THE HISTORY, GEOLOGY AND MINERALIZATION AT THE GOLDSTRIKE DEPOSIT, SOUTHWESTERN UTAH: AN UNUSUAL, OFF-TREND, CARLIN-TYPE GOLD-ANTIMONY DISTRICT

The Goldstrike Project is located in the Bull Run Mountains in Washington County, Utah, approximately 30 miles northwest of St. George. Placer gold was discovered in the area around 1895, and small amounts of gold were produced from placer and underground mines from 1910 to 1942 and again in the 1950’s. The area was largely dormant until the early 1980s, when the recognition of Carlin-style alteration and gold mineralization brought renewed interest to the district. Several companies explored the area and Tenneco Minerals eventually brought the project into production in 1987, with 210,000 ounces of gold and an equivalent amount of silver produced from 12 pits over a 6 km-long trend. The mine was acquired by USMX in 1994 and was shut down shortly thereafter due to low gold prices.

Liberty Gold acquired the project through the purchase of Cadillac Mining in 2014 and has been active ever since, compiling historic data and completing extensive geologic mapping, geochemical surveys, geophysical surveys, metallurgical studies and drilling 427,225 feet in 984 reverse circulation, sonic and core holes. A maiden resource was completed in 2018, followed by a Preliminary Economic Assessment.

In the Bull Run Mountains, Paleozoic carbonate and siliciclastic rocks were thrust over Mesozoic siliciclastic rocks near the leading edge of the Sevier thrust belt in Late Cretaceous time. These complexly folded and faulted rocks underwent erosion and peneplanation until the early Eocene, when the Claron Formation was deposited regionally over the erosional unconformity. The Claron Formation is overlain by Oligocene and Miocene tuffs and lacustrine limestones. A small gold mineralized mafic dyke in the main Goldstrike mine area returned a U-Pb age of 18.3 Ma and a granitic stock 10 km to the northwest associated with base metal skarn mineralization returned a U-Pb age of 13.5 Ma.

Cenozoic extension created a series of large, east-west oriented oblique-slip faults that created a series of east-west trending horsts and grabens with internal, northwest and north-northeast striking faults.

Alteration consists of decalcification, multiple phases of silicification, clay alteration and widespread oxidation. Disseminated gold mineralization is hosted in silicified and brecciated rocks along the unconformity between Paleozoic carbonate rocks and in the overlying Claron formation as well as in breccia zones along high angle, graben-bounding faults and the related smaller fault zones. The intensity of gold mineralization is also controlled by the thickness of the favorable lower Claron conglomeratic sandstone at the unconformity as well as the composition of the underlying Paleozoic carbonate rocks. Related trace elements include Ag, As, Sb, Te, Hg and Tl.

Recent exploration has also discovered several large zones of antimony mineralization in the eastern portion of the project area.

On the spectrum of sedimentary rock-hosted gold deposits in the Great Basin, Goldstrike most closely resembles a Carlin-type deposit, with notable differences.