Investigation of geophysical fields in pyrite deposits under mountainous conditions

Abstract

Geophysical surveys under mountainous conditions are generally complicated by various noises, primarily by rugged topography effects. A rational integration of mobile geophysical methods (gravity prospecting, magnetic prospecting and VLF technique has been substantiated and effective methods of interpretation have been developed for copper pyrite deposits of a Kuroko type (an important source of non-ferrous and noble metals) not infrequently occurring in mountainous regions. A special scheme for obtaining the Bouguer anomalies has been employed to suppress the terrain relief effects dampening the anomaly effects from the objects of prospecting. The scheme is based on calculating the difference between the free-air anomaly ( Δg F.a) and the field determined from a 3-D model of a uniform medium with a real topography. This scheme almost doubled the accuracy of the Δg B chart. The further interpretation includes the following basic steps: (1) singling out the object of search using summation of the amounts of information obtained in various fields; (2) revision of the geological section using the methods specially devised for quantitative interpretation of anomalies under conditions of a rugged topography, inclined polarization and an unknown level of the normal field; and (3) physical-geological simulation realized as man-computer selection with the use of an effective algorithm for solving a direct 3-D problem of gravity and magnetic prospecting under the conditions of complex mediums and rugged observation surfaces. The method has been successfully tested at various stages of geophysical investigation under a variety of geological conditions, including saturated prospecting on the Kuroko-type Kyzylbulakh deposit (Lesser Caucasus) which has been thoroughly investigated by mining and drilling operations.