New Zealand Journal of Geology and Geophysics abstracts

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Lithology, geochemistry, and structure of Moke Creek sulphide deposit host rocks, Otago Schist, New Zealand

Anton Barber
Dave Craw

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

Abstract  Three types of greyschist (fissile, dark grey, and light grey thickly segregated types) and subordinate greenschist make up most of the Otago Schist hosting the Moke Creek sulphide deposit. Greyschist in the study area is mostly of Torlesse Terrane affinity, with the exception of a sliver of Caples Terrane affinity schist preserved in the footwall of the Moonlight Fault. The three greyschist types are geochemically indistinguishable; however, the former two types contain higher contents of graphite, which may explain their darker field appearance. The greenschists are shown to represent metamorphosed MORB and within-plate basalts. Schist immediately hosting the Moke Creek sulphide deposit consists of both muscovite-rich and subordinate epidote-rich varieties. The former variety contains up to 6.4 wt% K₂O, whereas the epidote-rich variety is depleted in K₂O but contains >5 wt% CaO. It is suggested that sericitisation during hydrothermal alteration associated with sulphide deposition produced the mica-rich schist. The Moke Creek sulphide deposit shares many similarities with Besshi-type sulphide deposits formed by seafloor hydrothermal activity. The Moke Creek sulphide deposit may have been formed as vein-dominated roots to exhalative sulphide deposits. The sulphide layers and associated hydrothermal alteration zones were subsequently deformed into parallelism with lithological layering in the Otago Schist.

Keywords  Otago Schist; Caples Terrane; Torlesse Terrane; copper; hydrothermal

G01004 Received 7 February 2001; accepted 9 November 2001
New Zealand Journal of Geology & Geophysics, 2002, Vol 45: 193–205
0028–8306/02/4502–0193 $7.00/0 © The Royal Society of New Zealand 2002

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