X-Ray Fluorescence (XRF), petrography, and Energy-Dispersive X-ray Spectrometry (EDAX) have been used to determine the element concentration in samples and their distribution within minerals for 222 metamorphic rock samples from the Black Hills, S.D. Element concentrations in these samples are compared to sample location and known gold deposits in the Black Hills.
XRF data of rock chips from whole rock samples were collected using a portable XRF unit to determine major, minor and trace element abundances. Statistical analyses of the XRF data indicates a moderate to strong correlation between gold and the elements Mn (19 to 16,116 ppm), S (1,283 to 79,452 ppm), As (n.d. to 132 ppm), Pb (n.d. to 318 ppm), Cl (625 to 31,277 ppm), Ba (n.d. to 1,101 ppm), and Zn (n.d. to 266 ppm) thus indicating these elements may serve as proxy indicators of gold. The integration of elemental data with ArcGIS was used to test the spatial relationship of proxy elements to known gold deposits in the Precambrian core of the Black Hills.
Sixteen samples having gold concentration greater than 18 ppm were chosen for more detailed analyses. EDAX raster scans of these samples determined proxy element variations within individual mineral grains. Petrographic analyses were done to identify minerals and their textural relationships.
Sample proximity to known gold deposits in the Black Hills can be correlated with increases in minor and trace proxy element concentrations.