A gamma-ray spectrometric study of the footwall felsic volcanic and sedimentary rocks around Brunswick No. 6 massive sulphide deposit, northern New Brunswick

Abstract

Hydrothermal alteration in the footwall to the Brunswick deposits is manifested by feldspar- destructive alteration coincident with modal increases in chlorite at the expense of sericite. This phenomenon results in K depletion halos in the footwall to these deposits. In situ gamma-ray spectrometric measurements of the footwall rock outcrops around the Brunswick No. 6 deposit show that the exposed upper sequence of altered volcaniclastic rocks (quartz-augen schist + footwall sedimentary rocks) have lower K contents (average 2.0 ± 0.3 wt.%) than the lower sequence of less-altered pyroclastic rocks (3.5 ± 0.3 wt.%). eU is variable throughout but less abundant in altered rocks. eTh is variable in the upper volcaniclastic package due to sedimentary reworking or mass changes occurring during alteration. K/eTh ratios enhance the alteration trends by focusing on the relative change. Inexpensive rapid in situ gamma-ray spectrometric analyses are useful in alteration and possibly chemostratigraphic analysis in the Bathurst Camp.