Abstract Gems & Gemology, Spring 2013, Vol. 49, No. 1

Gem Olivine and Calcite Mineralization Precipitated from Subduction-Derived Fluids in the Kohistan Arc-Mantle (Pakistan)

Geochemical data in this study suggests that remobilized CO2 and H2O from a subducted island arc helped form the calcite + olivine-bearing veins in Kohsitan, Pakistan. The authors provide details on the geologic setting, mineralogy, and geochemistry of the vein assemblages, which can yield gem-quality olivine (peridot). The CO2 and H2O from island arc magmas and carbonates mixed with mantle fluids rich in Bo (as evidenced by ludwigite-vonsenite needlelike inclusions in olivine) as well as La, Ce, Ta, Cu, and Zn (from trace-element analysis). Fluid origin and emplacement are discussed at length, with emphasis on macro-geophysical mechanisms within the earth. Gem olivine production data and characterization of the rough were not provided.

Abstracted by Keith A. Mychaluk