新疆拜城高品质红宝石的形成机理研究

At present most researches about the genesis of ruby is restricted to observations and analyses of field samples. Due to the lack of direct evidence from experiments, the detailed ruby forming processes (e.g., recrystallization of aluminum - rich minerals, desiliconization reaction between aluminosilicate and carbonate minerals under hydrothermal conditions) and their p-T conditions, have been insufficiently developed. This project is focused on the genesis of high quality ruby in Baicheng, Xingjiang. By combining the petrologic and geochemical characteristics of ruby ore bodies, wall rocks and magmatic intrusions, with the homogenization temperatures of melt and fluid inclusions, the potential origins of ruby-forming materials, the possible chemical reactions as well as their p-T conditions that leading to the formation of ruby minerals, will be evidenced or restricted. Metallogenic mechanisms of Baicheng ruby deposit will be reasonably hypothesized, and verified from in-situ observation of the ruby forming reactions, which will be achieved by heating the mineral and fluid samples in the sample chamber of a hydrothermal diamond anvil cell (HDAC) to high p-T conditions. Furthermore, the influence of pressure, temperature, mineral and fluid composition on the formation of ruby minerals will also be investigated, by changing the mineral and fluid compositions and the p-T conditions in HDAC experiments. The main goal of this project is to ascertain the formation mechanism as well as the geological factors that control the formation and breaking processes of natural ruby minerals during metamorphic processes, and to gathering sufficient proofs to develop a genetic model that can be potentially applied in the prospecting for high quality gem corundum deposits in the future.

目前关于红宝石形成机理的研究主要集中于野外样品观察和分析，由于缺少来自模拟实验的直接证据，红宝石的具体形成过程（如富铝矿物重新结晶、铝硅酸盐矿物与碳酸盐矿物发生脱硅反应等）和温度压力条件并未确定。本项目围绕红宝石形成机理这一科学问题，以新疆拜城高品质红宝石矿床为研究对象，通过对红宝石矿体、岩体和围岩进行岩相学和地球化学分析，并结合熔融和流体包裹体均一温度研究结果，推测红宝石形成的物质来源、矿物反应过程和温度压力条件；在此基础上采用水热金刚石压腔对红宝石的形成过程进行实验模拟，观察和分析高温高压条件下不同矿物之间发生化学反应的过程和产物，确定红宝石的形成过程和条件；通过改变实验条件和反应物成分，研究温度、压力、矿物和流体成分对红宝石形成反应的影响，确定控制红宝石形成和破坏过程的关键因素，建立新疆拜城红宝石矿床的成矿模型。

为了解决变质成因红宝石的形成机理问题，本项目通过开展新疆拜城红宝石野外调查和室内岩相学分析研究，确定该地区红宝石主要以刚玉斜长岩脉产出，岩脉主要由刚玉和斜长石组成，同时还有大量方解石、铬云母等，斜长石等矿物蚀变特征明显，显示红宝石为铝硅酸盐与方解石交代反应成因。此外大理岩中同样有红宝石产出，这类样品由刚玉和结晶方解石组成，刚玉自形较好，未发现矿物发生交代反应线索，推测为富铝粘土矿物受热重新结晶而成。通过对碳酸盐矿物开展高温高压研究，确定了不同温度压力条件下方解石与文石和其他高压结构之间的相变关系，以及富水流体对方解石相变条件的影响，建立了利用方解石和白云石拉曼振动频率来标定体系压力的技术方法，并应用于红宝石形成条件的实验研究。此外，我们还通过高温高压实验确定了由铝土矿脱水形成刚玉的温度压力条件，并通过对比无水环境中刚玉的形成条件和方解石—文石在有水和无水条件下的相变机理，确定了富水流体在刚玉形成过程中具有重要作用。