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McConnochie Creek, Reefton, Buller District, West Coast Region, South Island, New Zealand

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Latitude & Longitude (WGS84): 42° 10' 58'' South , 171° 57' 58'' East
Latitude & Longitude (decimal): -42.18301,171.96631
Köppen climate type:Cfb : Temperate oceanic climate

Small granite body with an incipient greisen mineralogy.

A greissenised granite intrusion into the Greenland Group rocks, showing quartz veins with sulphide mineralisation as disseminations, veinlets, and infilling of micro-fractures. The indication is the location would not produce impressive specimens, although if the quartz was sliced and polished, it may reveal the sulphides at their best. Specimens may exist in local collections, but are not generally available.

The intrusion was originally a granodiorite, subjected to postmagmatic greissenisation during the Cretaceous period. It was discovered during prospecting in 1978. It is 11.5 kilometres south-east of Reefton, bordering the McConnochie Creek, the intrusion covering an area 1300 metres long by 300 metres wide. The northern end is overlain by the Quartose Coal Measures bed. The intrusion is emplaced along the Tobin Fault Zone, and is elliptical in shape, orientated north-east to south-west, dipping 70 degrees south-east.

During alteration, muscovite, silification, and albitisation occurred, with red-brown biotite along the margins where alteration was limited. Quartz is most abundant, with also plagioclase, microcline, muscovite, biotite, pink garnet (possibly spessartine), and minor illite-kaolinite, topaz, small tourmaline needles, adularia, Fe-oxides, and sulphides.

The plagioclase is sodic, showing as albite to oligoclase, some replaced with quartz, moderate sericite alteration, and minor clay alteration. Microcline and/or orthoclase forms large plates, where not obliterated by quartz-muscovite replacement. Albite forms a 'chessboard' structure, replacing K-feldspar. Muscovite forms large books, or fine flakes in quartz.

At the south-west end of the granite body, the rock is shattered, fractured and filled with quartz veins, containing sulphide mineralisation. There are at least three sub-parallel sheeted quartz vein systems, across an area 400 metres x 25 metres, dipping 75-80 degrees south-east. Individual veins range from a few mms to 2 metres wide, with sulphides in the quartz forming disseminations, veinlets, and fracture fillings, forming a net like structure.

Ore minerals in order of abundance are pyrite, chalcopyrite, marcasite, molybdenite, sphalerite, native bismuth, bornite, argentite, and rare cassiterite. Pyrite and marcasite form intergrowths, marcasite marginal to the pyrite. In wall rock the only sulphides are pyrite and marcasite, associated with carbonate veinlets, or as disseminations. Chalcopyrite forms massive blebs or veinlets, intergrown with molybdenite and sphalerite, that cross-cuts pyrite, and marcasite. There are locally numerous native bismuth inclusions in the chalcopyrite. Molybdenite is found as isolated grains, and tiny rod-like intrusions in quartz grains. Bornite, argentite, supergene covellite and chalcocite may marginally replace chalcopyrite.

Mineral List

18 valid minerals.

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org

Famennian - Frasnian
358.9 - 382.7 Ma

ID: 1348835
McConnochie Granite (Karamea Suite)

Age: Late Devonian (358.9 - 382.7 Ma)

Stratigraphic Name: Karamea Batholith; Karamea Suite; McConnochie Granite

Description: Brown-grey muscovite-biotite granite.

Comments: Basement (Karamea Batholith) igneous rocks. Age based on U-Pb zircon Muir et al, Tulloch unpublished

Lithology: Major:: {granite}

Reference: Heron, D.W. . Geology Map of New Zealand 1:250 000. GNS Science Geological Map 1. [13]

Ordovician - Late Cambrian
443.8 - 501 Ma

ID: 1312947
Greenland Group metasedimentary rocks

Age: Paleozoic (443.8 - 501 Ma)

Stratigraphic Name: Greenland Group; Greenland Group metasedimentary rocks

Description: Quartzose metasandstone and metamudstone, hornfelsed near plutons and locally schistose.

Comments: Western Province (Buller Terrane) Rocks

Lithology: Sandstone, mudstone, schist

Reference: Edbrooke, S.W., Heron, D.W., Forsyth, P.J., Jongens, R. (compilers). Geology Map of New Zealand 1:1 000 000. GNS Science Geological Map 2. [12]

Data and map coding provided by Macrostrat.org, used under Creative Commons Attribution 4.0 License

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Pirajno, F. (1982) Geology, geochemistry, mineralisation, and metal zoning of the McConnochie greissenised granite. Reefton district, Westland, New Zealand. New Zealand Journal of Geology and Geophysics, Vol. 25:4

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