Sulphur isotopes in a metamorphogenic gold deposit, Macraes mine, Otago Schist, New Zealand

Craw, D., Hall, A.J., Fallick, A.E. and Boyce, A.J. (1995) Sulphur isotopes in a metamorphogenic gold deposit, Macraes mine, Otago Schist, New Zealand. New Zealand Journal of Geology and Geophysics, 38(2), pp. 131-136. (doi: 10.1080/00288306.1995.9514645)

Abstract

The Macraes gold quartz vein deposit, New Zealand, is located in a shear zone cutting greenschist facies metasediments of the Otago Schist. The deposit has been interpreted as being metamorphogenic in origin as there is no evidence for coeval magmatic activity in the Otago Schist orogen. The immediate host rock at the Macraes deposit is pyritic (δ34S = ‐2.7 to ‐1.3%o) and locally weakly graphitic schist, a rare rock type in the Otago Schist. Sulphur isotope analyses of pyrite and arsenopyrite extracts from auriferous veins and wall‐rock schist provide a similar narrow range in δ34S values, from ‐3.0 to ‐1.0%o (n = 9). The lack of isotopically depleted sulphur, the narrow range in values, and the replacement sulphide textures help discount a primary bacteriogenic origin for host‐rock sulphide. Sulphide in both veins and wall rock is of hydrothermal origin. Sulphides in metasediments and metavolcanics elsewhere in the Otago Schist have δ34S in the narrow range ‐6 to +6%o. The sulphur isotope data are consistent with origin of hydrothermal sulphur within the metamorphic pile but provide no constraint on specific rock types which contributed the sulphur to the hydrothermal fluid. The study demonstrates that sulphur isotopic signatures near zero per mil can arise without any direct magmatic input into the mineralisation process.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Boyce, Professor Adrian and Fallick, Professor Anthony
• Authors: Craw, D., Hall, A.J., Fallick, A.E., and Boyce, A.J.
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: New Zealand Journal of Geology and Geophysics
• Publisher: Taylor and Francis
• ISSN: 0028-8306
• ISSN (Online): 1175-8791