| Description |
The Milford Flat Quadrangle and the Old Moscow Mine are located in the Star District of the eastern half of Beaver County, Utah. A. Milford Flat Quadrangle Sedimentary and igneous rocks occupy the northwestern corner of the Milford Flat Quadrangle; the remainder of the Quadrangle is alluvium. Sedimentary rocks, exclusive of the alluvium, range in age from Pennsylvanian to Jurassic. The Pennsylvanian rocks are represented by the Talisman Quartzite. The Permian age is represented by the Toroweap Formation and Kaibab Limestone. The Triassic rocks are represented by the Moenkopi Formation, Shinarump Conglomerate, and the Chinle Formation. The Navajo Sandstone represents the Jurassic age. The Milford Flat granodiorite stock and a number of lamprophyric and aplitic dikes intrude the sedimentary rocks of the area. The stock which is irregular in shape occurs in separated masses and covers an area of approximately one square mile. It is emplaced by stoping action rather than by forceful injection and is probably of Tertiary age. Lamprophyric dikes, few inches to three feet thick, are highly altered and have east-west or northerly trends. The aplitic dikes are few feet thick and strike northwestward. The sedimentary rocks of the area represent an eastern limb of a northeast trending anticline. They are cut by faults of several ages. The oldest are northwest-southeast normal faults. East-west transverse faults are both pre and post intrusion. Northeast-southwest normal faults are contemporaneous with the intrusion. Fissures on which no movement is evident are of east-west, northeast, and northwest trends. Hydrothermal alteration of the igneous and sedimentary rocks in the area includes bleaching and recrystallization of limestones and dolomites, and argillic, propylitic, siliceous, hematitic types of alteration of the igneous rocks. The mapped area has produced lead, zinc, silver, gold, and copper. Mineralization is classified into: 1) deposits within the granodiorite mass; 2) contact metasomatic deposits; 3) hydrothermal replacement and fissure filling deposits. No clear zonation of the mineralization is encountered. Ore deposition in the area is closely associated with the Milford Flat stock. B. Old Moscow Mine The Old Moscow Mine, one of the oldest and most productive mines of the Star District, is located in NE 1/4, SW 1/4, Section 25, T. 28 S., R. 12 W., about 13 miles southwest of Milford, Utah. Underground workings of the mine comprise an adit, two vertical shafts - the Old Moscow Shaft and the Burning Moscow Shaft, four access ible levels, stopes, raises, and winzes. Sedimentary and igneous rocks are exposed in the mine site and vicinity. The sedimentary rocks range in age from Devonian to Pennsyl vanian. The Devonian is represented by the Guillmete and Mowitza Formations, the Mississippian by the Monte Cristo Limestone, and the Pennsylvanian by the Calville Limestone. The sedimentary rocks are cut by east-west trending strike-slip faults and a number of fissures, most of which are at right angles to the bedding. Igneous rocks in the vicinity of the mine include a granite stock 1/4 mile southwest of the workings and a number of altered lamprophyric dikes of northerly and easterly trends. An aplitic dike is exposed on the fourth level of the workings. The ore occurs mainly in the dolomite and limestone of the Guillmete Formation underlying the Mowitza shales. Primary sulphide mineralization - galena, sphalerite, chalcopyrite, pyrite, and grenock ite - was encountered in a few places in the mine workings. Most of the ore mined came from the zones of oxidation and sulphide enrichment which are exposed along most of the workings. The ores at the mine are structurally classified into: 1) veins and 2) hydrothermal replacement pipes or chimneys. Ore controls are divided into: 1) location, 2) stratigraphic, 3) structural, 4) physical, and 5) host rock alteration control. Deuteric, hydrothermal and supergene alteration is wide spread in the mine workings and vicinity. Based on field examination, mineralogic association, and sulfur isotope analyses, the origin and genesis of the primary ores are be lieved to be of mesothermal solutions associated with the granite intrusiono Continuous shipment of lead-zinc-silver ore containing some copper and gold began in 1905 and continued through 1944 with short periods of interruption. No figures of yearly production from the property are available. Small quantities of sulphide ore are left behind in the accessible mine workings. However, large amounts of oxidized lead-zinc mineralization with some copper, gold, and silver on the walls and dumps of the mine suggests the possibility of future shipments of oxidized ores. |
