OCCURRENCE OF INORGANIC ELEMENTS IN MACERALS OF LOWER-RANK COALS AS DETERMINED BY ELECTRONMICROPROBE TECHNIQUES

摘要

In-situ elemental analysis of the individual macerals in lignites and sub-bituminous coalsfrom several Australian and Indonesian deposits by electron microprobe techniques typicallyshows the presence of small but significant proportions of Ca,Al and in some cases Fe;these elements do not appear to be related to separate crystalline mineral phases inside theorganic material.In cases where comparative data are available,the proportion of theseinorganic elements in the macerals is consistent with the concentrations of the sameelements released from the coals by ion exchange and selective leaching processes,andthey are regarded as representing the inherent non-mineral inorganics commonly reported inmore traditional geochemical analysis of lower-rank coal samples.In some cases theelements are more abundant in the vitrinites of the coals than in other maceral groups,but inother cases,despite differences in carbon,oxygen and sulphur contents,the concentrationof these inorganic elements is similar in all maceral groups present.With the exception of an unusual coal with a high organic sulphur content from the CrankyCorner Basin of New South Wales,these elements are not found in temporally orgeographically equivalent coals of higher rank,where the carbon content of the vitrinite isabove around 75%.This applies even in cases,such as the Bukit Assam deposit inIndonesia,where igneous intrusive effects have locally increased the rank of severalotherwise low-rank coal beds.The Cranky Corner Basin material has a similar carboncontent to other seams of equivalent age in the adjoining Sydney Basin,but has both a lowervitrinite reflectance and a significant concentration of Ca and Al in the maceral components.Although the bulk chemical composition of this particular coal has changed as expected withrank advance,the chemical structure of the macerals,especially the vitrinite,seems to haveremained similar to that associated with a lower-rank deposit,affecting both the reflectancevalue and the concentration of non-mineral inorganic components.