Geochemical signatures of potassium metasomatism in anthracite from the Himalayan fold‑thrust belts of Sikkim,India  

作　　者：Santanu Ghosh Anwita Ojha Atul Kumar Varma 

机构地区：[1]Coal Geology and Organic Petrology Laboratory,Department of Applied Geology,Indian Institute of Technology(Indian School of Mines),Dhanbad,Jharkhand 826004,India [2]Department of Earth Sciences,Indian Institute of Technology Bombay,Powai,Mumbai,Maharashtra 400076,India

出　　处：《International Journal of Coal Science & Technology》2022年第2期48-69,共22页国际煤炭科学技术学报（英文）

摘　　要：The present study focuses on the inorganic geochemical features of the bituminous coal samples from the Raniganj and the Jharia Basins,as well as the anthracite samples from the Himalayan fold-thrust belts of Sikkim,India.The SiO_(2)content(48.05 wt%to 65.09 wt%and 35.92 wt%to 50.11 wt%in the bituminous and anthracite samples,respectively)and the ratio of Al_(2)O_(3)/TiO_(2)(6.97 to 17.03 in the bituminous coal samples and 10.34 to 20.07 in the anthracite samples)reveal the intermediate igneous source rock composition of the minerals.The ratio of the K_(2)O/Al_(2)O_(3)in the ash yield of the bituminous coal samples(0.03 to 0.09)may suggest the presence of kaolinite mixed with montmorillonite,while its range in the ash yield of the anthracite samples(0.16 to 0.27)may imply the presence of illite mixed with kaolinite.The chemical index of alteration values may suggest the moderate to strong chemical weathering of the source rock under sub-humid to humid climatic conditions.The plot of the bituminous coal samples in the A–CN–K diagram depicts the traditional weathering trend of parent rocks,but the anthracite samples plot near the illite feld and are a bit ofset from the weathering trend.This may imply the plausible infuences of the potassium-metasomatism at post coalifcation stages,which is further supported by high K_(2)O/Na_(2)O ratio(29.88–80.13).The Fourier transform infrared spectra further reveal the hydroxyl stretching intensity of illite in the anthracite samples substantiating the efect of the epigenetic potassium-metasomatism.The decrease in total kaolinite intensity/compound intensity of quartz and feldspar may provide additional evidence towards this epigenetic event.

关 键 词：Himalayan fold-thrust belts ANTHRACITE Potassium metasomatism Kaolinite to quartz-feldspar intensity ratio Montmorillonite stretching and bending intensities Illite-stretching frequency 

分 类 号：P58[天文地球—岩石学]