Lyell Collection

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Discussion on genetic studies of red bed mineralization in the Triassic of the Cheshire Basin, northwest England

E. G. Poole writes: During the six-inch survey of the Nantwich district, it was observed that red bed mineralization is intimately associated with major post-Triassic faults which were used as feeder channels by the ascending mineralizing solutions (Poole & Whiteman 1966, pp. 56–58). The richest mineral deposits occur as lodes within the faults and contain copper, silver, cobalt and nickel ores. Barite is common in the fault planes and precipitated in the surrounding sandstones which are commonly bleached in the vicinity of the mineral lodes, the hematite being carried upwards by the mineralizing solutions and redeposited laterally (with barite) in the highly porous 'Lower Keuper' Sandstone Conglomerate (Helsby Sandstone). The hematitization of this sandstone exactly parallels the deposition of the Cumberland hematites in the Permian Brockram from laterally migrating magmatic solutions with the St Bees Shale acting as a traprock (Trotter 1945). The maximum age of the Cheshire Basin mineralization is provided by the alteration of the Acton Reynald Tertiary dyke at Grinshill (Poole & Whiteman 1966, pp. 57, 58), which agrees with the suggestion of Naylor et al. 1988 that mineralization is Tertiary or younger in age (p. 693).

I cannot agree, however, with the currently fashionable theory that Triassic sedimentation in the Cheshire-Shropshire Basin was influenced by syndepositional movements along the Red Rock or any other major fault. No such variations have been recorded in boreholes in the Stockport district (Taylor et al. 1963) or in the deep exploratory boreholes sunk through the lower part of the Trias in

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This 250-word extract was created in the absence of an abstract.

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