基于冷热剥蚀池LA-ICP-MS原位分析单个成矿流体包裹体元素组成研究

Chemical composition in a single ore-forming fluid inclusion is one of the most effective methods for studying and tracing the origin and the source of the paleo fluid in the stage of special diagenesis and metallogenesis and geological tectonic evolution period. In situ analysis of element composition of a single fluid inclusion by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is used in characterizing the mineralization processes, such as tracing the source of ore-forming fluid and metals, and deciphering the processes about fluid transport and metal deposition. However, it still has some limitations: 1) the success rate of analysis is seriously affected due to the inclusion cracking or bursting, because the instantaneous rapid temperature changes of the host mineral surface when the laser on. 2) When the small size inclusion is ablated, the mass spectrometry signal is weak, and the detection limit is very low and needs to be improved. This proposal will develop an in situ LA-ICP-MS method for the determination of elements in small natural single fluid inclusions (5-20µm size). An in-house designed frozen-heated ablation cell and an in situ aerosol extraction technology are developed to meet the high success rate and high sensitive detection for trace elements in fluid inclusion with the ultra pressure (or high homogenization temperature) or low homogenization temperature (<200 ℃). The proposed method will be applied to the study of the ore-forming fluid sources and the metal precipitation mechanisms of the Pb-Zn deposits of Huayuan ore-concentrated District, Northwest Hunan Province, China.

单个成矿流体包裹体中化学组成信息是研究和示踪特定成岩成矿阶段和特殊地质构造演化时期古流体成因和来源最有效的方法之一。激光剥蚀电感耦合等离子体质谱（LA-ICP-MS）原位分析单个流体包裹体元素组成，可精细刻画成矿流体与成矿物质来源、运移、沉淀及富集等过程。然而，该技术仍存在一定的局限性：1）激光剥蚀寄主矿物表面时，瞬时温度急剧变化极易导致包裹体出现裂隙或爆裂而严重影响分析成功率；2）微小尺寸包裹体剥蚀时释放瞬时质谱信号较弱，其检出限尚需改善。本项目拟建立5～20µm天然单个成矿流体包裹体LA-ICP-MS原位分析方法，利用自行设计的冷热激光剥蚀池，实现超压（或高均一温度）和低均一温度（<200℃）流体包裹体高成功率的“可控剥蚀”，并采用气溶胶原位提取技术实现单个流体包裹中微量元素的高灵敏检测。该技术拟应用于湘西花恒地区铅锌矿床的成矿流体演化特征与成矿金属沉淀机制研究。

单个成矿流体包裹体中化学组成信息是研究和示踪特定成岩成矿阶段和特殊地质构造演化时期古流体成因和来源最有效的方法之一。激光剥蚀电感耦合等离子体质谱（LA-ICP-MS）原位分析单个流体包裹体元素组成，可精细刻画成矿流体与成矿物质来源、运移、沉淀及富集等过程。针对该技术的两个主要局限性：1）LA剥蚀寄主矿物表面时，瞬时温度急剧变化极易导致包裹体出现裂隙或爆裂而影响分析成功率；2）微小尺寸包裹体剥蚀时释放瞬时质谱信号较弱，其检出限尚需改善。本课题基于所设计的半导体制冷剥蚀池（温度范围-35~200 ℃），并结合所建立的镜下操作流程和剥蚀策略，将单个流体包裹体剥蚀成功率由30%提升至70%以上；并开发了原位提取技术和高灵敏的组合技术，成功实现了多种元素分析灵敏度提升8-45倍；基于上述计算建立了LA-ICP-MS分析5～20µm天然单个成矿流体包裹体中微量元素的可靠方法，并成功应用于华北太行山中部地区晚中生代岩浆-热液金矿床相关的流体包裹体研究中，并根据其中Cs/Na和Rb/Na差异，初步反映了不同类别的流体包裹体具有不同的演化程度。