VOLCANOGENIC MASSIVE SULFIDE DEPOSITS

Host rocks of volcanogenic massive sulfide (VMS) deposits are characterized by extensive hydrothermal alteration. The alteration zone consists predominantly of chlorite near the Cu-Zn+Pb orebody and it grades into sericite at a distance from the ore. Such well defined alteration halo provides an excellent exploration target for VMS deposits.

Although high-grade metamorphism will obscure the primary alteration halo around the orebody, the metamorphic minerals reflect the original alteration assemblages. The photographs below show the (a) typical chlorite and sericite-rich (hydrothermal) assemblages and (b) their recrystallized, metamorphosed (upper amphibolite grade) equivalents. All photographs are 4mm long.