Anatomy of the Archean Anshan iron ore belt in the North China Craton: A geophysical approach

Abstract

The Anshan region of the North China Craton hosts significant iron ore reserves in the form of Archean banded iron formations (BIF). This study focuses on NW–SE trending layered iron ore bodies identified using aeromagnetic data with a 500m point spacing and a new method that combines structural analysis with the 3D inversion of magnetic susceptibility. This approach has identified two prominent parallel magnetic anomalies within the study area, with the bottom boundary of BIF body I estimated to be at a depth of ∼5600m and the bottom boundary of BIF body II at ∼5200m. The two BIF iron ore bodies are separated by granitoids associated with the Archean Anshan micro-continental nucleus. The area close to this micro-continental nucleus has undergone significant tectonic deformation, including ductile shearing. This shearing is the main control on the distribution of BIF iron ore belts in the Anshan area, in contrast to the previous view which folding was thought to control the distribution of BIF. Combining our new data with regional tectonic information yields a model where both folding and ductile shearing controlled the distribution of the main BIF ore bodies in the study area. This model provides insights into the distribution of iron ores in the Anshan area as well as a guide for future deep exploration in this region.