广东大宝山Cu-Mo多金属矿床成矿流体演化及金属元素沉淀机制的原位微量元素研究

The rapid development of multiple high-resolution in-situ analytical methods, especially for the fluid inclusions using LA-ICP-MS, provides powerful technique to the theoretical research of the magmatic-hydrothermal deposits. Important progresses have been made concerning the ore-forming mechanisms of numerous Yanshanian magmatic-hydrothermal deposits in South China, however, detailed studies on the hydrothermal fluid compositions and evolution are still lacked. Taking the Dabaoshan polymetallic deposit as an example, we expect to conduct a study of in-situ determination for trace elements using LA-ICP-MS on representative gangue minerals and fluid inclusions, aiming to classify the fluid evolution stages, measure the fluid compositions, constrain the fluid pressure and temperature conditions, and therefore to discuss the mechanisms of metal transportation, enrichment, and precipitation. The direct comparison of the fluid compositions between the Dabaoshan porphyry Mo system and the skarn-related strata-bound Cu-Pb-Zn system could provide an insight into the trigger of the spatial separation between Mo and Cu-Pb-Zn metals. On the basis of the above studies, the favorable parameters for mineralization will be ascertained and an associated model for the evolution of magmatic-hydrothermal fluids will be constructed, thus placing powerful constraints on the cause of large-scale mineralization during the Yanshanian stage in South China, and in turn, promoting the regional exploration.

近年来多种高精度原位微区分析技术，尤其是应用LA-ICP-MS测定单个流体包裹体微量元素组成方法的飞速发展，为岩浆热液矿床理论研究提供了新的有力手段。华南地区燕山期形成了大量岩浆热液矿床，其成因机制研究已经取得显著的进展，但仍缺乏对成矿流体成分和演化过程的精细解剖。本项目拟选择大宝山斑岩-矽卡岩型Cu-Mo多金属矿床为研究对象，综合应用脉石矿物和单个流体包裹体的LA-ICP-MS微量元素分析等方法，划分流体演化期次、测定流体组成、限定流体温度压力，进而探讨金属元素迁移-富集-沉淀的机制。通过直接对比大宝山矿区斑岩型Mo矿体与矽卡岩型似层状Cu-Pb-Zn矿体成矿流体成分特征，探讨Mo与Cu-Pb-Zn在空间上发生分离的原因。在此基础上查明有利的成矿因素，进而建立岩浆热液系统演化模型，为阐明华南燕山期大规模成矿作用的原因及促进区域找矿工作提供有力的理论依据。

华南地区燕山期形成了大量与中酸性岩浆活动相关的热液矿床，本项目通过综合应用多种原位微区分析技术对华南燕山期典型岩浆热液矿床进行了深入的剖析。以广东大宝山Cu-Mo多金属矿床为主要研究对象，并对比研究了同时期形成的广东圆珠顶斑岩Cu-Mo矿床。通过成矿流体期次划分、成矿流体成分分析、成矿流体温度压力计算，系统地厘定了大宝山和圆珠顶矿床的岩浆热液演化过程，深入地探讨了金属元素的迁移-富集-沉淀规律。.大宝山矿床从早期到晚期发育不同类型的石英脉。早期石英形成于静岩压力下，温度压力较高，矿化程度较低；晚期石英形成于静水压力之下，温度压力相对较低，矿化程度较高。单个流体包裹体成分分析表明，大宝山矿床初始岩浆流体的Mo含量较低而Cu、Zn含量较高，Mo主要在斑岩体内沉淀成矿，流体迁移至外围碳酸盐地层后形成似层状Cu-Pb-Zn矿床。圆珠顶矿床经历了岩浆作用-接触变质-热液演化三个阶段，形成了岩浆黑云母、变质黑云母、热液黑云母及绢云母。圆珠顶矿床成矿深度约为5.3km，成矿流体压力大，未经历流体显著的“沸腾”作用，因此成矿流体盐度较低，对应的成矿流体的Cl逸度也相对较低，从而限制了Cu元素的富集，制约了该矿床Cu成矿的规模。.此外，通过典型斑岩矿床岩浆-热液演化过程的解剖，结合全世界范围内不同斑岩矿床的流体演化特征，建立了斑岩矿床成矿流体演化模型，并提出NaCl饱和破坏金属络合物是导致斑岩矿床金属沉淀的关键机制。