德国哈茨山St.Andreasberg热液矿床方解石巨晶的碳氧同位素研究

• 作 者: 李龙 郑永飞 Ｍ．Ｓｃｈｏｅｌl Ｗ．Ｓｔａｈｌ
• 机 构: 中国科学技术大学地球和空间科学系,德国联邦地质调查所
• 出 处: 高校地质学报
• 发表日期: 1999年02期
• 关键词: 碳氧同位素 St.Andreasberg 热液矿床 德国哈茨山 同位素分带 方解石晶体 近地表 石脉 封闭体系 物理化学条件

在德国哈茨山ＳｔＡｎｄｒｅａｓｂｅｒｇ热液ＰｂＺｎ矿床的方解石脉中，发现了一个方解石巨晶。对该方解石三个不同方向上的Ｃ和Ｏ同位素分析发现，方解石晶体内部存在明显的ＣＯ同位素环带。通过对方解石同位素环带的理论模拟，发现在方解石生长过程中，有三种流体参与了作用。它们分别为Ａ：温度约为６０℃的近地表流体，δ１３Ｃ＝－１８５‰，δ１８Ｏ＝０‰；Ｂ：温度约为１４０℃的深源流体，δ１３Ｃ＝－７０‰，δ１８Ｏ＝＋１００‰；Ｃ：温度小于２０℃，δ１８Ｏ≤０‰，δ１３Ｃ≥－１４０‰的大气降水。作用过程有四个阶段：①方解石在流体Ａ中等温生长；②流体Ｂ开始与流体Ａ在封闭体系内均匀混合；③流体Ｂ缓慢注入的同时，发生了一次性流体Ｃ的快速不均匀混合；④流体Ｂ继续与Ａ缓慢混合，混合体系开放。流体混合的发现，为认识ＳｔＡｎｄｒｅａｓｂｅｒｇ热液矿床的形成机制提供了新的视野

In calcite veins of the St. Andrereberg hydrothermal PbZn deposit in the Harz Mountains of Germany, a giant calcite was found. C and O isotope analyzes of the calcite in three different directions show that there are obvious CO isotope bands in the calcite crystal. Through the theoretical simulation of the calcite isotope annulus, it is found that three kinds of fluids are involved in the growth of calcite. They are A: near-surface fluid with a temperature of about 60 ℃, δ13C = -185 ‰, δ18O = 0 ‰ B: deep source fluid with a temperature of about 140 ℃, δ13C = -70 ‰, δ18O = + 10  0 ‰; C: the temperature is less than 20 ℃, δ18O ≤ 0 ‰, δ13C ≥ -14  0 ‰ of the precipitation. The process of action has four stages: ① calcite isothermally grown in fluid A; ② fluid B begins to mix uniformly with fluid A in the closed system; ③ while fluid B is slowly injected, a rapid, inhomogeneous mixing of disposable fluid C occurs; ④ Fluid B continues to mix slowly with A and the mixing system is opened. The discovery of fluid mixing provides a new perspective for understanding the formation mechanism of StAndreasberg hydrothermal deposit