Investigation on the lignite deposits of Surkha mine (Saurashtra Basin, Gujarat), western India: Their depositional history and hydrocarbon generation potential

The huminite reflectance values (av. 0.31% Rr) show a good correlation with gross calorific values (av. 3917 cal/g) and average Tmax value (416 °C) of the lignites. Furthermore, the abundance of thermally unstable hop-17(21)-ene and ββ-hopane indicate immature stage of lignites. These lignites contain high TOC (av. 35 wt.%) and low ash yields. The volatile matter, carbon and oxygen contents are relatively high, whereas sulphur content is moderate, and hydrogen and nitrogen contents are comparatively low in all the lignite samples. The hydrogen index values vary between 53 and 538 mg HC/g TOC, the atomic values of H/C range from 0.47 to 1.04, and of O/C from 0.20 to 0.29. Overall, the lignite-bearing sequence is characterized by type II-III admixed kerogens (organic matters), and has potential to generate hydrocarbons upon maturation.