PALEOZOIC TECTONICS, BRINE MIGRATION, AND FORMATION OF HYDROTHERMAL ZEBRA DOLOMITE, SEDEX AND MVT DEPOSITS ALONG THE CARBONATE PLATFORM IN THE GREAT BASIN

Hydrothermal zebra dolomite is typically composed of alternating horizontal layers (approx. 1-10 mm) of dark, fine-grained dolomite and white, coarse-grained, sparry, void-filling dolomite. Worldwide, zebra dolomite is associated with oil fields, Mississippi Valley-type (MVT) Pb-Zn deposits, and Sedex Pb-Zn±Ba±Au deposits that are produced by movement of hot basinal brines through permeable strata and faults. Hence, its distribution marks brine-migration pathways.

Zebra dolomite localities extend from Death Valley, California, across Nevada, and into western Utah. In the Great Basin, zebra dolomite primarily occurs in the platform-margin to inner-shelf facies of Cambrian, Devonian, and Mississippian strata. It is genetically associated with Devonian Sedex Au, Zn, and barite in the Carlin trend (e.g., Meikle) and MVT Pb-Zn-Ag mineralization in the Goodsprings district and Death Valley region. Elsewhere, it served as a host rock for Cretaceous pluton-related polymetallic replacement deposits (e.g., Ruby Hill) and late Eocene Carlin-type gold deposits (e.g., Windfall, Meikle). Zebra dolomite is associated with high-angle fractures and faults that constitute flower structures and with dissolution processes that led to solution collapse and brecciation. Because of the resulting high-permeability textures and high Fe content, zebra dolomite was an ideal host for younger polymetallic replacement and Carlin-type gold deposits. Therefore, an improved understanding of the age, distribution, and chemical and isotopic signatures of zebra dolomite is relevant to development of genetic and exploration models for base and precious metal deposits in the Great Basin.

Field relationships and the regional distribution of hydrothermal zebra dolomite localities suggest that most formed in response to two (or more) Paleozoic tectonic events. Some zebra dolomites were produced during Devonian extension (e.g., Meikle), whereas others appear to have formed during Mississippian or younger contractional orogenesis (e.g., Goodsprings). Both types of tectonism likely stimulated movement of metal-bearing basinal brines.