Extraction of Gravity Anomalies Associated with Gold Mineralization: A Comparison of Singular Value Decomposition and Bi-Dimensional Empirical Mode Decomposition

Abstract

Two methods of both the singular value decomposition (SVD) and the Bi-dimensional empirical mode decomposition (BEMD) were applied in extraction of gravity anomalies associated with gold mineralization in Tongshi gold field, respectively in this paper. Conclusions drawn by the comparison study are as follows: (a) The ore-controlling factor in the Tongshi gold field illustrated in the images obtained from the original gravity data by the two methods is the same that the Tongshi intrusions with a negative circular gravity anomaly and the ring contact metasomatic mineralization zone around the Tongshi intrusions with the positive gravity anomaly. (b) The two methods reveal the same spatial relationship between the ore-controlling factor and various gold mineralizations that the skarn and porphyry types of gold deposits are located within the complex pluton and the Carlin and Crypto-breccia types of gold deposits located 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 does the distributions of the other geological units in the Tongshi gold field such as the Mesozoic volcanic sedimentary basin in NW orientation with obvious negative gravity anomaly and the conceal metamorphic base swell in NW orientation with the positive gravity anomaly located between the Tongshi intrusions and the Mesozoic volcanic sedimentary basin. The image produced by SVD might depict in more detail the inner structure of the Tongshi intrusions and the ring contact metasomatic zone than that produced by BEMD. The higher gravity anomaly areas in island shape within the ring contact metasomatic zone may be caused by the skarn bodies with iron-copper-gold mineralization. (d) Under the constraints of the ore-forming geological setting, the results obtained from the original gravity data by combination of the two methods can depict the relationships between the ore-controlling factors and the gold mineralizations more exactly than the alternative methods.