The evaluation of selected borehole geophysical methods in the search for gold bearing horizons in Haveri, Finland

Abstract

Borehole or down-hole geophysical methods are extremely valuable tools in deciphering the complex geology of sub-surface stratigraphic units and structures, and also the physical and chemical properties of underlying rocks. In mineral exploration, down-hole geophysical methods are used to "extend" surface geology, probe for hidden stratigraphic units and to map mineral concentrations. The main reason for the down-hole geophysical surveys in Finland was an attempt to identify gold bearing rocks and their formations. Further, borehole geophysics was performed to better understand the geology of the area. The following geophysical methods were used: Resistivity, Magnetic Susceptibility and Density (gamma-gamma). During the spring and summer of 1996 and 1997, sixteen drill holes were drilled on the Haveri property. Ten holes were selected for evaluation in this report. In general, down-hole geophysical data have been correlated with bore-hole core samples, assay values, lithology logs and with surface samples where available. In this report, the suite of down-hole geophysical survey methods is correlated with geochemistry values for comparison purposes and to evaluate the usefulness of down hole geophysics as a tool in the delineation and/or identification of gold bearing horizons. From the results of this study, it is concluded that borehole geophysics is not a useful tool for the detection of gold bearing horizons in Haveri. It is further concluded that geochemistry plays a much more definitive role and should be used more extensively and that borehole geophysical surveys be discontinued. Drill hole location and the exact analytical values (ppm and ppb) for the core samples are not shown in this report in order to protect confidentiality of information.