Geology of the Melco Gold Deposit, Oquirrh Mountains, Utah

Abstract The Melco deposit is the largest of five gold mines that constitute the 1.5 million ounces Barneys Canyon project. The deposits form an arc along the nose of the north-trending Copperton anticline. Gold mineralization formed in structurally prepared zones near Theologically contrasting formational contacts. Bedding plane slip during Mesozoic folding caused some deformation. The Melco deposit, located on the NW flank of the Copperton anticline, was localized in a structurally complex zone at the intersection of a N 55° E-trending strain corridor and N 30° E-striking high-angle faults. The latter faults provided conduits for Tertiary-age gold-bearing fluids and late stage carbon-pyrite-orpiment-realgar introduction. In cross section, gold distributions resemble an upright goblet with a stem but no base. These sediment-hosted deposits contain micron-sized gold as native metal and as inclusions within the arsenic-rich rims of zoned pyrite grains. The deposits are anomalous in As-Sb-Tl-Hg, and contain low silver and base metal values. Bleaching and decalcification are the most pronounced alteration effects. Silicification is present but subtle. The deposits lie at the outer edge of an asymmetrical pyrite-Au-As halo developed around the Bingham Canyon porphyry system. There is a growing body of evidence that these sediment-hosted gold deposits represent a distal precious metal event genetically related to late stage mineralization at Bingham Canyon, which lies 5 miles to the south.