New mineral occurrences and mineralization processes: Wuda coal-fire gas vents of Inner Mongolia
New mineral occurrences and mineralization processes: Wuda coal-fire gas vents of Inner Mongolia
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DOI：
10.2138/am.2005.1671
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发表时间：
2005-11
影响因子：
3.1
通讯作者：
G. Stracher;A. Prakash;P. Schroeder;J. McCormack;Xiangming Zhang;P. V. Van Dijk;D. Blake
中科院分区：
文献类型：
--
作者：
G. Stracher;A. Prakash;P. Schroeder;J. McCormack;Xiangming Zhang;P. V. Van Dijk;D. Blake
摘要根据X射线衍射和能谱分析，在内蒙古乌达煤田与地下煤火有关的煤层瓦斯喷口附近的石英长石砂和砂岩上，发现了五种独特的矿物组合，包括硫酸盐、钙铝石、明矾石、硬石膏、钙铝石、钴硅镁石、钙铝石和硅镁石，以及卤化物和一种未鉴定的相。首次报道了铝土矿、钴硅镁石、硅镁石和来自同一个出气口的未鉴定相的矿物组合。在室温下密封储存的过程中，钴硅镁石也会在铝矿、钴硅镁石、硅镁石和未鉴定相的隐晶质物质上以次生成核的形式出现。现场观察、排气气体分析、SEM图像和矿物成分表明，硫酸盐钙铝镁矾、明矾石、coquimite、钙铝镁矾、godovikovite和未鉴定相是在一系列复杂过程中结晶的，这些过程包括冷凝、热液蚀变、溶液结晶、排气温度波动、沸腾和脱水反应，而卤化物salammoniac在燃煤气体的升华过程中结晶。煤成气与石英长石岩反应或石英长石岩经热液蚀变并从富酸水溶液中结晶而形成的钙铝石和硬石膏。在五个天然气喷口发现的矿物组合的变化可能是由于煤层化学，涉及煤燃烧气体的交换反应，沉积物，岩石和水溶液的组成的差异之前，在表面的气体的呼出，以及温度和冷却速率在一个喷口。很少有研究已经解决了煤与沉积物，岩石和水溶液的相互作用和随后的成矿过程。煤火为发现稀有和新的矿藏提供了机会。这些矿物质具有潜在的重要环境意义，可能是传播毒素的载体。煤火也为在地质记录中识别保存下来的矿物组合提供了洞察力，这些矿物组合是古代火灾的诊断。
Abstract Five unique mineral assemblages that include the sulfates millosevichite, alunogen, anhydrite, tschermigite, coquimbite, voltaite, and godovikovite, as well as the halide salammoniac and an unidentified phase, according to X-ray diffraction and EDS data, were found as encrustations on quartzofeldspathic sand and sandstone adjacent to coal-fire gas vents associated with underground coal fires in the Wuda coalfield of Inner Mongolia. The mineral assemblage of alunogen, coquimbite, voltaite, and the unidentified phase collected from the same gas vent, is documented for the first time. Coquimbite also occurs as rosettes secondarily nucleated on a cryptocrystalline mass of alunogen, coquimbite, voltaite, and the unidentified phase during storage in a sealed container at room temperature. Field observations, analyses of vent gases, SEM images, and mineral compositions suggest that the sulfates millosevichite, alunogen, coquimbite, voltaite, godovikovite, and the unidentified phase, crystallized in response to a complex sequence of processes that include condensation, hydrothermal alteration, crystallization from solution, fluctuating vent temperatures, boiling, and dehydration reactions, whereas the halide salammoniac crystallized during the sublimation of coal-fire gas. Tschermigite and anhydrite formed by the reaction of coal-fire gas with quartzofeldspathic rock or by hydrothermal alteration of this rock and crystallization from an acid-rich aqueous solution. Variations in the mineral assemblages found at five gas vents are possibly due to differences in coal-bed chemistry, exchange reactions involving coal-fire gas, and the composition of sediment, rock, and aqueous solutions prior to the exhalation of gas at the surface, as well as the temperature and cooling rate at a vent. Few studies have addressed the interaction of coal-fire gas with sediment, rock, and aqueous solutions and the subsequent mineralization processes. Coal fires present opportunities for discovering rare and new mineral occurrences. These minerals have potentially important environmental significance and may be vectors for the transmission of toxins. Coal fires also provide insight for the recognition in the geologic record of preserved mineral assemblages that are diagnostic of ancient fires.