滇东北羊场磷矿区寒武系梅树村组沉积演化特征及古环境对磷成矿的制约
CSTR:
作者:
作者单位:

作者简介:

通讯作者:

中图分类号:

P619.21+3

基金项目:

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


Sedimentary evolution of the Cambrian Meishucun Formation in the Yangchang phosphate mining area and the constraints for paleoenvironment on phosphate mineralization, Northeastern Yunnan
Author:
Affiliation:

Fund Project:

  • 摘要
  • |
  • 图/表
  • |
  • 访问统计
  • |
  • 参考文献
  • |
  • 相似文献
  • |
  • 引证文献
  • |
  • 资源附件
  • |
  • 文章评论
    摘要:

    羊场磷矿床赋存于扬子陆块西南部梅树村组(1ms)浅海相地层中,研究区梅树村组沉积环境演化对区域找矿具有重要意义。本文采用岩石地球化学分析方法,对羊场磷矿区梅树村组的主量、微量元素地球化学特征进行分析,探讨矿区梅树村组地层沉积演化过程及磷矿富集部位。结果表明,矿区梅树村组的主量元素总体CaO、MgO含量较高,并具较高的烧失量。同时上部富含P2O5,下部含较高的SiO2。梅树村组一段(1ms1)形成于早寒武纪海侵早、中期,微量元素特征显示多元素富集,一段下亚段(1ms1-1) U、Mo富集系数超过地壳平均值的60倍,一段上亚段(1ms1-2) U、Mo富集系数超过地壳平均值的10倍,二者U、Mo富集的峰值差异较大,微量元素比值判断均处于贫氧或缺氧环境。稀土元素特征显示一段下亚段(1ms1-1)的Ce为无异常、Eu显示弱负异常,一段上亚段(1ms1-2)的Ce和Eu均为弱负异常。反映出梅树村组一段处于潮下低能环境,随时间推移,由下亚段1ms1-1到上亚段1ms1-2沉积演化过程由相对缺氧环境向相对氧化环境转变。梅树村组二段(1ms2)处于潮间带和潮下带高能环境,沉积物为内源沉积,是磷矿石赋存层位;微量元素特征表明其沉积环境为缺氧环境,稀土元素Ce显负异常,为氧化环境;说明梅树村组二段磷块岩中的胶磷矿是在干旱炎热的环境下,由潮下带氧化-还原界面之上过饱和富含磷质的海水中结晶析出,并沉积在海底封闭或半封闭缺氧环境。梅树村组三段(1ms3)位于潮上带或潮间带上部,沉积物为内源沉积,微量元素和稀土元素特征继承了梅树村组二段的特点,沉积时为炎热干燥气候下的氧化环境。综上认为,梅树村组地层的沉积环境演化过程经历了由海进初期-海进中期-海进晚期-海退期4个阶段,气候经历了由干旱炎热-温暖湿润-干旱炎热-干旱炎热4个阶段,海底环境经历了由还原-氧化-以还原为主,还原与氧化相互更替-氧化4个阶段的沉积过程。并指出羊场磷矿赋矿区位置处于扬子陆块滇东陆表海内浅滩之水下潮间带或潮下高能带,同时在海水相对封闭或半封闭的还原环境或半还原环境下,更利于胶磷矿的形成和富集。

    Abstract:

    The Yangchang phosphate deposit is located within the shallow marine strata of the Meishucun Formation (1ms) in the southwestern Yangtze block. Investigating the sedimentary environment evolution of the Meishucun Formation in this mining area holds significant implications for regional prospecting. This study conducts geochemical analyses of major and trace elements from the Meishucun Formation in the Yangchang phosphate mining area to explore the sedimentary evolution process and phosphate enrichment sites. The results indicate that the Meishucun Formation contains relatively high concentrations of CaO and MgO, with elevated loss on ignition. Notably, P2O5 is enriched in the upper part, while SiO2 is enriched in the lower part. The first member of the Meishucun Formation (1ms1), formed during the early to mid-Cambrian transgression, exhibits multi-element enrichment characteristics. Specifically, the enrichment coefficients of U and Mo in the lower submember (1ms1-1) exceed 60 times the average crustal value, whereas those in the upper submember (1ms1-2) exceed 10 times the average crustal value. Significant differences in peak values of U and Mo enrichment are observed between the two submembers. The lower submember (1ms1-1) shows no Ce anomalies and weak negative Eu anomalies, while the upper submember (1ms1-2) displays weak negative anomalies for both Ce and Eu. These findings suggest that the first member of the Meishucun Formation was deposited in a subtidal low-energy environment, transitioning from a relatively anoxic environment in the lower submember (1ms1-1) to a relatively oxidized environment in the upper submember (1ms1-2). The second member of the Meishucun Formation (1ms2), composed of endogenous sediments hosting phosphate ores, was formed in an intertidal or subtidal high-energy environment. Trace element characteristics suggest an anoxic environment, while negative Ce anomalies indicate an oxidized environment. This implies that the collophanite in the phosphorite of the second member crystallized and precipitated from supersaturated phosphorus-rich seawater above the subtidal oxidation-reduction interface under arid and hot conditions, subsequently depositing in a closed or semi-closed anoxic environment on the seafloor. The third member of the Meishucun Formation (1ms3), consisting of endogenous sediments formed at the upper part of the supratidal or intertidal zone, inherits trace and rare earth element characteristics from the second member, indicating an oxidizing environment under dry and hot climatic conditions. In summary, the sedimentary environmental evolution of the Meishucun Formation can be divided into four stages: early transgression, middle transgression, late transgression, and regression, corresponding to climatic changes from arid or semi-arid and hot to warm and humid, then back to arid and hot. The seafloor also underwent four stages of sedimentary processes: reduction, oxidation, mainly focused on reduction, reduction and oxidation alternate with each other, and oxidation. We conclude that the Yangchang phosphate mining area was situated in the underwater intertidal or subtidal high-energy zones within the shallow shoals of the eastern Yunnan epicontinental sea, Yangtze Craton, where the formation and enrichment of collophanite are more favorable in relatively closed or semi-closed reducing environments or semi-reducing environments of seawater.

    参考文献
    相似文献
    引证文献
引用本文

胡清华,夏建峰,周骞,等, 2025. 滇东北羊场磷矿区寒武系梅树村组沉积演化特征及古环境对磷成矿的制约[J]. 岩石矿物学杂志, 44(2):283~310.
HU Qing-hua, XIA Jian-feng, ZHOU Qian, et al, 2025. Sedimentary evolution of the Cambrian Meishucun Formation in the Yangchang phosphate mining area and the constraints for paleoenvironment on phosphate mineralization, Northeastern Yunnan[J]. Acta Petrologica et Mineralogica, 44(2): 283~310.

复制
分享
文章指标
  • 点击次数:
  • 下载次数:
  • HTML阅读次数:
  • 引用次数:
历史
  • 收稿日期:2024-05-13
  • 最后修改日期:2024-10-16
  • 录用日期:
  • 在线发布日期: 2025-03-31
  • 出版日期:
文章二维码