Abstract: Hydrothermal Vein Deposits Associated with a Tertiary Low-Angle Normal Fault, Salina, Utah

DIEHL, S. F., R. E. ANDERSON, J. D. HUMPHREY, and T. P. BARNHARD

Structural fabrics, diagenetic carbonate minerals, galena, and a hydrocarbon phase in veins record multiple fluid-flow events in the upper plate of a low-angle normal fault (i.e., detachment fault) near Salina, Utah. The faulting records extension at the eastern edge of the Basin and Range Province.

Veins are less than 1 mm to less than or equal to 10 cm thick and exhibit vuggy, open-space fabrics. Hydrocarbons (?) occur as irregular inclusions that outline crystallographic growth boundaries in sparry vein-filling calcite crystals. Delta{18}O values of sparry calcite are strongly depleted (-20 o/oo PDB), indicating a hydrothermal fluid source. Calculated temperatures of the original hydrothermal fluids range from 280 degrees C in calcite-filled veins in an upper plate fault (N 30 to 40 degrees E, 37 degrees SE.), to 220 degrees C in veins (N 30 to 40 degrees E, 10 to 15 degrees SE) below the fault.

In brecciated upper-plate rocks, galena is an early cement, precipitated on limestone-breccia clasts. Galena is partially altered to cerrusite, especially along cleavage planes. Subsurface Tertiary intrusives, widely exposed elsewhere in the lower plate of this fault system, may be the source of the metal-bearing fluids.

Structural fabrics in the veins, such as parallel sets of elongated limestone clasts and graded layers of micritic sediment in vugs, form geopetal textures parallel to the low-angle fault. These textures, and the coincidence of vein attitudes with fault fabrics, suggest fluid flow was coeval with low-angle faulting and upper-plate deformation.

AAPG Search and Discovery Article #90946©1997 AAPG Rocky Mountain Section Meeting, Denver, Colorado