Paleostress and Fluid Pressure Analysis of Vein Opening Using 3D Mohr Circle from the Quartz Vein Orientation Data of the South Delhi Terrane, Ambaji Area, NW India

Abstract

In many instances the sulphide mineralization is associated with quartz vein-related hydrothermal alteration zone. The syntectonic quartz veins display preferred orientation as their intrusion is controlled by normal stress (σn) acting across the foliation/fracture planes and the fluid pressure (Pf) of the quartz veins. The Pf and paleostress (ϕ = tectonic stress ratio) are measurable by using stereoplot and 3D Mohr plot. We have determined the above parameters from the quartz veins in the Cu–Pb–Zn mineralization belt of South Delhi terrane, NW India. The mineralization occurs in the mica schist and metabasalt. The rock types show three phases of folding (F1–F3), greenschist facies metamorphism and multiple phases of granite intrusion. Attitude of 170 quartz veins have been measured, the NE–SW direction is the most prominent. Though some of the quartz veins show a cross-cutting relationship, we have treated them broadly synchronous. Stereoplot shows a girdle distribution pattern with an elliptical void area at the centre and σ1σ2 plane strikes N52° E. Further, σ1 = 120°/75°, σ2 = 052°/07°, and σ3 = 323°/07° indicate that maximum extension was NW–SE. The θ2 = 12°, θ3 = 40°. R ' = 0.95, ϕ = 0.90 indicate high value for R ' leading to dilation of wide range of fractures and the high ϕ value suggesting uniaxial extension. 3D Mohr plot indicates that Pf fluctuated between σ2 < Pf < σ1. Since sulphide mineralization is related to quartz vein intrusion, we interpret similar stress field for mineralization.