Geology of the Aorere Goldfield, Northwest Nelson, New Zealand

Mason, Andrew John, 1991 (Andrew)

The Aorere Goldfield, discovered in 1857, is located in the Aorere District of Northwest Nelson, New Zealand. The goldfield contains six historic gold and/or silver mines, the most productive of which was the Johnston’s United Mine. Field mapping indicates that many of the historic mines lie along, or above, a low-angle fault, the Johnston Fault. This fault marks a lithological boundary between the overlying amphibolite facies Waingaro Schist and underlying greenschist facies Wangapeka Formation phyllites. Units in the goldfield have been synformally folded, and then cut by NE trending faults. This has resulted in down faulting of units in the west and juxtaposition of the Arthur Marble in the east.
Widespread late-stage muscovite-sulfide and carbonate-sulfide alteration is present throughout the goldfield and displays little to no correlation with mapped large-scale structures. Analysis of this alteration reveals no enrichment in Au or Ag, but sporadic enrichment in base metals. Limited trace element analysis coupled with assay results confirm that there is no correlation between arsenic content of sulfides and elevated Au.
Mines in the Aorere Goldfield are centred on quartz lodes and associated zones of deformation along and above the Johnston Fault. Quartz contains only rare sulfides, however pods of polymetallic sulfides within the deformation zone in Johnston’s United Mine have been found. Pb isotope analysis of galena from one polymetallic pod indicate an apparent age of mineralisation between ~140 and 340 Ma, with the source of Pb likely from surrounding metasedimentary rocks.
Supergene enrichment of gold along the permeable Johnston Fault is inferred to be the process by which gold was concentrated within the upper portions of mines, particularly the Johnston’s United Mine. The shallow extent of mine workings and an overlying erosional unconformity upon which Cenozoic sediments have been deposited are characteristic features of supergene enrichment. Further exploration is unlikely to locate gold or auriferous quartz at depth in the Aorere Goldfield due to the process of shallow supergene enrichment, and any deposit that is found is likely to be discontinuous with depth.

147p some A3 with map in back pocket

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