Ore and rock mass characterization using borehole geophysics

Abstract: A geophysical log represents the measurement of a geophysical parameter along a borehole, plotted against time or depth. A variety of geophysical logging tools exist that measure different geophysical parameters. Some geophysical instruments react to the lithological changes along the borehole, others to the fluid within or around the borehole, but very few react solely to a single feature. In every case the user must determine what effect the borehole and its surroundings have on the measurement. Interpretation of geophysical logs from sedimentary rocks (mainly for petroleum or water) is highly developed while in hard rocks the log responses are much more complex, and interpretation is a qualitative and subjective exercise. The key to successful use of borehole geophysics in underground constructions lies in the data interpretation and presentation. Virtually all types of underground constructions, in both mining for ores and tunneling, are preceded by investigations through boreholes to try to locate anomalous zones in the rock mass. The information from the boreholes forms the basis for the layout of the production. Diamond core drilling, with geological core logging, is the most commonly used method for rock mass investigations. Unfortunately, the many task-intensive steps and expense of this method limit the amount of samples one can obtain. In mining, the primary objects to detect are the orebody and its boundaries, since waste rock dilution occurs when uneconomic rock is mined and processed with economic mineralized ore Logging production holes, with geophysical tools, to identify the ore-waste contact for optimal blast design will result in reductions in dilution and oreloss.