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|Title:||Nature and origin of minerals in anthracite from eastern Pennsylvania|
|Author(s):||Daniels, Eric Joseph|
|Doctoral Committee Chair(s):||Altaner, Stephen P.|
|Department / Program:||Geology|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||Textural, chemical, and mineralogical analyses of authigenic clays in anthracite-rank coal from eastern Pennsylvania have allowed a better understanding of parameters controlling diagenesis and relationships among mineral authigenesis, coalification, and tectonic deformation. Minerals in anthracite occur as distinct assemblages associated with the following microenvironments: coal matrix, two orthogonal joint sets restricted to coal beds (termed systematic and non-systematic cleat), a third joint set (J$\sb3)$ which is systematic and permeates adjacent lithologies, and slip surfaces. Systematic and non-systematic cleat sets, and kaolinite within the cleat sets, formed during bituminization. All other authigenic clay minerals in cleat replaced pre-existing kaolinite ($\pm$quartz) during the latest stage of coalification (anthracitization) at T $>$ 200$\sp\circ$C and different replacement assemblages are often observed in co-existing orthogonal cleat sets. In localities from all four anthracite fields, kaolinite in the systematic cleat was replaced by rectorite, sudoite, and tosudite, which are clay minerals primarily associated with hydrothermal veins and ore deposits, as well as by berthierine, NH$\sb4$-illite, and pyrophyllite. Replacement minerals in associated non-systematic cleat consist primarily of NH$\sb4$-illite or pyrophyllite. J$\sb3$ assemblages typically consist of quartz + Fe-rich chlorite veins which precipitated from solution during the early stages of anthracitization and deformation (T = 200$\sp\circ$C). Slip surfaces formed during regional tectonic deformation, and minerals observed in slip surfaces include NH$\sb4$-illite, pyrophyllite, Fe-rich chlorite, and kaolinite. The chemical components for clay mineral authigenesis appear to have multiple sources: Al and Si from pre-existing kaolinite and quartz; N from local organic matter; Mg, Fe, Mn, and perhaps Cr, Ni, and Zn, largely from metasomatic hydrothermal fluids.
Minerals in the coal matrix and non-systematic cleat set are interpreted to represent authigenesis in a low permeability environment (closed system alteration), however, the sudoite-tosudite-rectorite assemblage in the systematic cleat set is interpreted to be the result of metasomatic hydrothermal alteration (open system alteration) by migrating basinal brines. Mineralogical differences between the two nearly perpendicular cleat sets is proposed to have resulted from permeability differences between the cleat that were maintained by anisotropic lateral stresses created by plate convergence during the Alleghanian orogeny. Hydrothermal alteration is likely related to large-scale basinal flow induced by Alleghanian-age uplift. Migrating fluids could also have transported heat from depth and thereby significantly increased the rate and degree of coalification in this region and helped to form anthracite-rank coal at shallower depths than previously proposed (perhaps $\leq$ 6 km instead of $\leq$ 10 km).
|Rights Information:||Copyright 1992 Daniels, Eric Joseph|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9215801|