REE-Y-Ti-Th mineralization in the albite bearing metasomatite and metasomatized rhyolite hosted in Choghart magnetite-apatite deposit, Central Iran: Interplay of evaporitic brines, hydrothermal-magmatic fluids

Macroscopic, microscopic and geochemical studies carried out on albite-bearing metasomatites and metasomatic rhyolites hosting the magnetite-apatite deposit of Chogharat indicate the presence of three generations of albite with different concentrations of REE-Y-Ti-Th, in response to T-P reduction and chemical changes of the fluids and the ratio of fluid to rock. The geochemical analysis of the low Ca/Na fluids shows a deficiency in REE-Th mineralization in the white albites, while in the fluids with medium Ca/Na, the REE mineralization (REE>Th) has occurred in the pinkish albites. In contrast, fluids with high Ca/Na indicate Th mineralization (Th>REE) in the red albites. The stable isotopes of C-O on the paragenetic calcites show REE-Y-Ti-Th mineralization of albites due to High-T hydrothermal fluids. Otherwise, the stable O-C isotopes of the Ghoghart apatites and stable isotopes of S in the ore deposits of the BMD verify the role of evaporitic brines and fluid-rock interaction on the mineralization. The presence of calcite and titanite, associated with the calcic-amphiboles and clinopyroxenes, Ca-inclusions in the thorite structure and Ca-content of the thorites, indicate thorite mineralization from the Co32- and Ca2+ fluids due to low activity of the chlorine. According to this study, the source of metasomatism is mainly evaporitic brines with a minor amount of magmatic and related hydrothermal fluids. Mineralization is the result of interaction of the magmatic and hydrothermal fluids of the Late Ediacaran- Early Cambrian plutonic/ subvolcanic intrusions with the evaporitic brines, derived from the synchronous evaporitic sequence.