Tertiary meteoric hydrothermal systems have altered the rocks exposed over more than S% of the land surface of the northwestern United States and southern British Columbia, including at least 25,000 1m? in Idaho. The systems typically involved convective circulation of fluid derived from ordinary meteoric groundwater& around crystallizing, calc-alksline, epizonal plutons eiiiP.laced into coeval volcanic cover rocks.These individual systems had widely ranging "lifetimes" of 10' to 1Cf >:~and operated ~ocally throu~out the Cenozoic, although the most profound devolopment of such activity occurred dunng Eocene time. Individual systems varied in size from a few tens of S'JUBre kilometers (Y ankec: Fork, I~o) or less ~ ~v~ral thousand square kilometers (Sawtooth and Castro nng zones, Idaho) Typically, reg~onsl propyhtization aacompanied the fluid circulation, although th~ .lJ!ghe~-tempe':B~re ~teration assemblages. were ~evel~ed locally as were intense alteration effects (e.g., silicification, senc1tization, etc.) near some ve1ns and m Jrurung districu. A significant amount, PC?bably 25-SO%, of the mineral production and pote!ltial i~ the region is closely related to Tertiary meteonc hydrothermal systems. Oxygen and hydrogen 1sotop•c data clearly demonstrate the close geologic association of meteoric hydrothermal systems amd mineralization in (1) the Paleocene, Cu-Zn-Pb-Mn Main Stage mineralization at Butte, Montana; (2) numerous Eocene epithermal deposits principally valued for Au and Ag but also including significant deposits of Cu, Pb, Zn, F, Sb, etc., as at Republic, Washington, and in several mining districts in the Idaho batholith and the Challi~ volcanic field; (3) several Eocene skarn deposits valued for W (lma, Idaho) and Cu (Mackay, Idaho); (4) Important leadsilver vein and replacement deposits of Tertiary (Bluebell, British Columbia) and of probable Cre~ceous and early Tertiary age (Wood River, Idaho); (S) several potentially economic Mo-, Be-, and U-beanng Eocene "porphyry" plutons; and (6) Miocene epithermal deposits, most prominently the Au and Ag bearing veins at Silver City and DeLamar, Idaho, the Hg deposits at the McDermitt caldera, Nevada and Oregon, and .
INIRODUCI10NOxygen and hydrogen isotopic ratios are the only intrinsic properties of H20 that are known to be both variable and easily measured; hence they provide the only unequivocal data on the origin of natural aqueous fluids [Craig et a/., 1956]. Application of these principles proves that fluids derived from meteoric waters played a critical role in the formation of numerous ore deposits of the western United States. Prominent examples are the epithermal Au and Ag deposits of Nevada, such as Tonopah, Goldfield, and the Comstock Lode [Taylor, 1973[Taylor, , 1974aO'Neil and Silberman, 1974], and several copper porphyry and vein deposits [Sheppard et al., 1969[Sheppard et al., , 1971. A particularly important example is the Main Stage mineralization of the zoned Cu-Zn-Pb-Mn deposit at Butte, Montana [Garlick and Epstein, 1966;Sheppard and Ta...