柴达木盆地西北部富锶机制及成矿元素迁移分布规律

Large strontium ore-deposits have developed in Northwestern of Qaidam basin during the Tertiary period. The main strontium mineral is celestine with very poor Ba content which precipitates at the boundary between the carbonates and gypsum phases.The large deposits mainly developed in the areas of Jianding hill, Dafengshan hill and Jianshan hill of northwestern of Qaidam basin.And also, dozens of strontium mineralization have distributed in study area. Previous studies have poor understanding on some aspects such as the formation of Sr-rich fluids with high Sr/Ba values, and the migration and distribution of Sr.However these aspects are very significant to interpret the mechanism of forming large celestine deposits in continental basins. Aiming to fill this gap, firstly we will collect samples systematically on typical evaporite sequences of the Jianding hill, Dafengshan hill and Jianshan hill. And then, based on the purpose of comparison, we will cellect both typical oilfield brine, the deep-source CaCl2 water and the modern Sr-tufa at the northwestern of Qaidam basin, and complete the chemical composition and δ13C, δD, δ18O, 87Sr/86Sr, δ34S analysis to build the geochemical comparison index system. And combined with the results of minealogy and fluid inclusion analysis to discuss the forming mechanism of Sr-rich fluid, the migration and distribution of Sr, the mechanism of Sr, Ba fractionation of basin fluid and the ore-forming principles. Further more, we will forecast the trend of enriching Sr in study area to guide the practice. This project will offer important evidence for the source and mechanism of ore-forming of large celestine deposits in northwestern of Qaidam basin, and also can enrich the metallogenic model theory of large celestine deposits in continental basin.

柴达木西北部第三系沉积了巨量的富锶矿层。其含锶矿物主要以贫Ba天青石为主，发育于碳酸盐相与石膏相之间，分布范围包括尖顶山、大风山和碱山等主要矿区，同时在柴西北地区还分布有十余处小型锶矿化点。以往研究中针对矿区高Sr/Ba比富锶流体的形成及成矿元素迁移分布规律等方面的认识相对缺乏，而这对于内陆盆地大型锶矿形成机理具有重要的理论意义。本项目拟以尖顶山、大风山及碱山地区赋矿的完整蒸发岩序列为研究素材，并结合柴西北地区典型油田卤水、深部CaCl2型水及现代含锶泉华样品，以其主微量化学元素组成及碳、氢、氧、锶、硫同位素分析建立地球化学对比指标体系，并综合矿物学研究与流体包裹体分析来探讨柴西北地区的富锶机制、锶的迁移转化规律、成矿流体Sr、Ba分馏机制及其沉积成矿机理，进而预测研究区锶的富集趋势。本项目的实施可为柴西北大型锶矿的物源及富集成矿机制提供重要证据，并可丰富陆相大型锶矿成矿模式理论体系。

柴达木盆地西北部发育有我国最大的内陆湖相沉积型天青石矿集区，其分布范围包括大风山、尖顶山、碱山等主要矿区以及十余处小型锶矿化点。天青石矿主要发育于碳酸盐岩相与石膏相之间，并与碳酸盐岩密切伴生，具有贫矿多（原生型）富矿少（次生型），高Sr/Ba比的特征。以往研究中针对锶矿来源，成矿机制及高Sr/Ba比流体的形成机制等方面认识较为薄弱，而这些对于理解内陆盆地大型天青石矿的形成机理具有重要的理论意义。本项目对采自大风山、尖顶山及碱山矿区的8个含矿蒸发岩序列的固体剖面样品和柴西北地区各类水体样品进行了沉积学、矿物学及地球化学等方面的研究，丰富了对成矿物质来源的认识，阐明了富Sr油田卤水与天青石成矿间的关系，提出了柴西北地区大型天青石矿床的成矿模式及高Sr/Ba比成矿流体的形成机制。研究表明，柴西北地区大型天青石矿床的主要锶源应是周边山系的风化剥蚀输入，而有机质作用下的富锶碳酸盐岩及其白云石化作用可能为次生天青石矿物的形成提供了丰富锶源；区域富锶油田卤水的形成与周边第三系地层的发育有密切关系，同时可能并未对区域大型天青石矿的形成提供显著物源；柴西北地区大型天青石矿的形成与盆地高山深盆背景下的“振荡干化”作用密切相关，在此背景下硫酸锶与硫酸钡间显著的溶解度差异直接导致了研究区高Sr/Ba比成矿流体的形成。