Petrological and mineralogical study of enclaves in plutons in the typical mining districts of Tongling, Anhui and its bearing on the process of magmatism-metallogeny

Abstract

Two types of enclaves occur in magmatic plutons in Tongling, Anhui. Enclaves of the first type are residuals of metamorphic rocks of high amphibolite facies, and those of the other type are magmatic rocks ranging from monzonitic to dioritic in composition. A combined petrological and mineralogical study has been carried out on the two types of enclaves in order to estimate their forming conditions and analyze their relations to their hosts, so as to have an insight into the material sources of magmatic rocks and associated mineral deposits and give a clue to better understanding the mechanism of magmatism-metallogeny. This leads us to propose a new metallogenic model for strata-bound skarn-type ore deposits associated with a syntectic type of magmatic rocks. The new model can be simply summarized as partial melting of old metamorphic basement rocks at depth and accumulating, differentiating and positioning of magmas to form deep-level and shallow-level magma chambers, followed by mixing of different magmas associated with their crypto-explosion, migration of gas-bearing ore fluids and precipitation of metals in fluids within the magmas.