Formation of the Chah-Gaz iron oxide-apatite ore (IOA) deposit, Bafq District, Iran: Constraints from halogens, trace element concentrations, and Sr-Nd isotopes of fluorapatite
Formation of the Chah-Gaz iron oxide-apatite ore (IOA) deposit, Bafq District, Iran: Constraints from halogens, trace element concentrations, and Sr-Nd isotopes of fluorapatite
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DOI：
10.1016/j.oregeorev.2021.104599
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发表时间：
2021-12
影响因子：
3.3
通讯作者：
Fatemeh Sepidbar;G. Ghorbani;A. Simon;Jinlong Ma;R. Palin;Seyed Masoud Homam
中科院分区：
文献类型：
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作者：
Fatemeh Sepidbar;G. Ghorbani;A. Simon;Jinlong Ma;R. Palin;Seyed Masoud Homam
通过对伊朗中部巴夫格成矿带恰赫-加兹铁氧化物磷灰石（IOA）存款矿床中磷灰石的结构、化学和Sr-Nd同位素组成的研究，探讨了该存款的成因。根据Cl/F和Cl/OH的比值，可识别出两代磷灰石。与块状矿体中磁铁矿共生的原生氟磷灰石化学成分均匀，Cl/F < 0.05，Cl/OH为0.01 ~ 0.07。相比之下，贫F磷灰石边缘存在于横切块状矿体的细脉中的磷灰石中，并散布在火成岩寄主岩石中，Cl/F和Cl/OH-磷灰石比值分别为0.08-0.12和0.15-0.79。贫F轮辋也缺乏轻稀土元素，钍和U，与存在的次生独居石，磷钇矿和钍石，形成的溶解-再沉淀耦合。辉长岩-闪长岩的全岩Nd-Sr同位素数据（（87 Sr/86 Sr）（I）= 0.7052 ~ 0.7064，ε Nd（t）= +1.3 ~+2.7）显示地幔源区，而高钾钙碱性钾玄质火山岩的εNd（t）= − 5.5 ~ − 7.6，清楚地反映了幔源基性岩浆与同化的元古代基底的混合作用。富F磷灰石和贫F磷灰石的初始87 Sr/86 Sr比值和Nd同位素值（分别为0.7038至0.7050和-0.3至+6.5）与辉长岩相似，支持原生氟磷灰石的岩浆来源，地壳贡献极小或无贡献，并表明具有负Nd同位素值的岩浆事件并未影响矿石的全岩Sm-Nd特征。来自氧化铁阶段的两种研究氟磷灰石的岩相学和地球化学及Nd-Sr同位素数据与恰赫-加兹IOA存款的火成/岩浆-热液成因相结合，热液叠加程度低，如贫F（富Cl）磷灰石边缘的形成所证明。磷灰石中相对恒定的Sr-Nd数据与来自同一演化岩浆热液系统的叠加、幕式热液流体一致。
The textures, chemistry and Sr-Nd isotopic compositions of apatite from the Chah-Gaz iron-oxide apatite (IOA) deposit in the Bafq metallogenic belt, central Iran, were studied to investigate the formation of this ore deposit. Two generations of apatite were recognized based on Cl/F and Cl/OH ratios. Primary fluorapatite, which is coeval with magnetite in the massive ore bodies, is chemically homogeneous and characterized by Cl/F < 0.05 and Cl/OH in the range of 0.01–0.07. By contrast, F-depleted apatite rims are present in apatite hosted in veinlets that crosscut the massive ore bodies and are disseminated in the igneous host rocks, and have Cl/F and Cl/OH-apatite ratios of 0.08–0.12 and 0.15–0.79, respectively. The F-depleted rims are also depleted in LREEs, Th and U, consistent with the presence of secondary monazite, xenotime and thorite that formed by coupled dissolution-reprecipitation. The whole-rock Nd–Sr isotopic data ((87Sr/86Sr)(I)= 0.7052 to 0.7064 and ɛNd(t) = +1.3 to + 2.7) of gabbro-diorite indicate an mantle source, while the high -K, calc-alkaline-shoshonitic volcanic host rocks have εNd(t) = − 5.5 to − 7.6, clearly reflecting mixing between mantle-derived mafic magmas and assimilated Proterozoic basement. The initial87Sr/86Sr ratios and ɛNd values of both F-rich and -depleted apatites (0.7038 to 0.7050 and −0.3 to + 6.5, respectively) are similar to gabbroic rocks and support a magmatic source for primary fluorapatite, with minimal or no crustal contribution, and indicate that the magmatic event with negative ɛNd values did not affect the whole-rock Sm-Nd signature of the ore. Petrography plus geochemical and Nd-Sr isotopic data of both studied fluorapatite, which come from iron oxide stage, are consistent with a combined igneous/magmatic-hydrothermal genesis for the Chah-Gaz IOA deposit, with low degrees of hydrothermal overprint, as evidenced by the formation of F-depleted (Cl-rich) apatite rims. The relatively constant Sr-Nd data in apatite are consistent with superimposed, episodic hydrothermal fluids from the same, evolving, magmatic-hydrothermal system.