The yengejeh diasporic karst bauxite deposit, NW Iran: Constraints on distribution and fractionation of major and rare earth elements

IF 2.2 4区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY
Ali Abedini , Ali Asghar Calagari
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Abstract

The Yengejeh diasporic karst bauxite deposit (NW Iran) was developed as discontinuous layers and lenses along the contact of dolomitic limestone of the Ruteh Formation (middle-upper Permian) and dolomite of the Elika Formation (Triassic). This deposit is constituted by two conspicuous subset layers, (1) green bauxite (GB) and (2) red bauxite (RB). The XRD analytic data revealed that diaspore is accompanied by chlorite and anatase in the GB subset and by hematite in the RB subset. Minerals such as pyrophyllite, kaolinite, illite, and rutile are present within the both subsets. The antithetical distributions of Al with Fe and Al with Ti in the deposit are indicative of the controlling role of climatic changes of the depositional environment and the function of post-formation diagenetic processes. The increment in certain geochemical ratios like La/Y, (La/Yb)N, and (LREE/HREE)N from the top toward the bottom of the horizon is designative of pH increase in depositional milieu by buffering of the percolating solutions, and of preferential scavenging of LREE by hematite. The positive Ce anomaly in the GB subset took place as the result of change in the oxidation state of this element from Ce3+ to Ce4+. However, the positive Ce anomalies in the RB subset implicates preferential scavenging of Ce onto hematite. The marked variation range in anomaly values of Eu/Eu* (0.38–1.01) at Yengejeh reveals that this index acted as non-conservative during the evolution of this deposit, and this behavior is related most likely to influences of post-formation diagenetic processes.

伊朗西北部 yengejeh 散居岩溶铝土矿:主要元素和稀土元素分布与分馏的制约因素
Yengejeh散居岩溶铝土矿(伊朗西北部)沿鲁特地层(中-上二叠统)白云质灰岩和埃利卡地层(三叠统)白云岩的接触面发育为不连续的层和透镜体。该矿床由两个明显的子集层构成:(1)绿色铝土矿(GB)和(2)红色铝土矿(RB)。XRD 分析数据显示,在 GB 亚层中,绿泥石和锐钛矿与斜长石伴生,而在 RB 亚层中,赤铁矿与斜长石伴生。在这两个子集中还存在辉石、高岭石、伊利石和金红石等矿物。矿床中 Al 与 Fe 和 Al 与 Ti 的反向分布表明了沉积环境气候变化的控制作用和成岩后成岩过程的作用。某些地球化学比率,如 La/Y、(La/Yb)N 和 (LREE/HREE)N 从地层顶部向地层底部的递增,表明沉积环境中的 pH 值因渗流溶液的缓冲作用而升高,以及赤铁矿对 LREE 的优先清除作用。GB 子集中的正 Ce 异常是由于该元素的氧化态从 Ce3+ 变为 Ce4+ 的结果。然而,RB 子集中的正 Ce 异常表明赤铁矿优先清除了 Ce。在 Yengejeh,Eu/Eu*异常值(0.38-1.01)的明显变化范围表明,在该矿床的演化过程中,该指标是非保守的,这种行为很可能与成岩后成岩过程的影响有关。
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来源期刊
Journal of African Earth Sciences
Journal of African Earth Sciences 地学-地球科学综合
CiteScore
4.70
自引率
4.30%
发文量
240
审稿时长
12 months
期刊介绍: The Journal of African Earth Sciences sees itself as the prime geological journal for all aspects of the Earth Sciences about the African plate. Papers dealing with peripheral areas are welcome if they demonstrate a tight link with Africa. The Journal publishes high quality, peer-reviewed scientific papers. It is devoted primarily to research papers but short communications relating to new developments of broad interest, reviews and book reviews will also be considered. Papers must have international appeal and should present work of more regional than local significance and dealing with well identified and justified scientific questions. Specialised technical papers, analytical or exploration reports must be avoided. Papers on applied geology should preferably be linked to such core disciplines and must be addressed to a more general geoscientific audience.
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