Quartz-Dolerite Dykes from Shirahatti Area, Dharwar District, Mysore State

The quartz-dolerite dykes occurring in the Shirahatti area have been chemically analysed and a detailed petrological and mineralogical investigation has been made. The mineralogical investigation of the feldspars and pyroxenes has been done on the 4-axes Universal stage after the methods of Reinhard, Burri, Hess, Nemato, Turner, and others. The nature of the feldspars and the twin laws confirm the views of Gorai. The optical study of the pyroxene reveals the presence of enstatite, pigeonite and sub-calcic augite. The petrochemical. investigation indicates that the basic magma which has given rise to these dolerites had undergone fractional crystallization resulting in the enrichment of acidic residuum and volatiles. The deuteric and hydrothermal alterations seen in the dolerite dykes are due to the action of volatiles in the final stages of the consolidation of the basic magma.