Geology of the tungsten, antimony, and gold deposits near Stibnite, Idaho

The deposits of tungsten, antimony, silver, and gold described in this report occur in an area about a mile wide and 3% miles long near the town of Stibnite, Valley County, Idaho.Ore has been mined from only two deposits in the area, the Yellow Pine and Meadow Creek mines of the Bradley Mining Co.The Yellow Pine mine was the largest source of tungsten and antimony ores in the United States from 1942 to 1944.Gold and silver ores also are taken from this mine.Only gold, antimony, and silver ores were mined in the Meadow Creek mine, which was closed in 1938.Quartz monzonite and related rocks of the Idaho batholith, locally containing large roof pendants of metamorphosed sedimentary rocks, are the principal rocks of the area.Intense and widespread faulting, controlled in part by older structures in the sedimentary rocks, has been accompanied by much shearing in the quartz monzonite.Dikes of basalt, quartz latite porphyry, trachyte, and rhyolite were intruded after the main faulting but before the final fault movements.Metalization took place in three stages, with intervening periods of fracturing.The first stage is represented by extensive replacements by gold-bearing pyrite and arsenopyrite, the second by less extensive replacement by scheelite within the gold ore bodies, and the third and final stage by replacements by stibnite and silver, localized in part by the same fractures that localized the scheelite.The main ore bodies occur along the Meadow Creek fault, a shear zone as much as several hundred feet wide cutting the quartz monzonite.The ore bodies are localized by changes in strike or dip of the main fault zone and by intersecting subsidiary faults associated with these changes.The tungstenantimony ore body at the Yellow Pine mine has the general shape of a flat upright funnel flaring to its widest diameter at the surface and tapering to a narrow neck, which extends below the bottom of the minable tungsten ore.The under side of the ore body is very irregular in detail.The highest grade of timgsten ore was concentrated toward the center of the mass and was surrounded by an envelope of antimony ore containing only a little tungsten.The richer gold ore bodies not only are clustered around the antimony "funnel" but are distributed elsewhere in and near the fault zone where there is little associated tungsten and antimony ore.Ore mined at the Meadow Creek mine contained 0.23 ounce of gold per ton and 1.6 percent of antimony.That mined at the Yellow Pine mine contained less gold but about 4 percent of antimony and 2 percent of WO8.The tungsten ore body at the Yellow Pine mine was exhausted in 1945.A total of 831,829 units of W08 were contained in the tungsten concentrates produced.Antimony and gold are still being produced from the mine.151 152 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1949-50^Reserves of antimony at the Yellow Pine and Meadow Creek mines were estimated on June 1, 1943, at nearly 40,000 tons of metallic antimony contained an indicated ore averaging more than 1 percent of antimony, and more than 20,000 tons in indicated gold ores averaging less than 1 percent of antimony.Additional amounts may be produced from now undeveloped prospects in the area.The antimony at the Yellow Pine and Meadow Creek mines, and presumably that in the other deposits, contains silver in the approximate ratio of half an ounce of silver to 20 pounds of antimony.The Yellow Pine mine will probably be a gold producer for many years to come because of its sizable reserve of indicated gold ore.Other mines and prospects in the area should add to the total gold output.The district is believed to contain nearly 600,000 ounces of gold in indicated ore averaging 0.1 ounce per -,ton or better, and about 140,000 additional ounces of recoverable gold in antimony .ore.