氯挥发过程的同位素分馏效应及应用——以成矿热液示踪为例

Due to using chlorine isotopes as a tracer for the origin and evolution of hydrothermal ore fluids lacking of confirming by related theories and experiments, two groups of experiments will be conducted based on previous studies, one is fractionation experiment in equilibrium which is in sealed system, and the other is in open system. The vapor and liquid samples are collected during the progressive evaporation, and the chlorine isotopic ratios of the samples are determined using a thermal ionisation mass spectrometry procedure based on Cs2Cl+ ion measurement. The objectives of the experiments are: to investigate the features of the δ37Cl values variation in process of chlorine volatilizing; to clarify the chlorine isotopic fractionation between the vapor and liquid. The mass spectrometry method is also improved to determined the chlorine isotopic ratios of the sample from hydrothermal ore deposits. Combined with experimental results, chlorine isotopes will be used to trace their isotopic fractionation in hydrothermal ore-fluid system in terms of typical deposits studies, including magmatic deposits and non-magmatic deposits. The tracing effect of chlorine isotopes is evaluated exactly. These studies will provide more fundamental information of hydrothermal ore-fluid system. At last, the chlorine isotopic system will be established as a complete system for tracing studies.

本项申请在充分调研和前期研究的基础上，针对利用氯同位素示踪成矿热液缺失氯挥发过程的同位素效应研究，设计了开放和封闭体系条件下挥发过程的氯同位素分馏实验，实验过程连续采样，通过基于检测Cs2Cl+的高精度正热电离质谱法测定样品氯同位素比值，查明挥发过程氯同位素组成的变化特征，弄清气液相之间的分馏关系。同时完善适合热液样品的氯同位素分析测试技术，结合分馏实验的结果，通过与岩浆作用有关和无关两类热液矿床的实例对比研究，揭示热液成矿体系中氯同位素的分馏效应和和分馏机制，正确评价氯同位素在两类矿床的示踪作用，丰富热液成矿体系中氯的地球化学资料，构建完整的氯同位素示踪体系。

本项申请在充分调研和前期研究的基础上，针对利用氯同位素示踪成矿热液缺失氯挥发过程的同位素效应研究，设计了挥发过程的氯同位素分馏实验，实验过程连续采样，通过基于检测Cs2Cl+的高精度正热电离质谱法测定样品氯同位素比值，查明了挥发过程氯同位素组成的变化特征，气相相对液相倾向富集37Cl（除了一些极端的动力学过程）。同时完善适合热液样品的氯同位素分析测试技术，结合分馏实验的结果，通过与低温和中高温两类热液矿床的实例研究，揭示热液成矿体系中氯同位素的分馏效应和和分馏机制，发现：低温矿床中，Cl同位素的变化是主要受控于不同Cl源流体的混合作用；中高温矿床中Cl同位素的变化则主要受控于Cl的挥发过程，即是Cl在气液两相之间的分馏作用。从而正确评价了氯同位素在两类矿床的示踪作用，丰富热液成矿体系中氯的地球化学资料，构建完整的氯同位素示踪体系。研究同时开展了相关矿床的Li同位素和Cl/Br比值研究，取得了较好的示踪效果。