Description
The Drum gold deposit was discovered by Nevada Resources, Inc., following an examination of the property in 1981 on the recommendation of a prospector (Nevada Resources, Inc., pers. comm., 1989). The mine area was part of what were then called the Yellow Cat claims, which included the largest jasperoid in the area, and the King Tut workings, which dated from the early years of mining activity. Mapping and sampling identified a low-grade gold orebody near the King Tut workings in what was then identified as thinly bedded and clay-altered argillaceous carbonate rock. Beginning November 1983, this orebody was mined and processed by Western States Minerals Corporation using open-pit and heap-leaching techniques. Development drilling and further sampling by Western States Minerals Corporation showed that the large jasperoid northeast of the King Tut contained scattered gold concentrations and was underlain by gold-bearing jasperoid. A second pit exploited this orebody. Production from the two pits was about 120,000 oz of gold, which were recovered from 3 million tons of ore at 0.04 oz/ton average grade (Western States Minerals Corporation, per$. comm., 1987). In 1988, Jumbo Mining Company bought the mine and proceeded to drill along the edges of the pits and mine by underground methods ore remaining in the, original pit.
*This ongoing study, done under the auspices of the L .5. Geological Survey Conterminous United States Mineral Assessment Program (CUSMAP), began after most ore had been removed from the Drum mine. Jumbo Mining Company and Western States Minerals Corporation kindly allowed access to the mine and surrounding area, and many of our observations are based on mapping in the vicinity of the mine and in the pits.
Geologic Setting of the Detroit Mining District Regional setting
The Drum Mountains are an uplifted and westward-tilted block of Proterozoic and Paleozoic clastic and carbonate rocks and Tertiary igneous rocks that are bounded by a range-front fault on the eastern flank. Geology of parts of the Drum Mountains is shown on maps by Lindsey (1979), Crittenden and others (1961), Newell (1971), Bailey (1974), and Dommer (1980). The eastern part of the Drum Mountains is underlain by Proterozoic and Cambrian quartzite that form rugged ridges as high as 2,225 m (7,298 ft). In contrast, the Cambrian carbonate rocks and subordinate shale that make up the western part of the Drum Mountains and that host the Detroit mining district form a gentler, more rolling topography. The Proterozoic and Paleozoic rocks are generally considered to be part of an allochthonous plate which was thrust eastward during the Cretaceous Sevier orogeny (Armstrong, 1968; Hintze, 1988). The plate probably rests on rocks at least as young as middle to late Paleozoic. No indications of large-scale extensional faulting, such as that reported in the Snake Range in eastern Nevada (Hartley and Wernicke, 1984), have been observed in the Drum Mountains.
The Drum Mountains are in the midst of an east-west-trending Tertiary volcanic field (Lindsey, 1982). Volcanism began with eruption of extensive flows and tuff, predominantly of andesitic and, less commonly, - shoshonitic composition, in Eocene time. This episode of volcanism was followed in latest Eocene and Oligo-cene time by eruption of ash-flow tuff, the formation of nested collapse calderas, and a change to rhyolitic volcanism. Bimodal volcanism began in Miocene time, about 21 Ma, and has continued into the Quaternary. During bimodal volcanism, lithophile-rich topaz rhyolite flows and domes and basalt flows erupted. Beryllium, fluorspar, and uranium episodes of mineralization were related to the silicic component of bimodal volcanism, and porphyry-related mineralization was associated with the Eocene to Oligocene calc-alkaline volcanism.
The Detroit mining district is hosted primarily by the Cambrian carbonate rocks. It extends from the Joy fault, a major ring fracture of the Eocene and Oligocene Thomas caldera that downdrops the rocks to the north (Shawe, 1972; Lindsey, 1982), south to about the Drum gold mine (Fig. 2). The district encompasses all the carbonate rocks from the quartzite-carbonate contact near the center of the Drum Mountains to the western side of the range where volcanic rocks lap onto the carbonate section. Although still considered part of the Drum Mountains and favorable for mineral deposits, the northern area is topographically distinct because it is made up largely of volcanic rocks that filled the Thomas caldera. As used in this paper, the Drum Mountains refer to the predominantly Cambrian sedimentary section south of the Joy fault that hosts the Detroit mining district.
The Drum gold mine is, at the southern end of the Detroit mining district, about 1 km (2.5 mi) from the center of the district. The mine consists of two pits, herein called the northeast and southwest pits (Fig. 4). A small manganese mine lies just outside the boundary of the northeast pit, and the old workings of the King Tut mine are exposed in the southwest pit (Fig. 2). According to company data, mining in the northeast pit primarily exploited jasperoid, whereas mostly clay-altered ore was removed from the southwest pit (Western States Minerals Corporation, pers. comm., 1 987). At the time of this study, the main ore zone was still exposed in the southwest pit, but had been removed by mining in the northeast pit. Drilling had delineated small, hidden orebodies on the edges of the pits.
Pre-mining maps show that the surface geology in the mine area was complex and that altered rock was mostly in the area of the northeast pit (Bailey, 1974; Dommer, 1980). The area of the northeast pit prior to mining was underlain by a large jasperoid, whereas in the area of the southwest pit the rocks were only locally silicified. The large jasperoid contained numerous quartzite pebbles (Nevada Resources, Inc., unpublished report, 1979), and is interpreted as having been silicified pebble dike or breccia complex. In the area of the southwest pit, clay-altered ore, identified by company geologists as thin-bedded limestone, was exposed at the surface.
Geology
Geologic Setting of the Detroit Mining District Regional setting
The Drum Mountains are an uplifted and westward-tilted block of Proterozoic and Paleozoic clastic and carbonate rocks and Tertiary igneous rocks that are bounded by a range-front fault on the eastern flank. Geology of parts of the Drum Mountains is shown on maps by Lindsey (1979), Crittenden and others (1961), Newell (1971), Bailey (1974), and Dommer (1980). The eastern part of the Drum Mountains is underlain by Proterozoic and Cambrian quartzite that form rugged ridges as high as 2,225 m (7,298 ft). In contrast, the Cambrian carbonate rocks and subordinate shale that make up the western part of the Drum Mountains and that host the Detroit mining district form a gentler, more rolling topography. The Proterozoic and Paleozoic rocks are generally considered to be part of an allochthonous plate which was thrust eastward during the Cretaceous Sevier orogeny (Armstrong, 1968; Hintze, 1988). The plate probably rests on rocks at least as young as middle to late Paleozoic. No indications of large-scale extensional faulting, such as that reported in the Snake Range in eastern Nevada (Hartley and Wernicke, 1984), have been observed in the Drum Mountains.
The Drum Mountains are in the midst of an east-west-trending Tertiary volcanic field (Lindsey, 1982). Volcanism began with eruption of extensive flows and tuff, predominantly of andesitic and, less commonly, - shoshonitic composition, in Eocene time. This episode of volcanism was followed in latest Eocene and Oligo-cene time by eruption of ash-flow tuff, the formation of nested collapse calderas, and a change to rhyolitic volcanism. Bimodal volcanism began in Miocene time, about 21 Ma, and has continued into the Quaternary. During bimodal volcanism, lithophile-rich topaz rhyolite flows and domes and basalt flows erupted. Beryllium, fluorspar, and uranium episodes of mineralization were related to the silicic component of bimodal volcanism, and porphyry-related mineralization was associated with the Eocene to Oligocene calc-alkaline volcanism.
The Detroit mining district is hosted primarily by the Cambrian carbonate rocks. It extends from the Joy fault, a major ring fracture of the Eocene and Oligocene Thomas caldera that downdrops the rocks to the north (Shawe, 1972; Lindsey, 1982), south to about the Drum gold mine (Fig. 2). The district encompasses all the carbonate rocks from the quartzite-carbonate contact near the center of the Drum Mountains to the western side of the range where volcanic rocks lap onto the carbonate section. Although still considered part of the Drum Mountains and favorable for mineral deposits, the northern area is topographically distinct because it is made up largely of volcanic rocks that filled the Thomas caldera. As used in this paper, the Drum Mountains refer to the predominantly Cambrian sedimentary section south of the Joy fault that hosts the Detroit mining district.
History
The Drum Mountains are in the eastern Great Basin of west-central Utah, about 50 km (31 mi) northwest of the town of Delta and about 90 km (56 mi) southwest of Eureka and the famous Tintic mining district (Fig. 1). The range is at the southern edge of the Tintic-Deep " Creek mineral belt. The mineral belt hosts many deposits, of which the best known are porphyry-related base- and precious-metal deposits at Tintic and the world-class beryllium deposit at Spor Mountain. The Detroit district, in the central part of the Drum Mountains (Fig. 1), has been mined at various times since the late 1800's for copper, gold, and manganese. For the past two decades, numerous gold-bearing jasperoids in the area have been exploration targets for low-grade, high-tonnage gold deposits. In 1981, the Drum gold deposit was discovered at the southern end of the Detroit district. It is one of the few known bulk-minable gold deposits in Utah.
The Detroit mining district was first organized as the Drum district in 1872, so called after a prospector of the same name (unpublished report, Pierre Peugeot, 1921). The district was reorganized as the Detroit mining district in 1879. From 1872 until about 1917, sporadic mining from a number of prospects recovered copper, gold, and silver from veins and replacements in carbonate rocks. Smelters were constructed during this period of mining activity to process the ore, but production records, though incomplete, indicate that the district was not a major producer of metals. From 1924 to 195 3, 72,462 tons of manganese ore at an average grade of 0.25 percent manganese were mined from replacement deposits in the district (Crittenden and others, 1961). In the 1960's, an altered porphyry stock and the adjacent alluvium-covered valley were drilled for porphyry-related copper, but only local copper concentrations were encountered. The district and surrounding area have also been explored for molybdenum, uranium, and tin. Exploration for low-grade, high-tonnage gold deposits followed the publication of USGS Circular 62 3 (McCarthy and others, 1969), in which numerous gold-bearing jasperoids were identified and gold concentrations as great as 100 parts per million (ppm) were reported.
