Origin of magnetite and apatite ores in the Esfordi magnetite-apatite ore deposit NE of Bafq, south Yazd: insights from mineralogy, geochemistry, microthermometry, O-H stable and U-Pb and Nd-Sm non-stable isotopes

Petrographic and mineralogical data indicate the widespread presence of five generations of apatite, two generations of monazite with minor xenotime in the Esfordi deposit. The O-H isotopic studies on the 1st- and 2nd-generations of apatites and massive fine-grained and vein-type apatites as well as their Sr and Mn contents, showed that the source of phosphorous was the sedimentary phosphorites. The ratio of 143Nd/144Nd vs 147Sm/144Nd and εNd vs P2O, and the difference of Nd isotopic ratios in the massive fine-grained and vein-type apatites indicate that they are not reproductively related to the host rhyolite and diorite. The similarity of 143Nd/144Nd vs 147Sm/144Nd and εNd vs P2O5 in the 1st- and 2nd-generations of apatite and the host rocks indicated that recrystallization of the apatites occurred during the magmatic and hydrothermal fluids circulation which were derived from the felsic to intermediate subvolcanic rocks. Difference in the age of the 2nd-generation apatites and the paragenetic- monazites ( 238U/206Pb and 207Pb/206Pb dating), the crystalline apatites and magnetite, the ilmenite exclusions in the magnetites, the dissolution evidences of different apatites and monazites generations, the content of Ti vs V, Al+Mn vs Ti+V and Mg+Al+Si vs Ti, and the O-H isotopes of the magnetite-apatite ores, all indicate the mixing of high-temperature magmatic and hydrothermal fluids rich in REE, P with Ca ±Fe evaporatic brines in different time periods, which caused a polygenic origin for the Esfordi deposit.