Borehole Spectral Gamma-Gamma Density Log Calibration in Massive Sulfides

摘要

The Geological Survey of Canada acquired spectral γ-γ density logging data in several underground boreholes at a Pb-Zn-Cu massive sulfide deposit, in order to field-calibrate the density logging tool for use in high-density/high-atomic-number (Z) base metal sulfide zones. Density determinations were always underestimated with the standard calibration procedure incorporating one energy window in the Compton scattering region of the spectrum. Core densities were also measured in the field on several drill core sections that were selected to represent waste rock, massive pyrite and Pb-Zn-Cu sulfide mineralization. A non-linear, multiple regression of core density against three energy windows covering the backscatter γ-ray energy spectrum from 50 to 500 keV provided a calibration equation that gave fairly accurate density estimates within the low-effective-Z (country rock) and high-effective-Z (base metal sulfide) media.