Cal Poly Geology Club Death Valley Field Trip – 2004

Talc DepositsTalc production was first reported from Death Valley in 1910, although the presence oflarge talc bodies had been noted as early as the late 1800’s. From 1910 until 1978, DeathValley was a significant producer, accounting for 10-20% of the annual U.S. total.Pressure from the Park Service closed the last mines in 1980, although substantial talcreserves remain. Talc mining outside the National Park has continued to the present day,although only one mine remains in operation.Talc deposits occur in the Crystal Springs Formation of Late Proterozoic (Precambrian)age at the south end of Death Valley (Fig. 1). The belt of deposits, encompassing 50mines and prospects stretches eastward to the Kingston Range. The most productive areaswere within the National Park in the adjacent Warm Spring and Galena canyons.Figure 1. Index mapMineralogy and Uses of TalcTalc is a hydrous magnesium silicate (Mg 3 (Si 4 O 12 )(OH),) containing 63.5% SiO 2 , 31.7%MgO and about 5% water. In nature, talc rarely occurs in pure form but rather isintergrown with other silicates such as tremolite chlorite, epidote and diopside. Thisresults in commercial talc of widely varying composition. In general the compositionalrange does not deter from the marketability of the talc.