Buller Coalfield: Millerton fire area: reconnaissance resistivity measurements

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Broadbent, M.; Mumme, T.C. 1977 Buller Coalfield: Millerton fire area: reconnaissance resistivity measurements. : . Report / Geophysics Division 120 26 p.

Abstract: Schlumberger and Square electrical resistivity soundings have been conducted in the Millerton Fire Area of the Buller Coalfield to determine whether the depth of burial and thickness of the coal may be reliably deduced. Resistivity columns initially inferred from the measurements showed little correlation with the geological logs of nearby boreholes. The resistivity of the coal was deduced to be probably between 10 and 60 ohm.m. This result was derived using the coal thicknesses revealed in the logs. Resistivities implied for other rocks of the coal measures lay between 17 and 5400 ohm.m. The lower resistivities (those less than 100 ohm.m) tended to be associated with thin clays or the upper parts of mudstones. The highest resistivities (those exceeding 1000 ohm.m) tended to occur near the dry fissured ground surface. The granitic basement had a resistivity in excess of 600 ohm.m. Dar Zarrouk curves have been drawn for resistivity models of the ground. The models represented the likely depths of burial of the coal (between 24 and 48 m) and thicknesses of the coal (between 0 and 12 m). It was deduced that it would be impossible to use electrical soundings to reliably determine the depth of burial and thickness of coal at many locations in the fire area