HIGH TEMPERATURE MAGMATIC GAS: MINERAL DEPOSITION AND GAS/WALLROCK REACTION

火山活动与矿床之间的联系早已被认识到，但火山活动究竟是如何导致矿床形成的仍然未知。由于熔岩和火山灰通常缺乏金属，火山学家推测，金属运输一定是在岩浆向地表上升过程中释放的气体中发生的。火山喷发羽流中的火山气体已被广泛研究，因为它可以直接取样。然而，火山气体已经通过气相沉积的矿物的沉淀和与火山大厦深处的岩石的反应，失去了火山地下结构的大部分金属负荷。由于高温喷气孔的稀缺和它们的极端危险，在天然气失去大部分溶解负荷之前，获取天然气的途径非常有限。到目前为止，这些问题使人们无法弥合火山活动与伴生矿床形成之间的知识鸿沟。这个项目将采用一种新的独特的实验设计，在实验室中模拟岩浆释放气体的过程。这项技术将用于描述岩浆气体从岩浆中释放出来时的化学性质，并观察其产生气相沉积相和与岩石发生化学反应时的化学变化。对新矿物的表征将利用布鲁克海文国家实验室同步加速器x射线的强度，这将允许对微米大小的颗粒进行分析，并提供金属如何融入晶体结构的信息。这项研究的结果将为对贫瘠和经济上重要的次火山地区的新认识提供基础，这将有助于未来在地球和其他行星体上进行经济矿床勘探。他们将进一步加深我们对气相沉积矿物稳定性和金属结合的理解-这是一个在材料科学工业中大量应用的主题。作为向这一行业、地质界和行星科学拓展的一部分，将开发一个可公开访问的数据库，以存储自然界中发现的各种矿物和材料的合成方法的电子版本。这个项目还有一个教育成分，旨在为地质学本科生提供实验经验，作为确保下一代地球科学家准备好一整套方法的第一步，这些方法可以进一步促进我们对自然过程的科学理解。本文研究了高温次火山岩区（或浅埋岩体上方）高温含氟氯化硫岩浆气体的组成演化。在这种状态下，岩浆气体通过矿物的沉淀和与围岩的反应，失去了大部分溶解的溶质负荷，开始向火山气体转变。将进行实验室规模的实验，以阐明(i)岩浆气体冷却过程中产生的矿物相的性质，（ii）这些矿物所包含的微量元素，以及（iii）微量元素融入气相沉积矿物的晶体学控制。这些实验将通过挥发饱和流纹岩和phonolite的减压沸腾来模拟天然岩浆气体的形成，并通过让这些气体在强热梯度下冷却来模拟气相沉积相的产生。通过将合成玄武岩和流纹岩玻璃在沸腾的岩浆释放出的气体流中进行反应，将研究气岩反应。这些反应实验将得到岩浆气/围岩反应的产物，并说明岩浆气/围岩反应对微量元素动员的影响。分析将结合体化学、扫描电镜和同步加速器x射线微探针技术（硬和弱能x射线荧光微分析、微束x射线吸收光谱和微衍射）来表征体化学输运、气相沉积材料和反应表面的微观相分布以及气相沉积矿物中的局部化学形态。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The association of volcanic activity with ore deposits has been long recognized, but exactly how volcanic activity leads to ore deposit formation remains unknown. Since lavas and ash are generally metal-poor, volcanologists have speculated that metal transport must occur by the gas given off during rise of the magma towards the surface. Volcanic gas in eruptive plumes has been studied extensively because it can be directly sampled. However, volcanic gas has already lost much of its metal load to the volcanic subsurface structure through precipitation of vapor-deposited minerals and by reaction with rock deep within the volcanic edifice. Access to the natural gas before it has lost much of its dissolved load is very limited because of the scarcity of high temperature fumaroles and their extreme hazard. These problems have, thus far, made it impossible to bridge the knowledge gap between volcanic activity and formation of associated ore deposits. This project will utilize a new unique experimental design to simulate this process of gas release from magma in the laboratory. This technique will be used to characterize the chemical nature of magmatic gas just as it is released from magma and to observe its chemical modification as it produces vapor-deposited phases and reacts chemically with rock. Characterization of the new minerals produced will take advantage of the strength of synchrotron X-rays at Brookhaven National laboratory, that will allow analysis of micron-sized particles and provide information of how the metals are incorporated into the crystalline structures. The results of this research will provide a basis for new understanding of barren vs. economically important subvolcanic regions that will aid in future economic deposit exploration on Earth and other planetary bodies. They will further our understanding of vapor-deposited mineral stability and metal incorporation– a subject applied heavily in the materials science industry. As part of outreach to this industry, the geological community, and planetary science, a publically accessible database will be developed to store electronic versions of synthesis methods for a variety of minerals and materials found in nature. This project also has an educational component geared to providing experimental experience to undergraduate geology students as a first step in ensuring that the next generation of geoscientists are prepared with an entire tool bag of approaches with which to further our scientific understanding of natural processes.This work focuses on the compositional evolution of high temperature F-Cl-S-bearing magmatic gases in the high-temperature subvolcanic region (or just above shallowly emplaced plutons). In this regime, magmatic gas begins its transformation to volcanic gas through loss of much of its dissolved solute load by precipitation of minerals and reaction with wallrock. Laboratory-scale experiments will be conducted in order to elucidate (i) the nature of mineral phases produced during cooling of the magmatic gas, (ii) the trace elements these minerals incorporate, and (iii) the crystallographic controls on trace element incorporation into the vapor-deposited minerals. These experiments will simulate the formation of natural magmatic gas by decompression boiling of volatile-saturated rhyolite and phonolite, and simulate the production of vapor-deposited phases by allowing this gas to cool in a strong thermal gradient. Gas/rock reaction will be investigated by reacting a synthetic basalt and rhyolite glass in the stream of gas given off by the boiling magma. These reaction experiments will yield the products of magmatic gas/wallrock reaction and indicate how magmatic gas/wallrock reaction affects trace element mobilization. Analysis will combine bulk chemistry, SEM, and Synchrotron X-ray microprobe techniques (hard and tender-energy X-ray fluorescence microanalysis, microbeam X-ray absorption spectroscopy, and microdiffraction) to characterize bulk chemical transport, microscopic phase distribution in the vapor-deposited material and on reaction surfaces, and localized chemical speciation in the vapor-deposited minerals.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.