Greenhorn K.aoge area. Montana

Archean gneiss, schist, amphibolite, and marble form the bedrock in this area, along the southeast edge of the map area. Mineral deposits include talc replacement bodies in marble, gold placers, and quartz veins bearing chiefly copper minerals. Since 1970, talc has been mined at the Willow Creek mine in significant quantities (Berg, 1976).

Hecla (Bryant, Trapper) district, Montana

Paleozoic sedimentary rocks form the flanks of a dome less than 1 mile north of the Pioneer batholith in this district, near the center of the map area. Paleozoic units are thinned on the flanks of the dome and are folded disharmonically and cut by thrust, tear, and normal faults. Ore deposits are chiefly replacement bodies localized by fractures and minor fold crests. The deposits are in favorable stratigraphic zones near the middle of the Hasmark Formation, at the top of the Hasmark directly beneath the Red Lion Formation, and near the middle of the Jefferson Dolomite, as interpreted by E-an Zen (U.S. Geological Survey unpub. mapping). Since its discovery in 1872, about $20 million in ore has been produced from the district (Geach, 1972).

Highland (Fish Creek, Red Mountain) district, Montana

Bedrock of this district, in the northeast part of the map area, consists of slate and quartzite of the Belt Supergroup and Paleozoic limestone, sandstone, and shale along the southeast border of the Boulder batholith. Ore deposits include veins, chimneys, and irregular contact deposits in marbleized Paleozoic limestone and irregular veins in quartz monzonite near the limestone contact. Sulfide ore consists of chalcopyrite, bornite, galena, pyrite, pyrrhotite, arsenopyrite, tetradymite, argentite, and pyrargyrite. Much of the ore was oxidized and contained native gold and silver and oxidized copper and iron minerals. Fish Creek placers were important producers of gold; the Butte Highlands mine was a major producer, mainly of gold.

Homestake district, Montana

Quartz monzonite of the Boulder batholith, intruded by numerous aplite, pegmatite, and diabase dikes, underlies this district in the northeast part of the map area. Ore deposits include gold placers and quartz veins containing gold, silver, and base metals. Veins containing gold and silver are short and irregular but are locally rich. Production from these mines has probably been small.

Little Pipestone district, Montana

Bedrock in this district, located in the northeast part of the map area, consists of Paleozoic sedimentary rocks that were intruded by monzogranite and granodiorite of the Boulder batholith. Little is known about the ore deposits, and the only minerals known to have been produced from the district are placer gold and gem-quality amethyst. Production has been small.

Lost Creek district, Montana

Metamorphism of rock along the contact between the Pioneer batholith and the Amsden Formation (Mississippian and Pennsylvanian) has produced a garnet-epidote skarn that locally contains scheelite in this district, located near the center of the map area. Scheelite is commonly disseminated in the garnet, especially where it is andradite rich (Collins, 1977). Tungsten was discovered at Lost Creek in 1907. During the 1950’s, 21,150 tons of 0.18 percent wo3 ore was produced (Pattee, 1960).

McCartney Mountain (McCarthy) district, Montana

A Late Cretaceous or Tertiary quartz monzonite stock has intruded folded and thrust-faulted Cretaceous sedimentary rocks in this district, located in the center of the east part of the map area. This complex is surrounded by a veneer of Tertiary and Quaternary volcanic and sedimentary rocks. Ore deposits include silver-bearing galena in quartz veins in hornfels and in the quartz monzonite stock. Oxidized ores rich in silver were exploited in the late 1800’s. Small amounts of silver-lead ore were shipped to smelters prior to the 1940’s. Drilling in 1980 and 1981 has been done on molybdenum occurrences on claims originally staked as part of the Silver King mine.

llelrose (Caap Creek, Soap Gulch, Wickiup Creek, Galena) district, Montana

East of the broad Big Hole River valley, in the northeast part of the map area, Paleozoic strata dip west and southwest and are in depositional contact with Archean crystalline rocks. Farther north the Archean rocks are faulted against conglomerate, quartzite, and argillite of Middle Proterozoic age. The Hell Canyon pluton of the Boulder batholith intrudes the Archean and Proterozoic rocks at the east end of the district. West of the Big Hole River valley, Paleozoic and Mesozoic strata are folded around northwest axes, and Cretaceous sediments have been intruded by a granodiorite pluton. The valley is underlain by Tertiary and Quaternary deposits. Gold placers in Soap and Camp Gulches were unproductive, due in part to water shortages. The most productive lode deposits have been quartz veins containing pyrite, chalcopyrite, and argentiferous galena, such as the Clipper-Columbia, and replacement silver-lead deposits in the Meagher Limestone, such as the Jackrabbit. Lode mining was well established by the 1880’s, when many of the mines provided ores to the Glendale smelter. The smelter closed in 1900, but several of these mines continued making small ore shipments to other smelters until the late 1940’s. Production has been small. Gossan, mined as smelter flux prior to 1900 at the King and Queen claims, formed by weathering of massive sulfide deposits in lower Belt strata. Since 1913 substantial amounts of phosphate have been produced from the Phosphoria Formation at the Maiden Rock and Canyon Creek mines

Monuaent (Bloody Dick, Beaverhead) district, Montana

A fault slice of highly sheared Early Proterozoic crystalline rock between allochthonous Lemhi Group quartzites is host to masses of vein quartz that contain secondary copper minerals in this district, located along the south edge of the map area. Lodes, discovered in the 1870’s or 1880’s, produced about 500 tons of shipping ore before the mines closed in 1929 (Geach, 1972).

Hoose Creek (Moosetown, HU1Rbug) district, Montana

Belt strata and Paleozoic strata, intruded by the monzongranite Humbug stock, underlie the district, located in the northeast part of the map area. Ore deposits include gold placers, and veins and replacements in Paleozoic carbonates near the monzogranite contact. The placers have been intermittently worked, with production estimated at several hundred thousand dollars in gold since 1866 (Dingman, 1932). Lode mines were discovered by 1868, and small shipments of ore were produced until the 1930’s.

Moose Lake district, Montana

Quartzite, limestone, and argillite, mainly of the Missoula Group and Helena Formation of the Belt Supergroup (Middle Proterozoic), are cut by numerous faults and are intruded by Cretaceous and (or) Tertiary igneous rocks consisting mostly of granodiorite, and monzogranite in this area, located in the northwest part of the map area. Mineral deposits consist of quartz fissure veins in granodiorite and in Belt quartzite. At the Senate mine, chalcopyrite, pyrite, and galena occur in quartz veins and sparsely disseminated in the wall rocks; production is reported to be small, although the exact amount is unknown.

Pioneer (Rescue, Trail Creek) district, Montana

This district, situated along the Montana-Idaho State line, is underlain by Lemhi Group and Missoula Group quartzite that have been intruded by Cretaceous or Tertiary two-mica granite of the Idaho batholith. Erosional remnants of Tertiary gravel remain along Ruby Creek and north of the North Fork of the Big Hole River. Ore deposits are chiefly gold placers derived, at least in part, from the Tertiary gravel. Gold placers, discovered on Pioneer Creek in 1862 and on most other creeks by the 1880’s, have been intermittently worked since, but production has been small.

SOURCES OF DATA https://pubs.usgs.gov/imap/1803c/report.pdf