S. A. Majidi; M. Lotfi; M. H. Emami; N. Nezafati
Abstract
The metallogenic zone of Bafgh-Saghand in central Iran hosts huge low-titanium iron oxide-apatite (IOA) deposits (also called Kiruna type iron deposits) with more than 1500 Million tons grading 55% iron. The genesis of these deposits including Chadormalu, Choghart, She-Chahun, and Esfordi has long been ...
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The metallogenic zone of Bafgh-Saghand in central Iran hosts huge low-titanium iron oxide-apatite (IOA) deposits (also called Kiruna type iron deposits) with more than 1500 Million tons grading 55% iron. The genesis of these deposits including Chadormalu, Choghart, She-Chahun, and Esfordi has long been a subject of debate. In this regard, several hypotheses such as magmatic, hydrothermal, carbonatititc, BIF, and sedimentary-exhalative have been proposed so far. In this study, 20samples of the magnetite ore from the deposits of Chadormalu, Choghart, She-Chahun, and Esfordi were selected and analyzed for their oxygen isotope values. Based on the analyses results, the variations of δ18O values in the deposits are meaningful and result from the characteristics of the ore forming processes involved. The δ18O values of the analyzed magnetite samples range from -0.1 to +2.2‰ and indicate the role of both orthomagmatic (>0.9‰) and hydrothermal (<0.9‰) processes in the formation of these deposits. On the other hand, the values lower than +0.3‰ can be attributed to secondary oxidation or hydrothermal processes and/or a combination of both. The oxygen isotope data of the investigated samples are identical to the deposits such as El Laco of Chile, Kiruna and Grängesberg of Sweden, and Zhibo and Chagangnuoer of China with a magmatic-hydrothermal genesis. According to the geological and analytical evidence obtained from the iron oxide-apatite deposits of the Bafgh-Saghand area, first a tonalite-trondhjemite-granodiorite, diorite, and granite magmatism related to a continental margin subduction at 533 to 525Ma has caused a magmatic mineralization of iron in the area, while a later hydrothermal process related to an alkaline intrusion (syenite and monzosyentie) has caused a hydrothermal mineralization. Therefore a magmatic-hydrothermal source can be suggested for the formation of the low-titanium iron oxide-apatite deposits of the Bafgh-Saghand area.
S. A. Majidi; M. Lotfi; M. H. Emami; N. Nezafati
Abstract
The Origin of Iron Oxide-Apatite deposits (IOA) with low Ti or Kiruna type deposits has long been a matter of debate. In this case, several provenances have been proposed for these deposits which include: magmatic, magmatic-hydrothermal, hydrothermal, banded iron formations, and sedimentary-exhalative. ...
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The Origin of Iron Oxide-Apatite deposits (IOA) with low Ti or Kiruna type deposits has long been a matter of debate. In this case, several provenances have been proposed for these deposits which include: magmatic, magmatic-hydrothermal, hydrothermal, banded iron formations, and sedimentary-exhalative. Bafq-Saghand metallogenic zone is located in central Iran and hosts several large IOA type deposits including Chadormalu, Choghart, Se-Chahun, and Esfordi with nearly ~1500 mt ore with an average grade of 55%. Mineralization of REE-rich apatite is very common in these deposits, an issue that could be utilized for the study of their genesis. Fifteen apatite samples from the deposits of Chadormalu, Choghart, Se-Chahun, and Esfordi were taken and analyzed using LA ICP-MS. According to the geochemical analysis, the apatite of the abovemnetioned deposits show high enrichment of Y, Na, and Si, while very low content of Cl. Total REE content varies from 0.36-2.25% in which the LREE show an enrichment indicating strongly fractionation from HREE. Strong negative Eu anomaly (0.69-0.256) is observed. Sr and Y contents in apatites are 165-365 and 743-1410 ppm, respectively. The Fe-OH-Cl diagram shows that apatites is situated in the Hydroxil-fluoroapatite domain. The results show that these deposits are similar to those of IOA type deposits (e.g. Kiruna, El Laco, Abagong, Avnik, etc.). Apatite mineralization is unlikely related to carbonatitic magmatism, but situated in the Kiruna type and mafic rocks domain. The main mineralization event was likely related to tonalite-trondhjemite-granodiorite (TTG) and diorite-granite of arc magmatism (525-532 Ma) which were intruded into the Cambrian volcano sedimentary units (as country rock). Then the hydrothermal processes following alkaline intrusion (syenite and monzosyenite) led to mineralization. In general, the iron oxide-apatite (IOA) mineralization with low Ti has occurred through the magmatic-hydrothermal processes in the Bafgh-Saghand zone.
