Diamond - Bullion - Alaska Mine group (Consolidated Bullion Mine; Diamond claim; Bullion claim; Alaska claim; Union Jack claim; Galena claim; Ione claim; Big Diamond vein; Galena-Bullion vein; Alaska vein), La Barr Meadows, Grass Valley Mining District, Nevada County, California, USAi

Regional Level Types
Diamond - Bullion - Alaska Mine group (Consolidated Bullion Mine; Diamond claim; Bullion claim; Alaska claim; Union Jack claim; Galena claim; Ione claim; Big Diamond vein; Galena-Bullion vein; Alaska vein)	- not defined -
La Barr Meadows	- not defined -
Grass Valley Mining District	Mining District
Nevada County	County
California	State
USA	Country

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A group of former lode Au-Ag mines located in sec. 1, T15N, R8E, MDM, on the SW flank of Osborn Hill, about 2 miles SE of the town of Grass Valley. Discovered in 1865. MRDS database stated accuracy for this location is 100 meters. The location point selected for latitude and longitude by the USGS represents the approximate boundary line between the Bullion and Alaska claims shown on Lindgren's 1896 1:14,400-scale Grass Valley Special Map (contained in Lindgren's 1896 Nevada City Special Folio) and transcribed onto the USGS Grass Valley 7.5 minute quadrangle.

The Diamond, Bullion, and Alaska mines, located on the west flank of Osborn Hill approximately 1.5 miles south of the famous Empire Mine, were consolidated and operated by Consolidated Bullion, Inc.

These claims cover three principal veins on the western flank of Osborn Hill, the Big Diamond, Galena- Bullion, and Alaska veins. The claims were operated as individual mines until later consolidation brought them under single ownership. The Bullion Mine was first worked in the 1860s. It later acquired the Diamond Mine, which is located about 2500 feet northwest of the Bullion shaft. The mine was closed for much of the late 1800s but was reopened in the early 1900s, closing again in 1906. The Alaska Mine adjoins the Bullion mine to the south and is on the southern extension of the Bullion vein. It was worked periodically until 1916.

In 1933, the Consolidated Bullion, Inc., consolidated and reopened these mines. While little information is available it is assumed the mines operated until 1942 when enactment of the Federal War Production Board's Limitation Order L-208 closed the few remaining mines that were operating in the Grass Valley District.

The Bullion Mine was developed to a depth of 1500 feet by means of an inclined shaft, which, starting in the hanging wall, encountered the vein at a depth of 300 feet then followed the vein. Levels were run as follows: 300- and 400-foot levels both driven 150 feet north and south of the shaft; 600-foot level driven 150 feet north; 700-foot level driven 300 feet north and 300 feet south; 900-foot level driven 250 feet south; 1000-foot level driven 500 feet north; 1100-foot level driven 700 feet north, and a 1500-foot level driven 750 feet north and south of the shaft. A crosscut was also driven from a point 200 feet south on the 900-foot level a distance of 150 feet west into the footwall of the vein (MacBoyle, 1919).

In the Diamond Mine, the vein was developed by a vertical shaft and an inclined shaft 290 feet deep. A 1000-foot tunnel was also driven on the vein. The deepest workings below the outcrop are about 125 feet deep, but 1200 feet of exploratory drifts have been driven on the vein, which varies in width from 1.5 to 3 feet wide (MacBoyle, 1919).

Mineralization is a vein deposit (Mineral occurrence model information: Model code: 273; USGS model code: 36a; Deposit model name: Low-sulfide Au-quartz vein; Mark3 model number: 27), hosted in Early Cretaceous granodiorite and Mesozoic-Paleozoic diabase. The ore body is tabular. Controls for ore emplacement involved mineralization that occurs as erratic ore shoots within mesothermal gold-bearing quartz deposited within fracture zones. Local alteration included ankeritic and sericitic replacement of wall rocks adjacent to veins. Local rocks include Mesozoic granitic rocks, unit 3 (Sierra Nevada, Death Valley area, Northern Mojave Desert and Transverse Ranges).

The Diamond, Bullion, and Alaska claims covered three principal veins on the western flank of Osborn Hill, the Big Diamond, Galena- Bullion, and Alaska veins. The veins strike northwest and dip 45 degrees easterly. Since they are roughly in line with one another, they were considered segments of a continuous vein system. Estimates of production from theses veins range as high as $3,500,000 (period values).

More mining was done on the Galena-Bullion vein than on any others of this group. The vein has an easterly dip of about 33 degrees, varies in width from 1 to 5 feet and carries free gold, pyrite, and a considerable amount of galena. The sulfides average 4% and are valued at $75 (period values) per ton. Ore values averaged $20 (period values) per ton of 815 fine gold.

The Big Diamond vein strikes N20W and like the Galena-Bullion vein, of which it is the northerly extension, dips 45E. The vein is 2 feet wide and produced an average of $20 (period values) per ton. The Little Diamond is an east-west vein dipping 48S that crosses the Big Diamond vein.

The Alaska vein is the southern extension of the Galena-Bullion vein and is similar to it in all respects.

Regional geologic structures include the Wolf Creek Fault Zone, Gillis Hill Fault and Melones Fault Zone.

Ore materials include free milling fine and coarse gold in quartz (815 fine) plus auriferous pyrite and galena. Gangue materials include quartz, calcite, chalcopyrite and sphalerite.

Total production has been reported to be approximately $3,500,000 (period values).

Mineral List

Mineral list contains entries from the region specified including sub-localities

10 valid minerals.