PRIMARY MINERALIZATION OF URANIUM-BEARING "SILICEOUS REEF" VEINS IN THE BOULDER BATHOLITH, MONTANA. PART I. THE HOST ROCKS

Journal Article · Fri Jan 01 00:00:00 EST 1960 · Economic Geology and the Bulletin of the Society of Economic Geologists (U.S.)

DOI:https://doi.org/10.2113/gsecongeo.55.1.56· OSTI ID:4193688

Wright, H D; Bieler, B H

Between 1952 and 1956 a study was made of some of the uranium-bearing hydrothermal veins in the northern part of the Boulder batholith, Montana. Three mines, the W. Wilson, G. Washington, and Free Enterprise, were investigated in detail. The veins are characterized by a microcrystalline quartz gangue containing sparsely scattered, very fine-grained sulfide minerals and uraninite. Above the present water table, secondary uranium minerals are abundant locally. Throughout the area the veins --called "siliceous reefs"--strike east to northeast, are of steep dip, and vary in thickness from a fraction of an inch to several feet. The country rock is granodiorite containing, in order of abundance, plagioclase (An/sub 30/ to An/sub 36/), quartz, orthoclase, biotite, and hornblende, with apatite, zircon, and sphene. Small bodies of aplite, pegmatite, and alaskite occur along some veins. The granodiorite adjacent to the veins is rather strongly altered. The alteration is similar throughout all of the deposits studied, in barren and orebearing portions alike. The essential minerals show a characteristic sequence of alteration, in the order hornblende, andesine, biotite, orthoclase, and quartz. Successive zones of alteration are characterized, from the vein outward, by maximum development of sericite (muscovite polytype 1M, in part), kaolinite, and montmorillonite. Other alteration products are quartz, pyrite, calcite, leucoxene, and chlorite. The alteration resulted in an increase in silica and ferric iron, a decrease in alumina, total iron, ferrous iron, lime, soda, and magnesia, and little change in potash, titania, phosphorus, carbon dioxide, and sulfur. Consideration of the stability fields of the sheet structure silicate minerals indicates little basis for interpretation of the temperatures prevailing during mineralization. (auth)

• Research Organization: Pennsylvania State Univ., University Park
• Sponsoring Organization: USDOE
• NSA Number: NSA-14-009634
• OSTI ID: 4193688
• Journal Information: Economic Geology and the Bulletin of the Society of Economic Geologists (U.S.), Vol. Vol: 55; Other Information: Orig. Receipt Date: 31-DEC-60
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

GEOLOGY, MINERALOGY, AND METEOROLOGY
ALUMINUM OXIDES
APATITES
CALCIUM CARBONATES
CARBON DIOXIDE
CRYSTALS
GEOLOGY
IRON SULFIDES
MAGNESIUM OXIDES
MINERALIZATION
MINERALS
MONTANA
PHOSPHORUS
POTASSIUM OXIDES
QUARTZ
ROCKS
SILICON OXIDES
SODIUM OXIDES
STABILITY
SULFIDES
SULFUR
THICKNESS
TITANIUM OXIDES
URANINITES
URANIUM MINERALS
URANIUM ORES
USA
VEINS
ZIRCONIUM OXIDES