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 ???????O of -0.1???1.7 ???, suggesting precipitation from fluids with ???????O 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 ???????O of -0.2???2.3 ??? which would be in equilibrium with fluids having a ???????O of 10.7???13.0 ??? at ~250oC. Such enriched isotopic fluids suggest interaction of magmatic fluids with cooler saline fluids that were probably derived from the underlying carbonate-rich sequences. Fluid inclusions in apatite 3 and quartz homogenise at 145???155oC and, together with a quartz ???????O of 16.0???17.1 ???, suggests precipitation from a fluid with ???????O of -0.7???2.1 ??? that is likely to have resulted from the introduction of a cooler, less saline and isotopically depleted fluid (such as sea water). The results of this study clearly indicate a significant role for fluids in the evolution of the Esfordi deposit but do not preclude a role for immiscible Fe-oxide???P-rich melts in the initial stages of the mineralising process.
| Identifer | oai:union.ndltd.org:ADTP/240712 |
| Date | January 2005 |
| Creators | Jami, Morteza, School of Biological, Earth & Environmental Sciences, UNSW |
| Publisher | Awarded by:University of New South Wales. School of Biological, Earth and Environmental Sciences |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Morteza Jami, http://unsworks.unsw.edu.au/copyright |
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