Tidal Wave (Twin Bridges, Bear Gulch, Goodrich Gulch, Dry and Wet Georgia Gulches) district, Montana

Small bodies of Cretaceous quartz monzonite and monzonite have intruded Archean gneiss and schist and Paleozoic limestone, sandstone, and shale that had been faulted and tilted in this district in the east-central part of the map area. These rocks are also cut locally by sills of porphyritic granite, syenite, and andesite and by dikes of aplite. The ore deposits in the district are vein and replacement deposits in limestone and veins in gneiss and schist. Sparse deposits occur in the quartz monzonite near its contact with the country rocks. Most of the veins contain gold and lesser amounts of lead, silver, copper, and zinc. Contact metasomatic deposits produced mainly copper and lead, but contain silver and gold as minor constituents.

Upper Basin Creek district, Montana

This district, south of Butte, is within the Burton Park and Climax Gulch plutons of the Boulder batholith, and it contains one vein deposit and placer deposits first worked during the 1860’s.

Virginia City (Alder Gulch, Williams Gulch) district, Montana

Quartz monzonite 197 (Kqm) The Alder Gulch placers, some of which lie along the southeast edge of the map area and extend for about 20 miles, were the longest and most productive ever discovered in Montana. The gold-bearing gravel in Alder Gulch is 30-50 feet deep and is most valuable about 6 feet above the weathered, plastic bedrock (Koschmann and Bergendahl, 1968). The gravels are of Quaternary age, and the gold was derived directly from the thousands of veins in the district (Lyden, 1948), some of which were also productive. The veins occur in Archean gneiss and schist, but may also be associated with Cretaceous or Tertiary aplite. The lodes are quartz veins and stringers that contain auriferous pyrite, galena, sphalerite, chalcopyrite, and lesser amounts of gold telluride, tetrahedrite, argentite, and stibnite. Most of the lode mines are east of the Dillon quadrangle; those located in the Dillon quadrangle part of the district are small producers and are 1i t tle known.

Whitehall (Cardwell) district, Montana

The rocks in this district, in the northeast corner of the map area, are shale, sandstone, and sandy limestone of Middle Proterozoic age conformably overlain by a thick sequence of Paleozoic rocks, mainly limestone. The sedimentary rocks are intruded by latite porphyry, andesite, and lamprophyre dikes. Ore occurs in a large breccia body, in veins in the sedimentary rocks, and in the latite porphyry. The ore contains auriferous pyrite, galena, and sphalerite in a quartz gangue. The major mine, the Golden Sunlight, has produced roughly three-quarters of the total recorded gold production of the district through 1959 (100,000 oz) (Koschmann and Bergendahl, 1968).

Wisdoa district, Montana

Granodiorite and tonalite of Cretaceous and Tertiary age intruded quartzite of the Missoula Group in this district in the west-central part of the map area. Aplite and pegmatite occur throughout the granodiorite and tonalite. Numerous small and narrow quartz-pyrite veins cut the plutonic rocks, many of them associated with aplite. Gold and silver are found in some of these veins but the concentrations vary irregularly and individual ore shoots are small. Mining began in 1869 and has continued to the present, but production has been small.

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