New Zealand Journal of Geology and Geophysics abstracts

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Mo-bearing granodiorite porphyry plutons of the Early Cretaceous Separation Point Suite, west Nelson, New Zealand

A. J. TULLOCH

Institute of Geological and Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand

S. D. C. RABONE

36 Owens Road
Epsom
Auckland, New Zealand

Abstract In west Nelson a 130 km long belt containing granodiorite stocks with associated subeconomic stockwork Mo mineralisation is correlated with the I-type Separation Point Suite and Western Fiordland Orthogneiss, both of Early Cretaceous age. Trace element characteristics of relatively unaltered samples of these Mo-granite stocks, and the Separation Point Batholith, indicate an arc setting for both groups of rocks, which predominantly represent partial melts of plagioclase-free oceanic slab of basaltic composition. The Separation Point Suite (including the Mo-granites) and Western Fiordland Orthogneiss suite chemistry is alkali-calcic due to high Na. However, high Na, Al, Sr (c. 1000 ppm at 70% SiO₂) and TiO₂, and low K₂O, Rb, Nb, and F, suggests comparison with granitoids similar to those that host porphyry copper deposits rather than alkaline, Climax-type igneous rocks, indicating grades of Mo mineralisation are likely to be low. The granodiorite plutons are associated with voluminous diorite-granite magmatism that occurred close to the end of long-lived (Permian to mid-Cretaceous) subduction in the New Zealand segment of the Gondwana margin.

Keywords granodiorite; granite; molybdenum; Nelson; Cretaceous; porphyry; Separation Point Suite

Received 30 January 1991; published 3 December 1993
New Zealand Journal of Geology & Geophysics, 1991, Vol. 36: 401—408
0028Ð8306/06/3604—0401 ©The Royal Society of New Zealand 1991

PDF file of entire paper: medium quality (795K); (scanned from paper original: notes about this process). Digitisation of this article from the printed journal was kindly facilitated by the Geological Society of New Zealand

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