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Pyrite (and marcasite) variation in the lower Kittanning coal of western Pennsylvania has been petrographically characterized using three parameters of size (categories rather than absolute size), morphology (framboidal, euhedral, dendritic, massive, and cleat), and microlithotype (organic) association. The samples analyzed consisted of 12 whole-channel samples from four surface mines. Six channels were collected to represent suspected marine environments of deposition, while the other six represent
The purpose of this study is to evaluate what influence paleoenvironments have on the nature of variation of pyrite in coal. To further the scope of this evaluation, the lower Kittanning samples were also compared to previously studied coals from the predominantly marine environments of western Kentucky.
Comparison of coals has been done using the percentages of pyrite in the microlithotypes vitrite and clarite. In the lower Kittanning coal, framboidal pyrite is generally less abundant and dendritic pyrite was not observed at all. Euhedral pyrite exhibited no clear variation between the two environments. Massive pyrite was more abundant in the set of samples from the mine with the highest average pyritic sulfur but otherwise exhibited no variation. In contrast, a larger percentage of pyrite in the western Kentucky coals examined is framboidal and dendritic. Mines examined in the Moorman syncline of western Kentucky do have a framboidal pyrite percentage comparable to the lower Kittanning samples, but the percentage of dendritic pyrite (particularly in the Western Kentucky No. 9 coal) s significantly higher for the western Kentucky coals.
Bulk petrography of the coals is similar with all having greater than 80% total vitrinite. The association of the pyritic sulfur does, however, change significantly between the various coals studied and particularly between the coals of western Kentucky and among the "marine" lower Kittanning samples and the "fresh water" lower Kittanning samples. Among the pyrite in the "fresh water" coals, massive (perhaps epigenetic) pyrite dominates the associations. In summary, the study of form and association of iron sulfides has the potential to give more information about variations in coal depositional environments than simply the study of bulk petrologic or bulk sulfur variations.
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