贵州普安矿区晚二叠世煤中贵金属元素的赋存状态和地质成因

Modes of Occurrence and Geological Origins of Noble Metal Elements in Late Permian Coals from the Pu' an Coalfield, Guizhou Province

运用电感耦合等离子体质谱(ICP-MS)和逐级化学提取技术(SCET)对贵州西部普安矿区晚二叠世煤中贵金属元素的含量、赋存状态和成因机理进行了研究。结果表明,贵州普安矿区2号主采煤层的矿物组成主要为低温热液流体成因的黄铁矿和陆源碎屑成因的粘土矿物;与中国煤煤相比,该煤中Rh(38ng/g)、Pd(640ng/g)、Ir(9ng/g)、Pt(98ng/g)、Au(16ng/g)和Ag(1620ng/g)明显富集,其中Pd、Ir、Au的含量分别是中国煤的4.3倍、9倍和5.3倍。逐级化学提取结果表明,2号煤层中所富集的贵金属元素主要赋存在硫化物结合态中,Rh、Pd、Ir、Pt、Au和Ag在硫化物态中的含量分别为720ng/g、15000ng/g、310ng/g、2380ng/g、360ng/g、32300ng/g,而以有机态和硅铝化合物结合态存在的贵金属元素含量低于或接近于这些元素在煤中的背景值,表明低温热液流体对煤中贵金属元素的富集起了决定作用。

The concentrations, modes of occurrence, and origins of noble metal elements in Late Permian coals from the Pu＇an coalfield were studied by using inductively coupled plasma-mass spectrometry （ICP-MS） and sequential chemical extraction technology （SECT）. The results show that the minerals in No. 2 coal seam of the Pu＇an coalfield are dominated by pyrite of low-temperature hydrothermal origin and clay minerals of detrital terrigenous origin, Compared with coals of China, Rh （38 ng/g）, Pd （640 ng/g）, Ir （9 ng/g）, Pt （98 ng/g）, Au （ 16 ng/g）, and Ag （ 1620 ng/g） are significantly high in No. 2 coal seam. The concentrations of Pd, Ir, and Au in No. 2 coal seam are 4.3, 9, and 5.3 times higher than those in coals of China, respectively. The SECT results indicate that the noble metals concentrated in No. 2 coal seam mainly exist in the sulfide association state. The concentrations of Rh, Pd, Ir, Pt, Au, and Ag in the sulfide association are 720 ng/g, 15000 ng/g, 310 ng/g, 2380 ng/g, 360 ng/g, and 32300 ng/g, respectively. However, the concentrations of noble metals occurring in organic and silicate associations were lower than or close to their background values in coal. The low-temperature hydrothermal fluids must have played a dominant role in the enrichment of noble metals in the coal.