A structural, paragenetic and geochemical study of the Energetic gold mine, Reefton Goldfield, New Zealand

Author:

Stick, George Nicholas, 1992 (George)

Year:

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Abstract:

The Reefton Goldfield produced over 67 tonnes of hard rock gold from 84 mines between 1870 and 1951, making it one of New Zealand’s richest goldfields. Reaching a depth of 692 m, the Energetic gold mine, in the Crushington group of mines was the third largest producer. Hosted in Greenland Group metasediments, the mine produced 208,992 ounces of gold during operation between 1870 and 1927 when it closed due to an underground collapse

This report details the first comprehensive study of the Energetic mine and the surrounding Greenland Group host rocks.

The Energetic shear zone hosts the Energetic mine on the eastern limb of the NE-striking Globe Hill Anticline. The shear zone comprises two variably mineralised faults that host three main quartz reefs. One NE-striking fault is controlled by both local bedding and cleavage whereas the other (NNW-striking) is controlled primarily by cleavage. The formation of these faults was the result of an ENE-WSW shortening direction, oblique to the local bedding but perpendicular to the NNW-striking, cleavage controlled fault.

Alteration surrounding the Energetic shear zone is asymmetric to the west, most noticeably through As and S concentrations obtained through geochemical analysis of the RDD0048 drillcore. This alteration appears to be lithologically controlled to argillite. The argillaceous units were preferentially sheared and their relative impermeability compared to greywacke units prevented fluids from migrating into and altering the surrounding host rock to the east.

Early hydrothermal fluids migrated into the wall rocks and altered carbonate spots in argillaceous units from ankerite to siderite proximal to mineralised zones. This compositional change is the most reliable exploration vector at the Energetic mine. Associated with this phase was the formation of wall rock sulphides that due to continual shearing were deformed and had antitaxial strain shadows form around them. The main stage of gold mineralisation along the Energetic shear zone is associated with dark grey quartz and stylolitic veins that contain pyrite. These veins are hosted in and cut early ductiley deformed quartz lodes. These veins and later crosscutting veins are more brittle in nature and indicate mineralisation along the shear zone may have been prolonged. Brittle structures have overprinted earlier ductile structures and are now the most prominent feature of mineralised rocks. The mineralised rocks are highly deformed and a succession of mineralised veins cut the rocks. Pressure solution effects are commonly associated with both ductile and brittle structures and show the prolonged nature of deformation along the shear zone.

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Thesis description:

155p

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OU geology Identifier:

2015Stick

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Location (WKT, WGS84):

POLYGON ((171.880595031720304 -42.127729991917725,171.893774311229606 -42.126428070975187,171.908555876473656 -42.126855592022544,171.906323098572074 -42.139416143324375,171.901092679509446 -42.141939711828954,171.880552946389031 -42.141026256121279,171.878953096002903 -42.139151961045954,171.879133589909372 -42.134364064327038,171.880595031720304 -42.127729991917725))

Abstract PDF File

http://download.otagogeology.org.nz/temp/Abstracts/2015Stick.pdf

Collection

Citation

Stick, George Nicholas, 1992 (George), “A structural, paragenetic and geochemical study of the Energetic gold mine, Reefton Goldfield, New Zealand,” Otago Geology Theses, accessed April 23, 2018, http://theses.otagogeology.org.nz/items/show/611.