A review of iron oxide transformations, rock magnetism and interpretation of magnetic anomalies: El Morro Mine (Brazil), a case study

Abstract

A review of iron oxide mineralogy and its relationship with rock magnetic properties is presented. Magnetic processes and models of a large area around the El Morro, Brazil mine in the Jacupiranga alkaline-carbonatitic deposit is discussed. Rock magnetic properties and opaque mineral observations suggest that titanomagnetite is the main magnetic phase. The magnetic anomaly suggests ore bodies of an east-west general strike. The largest body is in the northern part of the area. It measures at least 5 by 2 km. All bodies are located in an aeromagnetic domain of semi-ellipsoidal shape and northeast-southwest general strike. It is proposed that the anomalous zone is continuous to the north and that the whole area of economic interest may extend roughly 8x4 km in the northsouth direction. We modeled two N-S and E-W profiles and the best fit corresponds to several large irregular bodies. The most important mineralized bodies are located beneath the northward continuation of the magnetic high; this inference is supported by a gravimetric data. Other bodies are located under the magnetic low and extend to the south. The best fit of calculated to observed anomaly is obtained by using mostly induced magnetization.