The occurrence of buddingtonite in super-high-organic-sulphur coals from the Yishan Coalfield, Guangxi, southern China

This paper discusses the identification, abundance, modes of occurrence and origin of buddingtonite and associated minerals in three Lopingian coals from the Yishan Coalfield, Guangxi Province, southern China. The coals of this coalfield are preserved within carbonate successions and are characterized by super-high-organic sulphur contents (mostly 6-9%). Three different types of feldspars have been identified in these coals, buddingtonite, albite and minor K-feldspar. Both the albite and K-feldspar in the coal were largely derived from detrital materials of terrigenous origin, although some were authigenically deposited; they were subsequently subjected to corrosion/dissolution by percolating fluids. Buddingtonite was derived largely from K-feldspar via diffusion mechanisms through the substitution of K+ by NH4+, the latter coming from decomposition of organic matter in the coal, or from changes in the organic matter with rank advance. A small proportion of the buddingtonite was also derived from albite through the replacement of Na+ by NH4+.