扬子西缘羊场磷矿地球化学特征及其对成磷环境的指示
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P619.21+3;P595

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云南省地质勘查基金项目(D202001,K202101,K202301,Y202301)


Geochemical characteristics of the Yangchang phosphate deposit in western margin of the Yangtze Block and its indications of the phosphorus-forming environment
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    摘要:

    寒武纪生命大爆发与海水氧化还原条件息息相关,上扬子地区下寒武统磷块岩较完整记录了早寒武世古海洋环境信息。扬子西缘羊场磷矿床是赋存于下寒武统梅树村组的超大型磷矿床,可重建该时期古海洋环境。本文采用ICP-MS等手段,分析羊场磷矿床磷块岩及其围岩的元素地球化学组成特征,探讨其形成时的环境条件。结果表明,羊场磷矿床磷块岩CIA值为46.40~65.60,平均57.43,显示其风化程度较低,稀土元素总量ΣREE相对较低(140.0×l0-6~237.4×l0-6),但较富集Y(87.0×l0-6~183.2×l0-6);北美页岩标准化的稀土元素配分模式曲线相对平缓,LREE/HREE值为4.22~7.50,显示出轻重稀土元素分异不明显,具有明显的Ce负异常(δCe=0.22~0.42),Eu异常不明显(δEu=0.90~1.21),U/Th值为2.55~27.68,反映了磷块岩成矿过程中受到热水活动的影响;结合δCe、V/Cr、Y/Ho、Sr/Cu等元素分析认为,由底部震旦纪灯影组,到含磷层寒武纪梅树村组,直至上覆牛蹄塘组,古海洋氧化还原环境由底部的相对还原环境,向上变为氧化环境,直至顶部变为相对还原环境。古气候环境表现为寒冷干燥-温暖湿润交替出现的变化规律,古海水盐度表现为由咸水→半咸水→咸水→淡水的演化过程。综合分析后认为,羊场磷矿床磷块岩形成于相对氧化的咸水和较为干旱的古气候环境,并有热水活动参与成矿。

    Abstract:

    The Cambrian life explosion is closely related to the redox environment of plaeoocean, and the Lower Cambrian phosphorite in the Upper Yangtze Block has recorded a relatively complete information of the Early Cambrian. The Yangchang phosphate deposit in western margin of the Yangtze Block is a super-large phosphate deposit occurring in the Meishucun Formation of the Lower Cambrian, which can reconstruct the paleomarine environment of this period. In this paper, ICP-MS and other techniques were used to analyze the elemental geochemical composition characteristics of the phosphorite and its surrounding rocks and explore the geological environment of the Yangchang phosphate deposit. The results show that the CIA value of phosphorite is 46.40~65.60, with an average of 57.43, indicating that the weathering degree is low, the total amount of rare earth element (ΣREE) in phosphorites in this deposit is relatively low (140.0×l0-6~237.4×l0-6), but yttrium is relatively rich (87.0×l0-6~183.2×l0-6). The North American standardized rare earth distribution pattern is relatively flat, the LREE/HREE is of 4.22~7.50, shows that the diffrernce of light and heavy rare earth elements is not obvious, with obvious Ce negative anomaly (0.22~0.42), Eu anomaly is not obvious with δEu of 0.90~1.21, and U/ Th ratio of 2.55~27.68, which reflect that the phosphorite was affected by a certain influx of hydrothermal fluid during the sedimentary of phosphorites. Combined with the analysis of δCe, V/Cr, Y/Ho, Sr/Cu and other elements, it is indicate that from the bottom of Dengying Formation in the Sinian Period, to the phosphate-bearing layer Cambrian Meishucun Formation, to the upper cover Niutitang Formation, the ancient ocean redox environment changes from the relative reduction environment at the bottom to the oxidation environment upward until the top becomes the relative reduction environment. The paleoclimatic environment is cold and dry-warm and moist alternatively appear. The salinity of ancient seawater is the evolution process of salt water to semi-salt water to salt water to fresh water. The above analysis shows that the phosphorite deposit in a relatively oxidized saline water and arid climatic environment, and the climatic environment is relatively arid during sedimentation, and may be affected by the influx of hydrothermal fluid.

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周骞,米云川,赵勇,等, 2024. 扬子西缘羊场磷矿地球化学特征及其对成磷环境的指示[J]. 岩石矿物学杂志, 43(5):1119~1138.
ZHOU Qian, MI Yun-chuan, ZHAO Yong, et al, 2024. Geochemical characteristics of the Yangchang phosphate deposit in western margin of the Yangtze Block and its indications of the phosphorus-forming environment[J]. Acta Petrologica et Mineralogica, 43(5): 1119~1138.

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  • 收稿日期:2024-05-14
  • 最后修改日期:2024-07-24
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  • 在线发布日期: 2024-09-25
  • 出版日期: 2024-09-25