Morphology and Chemistry of Zircons from the Paleoproterozoic Cu (±Mo±Au) Hosting Granitoids of Malanjkhand Mine Area, Central India

Abstract

Abstract Morphology and chemistry of zircons from Paleoproterozoic granitoids (~2470 Ma) of Malanjkhand mine area, central India have been used to understand nature of parental magma and its evolutionary history. External morphology of non-metamict zircons belongs to S3, S1-2, G1, P2, S24 and S25 subtypes of Pupin’s typological scheme, which crystallized in a calc-alkaline, metaluminous hybridizing magma. The Zr/Hf ratios of zircons point to a low degree of differentiation of parental magma. Most zircons bear low sum of rare earth elements (ΣREE<700 ppm) indicating late stage of crystallization, whereas a zircon with anomalously high LREE and ΣREE probably indicates at an early stage of its crystallisation in the absence of other REE bearing accessory phases or might have been influenced later by hydrothermal fluids. The Nb content of zircons is similar to those commonly formed in high-K, calc-alkaline granitoid magma series. The zircon (Th/U>1) with high ΣREE (5019 ppm) and Ti (56 ppm) contents provides zircon crystallization temperature (TZr) of 938°C suggesting its crystallisation in a relatively high-T intermediate magma composition. However, zircons with Th/U<1 bear Ti content below the detection limit (33 ppm) due to their crystallization in a relatively more evolved aluminous melt fraction of parental calc-alkaline magma. All zircons exhibit positive Ce- and negative Eu-anomalies, which probably indicate mildly oxidising magma condition of zircon crystallization synchronous with plagioclase.