Coal Metamorphism and Igneous Intrusives in Colorado

An occurrence of coked bitumen, Raton Formation, Purgatoire River Valley, Colorado, U.S.A.

“…Coals can produce coke in nature when exposed to high temperatures associated with intrusions (via contact metamorphism) (Clegg, 1955;Cooper et al, 2007;Crelling and Dutcher, 1968;Dutcher et al, 1966;Fredericks et al, 1985;Ghosh, 1967;Rahman and Rimmer, 2014;Rimmer et al, 2009;Saghafi et al, 2008;Stewart et al, 2005). There has been some debate as to whether intruded coals always coke true to original coal rank.…”

Age of Basalt Intrusion Estimated by Organic Geochemistry

“…Kerogen exposed to the high temperatures of igneous intrusions exhibits the same general characteristics as kerogen which has followed normal geological maturation at lower temperatures for much longer time periods (Bostick, 1974). Vitrinite reflectance, for example, is increased (Dutcher et al, 1966;Baker et al, 1977), and atomic H/C ratios are decreased (Dutcher et al, 1966). In the few studies made of such samples, EPR spectra and pyrolysis data (Baker et al, 1977) also indicate increased degrees of thermal metamorphism.…”

“…In general, thermal effects are confined to the immediate vicinity of intrusions, extending into clastic sedimentary rocks a distance not more than twice the thickness of the dike or sill (Bostick, 1974;Correia and Maury, 1975;Kendrick et al, 1977). Dutcher et al (1966), however, detected thermal metamorphism in coal seams at a distance of 5 feet from a 1-foot-thick igneous sill. Differences in the effects of igneous intrusions on coal seams and on dispersed kerogen in shales may be due to differences in thermal conductivities and to the varying importance of convective heat transfer through superheated water in sediments of different permeability.…”

Heat‐model analysis of wall rocks below a diabase sill in Huimin Sag, China compared with thermal alteration of mudstone to carbargilite and hornfels and with increase of vitrinite reflectance

“…Due to the complex and indefinite heat‐transfer modes in overlying wall rocks, it is difficult to accurately compute the temperature experienced by underlying wall rocks [ Galushkin , 1997]. In addition, the changes in properties of wall rocks affected by thermal alteration and the thickness of thermal aureoles have been extensively discussed [e.g., Dutcher et al , 1966; Fredericks et al , 1985; Raymond and Murchison , 1992; Mayers and Simoneit , 1999; Qiu et al , 2000]. But the temperature under which thermal alterations happened are usually less investigated.…”