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    大兴安岭南段矽卡岩型铁锡矿成矿花岗岩年龄、岩石地球化学及其U−Nb−Ta−REE成矿远景讨论

    Age and petrogeochemistry of ore-forming granites, and the metallogenic prospects of U-Nb-Ta-REE in the southern section of the Daxing'anling Mountains for skarn-type iron-tin deposits

      摘要
    • 摘要:
      研究目的 大兴安岭南段是中国北方重要的锡多金属成矿带，黄岗和莫古吐矽卡岩型铁锡矿床是其中典型代表，其成因与高分异的碱长花岗岩或正长花岗岩有直接的时空和成因联系，花岗岩的岩石地球化学特征及其对找矿的意义还有待进一步研究。
      研究方法 通过锆石U−Pb定年、全岩主量、微量和稀土元素测试和矿物学研究，探讨成矿花岗岩的特征和对找矿的启示。
      研究结果 矿物学研究发现，成矿花岗岩样品中钠质斜长石、碱性长石、石英具有低温共结熔体结晶的特点，且镜下可见文象结构和蠕虫状石英。锆石U−Pb年龄显示，黄岗矿床碱长花岗岩结晶年龄131.8±2.0 Ma(MSWD=1.3)，大莫古吐矿床碱长花岗岩结晶年龄为为137.1±1.3 Ma(MSWD=0.8)，均侵位于早白垩世。全岩主量元素显示花岗岩具有高硅（73.97%~79.05%）、高碱（7.83%~8.88%），低钙、铁、镁、钛和磷的特征，为准铝质—弱过铝质（A/CNK=0.93~1.09）高分异花岗岩。全岩微量和稀土元素显示，花岗岩具有高Rb、Th、Pb，低Ba、Sr、P、Ti的特征，稀土元素配分曲线较平坦（LaN/YbN=0.96~12.04），具有强烈的负Eu异常（Eu/Eu*=0.01~0.03）及弱的负Ce到正Ce异常的过渡特点（Ce/Ce*=0.96~1.56），微量元素配分图具有弱的四分组效应（TE1,3=0.99~1.14）。成矿花岗岩中，随着分异程度的增加，Th、U、Nb、Ta、Yb元素富集。
      结论 大兴安岭南段黄岗和莫古吐矽卡岩型铁锡矿床成矿花岗岩为早白垩世高硅高分异花岗岩，其形成过程对U、Sn、Nb、REE等成矿元素具有显著的富集作用。本次年代学、矿物学和地球化学的研究结合区内地质、地球物理勘探、地球化学勘探、遥感研究进展显示，大兴安岭南段燕山晚期分异花岗岩分布区域除具有Sn−Pb−Zn−Ag多金属成矿潜力外，还具有U−Nb−Ta−REE的找矿潜力。

       

      Abstract:
      Objective The southern segment of the Daxing'anling Range constitutes a significant tin-polymetallic metallogenic belt in northern China. Representative deposits include the Huanggang and Mogutu skarn-type Fe-Sn systems, which exhibit direct spatio-temporal and genetic relationships with highly fractionated alkali-feldspar granites or syenogranites. Further investigation is warranted regarding petrogeochemical characteristics of these granites and their implications for mineral exploration.
      Methods This study explores the characteristics of the ore−forming granites and their implications for ore prospecting through zircon U−Pb dating, whole−rock major, trace and rare earth element testing, and mineralogical studies.
      Results The weighted average U−Pb ages obtained from zircon dating are 131.8±2.0 Ma(MSWD=1.3) and 137.1±1.3 Ma(MSWD=0.8), indicating that the emplacement of alkali feldspar granite in the Huanggang and Damogotu deposits occurred during the Early Cretaceous. The main elements of the whole rock show that the granite has the characteristics of high silicon (73.97%~79.05%), high alkali (7.83%~8.88%), low calcium, iron, magnesium, titanium and phosphorus, and is a metaluminous to weak peraluminous (A/CNK=0.93~1.09) highly differentiated granite. The trace and rare earth elements in the whole rock show that the granite is characterized by high Rb, Th and Pb, and low Ba, Sr, P and Ti. The rare earth element distribution map is relatively flat (LaN/YbN=0.96~12.04), with strong negative Eu anomaly (Eu/Eu*=0.01~0.03) and weak negative Ce to positive Ce anomaly transition feature (Ce/Ce*=0.96~1.56), and the trace element distribution map has weak tetrad effect (TE1,3=0.99~1.14). In the ore−forming granites, elements such as Th, U, Nb, Ta and Yb are enriched with the increase of the degree of differentiation.
      Conclusions The metallogenic granites of the Huanggang and Mogutu skarn−type Fe−Sn deposits in the Southern Section of the Daxing'anling Mountains are Early Cretaceous high−silica highly fractionated granites, whose formation process has a significant enrichment effect on ore−forming elements such as U, Sn, Nb and REE. Combined with the research progress of regional geology, geophysical exploration, geochemical exploration and remote sensing, this study of chronology, mineralogy and geochemistry shows that the areas with Late Yanshanian differentiated granites in the Southern Section of the Daxing'anling Mountains not only have metallogenic potential for Sn−Pb−Zn−Ag polymetals, but also have prospecting potential for U−Nb−Ta−REE.

       

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