The application of both singular value decomposition and bi-dimensional empirical mode decomposition in extraction of gravity anomalies associated with gold mineralization

Two methods of the singular value decomposition (SVD) and the Bi-dimensional empirical mode decomposition (BEMD) were applied respectively in extraction of gravity anomalies associated with gold mineralization in the Tongshi gold orefield in this paper. Conclusions drawn by the comparative study are as follows: (a) The two methods consistently reveal the ore-controlling factor in the Tongshi gold orefield on the basis of original gravity data: the Tongshi intrusion has a negative circular gravity anomaly and the ringed contact metasomatic mineralization zone around the Tongshi intrusion has a positive gravity anomaly. (b) The two methods consistently reveal the spatial relationship between the ore-controlling factors and various gold mineralizations: the skarn and porphyry types of gold deposits are located within the complex pluton and the Carlin and crypto-breccia types of gold deposits are situated within the contact metasomatic mineralization zone. (c) The image produced by BEMD not only reflects the structural features of the ore-controlling factor (Tongshi complex pluton) but also shows the distribution of other geological units in the Tongshi gold orefield such as the Mesozoic volcanic sedimentary basin in NW direction with obvious negative gravity anomaly and the concealed metamorphic base swell in NW direction with positive gravity anomaly located between the Tongshi intrusion and the Mesozoic volcanic sedimentary basin. (d)The image produced by SVD might depict the inner structure of the Tongshi intrusion and the ringed contact metasomatic zone in more detail than that produced by BEMD. The higher gravity anomaly areas like island-shaped bodies within the ringed contact metasomatic zone may be skarn bodies with iron-copper-gold mineralization. (e) Under the constraints of the ore-forming geological setting, the result obtained from the original gravity data by combination of the two methods can depict the relationship between the ore-controlling factors and the gold mineralizations more exactly than the result obtained only by one method.