Effects of contact metamorphism on the lithium content and isotopic composition of kerogen in coal

Lithium isotopes (δ7Li) in coals have been shown to increase with thermal maturity, suggesting preferential release of 6Li from kerogen porefluids. This has important implications for paleoclimate studies based on δ7Li buried marine carbonates, which may incorporate Li porefluids during recrystallization. Here, the content and isotopic composition macerals two coal seams intruded by dikes, were studied as a function temperature across gradient into unmetamorphosed coal. Samples collected Colorado (USA) Vermejo Fm. seam mafic-lamprophyre dike compared Dutch Creek No.2 felsic-porphyry dike; potential source Li-rich fluids. The Li-content Li-isotope compositions measured situ Secondary Ion Mass Spectrometry (SIMS). samples, VRo 0.68% (Tmax = 104 °C), contained <1.5 μg/g an average vitrinite −28.4 ± 1.6‰, while liptinite inertinite heavier, averaging −15.4 3.6‰ − 10.5 3.7‰, respectively. contact metamorphosed vitrinite/coke showed greatest change 18 37‰ heavier than vitrinite. coal, 1.15% 147 prior emplacement, released burial, less was observed between macerals. Overall, contents < 1 μg/g, had values 8 21‰ SIMS measurements near did not show indicative derived fluids, however previous bulk that included silicates slightly higher (2-3 μg/g) Li-contents dike, possible incorporation fluid metamorphic silicates. A negative correlation 12C+/30Si+ count ratios, indicating at temperatures becomes concentrated