Metamorphism of the Moke Creek lode, Otago, New Zealand

Abstract

A load pressure of 6·4 ± 0·4 kbar is estimated for the metamorphism and reequilibration of the Moke Creek sulphide lode near Queenstown (5132) on the basis of a recently published calibration of the iron content of sphalerite as a geobarometer, and the recognition of equilibrium sulphide textures. This estimate confirms previous estimates of a geothermal gradient of 15-25 0 c/km during greenschist facies metamorphism in this area of the Haast Schist Terrane. The author suggests a syngenetic origin for the lode.

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

“…The Moke Creek sulphide deposit itself has been mined on a very limited scale for contained copper, but there is no G01004;published 21 June 2002Received 7 February 2001accepted 9 November 2001 evidence of economic amounts of ore. Wood (1967) estimated that c. 45 000 t of sulphide ore are present. However, comparison of this minor occurrence with other similar, but economic, deposits in similar terranes elsewhere in the world (e.g., Henley 1975) during this study suggests that there is still potential for the discovery of larger deposits in the Otago Schist.…”

“…Sphalerite is an accessory mineral only. Pyrite is the early-formed primary sulphide and consists of rounded grains around which pyrrhotite has been deformed parallel to schist foliation (Henley 1975;Jamieson & Craw 1987). Such ductile deformation and flow of pyrrhotite and chalcopyrite has resulted in localised brecciation of schistose sulphide-rich layers (Jamieson & Craw 1987).…”

“…Numerous earlier workers (Wright 1966;Wood 1967;Henley 1975;Lowery 1979;Jamieson & Craw 1987) have described various aspects of the Moke Creek sulphide deposit itself, focusing on sulphide mineralogy. However, apart from generalised regional studies (Park 1909;Hutton 1940;Mortimer 1993), there is no published information on the host rocks of the Moke Creek sulphide deposit.…”

Mineragraphy and origin of copper-bearing sulphides at Waitahuna River, eastern Otago

“…These differences may result from the higher grade of metamorphism at Moke Creek, with its more advanced recrystallisation. Sulphides are coarser at Moke Creek (Wright 1966; this study), but Henley (1975) indicates that some Moke Creek sulphides are similar in grain size to those at Waitahuna River, or even finer.…”

“…Metamorphic grade of country rock Chlorite subzone 3 or Textural Zone 3B at Waitahuna River; chlorite subzone 4 (Hutton 1940;Wood 1962) or Textural Zone 4 (Henley 1975) at Moke Creek.…”