Geology, geochemistry, fluid inclusions and O–H stable isotope constraints on genesis of the Lake Siah Fe-oxide ± apatite deposit, NE Bafq, Central Iran

Abstract

The Lake Siah iron ± apatite deposit is situated in the Bafq Mining District (BMD), Central Iran. The iron ± apatite orebodies are hosted by a succession of rhyolite, rhyolitic tuff, trachyandesite, and andesite of Lower Cambrian age. The host rock has undergone widespread alteration and mineralization stages including Na (albite–quartz), followed by Na–Ca (albite–calcite–amphibole–magnetite ± quartz ± epidote), magnetite–apatite, K (biotite ± K-feldspar), hydrolytic (sericite–quartz), and argillic (kaolinite–montmorillonite ± dickite), respectively. Electron microprobe analyses (EPMA) from magnetite and hematite show significant variations of trace elements. Based on Ni/Cr + Mn and Ca + Al + Mn versus Ti + V diagrams, the majority of magnetite samples belong to Kiruna-type deposits. At least, three generations of fluid inclusions, including solid-bearing (L + V + S) (Type I), liquid-rich (L + V) (Type II-A), vapor-rich (L + V) (Type II-B), and liquid or vapor mono-phase (Type III), are recognized in quartz and apatite. The solid-bearing fluid inclusions in quartz completely homogenized at temperatures of 150 to > 530 °C with salinities of 30–58 wt% NaCl equiv. Liquid-rich fluid inclusions in apatite homogenized to a liquid phase at 175–210 °C, whereas the vapor-rich fluid inclusions homogenized to a vapor at 335–350 °C. Oxygen isotope analysis was carried out on quartz and magnetite. The hydrogen and oxygen isotopic compositions of quartz (δ18Ofluid values of 7.57–11.04‰) show that with progress in time the ore-forming solutions gradually evolved from a magmatic to meteoric-dominated source.