New Zealand Journal of Geology and Geophysics abstracts

---

Gold mineralisation near the Main Divide, upper Wilberforce valley, Southern Alps, New Zealand

J. A. BECKER
D. CRAW

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

T. HORTON
C. P. CHAMBERLAIN

Department of Earth Sciences
Dartmouth College
Hanover, NH 03755, USA

Abstract  Veins up to 8 m wide fill extensional fractures in Torlesse Terrane metasediments near the Main Divide in the upper Wilberforce valley, Canterbury, New Zealand. The upper Wilberforce veins are part of a prominent 40 km long, NNE-trending swarm of gold-bearing veins formed across the Main Divide during the late Cenozoic rise of the Southern Alps. The veins occur within, and near, a prominent set of faults which constitute the Main Divide Fault Zone. The veins are irregular in shape due to contrasting host rock properties, and have been only weakly sheared and deformed. Veins cut across greywacke beds and follow irregularly along argillite beds, on the 1-10 m scale. Quartz dominates vein mineralogy, but albite forms up to 45% of some veins, and minor chlorite, pyrite, arsenopyrite, chalcopyrite, and gold occur sporadically, especially in breccias near vein margins. Fluid inclusions in vein quartz homogenise at 180-253deg.C, and arsenopyrite composition (28.3-30.8 at.% As) suggest formation temperatures of 250-350deg.C. Elevated arsenic levels (up to 200 ppm above a background of 10 ppm) in some host greywackes and argillites suggest that hydrothermal activity pervaded host rocks as well as forming veins, but there is no textural evidence for this fluid flow. Late-stage carbonates in faults adjacent to the quartz veins, but which postdate the quartz veins, have d¹⁸O ranging from 11.1 to 25.6[[perthousand]], and d¹³C ranging from -12.5 to -1.1[[perthousand]]. These carbonates were deposited by a mixture of meteoric and crustally isotopically exchanged fluid as a shallow-level manifestation of the same hydrothermal system which deposited the quartz veins.

The upper Wilberforce veins structurally and mineralogically resemble some late Cenozoic gold-bearing vein systems in the Mt Cook area, 100 km to the southwest along the Southern Alps.

Keywords  gold; Southern Alps; hydrothermal system; fluid inclusions; stable isotopes; Torlesse Terrane

New Zealand Journal of Geology & Geophysics, 2000, Vol. 43: 199-215

0028-8306/00/4302-0199 $7.00/0 (c) The Royal Society of New Zealand 2000

PDF file of entire paper: medium quality (1733K); (scanned from paper original: notes about this process)

---

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