The study of the magnetic anomaly variation A and its relationship with iron ores

• First derivation of formulas for magnetic anomaly variation A and its max value. • Previous studies that iron ores show magnetic anomaly variation A was confirmed. • Previous studies’ 30% higher varying amplitude at magnetic anomalies claim was refuted. • The measurement method of A offers a new way to detect iron ore anomalies. • Key factors affecting magnetic variation A measurement were analyzed. Accurately and rapidly determining the relationship between induced magnetization ( M i) and remanent magnetization ( M r) of magnetic anomaly sources remains a critical challenge in magnetic exploration. It directly affects the reliability of geological interpretations inferred from magnetic survey data. Drawing on the temporal variations of the geomagnetic field, this study develops a set of theoretical formulas for the magnetic anomaly variation ( A ), its theoretical maximum ( A max ), and the variation rate ( ηa ), under the assumption of uniform magnetization and co-directional remanent magnetization with the geomagnetic field. The results demonstrate that the magnetic anomaly variation ( A ) can serve as an indicator of the relationship between M i and M r. Under specific conditions, the magnetic anomaly variation ( A ) can assist in identifying whether the magnetic anomaly source originates from an iron ore body. Overall, this study offers valuable insights for magnetic anomaly studies, with particular relevance to iron ore exploration.