Geological Magazine

Articles

The Graphite Deposit of Seathwaite in Borrowdale, Cumberland

R. G. J. Strensa1

a1 Department of Mineralogy and Petrology, University of Cambridge.

Abstract

Graphite was deposited in and around a diabase intruded along post-Borrowdale Volcanic, pre-Bala faults about 4,000 feet above the Skiddaw Slate–Borrowdale Volcanic boundary. Associated copper-lead-zinc mineralization follows faults of the same trend, and is isotopically dated at 470 million years (mid-Ordovician). The breakdown of carbon monoxide in the magmatic gases was promoted by substances (notably pyrite, iron oxides, iron silicates, and quartz) which catalysed the Boudouard reaction 2CO xs21CC CO2 + C. The PT conditions of deposition of the graphite and associated minerals are estimated at P ~ 1,000 bars, T ~ 120° to 600° C. Possible occurrences of natural interlamellar compounds of graphite are discussed.

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