Sulfide Exploration in Newfoundland
Using Gamma Spectrometry
On Pilley's Island, central Newfoundland, potassic alteration
associated with volcanic hosted massive sulphide deposits (fig. B) produces sharp
bull's-eye airborne anomalies (fig. A).
Using a GR-320 field spectrometer, these anomalies can be
easily quantified (fig. D) and mapped on the ground, permitting more efficient se of
expensive whole-rock major and trace element analyses, where required. Barren, unaltered,
mafic and felsic volcanic host rocks each produce distinct low-K fields (fig. D). Where
mineralizing solutions have affected these units, associated sericite and K-feldspar
alteration dramatically increase the K content, as shown by the Bumble Bee Bight altered
basalts (pictured fig. C) and felsic volcanics in the Mansfield showing.
Distinction of barren, rusty, pyritized rocks from pyritic,
mineralized sericite altered outcrops is made easy by using the GR-320 to detect and map
the associated potassic alteration. As illustrated in fig. D, the altered, mineralized
basalts retain their relatively low thorium signature despite intense alteration.
Similarly, the high thorium content of the felsic volcanics is preserved.
Although economic cenectrations have yet to be outlined in
these thick, felsic volcanic sequences, the very large volume of potassic alteration
suggests potential for large, blind, high grade Kuroko-style massive sulphide deposits.