德钦县羊拉铜矿区碳——氧同位素组成特征及其地质意义

Carbon and Oxygen Isotopic Compositions of the Yagra Copper Deposit in Deqen and Their Implication

本文对羊拉矿区层状夕卡岩矿体内的大理岩透镜体、矿体顶底板大理岩、岩体接触带的大理岩及区域上未受岩浆作用或矿化影响的大理岩的碳、氧同位素组成进行了系统的对比研究,其碳、氧同位素组成分别为:背景值:δ^(13)C_(PDB)=4.83‰,δ^(18)O_(SMOW)=22.65‰;矿体底板:δ^(13)C_(PDB)=3.07‰～4.07‰,δ^(18)O_(SMOW)=19.19‰～21.86‰;矿层(体)中:δ^(13)C_(PDB)=1.27‰～3.06‰,δ^(18)O_(SMOW)=18.76‰～21.57‰;矿体顶板:δ^(13)C_(PDB)=-0.34‰～3.42‰,δ^(18)O_(SMOW)=13.51‰～20.26‰;岩体接触带:δ^(13)C_(PDB)=-6.1‰,δ^(18)O_(SMOW)=8.32‰。这些数据表明,层状夕卡岩矿床(体)内及其顶底板围岩的碳、氧同位素组成多数在正常的沉积碳酸盐岩范围内。这说明,里农岩体的侵位并没有产生足够数量的热液流体与赋矿围岩进行广泛的物质交换,或者说,矿区含矿层位在其沉积—成岩后没有发生明显的水、热活动,从而进一步证明里农层状夕卡岩铜矿床的成因与里农岩体的侵位无明显的关系,属同生沉积成因。

Carbon and oxygen isotopic compositions of marbles, including marble lens in the stratiform skarn ore body from the Yagra mining area, the roof and floor marbles of the ore body, marbles in the contact zone of the Lilong granodiorite intrusion with wallrocks and those in the regional strata not influenced by mineralization and intrusion were studied systematically and comparatively with results as follows:Background:δ^(13)C_(PDB)= 4. 83‰, δ^(18)O_(SMOW)= 22. 65‰; the floor wallrocks of ore body:δ^(13)C_(PDB) = 3. 07‰～ 4. 07‰,δ^(18) O_(SMOW) = 19.19‰～ 21. 86‰; within ore-body:δ^(13)C_(PDB)= 1. 27‰～3. 06‰,δ^(18)O_(SMOW)= 18. 76‰～21. 57‰; the roof wallrocks: δ^(13)C_(PDB)= — 0. 34‰～3. 42‰,δ^(18)O_(SMOW)= 13. 51‰～20. 26‰; contact zone of granodiorite with wallrocks: δ^(13)C_(PDB)=-6.1‰,δ^(18)O_(SMOW)= 8. 32‰.These data indicated that most isotopic compositions of carbon and oxygen of the Lilong stratiform skarn deposit and its wallrocks are in the range of normal sedimentary carbonate rocks. Thus, it can be seen that the Lilong intrusion did not bring sufficient hydrothermal fluid to carry on extensive mass exchange with host rocks of the deposit. In other words, there were no obvious water and thermal activities in the strata-hosted ore after sedimentary-diagenesis, which further proves that there was no obvious relationship between the origin of the Lilong stratiform skarn copper deposit and emplacement of the intrusion. In short, the stratiform skarn copper deposit belongs to a syngenetic exhalative—sedimentary genesis.