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 injection, sequestration and leaching in Canada, USA and Europe. In 2013, GRAVILOG systems and crews will be available in Russia, Brazil and Australia. Scintrex has developed and will be testing a dual sensor GRAVILOG probe in early 2013. This talk will start with a brief review of the GRAVILOG development and specifications, followed by several recent case histories. The result from Donner Metals / Xstrata Zincâ??s Bracemac KT Zone in the Abitibi 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 to outline the body and estimate tonnage at Virginia Minesâ?? Coulon Lens 44 property in Quebec. Apparent bulk density measurements from four holes in Labrador Iron Minesâ?? James South Extension iron ore deposit near Schefferville, Quebec provide a quantitative estimate of tonnage, reducing drilling costs and time needed to obtain this information. GRAVILOG surveys are being conducted to establish baseline data in CO2 sequestration wells in Michigan and Texas prior to commencing injection. The injected CO2 will be monitored by future GRAVILOG surveys. 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.