Cal Poly Geology Club Death Valley Field Trip – 2004

processing costs were lower and shipping costs to the port of Los Angeles were alsolower since the shipping distance was reduced.Borate mining ceased in the Death Valley area until 1970 when Tenneco Oil beganproduction of colemanite from the Boraxo mine, later to be joined in 1976 by AmericanBorate from the Billie mine. Passage of Public Mining Law in 1976 placed severerestrictions on mining in National Parks and Monuments, essentially eliminating surfacemining. The result was the closure of all surface mines in Furnace Creek Wash. However,the Billie mine, an underground operation, remains in intermittent production.General GeologyBorate deposits of Death Valley (Figure) are of two types: (1) accumulations of ulexiteand associated minor borate minerals in Holocene playa lake beds that occupy the floorof Death Valley and (2) colemanite, ulexite, probertite and associated minor borateminerals in bedded lake sediments in the Pliocene Furnace Creek Formation in theFurnace Creek Wash area. All of the more recent mining has been from Furnace CreekWash.The Furnace Creek Formation lies between the Oligocene (?) to Pliocene Artist DriveFormation and the Plio-Pleistocene Funeral Formation. These units have been folded intoa broad syncline cut by steeplydipping faults with smalldisplacements. On the east, theseformations are separated from thePaleozoic rocks of the FuneralMountains by the northwest-trendingFurnace Creek fault and on the westthey are separated from the volcanicsand sediments of the BlackMountains by a frontal fault system.The Furnace Creek Formation iscomprised of 2500 meters ofinterlayered lucustrine sediments,pyroclastics, and basaltic volcanics.Deposits of colemanite and ulexite/-probertite are found several meters tohundreds of meters above the base ofthe formation. The main boratedeposits are interstratified with mudstone,shale, limestone andconglomerate. Most major depositsare truncated by steeply dippingfaults.The borate mines and properties of the DeathValley region.