California USA, 100 miles north of Sacramento and 90 miles west of Reno Nevada. The mine has good access by way of surface roads.

The Union Keystone mine is an underground placer mine located in the mother lode region near La Porte California. The mine consists of 1120 acres of contiguous unpatented placer claims in the Gibsonville mining district. The average elevation is 5500 feet. The claims overlie more than 2 miles of unmined tertiary gravel channels known as the Bellevue Channel, Bellevue Back Channel, or Blue Lead Channel. The historic Union Drift Tunnel, the Melones Fault, and a World War 1 chrome tunnel are located on the property. Very large 90 to 100 ounce nuggets and consistent gold made this one of the richest paying mines in the region in the late 1800s.

Gold-bearing Tertiary gravels of the mother lode region of northern California were deposited on metamorphic bedrock of meta-sediments and meta-igneous rocks. These comprise phyllite, schist, slate and greenstone intruded locally by peridotite, hornblendite, granodiorite and other intrusive rocks.

Gold mineralization occurred during the Jurassic Period, probably during the final stages of the intrusion of the Sierra Nevada batholith. Gold- quartz-carbonate mineralization in the California Mother Lode occurred as early as 152 m.y. ago and continued until at least 122 m.y. The Malones fault system was a major plumbing conduit and hydrothermal system that concentrated quartz and gold, providing rich sources for erosion of gold into the gravel channels. Gold occurs in quartz veins and mineralized country rock where veins are as much as 50 feet wide and several thousand feet long. Gold occurs in the free state and the area is famous for the large size of nuggets in the veins.

The tertiary channels run roughly parallel east-west while the northerly trending Malones Fault and it's splays, the main structures along which many of the gold rich deposits of the Mother Lode are found, cut across the channels. Gravels downstream of the faults created rich placer zones on the Union claims that produced nuggets of up to 100 ounces and heavy pay as proved by the Union and adjoining mines. Contact Seller for a full report.

In 1856 the Union mine was organized with 10 share holders. By 1864 the mine was in production with good prospects. In 1867 it was reported that the Union Mine had one of the finest tunnels and best conducted claims in the Sierra. The Union mine continued to be one of the best paying mines in the region producing large nuggets and consistent gold. Operations at the Union were terminated in 1898 when the surface buildings were destroyed by fire and water drainage into the workings became unmanageable. In 1936 and 1937, an attempt was made by T.C. Brown of San Francisco to reopen the drift tunnel.