Geology, geochemistry, mineralisation, and metal zoning of the McConnochie greisenised granite, Reefton district, Westland, New Zealand

Abstract

A high-level, small gramtic body, informally named McConnochie greisenised granite, was emplaced within Greenland Group rocks, probably above the roof region of a subjacent pluton, in the Reefton-Victoria Range area of Westland, New Zealand.The McConnochie greisenised granite is a highly evolved member of a granite series forming the western margin of the Karamea Batholith in the area of study and shows an apparent overall S-type chemistry. It was originally a granodiorite which was subjected to varying degrees of postmagmatic alteration (greisenisation) during the Cretaceous. The greisenisation affected both the original granodiorite body (endogreisen) and the surrounding country rock (exogreisen).Mineralisation occurs in both endogreisen and exogreisen rocks and consists of pyrite, marcasite, chalcopyrite, molybdenite, minor sphalerite, and native bismuth. Sn mineralisation probably occurred near the top of the greisenised granite cupola, but was later removed by erosion. This is shown by a vertical geochemical zonation in which Sn values decrease with depth in the drill core, whereas Cu and Mo are enriched in the lower and more greisenised parts of the granite body.It is possible that muscovitisation of biotite is, at least in part, responsible for the release of the ore metals during greisenisation and associated hydrothermal activity.

Petrographic Characteristics and Alteration Geochemistry of Granite-hosted Tungsten Mineralization at Degana, NW India

“…The release of these elements from the lattice of mica to form ore minerals is also documented by the presence of wolframite and fluorite in the cleavages and/or micro-fractures of zinnwaldite and muscovite in the greisenized granite at Degana. Pirajno (1982) at New Zealand has also reported similar characteristics. Shcherba (1970) also noted that apart from micas, plagioclase is also important carrier of metals.…”

Porphyry Mo and greisen W metallogeny related to the Karamea Batholith, South Island, New Zealand (Note)

“…Studies of granite-related mineralisation in west Nelson and Westland indicate that this mayaiso be so for the composite Karamea Batholith. Thus, it appears that the Tuhuan phase granitoids ofthe batholith are largely responsible for the greisen associated W-Sn mineralisation, while the batholith's Rangitata phase plutonic components are genetically and spatially linked with the porphyry Mo occurrences (Sm ale 1976;Rabone 1977;Eggers 1978;and Pirajno 1980) (see Fig. I B).…”

“…Reeeil'ed /9 Oetober /983. aeeepted 20 August /984 that the granitic terrane and immediate surroundings in west Nelson and Westland, were recognised to constitute a molybdenum metallogenic province (Williams 1974;Pirajno 1980). The presence of greisen-type occurrences in New Zealand had been known from at least two localities.…”

Geochemistry and mineralisation of the southern part of the Darran Complex, Fiordland, New Zealand

“…Also, it is not uncommon to observe that a spectrum of compositions exists between large plutons and smaller high-level stocks (Pirajno 1982;and unpublished data). The chemical and petrological variations observed in the areas investigated can be explained, in my opinion, by a derivation through a series of differentiates from magmas of maficintermediate composition, possibly derived from the partial melting of upper mantle or lower crustal rocks.…”

“…The purpose of the paper in question (Pirajno 1981) was not to pontificate "ex cathedra" on the geology of northeastern Fiordland, but only to present data on the principal aspects of mineralisation and its genesis in that geological environment.…”