Newly identified iron oxide-apatite deposit in Carboniferous marine volcanic rocks in the Beishan area and its implications for regional metallogeny: A case study of the Biyushan iron deposit, Inner Mongolia
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摘要:
北山地区发育众多赋存于石炭纪海相火山岩中的铁矿床, 其中内蒙古碧玉山铁矿床是该区典型的这类矿床之一。该矿床地处内蒙古自治区的西北缘, 勘查工作程度相对较低, 矿床成因研究程度较为薄弱。经过野外及初步的岩相学观察工作对内蒙古碧玉山铁矿床进行了研究。研究表明, 碧玉山铁矿床普遍具有磁铁矿-磷灰石的矿物组合, 其中磷灰石普遍经历溶解-再沉淀作用而导致内部含有大量细小的独居石包裹体。磁铁矿中普遍发育钛铁矿出溶结构, 具有高温的磁铁矿特征。这些特征与区域上发育的具有矽卡岩化及低钛磁铁矿的其他矿床明显不同, 而与典型的基鲁纳型(铁氧化物-磷灰石型)铁矿床在矿物组合及磷灰石、磁铁矿矿物学特征等方面非常相似。笔者对该铁矿的地质特征开展初步分析认为, 内蒙古北山地区碧玉山铁矿床属于赋存于海相火山岩中的基鲁纳型铁矿床, 这对该区基鲁纳型铁矿床的成矿理论及找矿勘查工作具有指导意义。
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关键词:
- 基鲁纳型(铁氧化物-磷灰石型)矿床 /
- 碧玉山铁矿 /
- 磁铁矿 /
- 磷灰石 /
- 矿床成因
Abstract:Objective Numerous iron deposits hosted in Carboniferous marine volcanic rocks occurred in the Beishan Orogenic Belt, Eastern Tianshan.The Biyushan iron deposit, located at the northwestern margin of Inner Mongolia, is a typical iron deposit hosted in Carboniferous marine volcanic rocks.
Methods In this study, we utilized field observation, microscope imaging, and scanning electron microscopy to charaterize the mineral assemblages of iron ores and microtextures of magnetite and apatite, in order to decipher the genesis of iron ores.
Results Our preliminary work has revealed that iron ores in the Biyushan deposit commonly have a mineral assemblage of magnetite-apatite, with apatite having abundant monazite inclusions due to the dissolution-reprecipitation processes.In addition, magnetite grains commonly have high Ti contents with ilmenite exsolution.Thus, the mineral assemblage of iron ores and mineralogical features of apatite and magnetite are similar to these of typical Kiruna-type deposits.
Conclusion Based on our preliminary analysis of geological characteristics, we suggest that the Biyushan iron deposit in Inner Mongolia is likely a Kiruna-type iron deposit hosted in submarine volcanic rocks that has not yet been documented.Therefore, these findings can guide future exploration of iron oxide-apatite deposits in this region.
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Key words:
- Kiruna (iron oxide-apatite) deposit /
- Biyushan iron deposit /
- magnetite /
- apatite /
- ore genesis
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图 2 碧玉山铁矿床典型铁矿石手标本及显微图片
a~c.磁铁矿-磷灰石型矿石手标本图;d~e.磁铁矿-磷灰石显微(反射光)图片;f.磁铁矿-磷灰石BSE图片,磷灰石内部含有大量独居石包裹体;g.磁铁矿(Mag1)中钛铁矿出溶结构;h.次生磁铁矿(Mag2)内部金红石与石英共生;i.原生磷灰石(AP1)与次生磷灰石(AP2)BSE图片,独居石包裹体分布于次生磷灰石内部。Mag.磁铁矿;Hem.铁矿;Py.黄铁矿;Ap.磷灰石;Mnz.独居石;Ilm.钛铁矿;Rt.金红石;Qz.石英;Di.透辉石;Chl.绿泥石。扫描电镜在中国地质大学(武汉)地质过程与矿产资源国家重点实验室利用配备能谱仪的Thermo Scientific Apreo 2 SEM高性能场发射扫描电子显微镜完成,实验条件:加速电压20 kV、电子束电流0.4 nA、工作距离10 mm
Figure 2. Hand specimens and photomicrographs of typical iron ores from the Biyushan iron deposit
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