Pioneer Mountains area

The Pioneer Mountains area, in the center of the map area, contains scattered mines and prospects that are not included in identified mining districts. The area is largely underlain by Proterozoic quartzite (probably allochthonous), Paleozoic sedimentary rocks, and Cretaceous plutons related to the Pioneer batholith. Deposits include base-and precious-metal veins discovered and developed during the late 1800’s, stockwork molybdenum deposits discovered since 1967, a stratabound copper occurrence, and barite veins.

Pipestone (Big Pipestone Creek) district, Montana

Bedrock of the district, in the northeast corner of the map area, consists of quartz monzonite of the Boulder batholith intruded by numerous alaskite stocks. Mineral deposit types present are quartz fissure veins containing free gold, mineralized zones in brecciated and recemented quartz monzonite, and a gold placer. Quartz veins have produced some ore but the brecciated zones have not been successfully worked. Lode mining was conducted mainly between 1921 and 1942, when 241 ounces of gold and 4,657 ounces of silver were produced (Roby, and others, 1960). Placer mining activity has been minor.

Pipestone Pass (Donald) area, Montana

This area, along the continental divide in the northeast part of the map area, is underlain by igneous rocks of the Boulder batholith, which include the Butte Quartz Monzonite and younger, more leucocratic igneous bodies intruding it. Molybdenite, pyrite, and minor chalcopyrite occur as disseminated flakes, crystals along fractures, and crystals in miarolitic cavities in alaskite, leucogranite, and pegmatite at several sites near Pipestone Pass. Minor gold placering occurred in the 1870’s. Molybdenum prospects date from the 1950’s

Polaris (Lost Cloud, Beaverhead) district, Montana

The Polaris district is located in the south-central part of the map area. The known ore deposit is associated with a N. 60° E.-trending mineralized fault zone that separates Middle Proterozoic quartzite on the northwest side from bleached, recrystallized dolomite of Cambrian or Devonian age on the southeast side. Ore occurs in veins adjacent to the main fault. Most of the ore was oxidized, but tetrahedrite and minor galena and sphalerite are probable primary sulfides. The district was an important silver producer between 1883 and 1900 when it produced $250,000 (Geach, 1972). Production since 1900 has been small and sporadic.

Quartz Bill-Vipond (Vipond Park) district, Montana

Associated igneous rocks Sources of data Paleozoic strata that underlie this district, in the center of the northern part of the map area, have been folded about northwest-trending axes and broken by northwest-and north-northeast-to northeast-trending faults. Ore deposits are veins and replacement bodies mainly in the Cambrian Hasmark Formation. The veins trend north-northeast and northeast. Production from the district between 1867 and 1962 has totaled an estimated $2 million, of which the bulk has come from silver-rich replacement deposits in the Lone Pine mine. Deposits there were localized by fractures in the Hasmark Formation and near a fold crest beneath the less permeable Red Lion Formation (Cambrian). The Cannivan stock, a multi-phase Late Cretaceous-Early Tertiary intrusion ranging from granodiorite to quartz monzonite, forms skarn at its contact with Paleozoic carbonates and hosts the Cannivan Gulch stockwork molybdenum deposit discovered in 1968 (Hammitt and Schmidt, 1982).

Renova (Cedar Hollow, Bone Basin) district, Montana

Rocks in this district, near the northeast corner of the map area, are Middle Proterozoic arkosic sandstone and argillite overlain by Paleozoic sandstone, shale, and limestone. Cretaceous volcanic rocks are also present. Dikes of andesite and quartz porphyry cut the ~ sedimentary rock. Veins cutting Proterozoic rock form most mineral deposits; however, the Mayflower mine, operating from 1896 to 1905, and the most productive iu the district, contained chiefly telluride ore along a bedding fault in Paleozoic limestone. It produced about $1,250,000, mainly gold (Winchell, 1914

Rochester (Rabbit) district, Montana

Rocks in this district, near the center of the eastern part of the map area, are dominantly schist and gneiss of Archean age that are locally intruded by small plutons of quartz monzonite, diorite, and aplite related to the Boulder batholith. Ore deposits are mostly northeast-trending veins in gneiss and schist; they contain gold, silver, arsenopyrite, pyrite, and lesser amounts of lead, zinc, and copper minerals in a quartz gangue. Much of the ore has been oxidized to a depth of 600 feet and consists of quartz, limonite, and oxidized copper and lead minerals. Discovered during the 1860’s, the district reached its peak between 1935 and 1942. Gold production has totaled about 100,000 ounces, from at least 40 mines (Sahinen, 1939). The Watseca mine was the largest.

Rock Creek (Browns Lake) district, Montana

.f>. The Rock Creek district, near the center of the map area, is at the east margin of the Pioneer batholith, where Cretaceous VI monzogranite and granodiorite have intruded Mississippian and Pennsylvanian Amsden Formation. Calc-silicate skarn locally contains scheelite. The Browns Lake mine, discovered in 1942, was the leading tungsten producer in Montana from 1954 through 1956. The property produced, through 1957, 625,107 tons, averaging 0.35 percent wo3 (Pattee, 1960).

Ruby Range area

Complexly folded Archean metamorphic rocks strike mainly northeast and are cut by northwest-trending normal faults in this area, occupying the southeast part of the map area. The metamorphic rocks consist of gneiss, schist, phyllite, marble, and quartzite intruded by younger Precambrian rocks including quartzofeldspathic gneiss, aplite, pegmatite, peridotite, and diabase; quartz veins may also be Precambrian. In the northeast these older rocks are unconformably overlain by Cambrian, Devonian, and Mississippian sedimentary rocks that are cut by major northwest-trending faults. The entire range is flanked by thick alluvial fans and fluvial terraces of Tertiary or early Quaternary age. The most important mineral deposits are talc bodies that formed by replacement of Archean marble and magnetite bodies in Archean bedded iron-formation. Copper, manganese, asbestos, nickel, chromite, and uranium occur in subeconomic quantities. Graphite was discovered in 1899; about 2,250 tons was produced between 1902 and 1920 (Geach, 1972). Talc production began in 1942 and has continued to the present.

Sheridan {Brandon, Ramshorn, Horse Creek, Wisconsin Creek, Mill Creek, Indian Creek, Quartz Hill, Bivens) district, Montana

This district, along the eastern edge of the map area, is underlain by Archean schist, gneiss, quartzite, marble, and iron-formation that are intruded by small quartz monzonite stocks and porphyry dikes and sills of Late Cretaceous or Tertiary age. Base-and precious-metal deposits consist of veins and replacement bodies in Archean rocks, chiefly marble. The chief sulfide minerals are pyrite, arsenopyrite, chalcopyrite, galena, and tetrahedrite in a gangue of quartz and small amounts of siderite. Iron, talc, chromite, thorite, and manganese are also present in the Archean rocks, but have not yet been exploited. Lode mines, discovered as early as 1864, produced gold ore steadily until about 1952. From 1905 to 1952 about 33,500 ounces of gold was produced, and of this about 2,100 ounces came from placers (Koschmann and Bergendahl, 1968).

Siberia (German Gulch) district, Montana

Plutons of intermediate composition have intruded Middle Proterozoic, Paleozoic, and Mesozoic strata in this area, on the north edge of the map area. Tertiary volcanic rocks cover part of the district. German Gulch was a major placer-gold producer. The silicified and pyritized Cretaceous argillite was probably the source of the placer gold and the altered rock area is currently being developed as a lode mine at the Beal lode

Silver Star (Iron Rod) district, Montana

Bedrock in this district, in the northeast part of the map area, consists dominantly of schist and gneiss of Early Proterozoic age that are locally overlain by metamorphic and sedimentary rocks that range in age from Middle Proterozoic to Pennsylvanian. All older rocks are intruded by monzogranite and granodiorite of the Boulder batholith, by smaller bodies of diorite and aplite, and by dikes and sills of silicic rocks, all of Cretaceous or Tertiary age. The most important ore deposits occur in northeast-trending veins in gneiss and schist (Sahinen, 1939). These veins were mined for gold and silver; also present are arsenopyrite, pyrite, and subordinate amounts of lead, zinc, and copper minerals in a quartz gangue. Contact deposits at the Broadway and Hudson mines form irregular shoots in Paleozoic limestone along the granodiorite contact. The Green Campbell and the Broadway, both discovered in the 1860’s, were the major mines.

South Boulder (Mammoth) district, Montana

Bedrock in this district, located along the east edge of the map area, consists of Archean quartzofeldspathic gneiss intruded by the Cretaceous age Tobacco Root batholith. Most mineral depo$its are gold or copper in quartz veins or ore shoots in gneiss, or in quartz monzonite of the batholith near gneiss contacts. Ore minerals include chalcopyrite, bornite, argentiferous galena, pyrite, sphalerite, and molybdenite. Gold mines operating during the late 1800’s, such as the Mammoth, profitably mined oxidized ores, but when these ores were exhausted, efforts to treat sulfide ores were unsuccessful and the district became unproductive (Winchell, 1914). Subsequent development concentrated on properties with copper veins, such as the Bismark mine.

Sula area, Montana

This area, in the northwest corner of the map area, is mostly within the Idaho batholith. Only a few mineral occurrences are known. Those listed include beryl occurrences, about which little is known. Locations of the sites are probably accurate only to within 1 mile.

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