ANALYSIS OF GREISEN-FORMING ANOROGENIC GRANITOIDS IN IRISH CREEK, VIRGINIA

The Irish Creek tin deposit is a greisen-related cassiterite deposit in the Blue Ridge of Rockbridge County, Virginia. The deposit formed in a granodiorite that intruded basement gneisses of the Pedlar massif. The intrusion was likely emplaced during a late phase of the Neoproterozoic rifting of Rodinia (~650 Ma), which produced largely A-type granitoids. Greisen deposits, however, are most commonly associated with S-type granites associated with arcs or backarcs. In this study we analyize the petrology and mineralogy of the Irish Creek deposit and host rocks to investigate the distinction of this greisen deposit and its mode of origin.

Samples were collected from the mine itself and from the surrounding granitoids of the region, with particular attention to collecting samples between the mineralized zone and the unaltered granitoid rock. We are using thin section analysis to explore the granitoid’s mineralogy and to assess the type of alteration based on the rock’s texture. We will employ X-ray diffraction analysis to produce more accurate information on the mineralogy of the rock and the ore body, and whole-rock geochemistry to determine the type of granitoid that hosts the deposit.