Geology, geochemistry and evolution of the Esfordi Phosphate - Iron Deposit, Bafq Area, Central Iran

• Main Author: Jami, Morteza
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: UNSW, Sydney 2005
• Subjects: Geology - Iran; Geochemistry - Iran; Kiruna
• Online Access: http://hdl.handle.net/1959.4/32745; https://unsworks.unsw.edu.au/bitstreams/0e6ad007-c0f6-4077-86af-d30b676f9854/download; https://doi.org/10.26190/unsworks/17736

Esfordi is a Kiruna-type Fe–P oxide deposit in the Bafq district of Iran. It formed within a predominantly rhyolitic volcanic sequence that formed in a continental margin tectonic regime and is of Cambrian age. The gently dipping, stratabound ore body is lenticular and displays a well-developed mineralogical zonal pattern. The Fe-oxide rich core contains a central zone of massive magnetite and a more hematitic brecciated rim. The overlying P-rich ore body contains massive and brecciated, apatite-rich variants with accessory hematite and actinolite. A zone of apatite-bearing veins and disseminations envelopes the Fe-oxide and P-rich zones and extends into overlying volcaniclastics that contain detrital magnetite ± apatite clasts. The main ore zones are surrounded by Ca-rich alteration, dominated by actinolite, extending ~100 m into the more permeable overlying volcaniclastics. Beyond this envelope is widespread development of secondary K-feldspar. Mesoscopic and microscopic observations reveal a paragenetic sequence containing four generations of apatite. The early stage is a LREE-rich apatite 1 that occurs within the massive and brecciated magnetite core. The second generation is large and brecciated apatite 2, associated with hematite and actinolite. Both apatite 1 and 2 exhibit widespread dissolution and reprecipitation to form a LREE-poor granular apatite that is generally associated with quartz-carbonate±REE minerals. The final stage involved an overprint of LREE-poor apatite 3-carbonate-quartz-actinolite-chlorite-epidote±bastnaesite±synchesite extending into the host rocks. Fluid inclusions in apatite 1 have homogenisation temperatures of 375-425oC and indicate salinities of 14–18 wt. % NaCl. The magnetite displays low δ¹⁸O of -0.1–1.7 ‰, suggesting precipitation from fluids with δ¹⁸O of 7.8–9.6 ‰ at ~400oC, consistent with a magmatic source. Fluid inclusions in apatite 2 homogenise between 195–295oC with indicated salinities of 13–19 wt. % NaCl. The associated hematite displays δ¹⁸O of -0.2–2.3 ‰ which ...