Case Histories      Back to Case Histories List

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.