Bidimensional empirical mode decomposition (BEMD) for extraction of gravity anomalies associated with gold mineralization in the Tongshi gold field, Western Shandong Uplifted Block, Eastern China

摘要

A bidimensional empirical mode decomposition (BEMD) program on a MATLAB platform was effectively used to handle gravity signals for the Tongshi gold field. This yielded a two-dimensional intrinsic mode function (IMF_3) image that meticulously depicts the spatial distribution relationship between various gold deposits and the different geological units of the gold field. By combining the IMF_3 image with geological features, the Tongshi gold field can be divided into three geological units. Unit I is made up of both Archean greenstone and Cambrian-Ordovician carbonate rocks and is defined as a concealed basement that exhibits weak negative and positive gravity anomalies. Unit II is defined as a Mesozoic volcanic sediment basin consisting of Jurassic and Cretaceous volcanic-sedimentary rocks, which developed on the concealed basement and exhibits an obvious negative gravity anomaly. Unit III, located on the concealed basement on the SW side of the Mesozoic volcanic-sedimentary basin, can be subdivided into subunits IIIa and IIIb. The former, with a negative circular gravity anomaly, indicates that the Tongshi complex consists of both Yanshan diorite-porphyrite and syenite-porphyry. Unit IIIb, with a positive ring gravity anomaly distributed around a negative circular gravity anomaly, indicates a possible contact metasomatic mineralization zone around the Tongshi complex. Almost all types of gold deposits are located within this contact metasomatic mineralization zone and thus the zone is a prospective area for gold deposits.