湘中寒婆坳矿区测水组无烟煤—煤系石墨变质温度研究

Investigation on the Metamorphic Temperature of the Series Naturally Graphitized Coals from Anthracite to Coaly Graphite from Ceshui Formation of Hanpo'ao Mining Area,Central Hunan

煤系石墨是由煤经构造—岩浆事件改造而成的煤系共伴生矿产资源。为探究无烟煤—煤系石墨的变质温度,以湖南新化寒婆坳矿区无烟煤—煤系石墨及其顶底板岩石、夹矸为研究对象,采用变质矿物组合特征、镜质体反射率地质温度计和拉曼光谱地质温度计等手段进行研究。结果表明:大规模岩浆侵入初期,煤层及其顶底板受热温度较高,但持续时间短,而煤石墨化过程和围岩变质过程相对缓慢,最终,煤系石墨及其围岩与周围环境的热力学平衡温度相对较低。多手段综合确定寒婆坳矿区无烟煤的变质温度为220~250℃,变质无烟煤的变质温度为330~370℃,煤系半石墨的变质温度为390~450℃,石巷里矿煤系石墨变质温度为500~550℃。寒婆坳矿区无烟煤—煤系石墨变质系列整体上处于中低温变质作用阶段。研究结果可为煤系石墨勘探靶区圈定提供科学指导。

Coaly graphite is an associated mineral resource occurrence at coal measure that transformed from coal during tectonic-magmatic events.The series naturally graphitized coals from anthracite to coaly graphite and their associated roof rocks,floor rocks,and partings of the Hanpo'ao mining area,central Hunan Province,were studied by using X-ray diffraction,clay mineralogy,combining with the metamorphic mineral assemblage characteristics,vitrinite reflectance geothermometer,and Raman spectroscopic geothermometer.The purpose was to study the minerogenetic temperature of these series naturally graphitized coals.The results show that in the early stage of large-scale magmatic intrusion,the heating temperature of coal and its country rocks is relatively high,but the duration is short,whereas the graphitization process of coal and the metamorphism process of country rocks are relatively slow,thus,the thermodynamic equilibrium temperature between coaly graphite and its country rocks is relatively low.The metamorphism conditions of the series naturally graphitized coals from anthracite to coaly graphite cannot be well constrained by a single approach,and the minerogenetic temperature of these series naturally graphitized coals should be calibrated by mineralogy,coal petrography and Raman spectroscopy.Metamorphic minerals such as andalusite and staurolite have been observed in the surrounding rocks of coaly graphite,indicating that coaly graphite is in the medium-grade metamorphism zone,but andalusite and staurolite have been changed into sericite by hydrothermal alteration in the later stage.The metamorphic temperature of anthracite is about 220~250℃,meta-anthracite is formed at 330~370℃,and the metamorphic temperature of semi-graphite and coaly graphite in the Shixiangli Mine are determined at 390~450℃ and 500~550℃,respectively.The metamorphism of the series naturally graphitized coals is at medium-to-low metamorphic stage.The results can provide scientific guidance for exploration and exploitation of the coaly graphite.