New Zealand Journal of Geology and Geophysics abstracts
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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