Placer gold along the upper portions of Gold Creek, near Deer Lodge, Montana, occurs in Pliocene(?) fossil alluvial placers, Pleistocene till, and alluvium. The upper Gold Creek placers yielded an estimated 175 to 200 kg gold during 1890 to 1990. The gold probably originated in veins, skarn, or replacement deposits in Paleozoic and Mesozoic sedimentary units near the contact with Late Cretaceous granodiorite of the Royal stock. Gold was initially concentrated in alluvial placers along the ancestral Gold Creek valley during late Tertiary (Pliocene) time. Pleistocene glaciers scoured the Pliocene placers from most parts of the valley, although the fossil placers were locally buried beneath till and gold was also incorporated into till that was deposited farther down valley. Gold from Pliocene and Pleistocene placers has locally been reconcentrated into alluvium as a result of postglacial stream incision. The placer gold occurs as coarse-sized, oval to elongate grains characterized by rounded protuberances and inclusions of quartz and sulfide minerals. In polished section the grains have alternating convex and concave borders interrupted by pits and embayments. Grain borders and interiors of embayments display supergene gold rims averaging 98.8 percent Au.Microprobe analysis of cores indicate average compositions of 83.6 percent Au and 16.5 percent Ag and spectrographic data indicate a trace element signature enriched in Cu, Pb, and Sb, which is compatible with derivation from mesothermal plutonic lode deposits associated with the Royal stock.

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Rattlesnake Creek area 25 Douglas Creek (Gird Creek) district 47 Wolf Creek district 2 Gamet Range area 26 Maxville area 48 Marysville (Silver Creek) district 3 Clinton district 27 Racetrack (Danielsville) district 49 Ophir (Snowshoe Creek, Carpenter 4 Copper Cliff district 28 Philipsburg district Creek) district 5 Coloma district 29 Red Lion (Hidden Lake) district 50 Dog Creek area 6 Gamet (First Chance) district 30 Lost Creek district 51 Austin district 7 Top O'Deep district 31 Blue-Eyed Nellie district 52 Scratchgravel Hills area 8 Elk Creek area 32 Olson Gulch district 53 Sevenmile Creek area 9 Bear Creek area 33 Johnson Basin district 54 Stemwinder Hill area 10 Garrison district 34 Georgetown (Southern Cross, Cable, 55 Helena (Last Chance) district 11 Sapphire Mountains area Gold Coin) district 56 North Boulder Mountains area 12 Welcome Creek district 35 Silver Lake district 57 Elliston district 13 Rock Creek area 36 Anaconda Range area 58 Rimini (Vaughn) district 14 Frog Pond Basin district 37, Deer Lodge Valley area 59 Clancy district 15 Moose Lake district 38 Blackfoot River area 60 Basin (Cataract) district 16 John Long Mountains area 39 Big Blackfoot (Ogden Mountain) 61 Wickes (Colorado) district 17 Alps district district 62 Amazon district 18 Black Pine (Combination) district 40 Lincoln Gulch area 63 Boulder (Comet) district 19 Henderson Creek area 41 McClellan Gulch district 64 Emery (Zosell) district 20 Flint Creek Range area 42 Seven-up Pete Gulch area 65 South Boulder Mountains area 21 Dunkleberg district 43 Stemple-Gould district 66 Oro FiQo district 22 Pioneer (Gold Creek) district 44 Nevada Creek area 67 Lowland district 23 Rose Mountain (Gold Creek)• district 45 Finn district 68 Big Foot (State Creek) district 24 Princeton (Boulder Creek) district 46 Little Prickly Pear area 69 Butte (Summit Valley) district 70 Pipestone district 37,000 tons of ore that averaged 45 percent copper were mined from the Anaconda claim and shipped to a smelter. By 1885, 25 companies were mining copper in the Butte district. The early shipments of high-grade copper ore were hauled by ox cart to Corinne, Utah, then by railroad to east coast ports, and finally by sea to Swansea, Wales, for smelting. After the completion of the Northern Pacific Railroad in 1883, ore was hauled to Portland, Oregon, and then by sea to Swansea. The high cost of transportation, however, combined with recognition that the deposits were of large size and high copper grades prompted construction of branch railroad lines and smelters to transport and process the ore locally. Much of the construction occurred between 1884 and 1900 and was financed by newly formed large mining corporations and holding companies. By 1906, Butte was the most important mining center in the U.S. and was second in the world after the Rand mines in South Africa. By the end of 1906, total production of the Butte district was estimated to be $650 million and Butte was producing about 20 percent of the world's total copper. One of the largest mining companies in Butte was...

This report is one of a series of reports that present, chiefly with maps at a scale of 1:250,000 and 1 :500,000, various aspects of the geology, geochemistry, geophysics, and mineral resources of the Dillon 1 °X2° quadrangle, southwestern Montana and east-central Idaho (fig. 1 ). These studies were made largely under the Conterminous United States Mineral Assessment Program (CUSMAP), the primary purpose of which is to determine the mineral resource potential of selected •1 °X2° quadrangles by means of a multidisciplinary approach. CUSMAP is intended to provide information on mineral resources to assist Federal, state, and local governments in formulating minerals policy and land-use policy and to produce sound scientific data that may be of value to private industry and the general public in mineral exploration and development.