Geologic descriptionBlack tourmaline and quartz-tourmaline rock partly to completely replace porphyritic biotite granite of the Cretaceous Taylor Mountains pluton (Travis Hudson, unpublished field data, 2005) Coarse euhedral tourmaline aggregates are well developed along a northwest-trending vertical fracture or fault in the granite. The tourmaline-rich zone is at least several feet wide; float blocks of tourmaline and quartz-tourmaline rock are up to 4 or 5 feet thick. These blocks are scattered on the surface in a line for about one to two hundred feet. The host granite has large euhedral K-feldspar phenocrysts up to 8 to 10 centimeters long in a fine- to medium-grained equigranular groundmass. The Bureau of Land Management sampled this occurrence in 2004 (Ellefson and others, 2005). Two rock samples contained 100 and 300 parts per million (ppm) arsenic, 107 and 106 ppm copper, less than 5 and 15 ppm tin, less than 0.01 tantalum, and 2.96 and 15.3 ppm uranium. These samples contained only 10 and 70 ppm boron and are therefore not representative of the tourmaline-rich rocks at this locality. T. K. Bundtzen (personal communication, 2005 ) also sampled these tourmaline-rich rocks in 2005. |
