Options
Genesis of the late-stage base metal sulfide mineralisation and its relationship with the regional deformation in Ambaji–Deri, South Delhi Terrane, North-West India
Journal
Geological Journal
ISSN
00721050
Date Issued
2022-08-01
Author(s)
Sharma, Neeraj Kumar
Chinnasamy, Sakthi Saravanan
Biswal, Tapas Kumar
Abstract
Proterozoic stratiform VMS-type Ambaji–Deri Zn–Pb–Cu deposits in the Aravalli-Delhi mobile belt of North-West India are hosted within meta-sedimentary sequences of the South Delhi Terrane. Several fracture-filled discordant late-stage base metal mineralised quartz veins have intruded along with the fractures and foliation at very high Pf (σ2 < Pf < σ1) with typical hydrothermal alteration zones. Temperatures estimated from hydrothermal chlorite vary from 226 to 293°C (mean. 260°C). 40Ar-39Ar dating of hydrothermal muscovite yielded a plateau age of 625.5 ± 3.3 Ma. Detailed fluid inclusion (FI) analysis reveals three types of primary and four types of secondary FI. Primary H2O-NaCl-CO2 ± N2 type 1a FI has medium to high salinity (11.21–21.96 wt% NaCl equivalent) and high density (0.90–1.04 g/cm3), while the secondary type 1b FI with same compositions are characterized by medium salinity (~12.6 wt% NaCl equivalent) and lower density (0.89–0.90 g/cm3). Phase separation/fluid immiscibility is the primary mechanism of mineralisation in the Ambaji–Deri that caused the original fluid to evolve separately as gaseous (CO2) type 2a, b and aqueous type 3a, b (H2O-NaCl) with similar salinity and density for the aqueous inclusions and low density for the gaseous inclusions (lowering up to 0.58 g/cm3). The ore-forming fluid with magmatic signatures possibly originated from the cooling G3 granites, remobilized the pre-existing metals, and precipitated at ~265°C and ~1 kbar at the epizonal depths in the dilated fractures. Later these fluids are mixed with meteoric water and evolved into low saline aqueous fluids that produced supergene alterations.
Subjects