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Open-File Report 2006-1259 

| Published 2006      Online Only                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       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| Geology and Mineral Deposits of the Snow Camp-Saxapahaw Area, Central        North Carolina By Robert G. Schmidt,1 Pablo Gumiel,2 and Alba Payás31U.S. Geological Survey, Reston, Va.2Instituto Geológico y Minero de España, Madrid, Spain3Servei Geológic de Catalunya, Barcelona, Spain                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        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| Abstract                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   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| The Snow Camp-Saxapahaw study area, in the Carolina        slate belt in the Southeastern United States, is notable for large zones        of high-sulfidation alteration in arc-related metavolcanic rocks. The        area has potential for additional significant pyrophyllite and related        aluminosilicate refractory mineral deposits and may have potential for        small- to medium-size gold deposits also associated with the high-sulfidation        hydrothermal systems.

The Carolina slate belt is an elongate zone of mostly low-grade metamorphic        rocks of Neoproterozoic to early Paleozoic age that extends from northeastern        Georgia to southern Virginia. It is dominated by volcanic rocks but locally        consists of fine-grained epiclastic sedimentary rocks. Plutons and subvolcanic        bodies have intruded the rocks of the Carolina slate belt in many places        and have been important in controlling the metamorphism and in localizing        hydrothermal alteration.

The Snow Camp-Saxapahaw area is mostly underlain by volcanic and volcaniclastic        rocks and lesser amounts of intrusive shallow plutons. The volcanic rocks        range in composition from basalt to rhyolite; however andesites, dacites,        and rhyodacites are the most abundant. The intrusive bodies are largely        granite and quartz monzonite; gabbroic bodies also are common. It was        possible to establish the relative ages of only part of these rocks.

Two northeast-trending fault zones and fractures divide the map area        into three structural blocks; the central block was tilted down to the        southwest to form a grabenlike structure. Most of the hydrothermally        altered rocks and all of the intensely altered zones are confined to        the downdropped block, which we think may have been calderalike in origin.        A major volcanic unit, the Reedy Branch Tuff, is limited to the southwestern        part of the graben and may be the youngest volcanic rock in the area.        Layered rocks record one or more strong folding events, but the diversity        of rock types, lack of recognizable stratigraphic markers, and uneven        distribution of outcrops prevented comprehensive structural studies.

Except for a few late plutons and dikes, all of the rocks of the area        have been metamorphosed in middle to upper greenschist facies, and contact        aureoles were recognized around some of the plutons. Several relatively        small bodies of granitic rock contain plagioclase grains in which primary        oscillatory zoning was unaffected by metamorphism. These were interpreted        to be post-metamorphic.

We think that there were three separate stages of hydrothermal alteration        in the complex volcanic terrane in the area. The oldest, an area of at        least 8.5 square miles (22 square kilometers), was subjected to an intense        hydrothermal alteration, ranging from peripheral zones of quartz-sericite-paragonite        through a patchy marginal zone of pyrophyllite, andalusite, and other        high-alumina minerals, to almost totally silicified core zones. The second        event resulted in large areas of weak to moderate sericitic and propylitic        alteration recognizable only in the Reedy Branch Tuff. The last event        was related to post-metamorphic plutons.

All of the pyrophyllite-andalusite deposits and perhaps most of the        gold and silver mineralization can be related to the first period of        hydrothermal alteration. The subsequent metamorphism did not produce        significant changes in mineral species in the zones of most intense hydrothermal        alteration. Gold- and silver-bearing sulfide minerals in fracture zones        along the southeastern margin of the graben may also have been deposited        during this earliest alteration stage. No metallic mineralization appears        to have occurred during the second event. A group of molybdenum-bearing        greisenlike bodies formed during the emplacement of the youngest plutons        during the post-metamorphic event. One gold-bearing sulfide zone occurs        in the exocontact of one such porphyritic stock.

Significant amounts of pyrophyllite-andalusite-bearing rock have been        extracted from the Snow Camp Mine and from several smaller pits. There        may be other undiscovered deposits in this area. Small gold mines were        operated here in the nineteenth century and probably in the early decades        of the twentieth century, but we found records of production and descriptions        in the geologic literature of only smaller prospects. No mines were being        operated here during our study. There may be other exploitable deposits        near and in the siliceous core zones of intense high-sulfidation alteration        and in fracture zones along the southeastern side of the graben structure.        Evaluation of the gold potential was based on the results of stream-sediment        sampling, on the analyses of sulfide-bearing rock from shear zones, on        the mining history of the area, and on comparisons with districts having        similar geology.
ContentsFiguresTablesConversion Factors AbstractIntroductionAcknowledgmentsClimate, Vegetation, Soils, and TopographyGeneral GeologyGeology of the Snow Camp-Saxapahaw AreaStructural GeologyHydrothermal Alteration and MineralizationMetamorphic GeologyGeochemical StudiesMines, Quarries, and Other Mineralized SitesMineral Potential of AreaRemote-Sensing StudiesReferences Cited |
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U.S. Department of the Interior |	U.S. Geological Survey	URL: http://pubsdata.usgs.gov/pubs/of/2006/1259/index.html	Page Contact Information: Publications Service	Center 4	Page Last Modified:  22:14:24 Sat 12 Jan 2013

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