青海省治多县查涌铜多金属矿床成矿年代学研究

三江"成矿带为我国重要的多金属成矿带,带内中北段玉树多彩矿集区发育多种类型的铜多金属矿床,资源潜力巨大,但成矿年龄不详,严重制约了对矿床和区域成矿规律的理解。因此,本次工作选取矿集区西北部查涌铜多金属矿床为研究对象,在详细地质踏勘的基础上,对其成矿年代进行了系统研究,以期填补该地区此类型矿床成矿年龄的空白。研究表明,查涌铜多金属矿床分别发育Cu-Mo矿体和Pb-Zn矿体,Cu-Mo矿体赋存在变质粉砂岩内,形成于石英硫化物阶段。角岩化砂岩中黑云母Mg-(Al^Ⅵ+Fe^3++Ti)-(Fe^2++Mn)的投图具镁质黑云母特征,Al2O3/Ti O2值介于6.359~10.087之间,Fe^2+/(Fe^2++Mg)值均一,为热液成因,且未受后期流体改造,40Ar-^39Ar同位素定年获得黑云母封闭年龄为129.59±1.58 Ma。穿切黄铜矿的辉钼矿Re含量为0.864×10^-6~9.624×10^-6,具壳源属性,其Re-Os同位素等时线年龄为124.75±0.86 Ma。热液黑云母与较晚的辉钼矿年龄相近,应为同期岩浆热液事件的产物。本次研究精确厘定了"三江"带中北段内一例典型的与岩浆热液成矿作用相关铜多金属矿床的成矿年龄,揭示出早白垩世的一期成矿事件,为"三江"成矿带的成矿规律总结和勘查找矿指明了新的方向。

Metallogenic chronology of the Chayong Cu-polymetallic deposit in Zhiduo County, Qinghai Province

The Sanjiang metallogenic belt is one of the most important polymetallic ore-forming belt in China. The Duocai ore concentration area possesses various types of Cu polymetallic deposits in its middle and north part,and its mineral resource potential is huge;nevertheless,the ambiguous mineralization age seriously restricts the understanding of the ore deposits and regional mineralization regularity. In view of such a situation,the authors selected the Chayong copper polymetallic deposit in this belt and conducted a complete systematic research on its mineralization chronology based on detailed field exploration and microscopic mineralogical identification so as to fill the research blank of the ore-forming age in this area. The results indicate that there are two kinds of orebodies in the Chayong copper polymetallic deposit,mainly Cu-Mo orebodies,which were developed in the metamorphic siltstone and mainly occurred at the quartz and sulfide stage. The biotite in hornfels shows that the points of Mg-(Al^Ⅵ+Fe^3++Ti)-(Fe^2++Mn) in diagram fall within the range of magnesium biotite,the value of Al2O3/TiO2 is between6. 359 and 10. 087 and the ratio ofFe^2+/(Fe^2++Mg) is comparatively uniform. Based on the above data,the authors hold that it is hydrothermal biotite unmodified by late fluids. The authors confirmed the closure age of hydrothermal biotite by the40 Ar-^39 Ar plateau age of 129. 59 ± 1. 58 Ma. In addition,molybdenites which penetrate into chalcopyrite have the rhenium content from 0. 864 × 10^-6 to 9. 624 × 10^-6. These values indicate that the metallogenic material of molybdenite was probably derived from the crust. The Re-Os isochron age of molybdenite is124. 75 ± 0. 86 Ma. In conclusion,the age of hydrothermal biotite is similar to that of molybdenite,and it is held that both of them should belong to the same period of magmatic hydrothermal event as shown by their closure age.This study accurately determined the metallogenic age of a typical magmatic hydrothermal Cu polymetallic metallogenic deposit in the middle and northern part of the Sanjiang metallogenic belt,revealing that there was a mineralization event during the Early Cretaceous,and these data indicate a new direction for studying regional metallogenic regularity and for prospecting work in the Sanjiang metallogenic belt.