Open-File Report 2006-1259

Published 2006
Online Only

Geochemical Studies

Samples of altered and unaltered rocks, residual soils, and stream alluvium were taken to gain a better understanding of the metallic mineralization in the area and were analyzed using methods described in Baedecker (1987). Composite chip and representative grab samples were taken for analysis from 85 rocks in the area, almost all of them visibly mineralized or strongly hydrothermally altered. Locations of these samples are given in figure 3, and analyses are given in table 8, table 9, and table 10. Of these, 70 were sulfide-bearing altered rocks and sulfide gossans. Seventy-eight of the rock samples were analyzed for gold by fire assay or flame atomic absorption, and most of these for other elements by emission spectroscopy; the results are given in table 8, table 9, and table 10. More than 160 composite soil samples were analyzed by X-ray spectroscopy, mainly to study the distribution of minor amounts of copper, molybdenum, tin, and silver. The locations are shown in figure 4A and figure 4B, and the results of analyses are given in table 11A and table 11B. Almost half of the soil samples were taken in three small areas as part of a detailed examination of areas of greisenlike rock. Ninety-eight panned stream sediments and soil concentrates, including 48 reported previously by D'Agostino and Schmidt (1986) (fig. 5 and table 13) were collected and examined for visible gold and other heavy minerals. Eighty-three samples of fine alluvium from small streams were analyzed by emission spectroscopy for a broad array of elements and by fire assay for gold (fig. 5 and table 12).

Greisenlike Rocks Containing Anomalous Molybdenum

Molybdenite was a common accessory in three areas of greisenlike rock present only as float (fig. 4B). The float contains molybdenite-rich ocher in boxworks that have structures characteristic of oxidized molybdenite as described by Blanchard (1968, p. 160). The locally abundant greisenlike rock consists of large pieces as long as 16 in (40 cm) in the eastern area, whereas only small fragments were found in the central and western sampled areas. The maximum amount of molybdenum in the rock samples was 850 parts per million (ppm) (site 6584, table 9; fig. 3, sector H), and the maximum amount of tin was 43 ppm (site 6938, table 9; fig. 3, sector D). Residual bits of pyrite remain in some of the samples. Two analyses of greisenlike rocks (sites 6938 and A365, fig. 3, sector D) contained 700 and 800 ppm fluorine, within the normal range for granitoid rocks, and chlorine was less than the analytical threshold of 40 ppm.

Sulfide-Bearing Rocks and Gossans

Composite rock chip samples collected to be representative of much larger volumes of rock were obtained from 59 sites, the locations of which are given in figure 3, and the analytical results are given in table 8, table 9, and table 10. These samples were collected from sulfide-bearing shear and fracture zones, or from rocks with no visible sulfide that we thought resembled gold-bearing rocks in other districts that had undergone high-sulfidation alteration. An area, tens of feet in diameter, of large siliceous gossan boulders and probably small gossan outcrops (site 6277, fig. 3, sector G) was located close to small outcrops and many large float boulders of unmetamorphosed, coarsely porphyritic dacite (Cg). Both the size and character of the gossan are unusual for the Snow Camp-Saxapahaw region. The dacite was propylitically altered, and a genetic relation to the sulfide-rich protolith of the gossan was assumed. The gossan now contains abundant voids in the remaining quartz resulting from the dissolution of sulfide. Most voids are 5/16 to 3/8 in (0.5 to 1.0 cm) in diameter, but some are as large as 2 in (5 cm) and are lined with nearly black and mostly lustrous limonite. The rock has been much hardened by very strong silicification for 2 to 3 in (5–8 cm) outward from old fractures. One composite sample of the gossan (site 6277, table 10, fig. 2 and fig. 3) was analyzed and found to contain 0.43 ppm gold, 0.2 ppm silver, 10 ppm molybdenum, and 9.4 ppm tin, but no significant amounts of other metals.

Several rock chip samples were taken at mine and prospect sites such as the Mazejka gold prospect and the Braxton Mine area. A single sample from sulfide-bearing rock at site CA25 (approximate location, fig. 2 and fig. 3, sector J, near a strand of the South Fork fault system) contained 0.925 ppm gold.

Soils Sampled for Chemical Analyses

Most analyzed soils were taken from known and suspected areas of hydrothermal alteration, and a few were taken from adjacent unaltered areas. Each soil sample was a composite of 10 to 15 small scoops of roughly equal size collected from an area 15 to 30 ft (5–10 m) in diameter; sample locations are shown in figure 4A and figure 4B. Where undisturbed soil profiles were present, the samples were dug from the "A" horizon below the surficial organic layer. Samples were analyzed for molybdenum, copper, tin, and silver. Results of those taken in the map area, except sectors D and part of sector H (fig. 4A), are given in table 11A, and those associated with molybdenum-bearing, greisenlike, muscovite-quartz rocks were sampled at evenly spaced sites in three areas near Eli Whitney (fig. 4B and table 11B). All four elements were generally anomalously abundant near areas of greisenlike rocks.

Most soil samples, with molybdenum contents over 15 ppm and copper contents more than 80 ppm, are clustered at the southern quarter of sector D and the northern quarter of sector H (fig. 4B). The source of the soil molybdenum was almost certainly the weathering of molybdenite and other minerals in the muscovite-rich, greisenlike rock.

Eighty-three unpanned stream sediment samples were collected from sites shown in figure 5, and the analytical results for gold are given in table 12. Streams draining already known areas of gold occurrence were not generally sampled in this study.

Results of Panning Soil and Stream-Sediment Samples and Analyzing Stream Sediments

Thirty-one soil samples from areas that had an unknown potential for gold were panned and the results given in table 13. The results of panning 40 stream sediments were reported by D'Agostino and Schmidt (1986), and their findings are included in figure 5 and table 13, along with those from 19 additional samples collected by Charles Thomas (U.S. Geological Survey) and examined by John D'Agostino (U.S. Geological Survey). Stream sediments were taken from silt-size deposits in the streambeds and low banks.

 
 

The text of this report is provided as HTML. All figures are provided as high-resolution Portable Document Format (PDF) files. All tables are provided as Microsoft Office Excel (.xls) files.
 
To view and print Portable Document Format (PDF) files you will need Adobe Reader software. Download the latest version of Adobe Reader, free of charge.
 
Download Suggestion for Portable Document Format (PDF) Files
Recommended download procedures due to large file size—right-click (PC) or control-click (Macintosh) and save file to hard drive. Opening file from hard drive will result in a faster load time.
 

Accessibility FOIA Privacy Policies and Notices

Take Pride in America home page. FirstGov button U.S. Department of the Interior | U.S. Geological Survey
URL: http://pubs.usgs.gov/of/2006/1259/geochem_studies.html
Page Contact Information: Publications Service Center 4
Page Last Modified: 22:14:22 Sat 12 Jan 2013