Structural implications of paleofluid pressure and paleostress estimates of the quartz veins from sulfide deposits of the Ambaji-Deri region, Neoproterozoic South Delhi Terrane, Aravalli-Delhi Mobile Belt, North-West India

Quartz vein-related sulfide mineralization is dependent upon paleostress and paleofluid pressure conditions. Neoproterozoic South Delhi Terrane, Aravalli-Delhi Mobile Belt, North-West India is characterized by quartz veins hosted Cu-Pb-Zn mineralization around the Ambaji-Deri area of Gujarat and Rajasthan. Stereoplot of the pole of quartz veins majorly shows a girdle distribution indicating elevated Pf (pore fluid pressure) condition (Pf > σ2) and minor cluster distribution implying low Pf condition (Pf < σ2). The thickness of veins shows the power-law distribution (D = 0.406), inferring that mineralization is associated with thicker veins. Pf was measured from the fluid inclusions in the quartz veins, which were aqueous-carbonic, carbonic-biphase and aqueous-biphase types. The isochores yielded a P-T value of about ∼ 265 °C and 95 MPa (highest Pf) and ∼ 50 MPa (lowest Pf). θ1, θ2 and θ3 values obtained from the stereoplot for each distribution pattern were used to draw the 3D Mohr circle, which estimates effective principal stresses are σ1 > Pf > σ2; σ1′ = 98 MPa; σ2′ = 92 MPa and σ3′ = 20 MPa at the highest Pf and Pf < σ2; σ1′ = 133 MPa; σ2′ = 73 MPa and σ3′ = 47 MPa at the lowest Pf. High Pf values led to reprecipitation of monazite along with sulfides; the U-Th-Pb EPMA age of monazite yielded the ages of ca. 644 to 515 Ma for sulfide mineralization.