BORATE DEPOSITS IN THE UNITED STATES: DISSIMILAR IN FORM, SIMILAR IN GEOLOGIC SETTING.

Borate deposits in the western United States have several geologic characteristics in common: All primary deposits are about 20 my or less in age, and they are observed or inferred to be stratigraphically associated with volcanic activity and thermal springs. Most of them lie at least partially in the lacustrine facies of their host formations which implies the existence of closed basins created by contemporaneous tectonic activity. The preservation of the borate and other dissolved salts requires the climate to have been sufficiently arid for evaporation to offset most of the inflow and prevent the loss of salts by overflow.