Bulletin, 134. izdajaMontana College of Mineral Science and Technology, 2007 |
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7.5-minute quadrangle abundant alluvial deposits alluvial sapphires alluvium altered aluminum silicate American Gem andalusite apatite basal bedrock source biotite blue sapphires Boulder batholith Bow sapphire occurrence Butte-Deer Lodge area color colorless conchoidal fractures corundum cubic yard debris flow dredge Dry Cottonwood Creek exposed Figure Fork of Dry garnets garnets were recovered grains Grand Pre Flat gravel grooves hexagonal high specific gravity identified igneous rock Lowland Creek Volcanics magma magnetite Marc Bielenberg meadow metamorphic rocks mineral inclusions Nancy Equall NE¼ pale green pebbles phires Photo by Nancy Photo by R.B. Photomicrograph placer mining plagioclase planes potassium feldspar Prospects Prospects quartz R.B. Berg Rock Creek rutile sample sapphire deposits sapphire-bearing sapphires from Lowland sapphires recovered Scanning electron micrograph sieve sillimanite Silver Bow occurrence Silver Bow sapphire Smedes South Fork specific gravity specimen spinel thin section tion tuff U.S. Geological Survey upstream volcanic rock zircon