RT Journal Article
T1 The graphite deposit at Borrowdale (UK): A catastrophicmineralizing event associated with Ordovician magmatism
A1 Ortega Menor, Lorena
A1 Millward, David
A1 Luque del Villar, Francisco Javier
A1 Fernández Barrenechea, José María
A1 Beyssac, Olivier
A1 Huizenga, Jan-Marten
A1 Rodas, Magdalena
A1 Clarke, S.M.
AB The volcanic-hosted graphite deposit at Borrowdale in Cumbria, UK, was formed through precipitation from C–O–H fluids. The δ13C data indicate that carbon was incorporated into the mineralizing fluids by assimilation of carbonaceous metapelites of the Skiddaw Group by andesite magmas of the Borrowdale Volcanic Group. The graphite mineralization occurred as the fluids migrated upwards through normal conjugate fractures forming the main subvertical pipe-like bodies. The mineralizing fluids evolved from CO2–CH4–H2O mixtures (XCO2 = 0.6–0.8) to CH4–H2O mixtures. Coevally with graphite deposition, the andesite and dioritic wall rocks adjacent to the veins were intensely hydrothermally altered to a propylitic assemblage. The initial graphite precipitation was probably triggered by the earliest hydration reactions in the volcanic host rocks. During the main mineralization stage, graphite precipitated along the pipe-like bodies due to CO2 → C + O2. This agrees with the isotopic data which indicate that the first graphite morphologies crystallizing from the fluid (cryptocrystalline aggregates) are isotopically lighter than those crystallizing later (flakes). Late chlorite–graphite veins were formed from CH4-enriched fluids following the reaction CH4+O2 →  C + 2H2O, producing the successive precipitation of isotopically lighter graphite morphologies. Thus, as mineralization proceeded, water-generating reactions were involved in graphite precipitation, further favouring the propylitic alteration. The structural features of the pipe-like mineralized bodies as well as the isotopic homogeneity of graphite suggest that the mineralization occurred in a very short period of time.
PB Elsevier Science Ltd
SN 0016-7037
YR 2010
FD 2010
LK https://hdl.handle.net/20.500.14352/42456
UL https://hdl.handle.net/20.500.14352/42456
LA eng
DS Docta Complutense
RD 22 jul 2024