A research on the application of Tilt-depth method

Tilt-depth has been widely applied in magnetic exploration all over the world. Previous theoretical researches indicate magnetic Tilt-depth method possesses lower first-order than the Tilt-depth method in gravity field. Via models experiment, we do further comparative study and analysis on Tilt-depth method both in magnetic and gravity field. Both the mathematic study and model test demonstrate that Tilt-depth works better on shallow source exploration than deep source. The reason is that Tilt-depth methods, both in magnetic and gravity, are derived from contact model which is applicable for the shallow source in application. We show that such methods results in large error or incorrect depth estimation for deep geologic sources. The study combined several numerical models at different depths, the results indicate that the deeper the top depth of the sources, the larger error of the estimated depth. Subsequently, we process field magnetic data over Weigang Mine in Jiangsu province, south China. We also make comparison between our processing results with previous drill information. It shows that we use the method to calculate correct depth in shallowest magnetite south part of the studied area. The method, however, generates huge error in determining the depth in the deepest magnetite north part of the studied area. In this study, our research results reveal that the top depth estimation, from the distance between the +45° and -45° contours from the Tilt angle, are only suit for shallow exploration and can't be popularized simply. Hence, it is very necessary to work more for the new methods which are suitable for deep sources in the future research.