Deformation and metamorphism of gold-sulphide lodes in the Bhukia–Jagpura gold prospect, Rajasthan: Implications for ore genesis

Abstract

The role of polyphase deformation in controlling the emplacement of gold-quartz lodes in dilational regimes is demonstrated from the Proterozoic Bhukia–Jagpura gold prospect in south Rajasthan. Earlier researchers deciphered the gold-sulphide mineralisation event as synchronous to the second phase of deformation (D2) without convincing microstructural or metamorphic evidences. In this contribution, we correlate the deformation and metamorphic imprints in the host rocks with those in the gold-sulphide mineralised zone, and present a new interpretation for the relative timing of gold emplacement vis-a-vis deformation. The ore-forming process first involved layer-parallel influx of ore-bearing hydrothermal fluids along S1 schistosity in the host rocks, synkinematic with respect to the first phase of deformation (D1). This initial ore concentration experienced metamorphism isofacially (~500°C at 5.3 kb) along with its host rocks during D1, and subsequently underwent extensive remobilisation, giving rise to gold-bearing silicified lodes along the hinges and axial surfaces of F2 folds during D2.