Gamma Spectrometry in the Northwest
Territories, Canada for
An exciting new polymetallic deposit has been discovered at
Lou Lake, Northwest Territories, where a recent, multiparameter airborne geophysical
survey has delineated a large 3 by 4 km area of intense potassium enrichment (fig. A)
coincident with low eTh/K ratio (fig.B) and high total field magnetic anomalies.
The anomalous area contains numerous Au-Co-Cu-Bi-W bearing
arsenopyrite-pyrite-magnetite veins and disseminations, localized along the unconformity
between early Proterozoic metasediments/ granites and overlying, gently dipping rhyolitic
volcanics. Fig. C shows one of these polymetallic veins bordered by potassically altered
rhyolite, Preliminary drill indicated resources for the Bowl Zone, in the Lou Lake area,
as of January 1997, include 42 million tonnes grading 0.85g/t gold, 0.11% bismuth, 0.1%
cobalt, 0.05% copper and 0.03% tungsten oxide.
Using a GR-320 spectrometer the degree of alteration in the
extensive hydrothermal system can be quickly detected and quantified. Traverses along
selected grid lines in the mineralized zone (fig. D) produced in-situ assays of up to 15%
K in rocks which would normally contain less the 4% K.
As with many deposit types, low eTh/K ratio in the
hydrothermally altered rocks permits distinction of K anomalies that have exploration
significance from those related solely to lithological variations. These patterns, in
conjunction with ongoing metallogenic, geological and other geophysical studies, have
helped industry focus on an important new exploration target, comparable to the giant
Olympic Dam deposit in South Australia.