Download Guidebook as .pdf (2.2 Mb) - Carolina Geological Society

More documents

Recommendations

Info

______________________________________________________________________________________ 2008 annual meeting – Spruce Pine Mining District: Little Switzerland, North Carolina ______________________________________________________________________________________ A NOTE ON URANIUM MINERALS FROM THE SPRUCE PINE AREA, NORTH CAROLINA Richard Warner 1 , Stephen Poterala 2 and Chris Fleisher 3 1 Department of Environmental Engineering & Earth Sciences, Clemson University, Clemson, SC 29634- 0919 2 Department of Materials Science & Engineering, Pennsylvania State University, University Park, PA 16802 3 Department of Geology, University of Georgia, Athens, GA 30602-2501 INTRODUCTION Uranium minerals are often found in granitic pegmatites, where they nearly always occur as minor constituents of insufficient quantity to be mined (Page, 1950). Their occurrence in this geologic setting is a consequence of the fact that uranium behaves as an incompatible element in magmatic systems. The size and charge of uranium ions make their substitution for major ions in common silicate minerals difficult, with the result that uranium is concentrated at the felsic (e.g., granitic) end of magmatic differentiation series (Rogers and Adams, 1969; Krauskopf and Bird, 1995). Thus, the mean uranium content of igneous rocks ranges from 0.8 ppm in mafic rocks to 4.0 ppm in granite (Rogers and Adams, 1969; Plant and others, 1999). The separation of a water-rich fluid phase both promotes the growth of exceptionally coarse crystals, characteristic of pegmatites, and further concentrates uranium, such that some pegmatites eventually crystallize one or more uranium-rich minerals. The uranium minerals occurring in pegmatites include both primary (i.e., magmatic) minerals and various secondary minerals. Chief among the primary uranium minerals is the simple oxide, uraninite (UO 2 ). It typically is associated with muscovite-rich pegmatites (Page, 1950). Also important are uranium-bearing multiple oxide minerals (Frondel, 1958): these are principally niobate-tantalate minerals and often contain significant amounts of the rare earth elements (REE). Samarskite is the most common example, and may contain 10-20 weight percent UO 2 . Other primary uranium-bearing minerals include the REE-phosphate, monazite, and silicate minerals such as zircon and allanite. The latter minerals, though more abundant in pegmatites, generally contain much less uranium (usually far below 1 weight percent UO 2 ). A wide variety of secondary minerals, of variable water content, are derived from the partial or complete alteration of uraninite and other primary uranium minerals. Gummite, uranophane, autunite and torbernite are but a few of the many secondary minerals that can be formed (Page, 1950; Frondel, 1958). Pegmatites of the Spruce Pine mining district have long been known to host uraninite and related uranium minerals and constitute one of the principal occurrences of such minerals in the eastern United States (Ross and others, 1931). Allen (1877) reported chemical analyses of samarskite and hatchettolite (a niobate-tantalate mineral belonging to the ______________________________________________________________________________________ Page 29 ______________________________________________________________________________________
______________________________________________________________________________________ 2008 annual meeting – Spruce Pine Mining District: Little Switzerland, North Carolina ______________________________________________________________________________________ pyrochlore group) from Mitchell County, North Carolina. Kerr (1877) and Genth (1879) examined uranium minerals from the Flat Rock mine in Mitchell County and found them to consist of uraninite and a mixture of alteration products. Hidden (1881) noted the occurrence of uraninite and its alteration products at Flat Rock and two other mica mines in Mitchell County. An analysis of uraninite from the Flat Rock mine was included by Hillebrand (1891) in his general survey on the composition of uraninite. Sterrett (1923) noted four mines from the Spruce Pine area (Flat Rock; Deer Park; Deake; W. W. Wiseman) from which uranium minerals were found; with reference to the W. W. Wiseman mine, the uraninite alteration minerals pitchblende, gummite and uranophane were identified, and also rare-earth minerals (e.g., samarskite). The new mineral name clarkeite was proposed by Ross and others (1931) for a sodic uranyl oxide associated with uraninite, gummite and uranophane and originally found at Spruce Pine. These authors surmised that clarkeite formed during a late hydrothermal stage whereby alkalibearing solutions caused its alteration from primary uraninite. Maurice (1940) included uraninite and several of its alteration products (clarkeite, gummite, uranophane, autunite, and torbernite) plus samarskite and other less common niobate-tantalate minerals such as columbite, euxenite, fergusonite, hatchettolite, and microlite among the accessory minerals characteristic of Spruce Pine district pegmatites. Additional listings of the various uranium minerals known to occur in the Spruce Pine area were published by Parker (1952) and Brobst (1962), along with information on specific mines where they have been found. However, by far the most thorough compilation of uranium mineral localities in the Spruce Pine area was published by Lesure (1968) in his exhaustive compendium of mica deposits in the Blue Ridge of western North Carolina. Of more than 700 mica mines described from the Spruce Pine district, eight (a little over 1 percent of the mines) were noted as containing uraninite. Another dozen mines were indicated to host unspecified uranium minerals, while samarskite was noted to occur at eight mines. About half of the latter were stated to contain uraninite or uranium minerals as well, yielding a total of 25 mines at which uranium containing minerals have been identified. Because many of the previous studies either focused on samples from a single locality or emphasized the occurrence of secondary uranium minerals, and very few microprobe mineral analyses have been published in the literature, we have undertaken a mineralogical characterization study of uranium minerals from selected mine localities in the Spruce Pine district. Based on the mine description summaries catalogued by Lesure (1968), specific pegmatites were chosen to visit and collect samples for study. Our efforts for the most part have been directed towards the primary uranium mineralogy of the pegmatites, with the goal of ascertaining how much compositional variability exists, both within a single deposit and from one pegmatite to another, in the various uranium minerals. ______________________________________________________________________________________ Page 30 ______________________________________________________________________________________
Page 1: Carolina Geological Society 2008 Fi
Page 4 and 5: ___________________________________
Page 6 and 7: ___________________________________
Page 8 and 9: The Spruce Pine Mining District - A
Page 10 and 11: GEOLOGY The geologic history of Spr
Page 12 and 13: The Sink Hole at Bandana: A Blue Ri
Page 14 and 15: of the site on U.S. 226, between Sp
Page 16 and 17: additional quality, mica’s dielec
Page 18 and 19: 1919). Holmes and others have specu
Page 20 and 21: FIGURE 1 William H. Holmes, taken d
Page 22 and 23: FIGURE 6 View in 1936 of “ancient
Page 24 and 25: FIGURE 10 View of the Seip Mound, R
Page 26 and 27: ___________________________________
Page 28 and 29: ___________________________________
Page 30 and 31: ___________________________________
Page 32 and 33: ___________________________________
Page 34 and 35: ___________________________________
Page 36 and 37: ___________________________________
Page 38 and 39: ___________________________________
Page 40 and 41: ___________________________________
Page 42 and 43: ___________________________________
Page 44 and 45: ___________________________________
Page 46 and 47: ___________________________________
Page 50 and 51: ___________________________________
Page 52 and 53: ___________________________________
Page 54 and 55: ___________________________________
Page 56 and 57: ___________________________________
Page 58 and 59: ___________________________________
Page 60 and 61: ___________________________________
Page 62 and 63: Figure 2 Warner and others (2008) p
Page 64 and 65: Y+REE Samarskite-(Y) Calciosamarski
Page 66 and 67: Ti Betafite Pyrochlore Nb Microlite
Page 68 and 69: Table 2 Analyses of Uraninite Alter
Page 70 and 71: Table 4 Uraninite Age Determination
Page 72 and 73: ___________________________________
Page 74 and 75: ___________________________________
Page 76 and 77: ___________________________________
Page 78 and 79: ___________________________________
Page 80 and 81: ___________________________________
Page 82 and 83: ___________________________________
Page 84 and 85: ___________________________________
Page 86 and 87: ___________________________________
Page 88 and 89: ___________________________________

Download Guidebook as .pdf (2.2 Mb) - Carolina Geological Society

Create successful ePaper yourself

Delete template?

Save as template?