Crystallization of columbite-tantalite in pegmatites: Experimental constraints and implication for natural systems

伟晶岩中铌铁矿-钽铁矿的结晶：实验限制和对自然系统的影响

• 批准号: 63444183
• 负责人: Professor Dr. Francois Holtz, Ph.D.
• 金额: --
• 依托单位: Institut für Mineralogie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2008
• 资助国家: 德国
• 起止时间: 2007-12-31 至 2010-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/63444183?language=en
• 关键词: Crystallization; columbite; tantalite; pegmatites; Experimental

Tantalum (Ta) is a key element of the high-tech industry and economic concentrations of Tabearing minerals occur exclusively in granitic pegmatites, mainly as minerals from the columbitetantalite group [(Mn,Fe)(Nb,Ta)206]- Our understanding of the formation of economic Ta ore deposits requires information on the crystallization conditions of Ta-bearing minerals, such as crystallization temperature and Ta solubility in pegmatitic melts, which is not available up to now. Crystallization processes ih pegmatitic systems can occur over a wide temperature range from 900 to 400°C and constraints on crystallization temperatures are crucial to model the reactions leading to the formation of Ta-bearing minerals in economic concentrations. The goal of an ongoing proposal was to get experimental data on the crystallization conditions of columbite-group minerals. The project was built around two points: i) solubility measurements of the manganese end members of the columbite-group minerals as a function of temperature in highly-fluxed pegmatitic melts and ii) the calibration of thermometers to constrain the temperature range of crystallization of Tabearing minerals (Ta in zircon and Zr in tantalite; stability field of manganotantalite and ferrotapiolite pairs). The experiments were conducted in parallel with investigations of the geochemistry and textural features of zircon associated with Ta mineralization in natural pegmatites. Different types of experiments have been conducted with success in the last 14 months. The available results are very promising and should have a strong impact on our knowledge of processes leading to Ta mineralizations. To complement with success the tasks (i) and (ii) listed above, complementary studies are necessary and justify the prolongation of the project for a few months. During this prolongation, we will focus on 3 points: I) we will determine in more detail the solubility dependence of manganotantalite and zircon on the ASI [Al/Na+K+Li)] of the melt, in order to characterize the role of excess Al and excess alkalis on the complexing of rare metal cations in silicate melts; 2) we will calibrate the Zr-in-tantalite thermometer down lo low temperatures; and 3) we will investigate the incorporation mechanisms of hafnium and tantalum in zircon because natural zircon associated with tantalite always coniain significant amounts of Hf.

钽 (Ta) 是高科技产业的关键元素，含钽矿物的经济集中度仅存在于花岗伟晶岩中，主要是来自铌钽铁矿族的矿物 [(Mn,Fe)(Nb,Ta)206]- 我们对经济的钽矿床的形成需要有关含钽矿物的结晶条件的信息，例如结晶温度和伟晶岩熔体中的钽溶解度，这是伟晶岩系统中的结晶过程可以在 900 至 400°C 的宽温度范围内发生，并且结晶温度的限制对于模拟形成经济浓度的含钽矿物的反应至关重要。一项正在进行的提案的目的是获得有关铌铁矿族矿物结晶条件的实验数据，该项目围绕两点建立：i）锰端元的溶解度测量。铌铁矿族矿物作为高通量伟晶岩熔体中温度的函数，以及 ii) 校准温度计以限制塔轴承矿物（锆石中的 Ta 和钽铁矿中的 Zr；锰钽铁矿和铁橄榄石对的稳定场）的结晶温度范围。这些实验与自然中与 Ta 矿化相关的锆石的地球化学和结构特征的研究同时进行。在过去 14 个月中，已经成功进行了不同类型的实验，现有的结果非常有希望，并且应该对我们对 Ta 矿化过程的了解产生重大影响，以成功完成任务 (i) 和 (。 ii) 如上所述，补充研究是必要的，并证明该项目延长几个月是合理的。 在延长期间，我们将重点关注 3 点： I) 我们将更详细地确定锰钽铁矿和锆石的溶解度依赖性。熔体的 ASI [Al/Na+K+Li)]，为了表征过量 Al 和过量碱对硅酸盐熔体中稀有金属阳离子复杂化的作用；2) 我们将校准 Zr-in-钽铁矿温度计的温度较低；3）我们将研究铪和钽在锆石中的结合机制，因为与钽铁矿伴生的天然锆石总是含有大量的铪和钽。铩。