APPLICATION OF AN ENHANCED THETA-BASED FILTER FOR POTENTIAL FIELD EDGE DETECTION: A CASE STUDY OF THE LUZONG ORE DISTRICT

Edge detection plays an important role in interpreting potential field data, and is widely used to delineate geologic boundaries and structures. Geologic boundaries can be determined by tracing the enhanced analytical signal, and many filters are developed to detect and enhance the edges. Horizontal and vertical derivatives are commonly used to enhance edge features, but they can only outline the edges of large-amplitude anomalies. In order to display large and small amplitude anomalies simultaneously, some balanced filters have been proposed. We define new filters based on the Theta map method, using 2^nd order horizontal and vertical directional derivatives, and display large and small amplitude edges simultaneously. These methods were tested on synthetic gravity data, and compared with other traditional filters; the results show that the new filters can achieve better results and reveal more details. The method has been applied to gravity-magnetic data acquired in the Luzong ore district in the Middle-Lower Yangtze River Valley Metallogenic Belt (MLYB, Eastern China). Based on the relations between lithology, density and magnetic susceptibility, the calculated results were analyzed. The edge detection results accurately depict the location of the Tanlu fault zone. A gravity boundary north of the Yangtze River is interpreted to be part of the Yangtze River fault. The identified boundaries from the magnetic data are consistent with the margins of the Luzong basin, and indicate that the bounding faults dip towards the basin. Some ring-like closed boundaries occur in the periphery of the Luzong basin. Recent exploration results confirm that there are buried intrusions beneath the gravity-magnetic anomaly bodies, where Fe-Cu skarn mineralization is present. The results of this study provide significant insights for regional deep-level Fe-Cu exploration.