Trace element geochemistry of magnetite from the Mahura iron placer deposit, Markazi province, Iran: implications for magnetite provenance rocks

IF 1.1 4区 地球科学 Q3 GEOLOGY
Elham Firouzi, Farhad Ehya, Mohammad Ali Aliabadi, Razieh Mohammadi
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Abstract

The Mahura iron placer deposit is located 55 km northeast of Arak city in the Markazi province, Iran. From a geological point of view, it is located in the Central Iran Zone. In this study, the trace element geochemistry of magnetite is used to determine the origin of placer magnetites in the Mahura deposit. Magnetite is the most important placer mineral that occurs as micrometer-sized grains in the Quaternary alluvium. The alluvium consists of sandy, silty and clayey sediments containing a considerable amount of volcanic rock fragments of various sizes. The results of the petrographic studies and the whole-rock geochemistry indicate that the volcanic rock fragments are mostly andesite and basaltic andesite. These volcanics contain 4 to 10% magnetite as disseminated grains in the groundmass and as inclusions in plagioclase and amphibole phenocrysts. The mineral chemistry of the placer magnetites indicates 2.59–3.33% Ti, so that they can be considered as titanomagnetite or as a solid solution between magnetite and ilmenite. The chemical composition of the magnetites in the volcanic rock fragments also falls within the range of titanomagnetite with a tendency towards magnetite in the TiO2-Fe2O3-FeO system. The composition of the placer magnetites and magnetites in the volcanic rock fragments are plotted in the magmatic field in Ti-Al and Ti versus Ni/Cr diagrams. The diagrams Ti + V versus Ni/(Cr + Mn) and Ti + V versus Ca + Al + Mn indicate that placer magnetites and magnetites in the volcanic rock fragments belong to the Fe-Ti, V deposits. In the V-Ti diagram, all magnetites fall into the range of titaniferous iron ores. The comparison of the trace element composition of placer magnetites and magnetites in the volcanic rock fragments in the elemental diagrams above showed that all magnetites have the same origin, so that the placer magnetites were most likely released from the volcanic rock fragments by erosion over time. On the other hand, the comparison of the chemical composition of the volcanic rock fragments in the alluvium with that of volcanic rocks from the Ashtian area north of the Mahura deposit in the petrogenetic diagrams reveals similar nature for these rocks and that the magnetite-bearing volcanic rock fragments originate from the Ashtian Basin.

Abstract Image

伊朗马尔卡济省马胡拉铁矿床磁铁矿的微量元素地球化学:对磁铁矿产地岩石的影响
马胡拉铁矿床位于伊朗马尔卡济省阿拉克市东北 55 公里处。从地质角度看,它位于伊朗中部地区。本研究利用磁铁矿的痕量元素地球化学来确定马胡拉矿床块状磁铁矿的来源。磁铁矿是最重要的块状矿物,以微米大小的颗粒出现在第四纪冲积层中。冲积层由砂质、淤泥质和粘土质沉积物组成,其中含有大量大小不一的火山岩碎片。岩相学研究和全岩地球化学研究结果表明,火山岩碎块主要是安山岩和玄武安山岩。这些火山岩中含有 4%至 10%的磁铁矿,作为散粒存在于地层中,并包裹在斜长石和闪石表晶中。块状磁铁矿的矿物化学成分显示 Ti 含量为 2.59-3.33%,因此可将其视为钛磁铁矿或介于磁铁矿和钛铁矿之间的固溶体。火山岩碎片中磁铁矿的化学成分也属于钛磁铁矿范围,倾向于 TiO2-Fe2O3-FeO 系统中的磁铁矿。块状磁铁矿和火山岩碎块中磁铁矿的成分在岩浆场中绘制成 Ti-Al 图和 Ti 与 Ni/Cr 图。Ti + V 与 Ni/(Cr + Mn)和 Ti + V 与 Ca + Al + Mn 的关系图表明,块状磁铁矿和火山岩碎块中的磁铁矿属于 Fe-Ti、V 矿床。在 V-Ti 图中,所有磁铁矿都属于钛铁矿。通过比较上述元素图中的块状磁铁矿和火山岩碎屑中的磁铁矿的微量元素组成,可以看出所有磁铁矿的来源相同,因此块状磁铁矿很可能是经过长期侵蚀从火山岩碎屑中释放出来的。另一方面,将冲积层中火山岩碎块的化学成分与岩石成因图中马胡拉矿床以北阿什田地区火山岩的化学成分进行比较,发现这些岩石的性质相似,含磁铁矿的火山岩碎块源自阿什田盆地。
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来源期刊
Carbonates and Evaporites
Carbonates and Evaporites 地学-地质学
CiteScore
2.80
自引率
14.30%
发文量
70
审稿时长
3 months
期刊介绍: Established in 1979, the international journal Carbonates and Evaporites provides a forum for the exchange of concepts, research and applications on all aspects of carbonate and evaporite geology. This includes the origin and stratigraphy of carbonate and evaporite rocks and issues unique to these rock types: weathering phenomena, notably karst; engineering and environmental issues; mining and minerals extraction; and caves and permeability. The journal publishes current information in the form of original peer-reviewed articles, invited papers, and reports from meetings, editorials, and book and software reviews. The target audience includes professional geologists, hydrogeologists, engineers, geochemists, and other researchers, libraries, and educational centers.
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