Paper No. 41-2
Presentation Time: 1:00 PM-5:00 PM
INDICATOR MINERAL ANALYSIS IN STREAM SEDIMENTS BORDERING THE NORTH AMERICAN EMERALD MINE IN ALEXANDER COUNTY, NORTH CAROLINA
The North American Emerald Mine (NAEM), located in Alexander County, North Carolina, contains V-Cr-bearing beryl deposits that have produced the most valuable emeralds ever found in North America, and is the only confirmed location of Cr-bearing spodumene, known locally as hiddenite. These emeralds and spodumene occur within quartz veins and open cavities, but rarely form within the same cavity assemblage. Other identified veins and cavity assemblages in this area include calcite-bearing and amethyst. These four cavity types run throughout the Inner Piedmont Belt of western North Carolina in northeast oriented, subvertical fractures in middle- and upper- amphibolite facies metamorphic rocks. The host quartz veins are thought to be of hydrothermal origin, precipitating under relatively low pressure conditions within 230°C - 290°C. This project analyzes the mineralogical characterization of the NAEM through an analysis array of the dense stream sediments sampled from the Wallace Creek and the South Yadkin River, which border and converge along the southeast border of the mine site. Within the stream sediments, emeralds and indicator minerals are selected for chemical analysis to determine the formation history of the deposit and potential locations of higher concentrations of emeralds. Formation indicator minerals and other minerals of interest such as beryl and spodumene found in the sediments are further analyzed by precise chemical analysis. This work further characterizes the indicator minerals within the four cavity types present at NAEM and the role of the chromophore V in the emerald’s coloration. Mineral analysis includes visual observations by polarized light microscopy and scanning electron microscopy, mineral phase identification by X-ray diffraction, and chemical composition by energy dispersive spectroscopy and wavelength dispersive spectroscopy.