The deep-seated coal deposits of the Chintalapudi sub-basin, Godavari Valley Coalfield, Andhra Pradesh, India and their petrographic significance

Abstract

The present work has been undertaken to generate coal petrographic database regarding the constitution and rank of the deep-rooted subsurface coal seam succession encountered in three bore-holes (MCP-1, 2 and 3) at closer vicinity of Chintalapudi area of Godavari Valley Coalfield. Deposition of coal in the valley is mostly confined to the Barakar Formation. However, the recent sub-surface explorations have shown the existence of the Kamthi sediments in the Ramagundam and Chintalapudi areas of the Coalfield. The coal seam encountered at the maximum subsurface depth of 560.43 m has been petrographically analysed during the present investigations. The study has revealed that coal seam D of (B. H. No. MCP-1), seams, LK-2, LK-3, LK-6, LK-7 and LK-8 (B. H. No. MCP-2) and the seam I and F (B. H. No. MCP-3), contain vitrinite group of macerals in abundance (40-77%). Seam G, despite having comparatively low frequency of vitrinite (35%) but retain dominance. The middle region of seam D (B. H. No. MCP-3), however, contains inertinite in abundance which points towards a distinct change in the climatic scenario in the basin. Liptinite (11-18%) and inertinite (5-7%) macerals in general are sparsely distributed. Mineral matter has been recorded between 16 and 27%, barring seam, LK-2 and D which contain its higher frequency (32-33%). Generally, a wide range of variation in random (Ro mean%) vitrinite reflectance, i.e. 0.43% to 0.59% has been recorded, which indicates the attainment of sub-bituminous B and high volatile bituminous C rank. Abrupt increase in reflectance has been noticed (0.69%) in the coals of seam LK-6 (pellet No. 6), indicating the attainment of high volatile bituminous B stage. Most of the coal seams of this area have vitrinite rich (vitric) constitution. However, a few coal samples viz., seam LK-7 (pellet No. 4), seam D (pellet Nos. 4 & 5) and the coal representing seam G contain mixed type of coal. The palaeo-depositional model, however, has indicated the existence of wet moor with intermittent moderate to high flooding, as the dominating phase with occasional invasions of brackish water influx and a few alternating dry spells, causing oxic and anoxic moor condition.