New Zealand Journal of Geology and Geophysics abstracts

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Structure, geomorphology, and gold concentration in the Nokomai valley, Southland, New Zealand

L. C. KERR
D. CRAW
R. J. NORRIS
J. H. YOUNGSON

Geology Department
University of Otago
P.O. Box 56
Dunedin, New Zealand

P. WOPEREIS

L&M Mining
P.O. Box 13 442
Christchurch, New Zealand

Abstract  The NNE-striking faults of the Nokomai valley, Southland, New Zealand, are the southern extension of the Nevis-Cardrona Fault System, and have similar deformation style. This fault zone defines the boundary between broad, smooth, central Otago ranges and basins dominated by a deformed regional unconformity cut into the basement, and rugged mountains and deeply incised bedrock valleys to the west. Nokomai valley topography is dominated by bounding ranges: Slate and Hector Ranges to the west, and Garvie Range to the east. These ranges are rising on NNE-striking oblique reverse faults, which dip beneath the ranges in the upper and lower Nokomai valley. The middle reaches of the Nokomai valley are cut by a complex set of NE-ENE strike-slip faults with some reverse component. These faults pass through the headwaters of eastern tributaries of the main Nokomai River, which itself passes through a bedrock gorge. Structural depressions have developed in the upper and lower Nokomai valleys, where the oblique reverse faults strike NNE, and these depressions have accumulated auriferous river gravels. The gold is derived from a variety of sources, including at least one auriferous quartz vein still exposed. Most gold has accumulated in basal lags in gravels in the lower Nokomai, including a major tributary, Victoria Gully. The gravels in the basal lags are older than c. 22 000 yr, based on radiocarbon dating of overlying peats. The whole Nokomai catchment is being uplifted, and early-formed gold accumulations are being eroded and re-concentrated in younger channels. Similar gold recycling processes have occurred along the whole Nevis-Cardrona Fault System, which is at an ideal stage of topographic development for alluvial gold accumulation.

Keywords  gold; structure; faults; central Otago; Southland; Nevis; Cardrona; late Cenozoic; quartz veins

New Zealand Journal of Geology & Geophysics, 2000, Vol. 43: 425-433

0028-8306/00/4303-0425 $7.00/0 (c) The Royal Society of New Zealand 2000

PDF file of entire paper: medium quality (1004K); (scanned from paper original: notes about this process)

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