内蒙古北山花石头山萤石矿床成因:萤石微量、稀土和H-O同位素制约

Genesis of the Huashitoushan Fluorite Deposit,Beishan,Inner Mongolia:Constraints from Trace Elements,REE and H-O Isotope Geochemistry of Fluorite

花石头山萤石矿是北山成矿带东段新发现的具有中-大型潜在资源的萤石矿床,矿体位于梭梭井黑云母二长花岗岩外接触带,受NE向、近SN向断裂构造控制,赋矿围岩主要为西双鹰山组石英砂岩和粉砂岩夹灰岩透镜体。笔者在对花石头山萤石矿床地质特征研究基础上,开展萤石微量、稀土和H-O同位素地球化学特征研究。结果显示,9件萤石样品均表现出MREE相对LREE和HREE强烈富集,标准配分曲线呈“倒V”型。Eu的正异常(1.11~1.25)和Ce的负异常(0.90~0.95)指示成矿流体来源相同且为较低温度的弱氧化环境。此外,萤石样品的La/Ho-Y/Ho特征也表明形成这些萤石的成矿流体可能为同期同源的富F流体。5件萤石中的δD_(V-SMOW)和δ^(18)O_(V-SMOW)值分别为-109.7‰~-99.4‰(平均值为-104.3‰)和-3.1‰~-1.9‰(平均值为-2.3‰),表明成矿流体为岩浆水和大气降水的混合热液。Tb/La-Tb/Ca特征进一步表明花石头山萤石矿床是岩浆热液作用的产物。此外,全部萤石样品中仅Sb元素相对围岩(西双鹰山组、北山地区和地壳)表现为不同程度富集,其余元素均呈不同程度亏损。两件黑云母二长花岗岩的稀土标准配分曲线呈右倾型,LREE相对HREE强烈富集。结合矿床地质特征,认为花石头山萤石矿床形成于中低温弱氧化还原环境,成矿流体为岩浆水和大气降水的混合热液,成矿物质F主要来源于黑云母二长花岗岩,Ca主要来源于西双鹰山组,成因类型为中低温热液充填型矿床。

The Huashitoushan fluorite deposit is a newly discovered fluorite deposit with medium-large potential resources in the eastern part of the Beishan metallogenic belt.The orebodies are located in the outer contact zone of the Suosuojing biotite monzogranite and are controlled by NE and NS faulted structure.The host rock is mainly quartz sandstone and siltstone with limestone lens of Xishuangyingshan Formation.On the basis of studying the geological characteristics of the Huashitoushan fluorite deposit,carry out the studies of trace element,REE and H-O isotope geochemistry.The results show that 9 fluorite samples showed strong enrichment of MREE relative to LREE and HREE,and the standard partition curve showed an"inverted V"shape.Positive Eu anomaly(1.11~1.25)and negative Ce anomaly(0.90~0.95)indicate a weakly oxidizing environment with the same source of ore-forming fluids and lower temperature.In addition,the characteristics of La/Ho-Y/Ho of the fluorite samples Indicate that the ore-forming fluid may be a contemporaneous and homologous F-rich fluid.TheδD_(V-SMOW)values of the 5 fluorites ranged between-109.7‰and-99.4‰(average value is-104.3‰),while theδ^(18)O_(V-SMOW)values ranged between-3.1‰and-1.9‰(average value is-2.3‰),which indicating that the oreforming fluid is a mixed hydrothermal solution of atmospheric water and magmatic water.The characteristics of Tb/La-Tb/Ca also indicates that the Huashitoushan fluorite deposit is magmatic hydrothermal.Moreover,only Sb in all fluorite samples is enriched compared to wall rock(Xishuangyingshan Formation,Beishan Oregenic Belt and Crustal),while other elements are depled,which indicating that the fluorite deposit belongs to the category of medium-low temperature deposits.The REE standard distribution curves of two biotite monzogranites show a right inclination,and LREE is strongly enriched relative to HREE.Combined with the geological characteristics of the deposit,it is believed that the Huashitoushan fluorite deposit was formed in a weakly oxidizing environment with lower temperature.The ore-forming fluid is a mixed hydrothermal solution of magmatic water and atmospheric water,the ore-forming material F is mainly derived from biotite monzogranite,and the Ca mainly comes from the Xishuangyingshan Formation.Therefore,it can be inferred that the Huashitoushan fluorite deposit is a medium-low-temperature hydrothermal,structure filling type deposit.