3-D Mohr circle analysis of vein opening, Indarama lode-gold deposit, Zimbabwe: implications for exploration

• Published in: Journal of structural geology Vol. 26; no. 6; pp. 1275 - 1291
• Main Authors: McKeagney, C.J, Boulter, C.A, Jolly, R.J.H, Foster, R.P
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.06.2004
• Subjects: Fractures; Gold; Mineralisation; Stress; Veins; Zimbabwe; Gold; Zimbabwe; Fractures; Veins; Mineralisation; Stress
• ISSN: 0191-8141; 1873-1201
• DOI: 10.1016/j.jsg.2003.11.001

The Indarama lode gold deposit is hosted by vertically-dipping basalt in the Late Archaean Midlands Greenstone Belt of Zimbabwe. Major deformation events at 2.68 and 2.58 Ga established a complex array of fractures. A limited range of orientations of this fracture network opened towards the end of the younger deformation event, creating a lode pattern where 92% of mineralised veins dip at less than 50°, mainly to the E and W, and most strike directions are represented. A clustered distribution of poles to the quartz–carbonate veins indicates a constrictional stress field at the time of vein opening where σ 1 and σ 2 were near horizontal, (directed NNW–SSE and ENE–WSW, respectively), and σ 3 was near vertical. 3-D Mohr circle analysis demonstrates that σ 2 was approximately 67% of σ 1 (the stress ratio) and that the driving pressure ratio ( R′) was approximately 0.4, reflecting the role of fluid pressure, mean stress, and the maximum shear stress in controlling conditions of fracture opening.