CHALCANTHITE IN FLOAT FROM A KYANITE MINE, CENTRAL VIRGINIA

Kyanite mining corporation, Dillwyn, Virginia has been in operation for over 50 years and is the largest kyanite mine in the world. During mining operations in late 2005 and early 2006 a unit that was approximately 9 meters thick was encountered that commonly developed a light blue mineralization crust after being exposed to the atmosphere over a period of two to four weeks. During a visit to the mine in September 2006 some relict boulders of this ore were observed in the float material. Fine grained efflorescent coatings 1 to 7 millimeters thick of the blue mineral were commonly observed on float rock of the ore. Field and laboratory tests indicated the mineral was completely water soluble and qualitative tests with 0.3 M BaOH indicated the presence of sulfate. This coating was investigated to determine the nature of the mineralogy and assess any environmental impact.

SEM and EDS investigation indicates that the cations present are solely Cu and S, with O being the only anion observed. Crystals commonly occur as near-anhedral pinacoids commonly 5 to 15 micrometers in maximum dimension. Smaller euhedral crystals approximately 1 to 2 micrometers in length occur on the surfaces of larger crystals. Near-anhedral crystals commonly have fractures one micrometer wide and tens of micrometers in length. These fractures combined with the fine grain size enhance the dissolution of the mineral. Powder X-ray diffraction identifies the mineral as chalcanthite, (copper sulfate pentahydrate).

Under normal freshwater pH conditions the Cu2+ ion is stable and is toxic to bacteria and invertebrates. Although the quantities observed here likely pose no major environmental threat, if an ore body is encountered again with similar properties the material should be closely monitored.