AN UNUSUAL GLAUCONITE ASSOCIATED WITH HYDROCARBON IN REEF-LIMESTONES, NEAR CASTLETON, DERBYSHIRE

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Abstract
Summary: Green, dioctahedral, iron-poor, aluminous glauconite, associated with solid hydrocarbon, occurs in stylolites and intra-rubble, scaly aggregates in proximity to fluorite-galena-sphalerite-baryte-calcite scrins and veins in apron-reef limestones of B 2 age, in Cave Dale and Odin Vein near Castleton, Derbyshire. The glauconite [K 1.31 Na 0.02 Ca 0.01 (A1 2.59 Fe‴ 0.12 Fe″ 0.43 Mg 0.93 Ti 0.01 V‴ 0.12 Cr 0.03 Mn 0.001 ) (Si 7.26 Al 0.71 B 0.03 ) O 20 (OH) 4 ] is a type 1M polymorph. An epigenetic origin is indicated by the mineral paragenesis and mode of occurrence. The mineralization probably occurred at relatively low temperatures since the fluorite accompanying the glauconite is purple. Reef-limestone lithology and a contemporaneous impermeable shale cover probably controlled the mineralization. Microstylolites facilitated the entry of hydrocarbons and, to a less extent, glauconite, perhaps as fluids, the end-products of the higher temperature galena-sphalerite-colourless fluorite mineralization in the area.

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