安徽庐枞盆地泥河铁矿床成矿流体特征及其对矿床成因的指示

Ore-forming fluid characteristic of Nihe iron deposit in Lu-Zong basin,Anhui Province and its significance to ore genesis

庐枞盆地位于长江中下游断陷带内,地处扬子板块北缘,是长江中下游成矿带中重要的铁铜多金属成矿区。庐枞盆地西北部勘探新发现的大型泥河铁硫硬石膏矿床,矿床中硬石膏在不同蚀变-矿化阶段均广泛发育,具有鲜明的成矿特色,是玢岩型铁矿床成矿流体研究的理想对象。本次工作在详细野外地质和室内研究基础上,对矿床不同成矿阶段硬石膏等脉石矿物中流体包裹体开展较系统的包裹体岩相学、显微测温学和拉曼光谱学研究。鉴定出矿床中的包裹体类型有Ⅰa型原生包裹体(L+G),Ⅰb型次生包裹体(L+G)和Ⅱ型包裹体(L),均属盐水体系。拉曼探针分析结果显示包裹体的主要成分为盐水溶液,气相成分含有微量的CO2、N2和CH4。各成矿阶段矿物中包裹体测温工作表明,硬石膏-辉石-磁铁矿阶段、硬石膏-黄铁矿-磁铁矿阶段、高岭石-硬石膏-石英-黄铁矿阶段和重晶石-方解石-硬石膏阶段成矿流体温度的峰值分别为460.0～380.0℃、350.0～270.0℃、250.0～190.0℃和190.0～150.0℃,成矿流体盐度的平均值分别为14.11%NaCleqv,10.73%NaCleqv,4.03%NaCleqv和3.26%NaCleqv,成矿流体经历了从中高温中等盐度流体向中低温低盐度流体的演化过程。在此基础上初步分析了矿床成矿流体系统的演化过程和成矿机理,建立了泥河矿床的成矿模式。

The Lu-Zong Mesozoic volcanic basin is located in the Lower Yangtze River faultdepression zone, where is the north margin of the Yangtze Block. Nihe deposit located in the northwest part of Lu-Zong basin, which is a new found large iron-sulfuranhydrite deposit. Anhydrite is a suitable mineral for fluid inclusion study as it is widely developed in each alteration-mineralization stage of Nihe deposit. Based on detail field study, the fluid inclusions in anhydrite of different stages were studied by fluid inclusions petrography, microthermometry and Raman spectrometry. Our results show that three types of fluid inclusions exist： I a type primary fluid inclusions （L ＋ G）, I b tpye secondary fluid inclusions （L ＋ G） and 11 type fluid inclusions （L）. The Laser-Raman micro- spectroscopy results show that the compositions of fluid inclusions are mainly H20 with trace CO2, N2 and CH4. Microthermometry results show that the average homogenization temperature of fuild inclusions in anhydritepyroxenemagnetite stage, anhydrite-pyritemagnetite stage, kaoliniteanhydritequartzepyrite stage and barite-calcite-anhydrite stage are 460. 0～380.0℃, 350. 0 ～270. 0℃, 250. 0 ～ 190.0℃ and 190.0 - 150. 0℃, salinity are 14. 11% NaCleqv, 10. 73% NaCleqv, 4.03% NaCleqv and 3. 26% NaCleqv, respectively. The oreforming fluids evolution is from medium-high temperature and medium salinity to low temperature and low salinity. The oreforming process and metallogenetic model has been discussed in the paper.