GRAVILOG: An update on the development and use of Borehole Gravity for Mining Exploration

Abstract

Scintrex GRAVILOG borehole gravity meters are now successfully deployed by Abitibi Geophysics crews in boreholes for mining exploration in Canada and USA, and by Scintrex and Micro-g LaCoste crews in wells used for CO2 injection, sequestration and leaching in Canada, USA and Europe. In 2013, GRAVILOG systems and crews will be available in Europe, Russia, Brazil and Australia. Scintrex has developed and will be testing a dual sensor GRAVILOG probe in early 2013.A brief review of the GRAVILOG development and specifications is presented, followed by several recent case histories. The result from Donner Metals / Xstrata Zinc’s Bracemac KT Zone in the Matagami region of Quebec is the first documented use in mining exploration of borehole gravity to measure excess mass coincident with a borehole EM conductor. Forward modeling and inversion of GRAVILOG data from multiple holes has proven effective in outlining the mineralization and estimating the tonnage of the Virginia Mines’ Lens 44 on the Coulon property in Quebec. Apparent bulk density measurements from multiple holes at the Labrador Iron Mines’ James South Extension iron ore deposit near Schefferville, Quebec reduce drilling costs and time needed to obtain this information.A major source of error in bulk density measurements of thin beds is minimized by the dual sensor GRAVILOG system. In addition to eliminating the error in the depth interval between the sensors, common mode noise rejection improves the gravity difference data.