Zeolite and associated mineral occurrences in high-sulphur coals from the middle Miocene upper coal seam from underground mines in the Cayirhan coalfield, (Beypazar?, Central Turkey)

Three sampling profiles (BA, BB, and BC) from, respectively, the A, B, and C sectors of the cayirhan coalfield representing the working Tv and Tb splits of the Middle Miocene-age upper seam were investigated for mineralogical and elemental compositions. The Tv and Tb splits are mainly separated by a 70-100-cm thick tuffaceous clastic rock/marl parting in the study area, and the thickness of the Tv and Tb splits varies from 1.50 to 1.70 m, and 1.55 to 1.80 m, respectively. In both the Tv and Tb splits, Cr, Ge, As, and Zr are enriched, while Th and U are enriched only in the Tv split in all sampling profiles. This study indicates that the most significant difference between the Tv and Tb splits is in mineralogical composition. In contrast, zeolites (analcime and clinoptilolite) and carbonate minerals are detected as dominant to abundant phases in the Tv and Tb splits in the BA and BB profiles, while zeolite minerals are only identified as accessory phases in the BC profile. In addition, plagioclase grains are commonly identified in the BA and BB sampling profiles, whereas authigenic K-feldspars are more common in the sampling profile BC. The abundance of analcime and clinoptilolite, and their co-existence with syngenetic carbonate minerals in the BA and BB sampling profiles could imply that the alteration of volcanic inputs along with Ca-rich water influx into palaeomires seems to have resulted in favourable alkaline conditions and ion support for natural zeolite formation in the palaeomires. In contrast, the accessory presence of zeolite minerals and the common occurrence of authigenic K-feldspar grains in the sampling profile BC could imply that the semi-open hydrogeological system seems to allow transferring necessary ions for natural zeolite formation to other parts of palaeomires. Overall, the variations in mineralogical and elemental composition seem to be controlled by a combination of water chemistry and hydrogeological conditions within palaeomires and the geochemical properties of volcanic inputs into palaeomires.

Automated summary

This study investigated the mineralogical and elemental compositions of three sampling profiles from different sectors of the Cayırhan coalfield. The most significant difference between the Tv and Tb splits was found to be in the mineralogical composition. The presence of zeolite minerals and carbonate minerals in the Tv and Tb splits of the BA and BB profiles suggests favorable alkaline conditions for natural zeolite formation. In contrast, the presence of zeolite minerals and authigenic K-feldspar grains in the BC profile implies a semi-open hydrogeological system for transferring necessary ions for zeolite formation.