A study of iron deposits in the Anshan area, China based on interactive inversion technique of gravity and magnetic anomalies

The Anshan area in Liaoning province, Northeast China is famous for the richest banded iron formation (BIF) sources in the country. Whether they belong to volcano-sedimentary formation (Algoma-type) or sedimentary formation (Superior-type) remains controversial. Here we apply an interactive inversion technique on profile of gravity and magnetic anomalies to study the deep geological structure of the Anshan area. Combined with previous petrological and sedimentological studies on these rocks, the inversion results indicate that both Donganshan and Qidashan iron deposits consist of several syncline-shaped iron ore bodies. Among these, the majority might be considered as part of Archean and Paleoproterozoic Superior-type mineralization, whereas Algoma-type mineralization has been recognized only in the intervals during the volcanic eruption. Exploration for deep-seated iron deposits outside the Anshan area has led to the discovery of large amount of iron ores. Although the large aeromagnetic anomaly could be the signal of the buried huge iron ore bodies at depth in Anshan area, this has not been confirmed by deep drilling exploration. In order to solve this puzzle, we computed the aeromagnetic and gravity anomalies along a profile in the proven iron deposit of the Donganshan–Qidashan district. The results reveal marked contrast between the calculated and observed anomalies. Based on these results and previous studies on the metallogenic features, we predict the presence of large iron ore bodies at depth beneath the Anshan area.