The Snow Camp-Saxapahaw study area is in the Carolina slate belt within the central North Carolina Piedmont (fig. 1). It is an area, 9.86 miles (mi) (16.0 kilometers (km)) north-south by 10.3 mi (16.74 km) east-west, in southern Alamance County and northernmost Chatham County, about 19 mi (30 km) west of Chapel Hill and 12 mi (20 km) south of Burlington.
The Snow Camp-Saxapahaw area was studied because it contains a complex of arc-related volcanic rocks and several centers of intense high-sulfidation hydrothermal alteration, and it is within a region where several similar alteration centers contain gold deposits. Possible analogs of alteration style are known worldwide in young volcanic arcs, many of which contain significant metal enrichment, especially in gold. The metallic resource potential of the Carolina slate belt is supported by a 1992 annual production of over 6 metric tons (6.6 short tons) of gold, mostly from South Carolina (Sikich, 1992). Major objectives of the study were to identify and outline any large areas of high-sulfidation hydrothermal alteration zones, to identify the types of associated mineral deposits, and to develop an interpretive model for their origin. A further objective was to expand our understanding of how satellite remote sensing might be used in exploration for mineral resources in an area of mixed farms and forests. This was done in coordination with studies in the Carolina slate belt supported by the United States-Spain Joint Committee for Science and Technological Cooperation and North Atlantic Treaty Organization (NATO) Collaborative Project No. 530/88.
Geologic mapping was done from 1985 to 1990, using U.S. Geological Survey topographic quadrangle maps at 1:24,000 scale (fig. 2). Earlier visits had been made to hydrothermally altered areas from Georgia to southern Virginia, especially to those reported to have associated metallic mineralization. These visits noted large, mostly unmapped and some previously unknown areas of intense hydrothermal alteration in the Snow Camp-Saxapahaw area; therefore, this area was chosen for joint field studies.
The sporadically exposed rocks gave up their secrets reluctantly. Although outcrops are locally abundant along streams and on steep slopes, there are many large tracts where exposures are sparse and only tentative interpretations of complex geologic relations could be made. Detailed geologic mapping was done of all areas of strong alteration and near other signs of mineralization, and in certain areas that were critical for understanding the nature and effects of plutons and the sequence of volcanic rocks. Areas with no indications of hydrothermal alteration or mineralization, such as the Cane Creek Mountains and the southeastern corner of the area, were mostly examined on a reconnaissance basis.
Geologic mapping by E.H. Hughes (Hughes, 1987) provided a basis for interpreting the central most-altered area near the Snow Camp pyrophyllite mine (fig. 2, sector J), and her subsequent mineralogical studies verified the presence of minerals characteristic of high-sulfidation alteration. Her X-ray diffraction studies of over 40 samples of rock from the largest alteration centers assisted our later macroscopic mineral identifications in the field. Stream sediments panned by J.P. D'Agostino in April and June 1986 (D'Agostino and Schmidt, 1986) defined several areas of gold occurrence described in this report. Closely spaced soil samples were collected from sites overlying molybdenum-bearing greisenlike rocks in four areas south of Saxapahaw. These were analyzed for a variety of elements, the most significant being copper, molybdenum, and tin. Two mining companies carried out relatively small exploration programs in the area during the course of our study. Drill cores obtained in one program were made available for our study by the landowner.
Earlier detailed geologic mapping was done by Wilkinson (1978) in the southeastern corner of the study area. Geologic boundaries adapted from Wilkinson's mapping were used with slight modification (fig. 2, fig. 3, fig. 4A, fig. 4B, and fig. 5). Geobotanical studies of soil nutrient depletion in areas of intense hydrothermal alteration were reported by Payás and others (1993).
For convenience in locating field data points, figure 2, figure 3, figure 4A, figure 4B, and figure 5 were divided into 16 rectangular areas or sectors, designated A through P, and the appropriate sector was given for each data point when it is cited in the report. Six hills or highland areas of intensely altered rock, shown in figure 2, figure 3, figure 4A, figure 4B, and figure 5, are referred to herein as Ore Hill (sector N), Sheeprock (sector J), Mine Ridge (sector J), Major Hill (sector F), the Central Highland (sector G), and the Northeast Highland (sector C). Only the names Sheeprock and Major Hill are generally used by local residents. Ore Hill is a local name, but may not be well known. Numbered locations cited in the text as well as mines and prospects are shown in figure 2, and locations of analyzed rock, soil, and stream-sediment samples are shown in figure 3, figure 4A, figure 4B, and figure 5. Samples were assigned the same number as that of the field site where they were collected. We followed the guidelines of the International Union of Geological Sciences for the nomenclature of the volcanic and plutonic rocks of the area (Streckeisen, 1973, 1979). Note that permission of current landowners should be obtained before entering any properties.