Appinitic intrusions in the English Lake District

Fortey, N. J.; Cooper, Anthony H.; Henney, P. J.; Colman, T. B.; Nancarrow, P. H. A.

doi:10.1007/bf01159737

Cited by 8 publications

(1 citation statement)

References 47 publications

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“…It should be emphasized that although a signifi cant number of hypabyssal mafi c bodies of similar composition mapped through out the Skiddaw Group crop out to the north of Borrowdale (Fortey et al 1994), none of these is known to have associated graphite deposits, nor have the few intrusions of this type that occur within the Borrowdale Volcanic Group outcrop. The reason for the Borrowdale graphite deposit to occur in its location is most proba bly related to the fact that the associated diorite intrusion is in the immediate hanging wall of the Burtness Comb Fault (Fig.…”

Section: Borrowdale Depositmentioning

confidence: 99%

Key factors controlling massive graphite deposition in volcanic settings: an example of a self-organized critical system

Luque

Menor

Barrenechea

et al. 2012

JGS

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Massive graphite deposition resulting in volumetrically large occurrences in volcanic environ ments is usually hindered by the low carbon contents of magmas and by the degassillg processes occurring during and after magma emplacement. In spite of this, two graphite deposits are known worldwide associated with volcanic settings, at Borrowdale, UK, and Huelma, Spain. As inferred from the Borrowdale deposit, graphite mineralization resulted from the complex interaction of several factors, so it can be considered as an example of self-organized critical systems. These factors, in turn, could be used as potential guides for exploration. The key factors influencing graphite mineralization in volcanic settings are as follows: (1) an unusually high carbon content of the magmas, as a result of the assimilation of carbonaceous metasedimen tary rocks; (2) the absence of significant degassing, related to the presence of sub-volcanic rocks or hypabys sal intrusions, acting as barriers to flow; (3) the exsolution of a carbon-bearing aqueous fluid phase; (4) the local structural heterogeneity (represented at Borrowdale by the deep-seated Burtness Comb Fault); (5) the structural control on the deposits, implying an overpressured, fluid-rich regime favouring a focused fluid flow; (6) the temperature changes associated with fluid flow and hydration reactions, resulting in carbon supersaturation in the fluid, and leading to disequilibrium in the system. This disequilibrium is regarded as the driving force for massive graphite precipitation through irreversible mass-transfer reactions. Therefore, the formation of volcanic-hosted graphite deposits can be explained in terms of a self-organized critical system.

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Section: Borrowdale Depositmentioning

confidence: 99%

Key factors controlling massive graphite deposition in volcanic settings: an example of a self-organized critical system

Luque

Menor

Barrenechea

et al. 2012

JGS

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The graphite deposit at Borrowdale (UK): A catastrophic mineralizing event associated with Ordovician magmatism

Menor

Millward

Luque

et al. 2010

Geochimica et Cosmochimica Acta

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The volcanic-hosted graphite deposit at Borrowdale in Cumbria, UK, was formed through precipitation from C-O-H flu ids. The 0 13 C data indicate that carbon was incorporated into the mineralizing fluids by assimilation of carbonaceous met a pelites 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 min eralizing fluids evolved from COrCH4-H20 mixtures (XC02 = 0.6-0.8) to CHCH20 mixtures. Coevally with graphite depo sition, 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 + 2H20, 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.

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Ordovician appinites in the Wugongshan Domain of the Cathaysia Block, South China: Geochronological and geochemical evidence for intrusion into a local extensional zone within an intracontinental regime

Zhong

Liu

et al. 2014

Lithos

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Appinitic intrusions in the English Lake District

Cited by 8 publications

References 47 publications

Key factors controlling massive graphite deposition in volcanic settings: an example of a self-organized critical system

Key factors controlling massive graphite deposition in volcanic settings: an example of a self-organized critical system

The graphite deposit at Borrowdale (UK): A catastrophic mineralizing event associated with Ordovician magmatism

Ordovician appinites in the Wugongshan Domain of the Cathaysia Block, South China: Geochronological and geochemical evidence for intrusion into a local extensional zone within an intracontinental regime

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