Bar. In the Central Sierras the Foothill and Calaveras terranes are separated by the Melones fault zone. To the east of the Melones fault is located the Sonora fault. The south/north Sonora fault is the local pocket region extending from downtown Sonora northwest towards the Tuttletown area.

https://onlinelibrary.wiley.com/share/YXQ2RVY5BVTZ893XVT8Y?target=10.1111/j.1365-3121.2008.00834.x


Penon Blanco basalt along the Penon Blanco Ridge.

image.thumb.jpeg.c372d66c8c96c6933090b4fafafb37ce.jpeg
Photo, by others, taken on northwest side of the Highway 49 bridge over the Tuolumne river. Foothill Slates/ Penon Blanco basalt contacts run north/south. The east side contact sediment slope ranges from 40 to over 60 degrees.

 

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