Geology and geochemistry of the Barneys Canyon gold deposit, Utah

Barneys Canyon is a sediment-hosted, disseminated gold deposit located 7 km from the large, gold-rich, Bingham porphyry copper deposit. Host rocks for gold mineralization are the Permian Park City dolomite and siltstone and the Kirkman-Diamond Creek sandstone. The gold deposit is approximately 430 m long, 370 m wide, up to 90 m thick and contains 8.5 million metric tons (t) of reserves averaging 1.6 g/t gold. Intrusive igneous rocks are conspicuously absent. The gold deposit is located on the northern flank of the northeast-trending Copperton anticline, an overturned box fold. A small east-striking, south-dipping thrust fault, the Barneys Canyon thrust fault, with 200 m displacement, repeats the Park City Formation, and north-south-striking steep normal faults form a graben in which the gold deposit is located. The Barneys Canyon thrust fault predates mineralization and the Phosphate normal fault postdates mineralization.

Alteration of the host rocks is similar to other sediment-hosted, disseminated gold deposits but at lower alteration mineral abundances. Kaolinite and illite comprise less than 10 percent of the altered rock. Silicifica-tion is minor, barite is rare, and pyrite and marcasite are common, but not abundant. Trace As, Sb, Hg, Tl, and Ba show pronounced increase.

K/Ar age determinations on vein illite from ore grade (1.5 ppm gold) bedding-plane gougelike material yield Jurassic ages.

Fluid inclusion measurements from barite and jasperoid show a mean salinity of 1.7 wt percent NaCl equiv and homogenization temperatures of 130° to 393°C with weak modes at 350 and 230°C, suggesting that two fluids have interacted with rocks at Barneys Canyon. Kaolinite-bearing assemblages formed below 280°C. Pressure correction at hydrostatic pressure is 12°C.

Fluid inclusion measurements, geochronology, structure, trace elements, and distance from Bingham are inconsistent with genesis of the Barneys Canyon deposit as part of the Bingham porphyry copper system. It is unlikely that genesis of the Barneys Canyon gold deposit involved igneous activity.