Combined igneous and hydrothermal source for the Kiruna-type Bafq magnetite-apatite deposit in Central Iran; trace element and oxygen isotope studies of magnetite

摘要

The main deposits of the Bafq district (Choghart, Se Chahun and Chadormalou deposits) are magnetite-apatite ore bodies with Early Cambrian age, hosted by Early Cambrian volcano-sedimentary rocks, showing lava flow structure with miarolitic cavities and occasional brecciation. The texture and geochemistry (trace elements and O-isotope) of the studied magnetite crystals show three types of magnetite with different proportions in different parts of the district and the deposits. These are primary ignious magnetite and high-temperature hydrothermal magnetite in the massive parts of the deposits and foam-like magnetite in the veins or in the fractures of the massive part. The lack of zonation, high Ti/Fe ratios and delta O-18 values (2 parts per thousand ) indicate that massive magnetites formed at high temperature condition, while foam-like magnetite recrystallized at lower temperature. Textures and Co, V, Ti, Al, and Pb contents are used to distinguish ignious magnetites from the high-temperature hydrothermal magnetites. Foam-like magnetites contain lower REE and has lower delta O-18 values (2 parts per thousand ) over bar) than the massive magnetites.