GRANITOIDS AROUND THE MALANJKHAND COPPER-DEPOSIT - TYPES AND AGE RELATIONSHIP

On the basis of field relations, petrography and chemistry, three type s of granitoids are recognized at Malanjkhand in and around the copper deposit over an area of about 200 km2. These are (i) a fine grained ' leucogranite' of restricted occurrence in the surrounding area (Gr-I); (ii) coarse-grained, grey in most parts, gneissose granitoid of regio nal extension (Gr-II); and (iii) the pink-feldspar bearing massive typ e hosting the mineralization with occasional representatives in the su rrounding country (Gr-III). Gr-I comes out as a distinct entity on the basis of cross-cutting relation and mineralogical and chemical compos ition, the Rb-Sr whole rock isochron also giving a younger age than th e other two groups irrespective of the regression model used. Gr-II co mes out as the oldest unit but its age relationship with Gr-III cannot be established unequivocally. An uncorrelated error regression model establishes the age relationship as Gr-I < Gr-III < Gr-II, whereas a t wo-error regression model establishes temporal closeness between Gr-II and III.