Preliminary report on part of the Oat Hill quicksilver mine, Mayacmas district, Napa County, California

Oat Hill quicksilver mine, located in the Mayacmas district of northern California, and credited with having produced more than 160,000 flasks of quicksilver, was sampled cooperatively by the Buray of Mines and Geological Survey during 1944. 28 diamond drill holes totaling 8,120 feet were drilled by the Bureau of Mines in four of the six principal veins to sample virgin low-grade reserves and stope fill, and reserves in the other two veins were estimated from existing underground workings and by inferences from drill holes in nearby veins.

The writer estimates a total of 10,220 flasks of quicksilver in indicated and inferred reserves totaling 320,000 tons.

Indicated reserves minable under 1943 conditions are estimated at 1,960 flasks of quicksilver in 75,000 tons averaging 3.0 lbs Hg per ton.

Inferred reserves minable under 1943 conditions are estimated at 4,640 flasks of quicksilver in 109,920 tons averaging about 3.2 lbs Hg per ton. Inferred reserves believed minable only under economic conditions much more favorable than even those of 1943 are estimated at 2,620 flasks of quicksilver in 135,080 tons averaging a little less than 1.5 lbs Hg per ton.

About two-thirds of the indicated reserves are accessible in underground workings. All other reserves are estimated approximately without access underground. Several areas not sampled may possibly contain reserves.