New Zealand Journal of Geology and Geophysics abstracts

---

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

D. CRAW

Department of Geology
University of Otago
P.O. Box 56
Dunedin, New Zealand

A. J. HALL

Department of Geology and Applied Geology
University of Glasgow
Glasgow G12 8QQ, Scotland

A. E. FALLICK
A. J. BOYCE

Scottish Universities Research and Reactor Centre
East Kilbride
Glasgow G75 0QU, Scotland, U.K.

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 (d³⁴S = -2.7 to -1.3[[perthousand]]) 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 d³⁴S values, from -3.0 to -1.0[[perthousand]] (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 d³⁴S in the narrow range -6 to +6[[perthousand]]. 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.

Keywords  sulphur isotopes; hydrothermal; gold; Otago Schist; Torlesse Terrane

New Zealand Journal of Geology and Geophysics, 1995, Vol. 38: 131-136

0028-8306/95/3802-0131 $2.50/0 (c) The Royal Society of New Zealand 1995

PDF file of entire paper: medium quality (605K); (scanned from paper original: notes about this process)

---

This year's abstracts | Journal home page | All abstracts | Publishing home page