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，含钽矿物的经济富集只发生在花岗质伟晶岩中，主要是来自铌钽矿群的矿物[(Mn,Fe)(Nb,Ta)206]-我们对经济Ta矿床形成的理解需要含Ta矿物的结晶条件的信息，如结晶温度和Ta在伟晶岩熔体中的溶解度，目前还没有。伟晶岩体系的结晶过程可以在900至400°C的宽温度范围内发生，对结晶温度的限制对于模拟导致经济浓度含ta矿物形成的反应至关重要。正在进行的一项提议的目标是获得关于钶钽铁矿群矿物结晶条件的实验数据。该项目围绕两点建立：1)测量高通量伟晶岩熔体中钴矿群矿物中锰端成员的溶解度，作为温度的函数；2)校准温度计，以限制含钛矿物结晶的温度范围（锆石中的Ta和钽石中的Zr；锰钽石和铁橄榄石对的稳定场）。实验同时进行了与天然伟晶岩中Ta矿化有关的锆石地球化学和结构特征的研究。在过去的14个月里，进行了不同类型的实验，并取得了成功。现有的结果非常有希望，并且应该对我们对导致Ta矿化的过程的认识产生强烈的影响。为了成功完成上述(i)和（ii）项任务，有必要进行补充研究，并证明将项目延长几个月是合理的。在此期间，我们将重点关注3点：1)我们将更详细地确定锰钽矿和锆石对熔体ASI [Al/Na+K+Li]溶解度的依赖性，以表征过量Al和过量碱对硅酸盐熔体中稀有金属阳离子络合的作用；2)我们将对钽酸锆温度计进行低温校准；3)我们将研究铪和钽在锆石中的掺入机制，因为与钽矿伴生的天然锆石总是含有大量的Hf。