David L. Bowling

Thesis: The Geology and Genesis of the Apex Gallium-Germanium Deposit, Washington County, Utah

Support: Musto Exploration, Inc., University of Utah

Abstract

Gallium and germanium mineralization occurs in a breccia pipe developed in the thick Paleozoic carbonate sequence of the southern Beaver Dam Mountains, southwestern Utah. The ore zone at the Apex is centered in a subvertical, approximately elliptical (30 x 110 m) pipe with only minor stratigraphic and fracture controlled extensions into the surrounding country rock. The pipe, presently exposed in the mine to a depth of 365 m, extends from its surface outcrop in the lower Pakoon Dolomite down through the middle Callville Limestone; its downward termination is unknown.

The country rocks surrounding the breccia pipe have been extensively altered, and now are concentrically zoned around the breccia pipe. As the pipe is approached, unaltered limestone gives way to a silicious dolomitized zone (3 - 20 m thick), and finally to a totally silicified zone 0 to 9 m thick.

The proposed genetic sequence is: 1) formation of the solution collapse breccia pipe by massive limestone dissolution by meteoric waters; 2) dolomitization of the pipe by low temperature (<90%#176;C) waters; 3) mineralization of the pipe by hot (up to 330%#176;C) low-salinity (<0.02 NaCl weight percent equivalent) hydrothermal waters. Mineralization consists of stage I quartz, muscovite, goyazite/svanbergite and minor sulfides followed by stage II quartz and goyazite/svenbergite. Ore mineralization consists of Ga-bearing jarosite family minerals and Ge-bearing goethite. Textural, chemical and physical evidence suggests that at least some of the ore-bearing minerals may be hypogene (stage II) in origin. The deposit has been overprinted by a variety of base metal carbonates, hydrous oxides, phosphates and arsenates. K/Ar dating of two plumbian jarosite samples gave late Miocene ages. These ages correlate well with the timing of late Cenozoic Basin and Range extensional structural activity in the southern Beaver Dam Mountains.

The source rock(s) for the gallium and germanium are inferred to be the Precambrian basement and/or the Bright Angel Shale.

Dave assists driller, Apex Mine.

Bowling, D.L. and Petersen, E.U., 1987, Breccia pipe-hosted gallium-germanium mineralization: Geology of the Apex mine, southwestern Utah: Geological Society of America Abstracts, 19, 7, 596.

Petersen, E.U., Bowling, D.L. and Mahin, R.A., 1988, Geology, mineralogy and genesis of the Apex Ga-Ge Deposit, Tutsagubet District, Utah: Symposium on Precious and Rare Metals Abstracts, New Mexico Tech. State Mining and Mineral Resource Institute, Albuquerque, New Mexico, April 6-8, 1988. pdf

Petersen, E. U., Bowling, D. L., Mahin, R. A. and Bowman, J.R., 1989, Geology, mineralogy, and genesis of the Apex Ga-Ge deposit, Tutsagubet District, Utah: in A. E. Torma and I. H. Gundilier, Eds., Precious and Rare Metal Technologies, Amsterdam, Elsevier, 511-530.