Constrained inversion of gravity data over the Ovoid and Mini-Ovoid in the Voisey's Bay Ni-Cu-Co deposit, Labrador

摘要

The Voisey's Bay Nickel-Copper-Cobalt deposit provides a unique opportunity to test the latest minimum-structure gravity inversion program developed by the University of British Columbia-Geophysical Inversion Facility (UBC-GIF). The success of generating geologically meaningful results depends on the inherent uncertainty and spatial properties of the raw gravity data set, and on the statistical properties and spatial distribution of the rock density data. The objective of this study is to examine the effects of the initial survey configuration and the knowledge of subsurface parameters on the refinement of the inversion models. Density models derived using geostatistical methods can be assigned weights which reflect model confidence and spatial correlations. The spatial distribution of the borehole samples and the developed geostatistical models control the lateral and vertical resolution of the inversion. -- The constraints applied in the gravity inversion were in the form of data from a significant number of drill holes penetrating the Ovoid and Mini-Ovoid. From these, refined models of the depth of the overburden and of the density distribution within the body were developed. To explore the utility of gravity inversion as a forecasting and planning tool, inversions were constrained using density models derived from 50%, 25% and 5% of the original number of drill logs. Reasonable models of the Ovoid were obtained when the thickness of the overburden was constrained. The inversion results indicate that incorporating drill log information into the inversion process, early in a drilling program, can improve our knowledge of the subsurface density distribution.