Petrogenesis of Iron ORE Deposits in Hakimpur, Dinajpur District, Bangladesh

Abstract

In Bangladesh, Hakimpur iron deposits has just primarily discovered in Rangpur saddle. In this research, for understanding the tectonogenesis with different rock types and geochronology, the data were obtained from thin section petrography, XRF (X-ray fluorescence), ICP-MS (inductively coupled plasma mass spectrometry), EPMA (Electron Microprobe Analyzer), FE-SEM (Field Emission Scanning Electron Microscope), XRD (X-ray Diffraction), petrography and Raman spectroscopy of fluid inclusion. The Fe-rich deposits in Hakimpur (Bangladesh) are characteristically superior-type banded iron formation (BIF) that shows alternating quartz-rich light and magnetite-rich dark bands, constituting chiefly of opaque minerals (i.e., magnetite, hematite and/or limonite) (35–45 %) and quartz (20–23 %). The BIF bands are found interleaved with amphibolite, biotite schist, and quartzite. The average concentrations of Al2O3, TiO2 and ∑REE in the Hakimpur BIFs are 0.95 wt.%, 0.11 wt.% and 133.75 ppm, respectively. These values indicate that the Hakimpur iron deposits primarily originate from iron-rich chemical sediments, possibly influenced by the addition of terrestrial or volcanic materials. However, markedly low content of trace element compositions such as Cr (<20–110 ppm), Ni (<20–70 ppm), Co (1–43 ppm), V (<5–292 ppm) and Sc (5–54 ppm) clearly indicate the incorporation of terrigenous sediments with passively volcanic materials. REE–Y signatures, Eu/Eu*PAAS, Y/Ho, Eu/Sm and Sm/Yb ratios also suggest the Hakimpur BIFs formed through the precipitation of a blend of low-temperature hydrothermal fluids and seawater, accompanied by a notable detrital contribution. The presence of negative CePAAS anomalies indicates the impact of the global 'Great Oxidation Event' during the depositional period. The combination of geochemical analysis and petrographic investigations reveals that the BIF and rocks associated with BIF originate from chemically precipitated sedimentary origin or sedimentary protoliths. The evidence of isotope (δ18O) and fluid inclusion reflect clay minerals were altered during diagenesis and metamorphism in the sediments as- clay (illite) → chlorite → biotite → amphibole, which is also evident in petrographic results by biotitization, chloritization, silicification, epidotization and saussuritization. The U-Th-Pb geochronological analysis of monazite chemistry provides evidence suggesting that the deposit underwent a solitary medium- grade metamorphic event at 1728±28 Ma (1.73 Ga), coinciding with the magmatic event in the basement rocks of Bangladesh at that time. The metamorphism was took place by the hydrothermal action in orogenic system during concurrent magmatism of Palaeoproterozoic basement complex. Minerals chemistry of amphiboles and biotites of the BIF-hosted rocks also supported this view of the calc-alkaline subduction related orogenic system as demonstrated in the tectonogenetic model. Furthermore, thermobarometric analysis and assessment of oxygen fugacity based on studied minerals such as amphibole (T= 591‒621 °C and P= 6‒8 kbar), biotite (T= 511–582 °C), zircon (T= 677–692 °C), and coexisting magnetite and ilmenite assemblages (T= 522–809 °C and fo2= 10-23.9 to 10-11.9) indicate that the rocks associated with BIF experienced a medium to high-grade metamorphism. This aligns largely with the crystalline temperature characteristics of the basement rock in Bangladesh.