Physical properties and petrologic description of rock samples from an IOCG mineralized area in the northern Fennoscandian Shield, Sweden

Abstract

The Tjårrojåkka Fe–Cu-prospect in northern Sweden is considered an example of a Fe-oxide Cu–Au (IOCG) deposit and is hosted in metamorphosed Paleoproterozoic volcanic and intrusive rocks. Rock samples from 24 outcrops were collected for petrophysical analysis (magnetic susceptibility, remanent magnetization, variation of magnetic susceptibility with temperature, Curie temperature and density). The major Cu-prospect in the area has been studied by magnetic and electron microprobe analyses of four selected rock samples. The samples are from an exploration well that intersects the main Cu-mineralized body. The magnetic analyses show that magnetite is the dominant magnetic mineral, while hematite and other Fe-minerals are present in minor amounts. The electron microprobe observations confirm the presence of magnetite and further indicate that hematite is an alteration product of magnetite. Moreover, microprobe observations indicate that Fe-sulfides are present in negligible amounts in the samples from the Tjårrojåkka area. The strong spatial relationship of Cu-minerals (e.g., chalcopyrite) and the oxidation of magnetite to hematite suggest that the presence of rocks with low magnetic susceptibility in areas dominated by high susceptibility rocks may be a signal of related Cu-prospects.