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NEVADA

The Lost Ross Mine

GEOLOGY OF THE AREA

The Jarbidge Mountains of Nevada are located in the northernmost part of Elko County, just below the Oregon border. The heart of the range contains a number of peaks exceeding 10,000 feet including Jarbidge Peak, Marys River Peak, the Matterhorn, Cougar Peak, and Gods Pocket Peak. The range is vast and extremely rugged, comprising nearly 200 square miles of broken peaks and valleys.

The Jarbidge Mountains are a product of Tertiary volcanism. The bulk of the range consists of rhyolitic lava flows and associated shallow intrusives of late-Tertiary age. Just north of the town of Jarbidge a vast terrain of welded and nonwelded silicic ash-flow tuff is exposed. This blanket of ash-flow tuff extends northward into Oregon. West of Jarbidge, a large exposure of ancient Precambrian to lower Paleozoic sedimentary rocks occurs. These metasediments are intruded by a younger, Laramide-age granitic pluton. Similar exposures of ancient sedimentary rock occur in the southern portion of the range near Charleston. These metasedimentary rocks are part of two large, triangular fault blocks that peek

out from beneath the younger volcanic cover. These wedges of ancient sedimentary rock crop out north and east of Charleston. They are composed of quartzite, limestone, chert, shale, phyllite, and minor conglomerate.

The Jarbidge Mountains are scored by a multitude of small faults, most of which trend roughly north-south. The younger ash-flow tuffs north of Jarbidge are relatively free of faults compared to the older rhyolites to the south. Faulting is quite pervasive in the older rhyolite flows that make up the bulk of the Jarbidge Mountains.

Mineralization in the Jarbidge Mountains consists mostly of gold and silver-bearing fissure veins hosted within the local volcanic rocks. This is the case at Jarbidge and at Rowland. In the Charleston District, the host rock is much older. There, the gold-bearing veins are emplaced in Paleozoic sedimentary rocks. The veins occur along the periphery of a small, late-Cretaceous granitic intrusion.

PROSPECTING POTENTIAL

The Jarbidge Mountains have been heavily prospected, especially since the great Bourne discovery of 1908, but the range is vast, remote, and extremely rugged. It is entirely conceivable that a small gold-bearing ledge still lies hidden somewhere in the Jarbidge Mountains.

The rich Jarbidge District has produced more than $10 million worth of gold and silver during its lifetime. The Jarbidge veins almost invariably occur in faults and fissures within the oldest Tertiary volcanic rocks. The early miners quickly found that the richest deposits were always in veins that trend northeast-southwest.

Prospectors may want to concentrate on the many fault zones in the heart of the range, east and southeast of Jarbidge. The Tertiary rhyolites in this area are cut by a number of small faults, some of which trend northeast-southwest. Certainly, a metal detector would be useful in the search for gold-bearing float in the volcanic rubble that drapes the mountain slopes and canyon floors of the range.