Summary of the Geology of the Bingham District, Utah

Abstract

ABSTRACT The Bingham District is a large polymetallic mining district centered on an Eocene porphyry copper deposit 20 miles southwest of Salt Lake City, Utah. Since its discovery in 1863 the district has at various times been a silver-lead, gold, lead-zinc-silver, and copper-gold-molybdenum district. The Bingham District is located in a zone of overlap between the Basin and Range extensional terrain and the Cordilleran fold and thrust belt. Permian quartzites and limestones were folded and thrust-faulted during several Mesozoic orogenies and then intruded by 39.8 to 37.5 Ma calcalkaline monzonite, quartz monzonite, and quartz latite. Volcanic breccias and flows petrochemically similar to the intrusions were erupted from centers close to the deposit from 39 to 33 Ma. The Bingham Porphyry Copper Deposit exhibits the concentric alteration and mineralization zoning characteristic of many porphyry deposits. However, the deposit is notable for the magnitude and intensity of the various kinds of mineralization present:It is one of the largest copper deposits in the world with pre-mining reserves of almost 3 billion tons of 0.67 percent copper ore.Nested within the copper orebody are overlapping zones of molybdenum, gold, and silver mineralization that mimic the shape of the copper deposit and contain greater than 0.1 percent MoS2, 0.01 ounces per ton gold, and 0.5 ounces per ton silver respectively.Major copper-gold skarn deposits flank the copper orebody on two sides. They include the Carr Fork Deposit (61 million tons of 1.90 percent copper, 0.01 ounces per ton gold, and 0.31 ounces per ton silver) and the North Ore Shoot Deposit (82 million tons of 2.81 percent copper, 0.05 ounces per ton gold, and 1.57 ounces per ton silver).Vein and replacement lead-zinc-silver deposits located in a halo around the porphyry and skarn deposits have produced 28 million tons at an average grade of 8.6 percent lead, 6.6 percent zinc, 5.0 ounces per ton silver, and 0.039 ounces per ton gold. The Barneys Canyon and Melco Deposits located five miles north of the porphyry copper deposit have combined pre-mining reserves of 19 million tons at a grade of 0.05 ounces per ton gold. They are sediment-hosted gold deposits characterized by sub-micron sized disseminated gold mineralization, an arsenic-antimony-barium-mercury-thallium geochemical signature, low silver and base metal contents, and an almost complete absence of quartz veining. The deposits lie at the outer edge of an extensive arsenic-gold geochemical halo about the Bingham Porphyry Copper Deposit, but chronological and genetic relationships to the porphyry deposit have not been clearly established.