Ultralow‐radiation‐intensity spectrometric probe for orebody delineation and grade control of zinc‐lead ore

A fully spectrometric gamma—gamma probe using an ultralow‐activity gamma‐ray source (i.e., <2 MBq) has been developed. The prototype low‐radiation‐intensity probe was tested at a zinc‐lead deposit in Queensland, Australia. The probe showed an excellent capability for orebody delineation. Lithological profiles derived from logging data showed sharp anomalies both in selected spectral regions and in spectral ratios during probe transition from orebody to barren rock, or vice versa. In comparison to standard geochemical analysis, the instrument demonstrated good potential for quantitative determination of lead and zinc content in ore with rms error of 0.3% and 2.4%, respectively. Delineation of nonlithological boundaries, through an application of a cutoff‐grade algorithm, has been demonstrated as a practical stand‐alone mine control tool.