3D Geological Model of Fanchang Area Based on Priori Information Constrained: A Case History

We present a case study on using integrated geologic model in mineral exploration at depth. Fanchang area in Anhui province, is one of most important area in the middle and lower Yangtze River. It has significant potential to find iron ore at depth. Understanding the 3D structure, delineating the locations and variations of the intrusions and ore-controlling strata in the study area are essential for selecting deep mineral targets. A pilot 3D geologic model, coving an area of about 1408 square kilometers(km) and extends to a depth of 5 km, has been constructed by geophysical inversions to define the geometry, depth, and physical properties of geological bodies at depths. The model has confirmed most previous knowledge, but also revealed new features of different folds and intrusions, geologic formations of deep rock masses and the spatial distribution of stratum, those are important for planning future exploration at large depths. The process of building the 3D geologic model in our study consists of four major steps, as follows.

Firstly, we should determine the basic information of Model, including the 3D limits of the model area, the basic geological and structural unit, and the tectonic contact relations and the sedimentary sequences between these units.

Secondly, a series of 2D geological cross sections over the model area are built by using all kinds of prior information, including surface geology, borehole data, seismic sections, and local geologists' knowledge and intuition. And then, we put these sections into a 3D environment according to their profile locations to build a 3D model.

Thirdly, we calculate the potential field responses of the 3D model, and compare the predicted and observed data, and then adjust the model until a satisfactory accuracy of errors is achieved.

Finally, we export the 3D model into a 3D visualization platform. The 3D visualization of the results assists in understanding the spatial relations between various intrusive units and the ore-bearing strata.

A number of deep targets have been predicted by combining the conceptual mineralization model in the district with the 3D geological model. Our study demonstrates the potential of using geophysical data with geologic constraints to build 3D models in structurally complex areas for the purpose of mineral exploration at depth.