三江中段铜多金属矿床流体成矿作用:微量元素地球化学证据

Geochemical constraints of trace elements on ore-forming fluids in the copper polymetallic deposits in the middle Sanjiang Belts

研究区属"三江成矿带"中段,包含三个不同的地质构造单元,由西向东依次为金沙江混杂岩带、中咱地块、义敦岛弧带。本文通过对这三个构造单元中代表性铜多金属矿床中热液石英脉进行系统的采样和微量稀土元素分析,讨论了各构造单元中石英脉的微量及稀土元素地球化学特征及分布模式,在此基础上结合研究区的地质背景及演化,进一步讨论石英脉中微量元素的指示意义。结果表明:1)研究区石英脉中Cu、Zn等成矿元素与亲岩浆元素呈较好正相关,指示成矿与岩浆活动的联系,微量元素地球化学特征指示中咱地块成矿流体与岩浆活动的联系较为密切;2)中咱地块石英脉稀土元素地球化学特征与义敦岛弧带和金沙江混杂岩带成矿流体差异较大,中咱地块流体稀土元素接近于地幔的稀土组成特征,稀土元素配分曲线为近于水平的平缓曲线,稀土元素特征参数表明形成于相对还原的环境,反映出深部来源很可能是中咱地块成矿流体的主要物质来源;3)石英微量元素地球化学特征的研究为本区区域构造演化提供了佐证,金沙江混杂岩带和义敦岛弧带的成矿流体特征较为相似,而在中咱地块与扬子陆块夹持间形成的义敦岛弧带成矿流体与中咱地块存在较大的元素地球化学差异。本文通过对石英的微量元素、稀土元素地球化学特征的研究为该区的区域成矿特征、热液流体成因和构造演化提供了证据,并对西南三江地区的找矿理论提出了建议。

Located in the middle Sanjiang Belts,the study area could be tectonically divided,from west to east,into the Jinshajiang tectonic melange belt,the Yidun island arc and the Zhongzan block. Through systematical field sampling and analysis of the hydrothermal quartz veins from the copper polymetallic deposits in the middle Sanjiang Belts, the content characteristics and distribution pattern of trace-rare earth elements in the quartz veins are discussed in each tectonic unit. Based on geological background and evolution in the study area,the denotative and tracing meaning of the trace elements in quartz vein are further studied. The results show that： 1） There is a positive correlation between the ore-forming elements（ e. g. Cu,Zn） and the magmatopile trace elements,which indicates the mineralization is related to magmatic activity. And the trace elements in quartz vein indicate that the ore-forming fluid in Zhongzan block has the closest relationship with the magmatic activity. 2） There is a significant difference that the REE geochemical characteristics in quartz vein from the Zhongzan block compared with the Jinshajiang tectonic melange belt and the Yidun island arc. Formed in the relatively reductive environment,REE in quartz vein from the Zhongzan block accord well with the mantle with the sub-horizontal REE curve and the δEu anomalies,which indicates the main material source of the fluid is likely to be the deep source. 3） According to the geochemical characteristics of trace and rare earth elements in quartz vein,there are similar geochemical characteristics in the metallogenic fluid sources between the Jinshajiang tectonic melange belt and the Yidun island arc for their similar role in the geological evolution history. While there is a remarkable difference that the geochemical characteristics in the Zhongzan block compared with the Yidun island arc. The research results provide evidence for the regional metallogenic events,the genesis of hydrothermal fluid and tectonic evolution,and prospecting suggestions of the copper and polymetallic deposits are proposed for the Sanjiang Belts.