Volcanogenic mineralization related to the Snowdon Volcanic Group (Ordovician), Gwynedd, North Wales

Reedman, A. J.; Colman, T. B.; Campbell, S. D. G.; Howells, M. F.

doi:10.1144/gsjgs.142.5.0875

Cited by 27 publications

(26 citation statements)

References 17 publications

(16 reference statements)

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“…7) allowing the fluids to move further away from the main fracture and brecciate the host rock. The timing of the mineralisation with respect to the quartzsulphide veins seen elsewhere in the caldera (Reedman et al, 1985) cannot be established without isotopic and other information. The subjacent placer magnetite mineralisation appers to be fortuitous in its proximity to the hydrothermal magnetite deposits; there is no genetic link because of the very different mineral chemistry.…”

Section: Discussionmentioning

confidence: 99%

“…The analyses of the magnetite and pyrite in Cwm Tregalan (Reedman et al, 1985) show that pyrite has a high Co:Ni ratio of 6:1 which is characteristic of volcanogenic pyrite (Bralia et al, 1979). Magnetite has a low TiO2 (0.4%) and V203 (0.4%) content.…”

Section: Mineral Chemistrymentioning

confidence: 99%

“…The LRTF, and the overlying Bedded Pyroclastic Formation (BPF), host base metal sulphide mineralisation at, or near the contact, in synvolcanic faults (Reedman et al, 1985).…”

Section: Geological Settingmentioning

confidence: 99%

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Volcanogenic quartz-magnetite-hematite veins, Snowdon, North Wales

Colman¹

1991

Mineral. mag.

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In the Ordovician Snowdon Volcanic Group caldera quartz-magnetite-hematite-pyrite assemblages occur in a breccia vein in rhyolitic tuff and vein swarms in basalt. The veins developed pre-cleavage. Elevated levels of tin and tungsten in the veins, and of fluorine in the wall rocks, suggest a magmatic contribution to the mineralising fluids. The chemistry of the veins differs from that of the base-metal sulphide veins found elsewhere in the caldera.

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Section: Discussionmentioning

confidence: 99%

Section: Mineral Chemistrymentioning

confidence: 99%

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Volcanogenic quartz-magnetite-hematite veins, Snowdon, North Wales

Colman¹

1991

Mineral. mag.

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“…Although the ashflow tufts at Bwlch Mine, in which the mineralization is presently hosted, are probably quite distal from source, heat required to drive hydrothermal fluids would probably have been provided by nearby contemporary high level intrusions such as that at Penmaenmawr, located only 8 km to the southwest. Indeed much of the vein copper mineralization in Central Snowdonia has been related to hydrothermal circulation associated with volcanism, high-level intrusion and caldera collapse during development of the Ordovician volcanic pile (Reedman et al, 1985). More detailed work on the Bwlch Mine assemblage is currently in progress and further occurrences of antimony mineralization in North Wales are being investigated, particularly with a view to testing their epithermal nature and volcanic association.…”

Section: Discussionmentioning

confidence: 99%

Lead-Antimony Mineralization at Bwlch Mine, Deganwy, Wales

1988

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Gwynedd, is one of the lesser known localities in the British Isles for lead sulphantimonide minerals, and recent work by the authors has identified a wider range of these than previously reported. All of the samples referred to in this paper are lodged in the mineral collection in the Department of Geology, National Museum of Wales, under accession numbers NMW 82.1G., NMW 83.44G. and NMW 85.70G. Location and geological setting Bwlch Mine (SH 7870 7944) is located some 200 m NW of Bwlch. Little is known of the early history of the mine, but it received a brief mention by Russell (1944) who investigated specimens of stibnite he had discovered in the collections of the Museum of Practical Geology and of the Royal Geological Society of Cornwall. During this work he also established the presence of semseyite and jamesonite. It was while attempting to verify these latter minerals that the present study developed. The mine is driven into a small hill composed of highly altered, nodular ignimbrite of Caradoc (Ordovician) age, belonging to the Capel Curig Volcanic Formation (M. J. C. Nutt, pers. comm., 1986). At present there is no access to previouslyworked levels and material can only be collected from a small overgrown waste dump. At Bwlch Mine the antimony minerals occur typically in irregular patches, and in thin veins and stringers up to 2 cm (but more usually of the order

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“…In the model of Reedman et al (1985) the Snowdon mineralization was the result of a sub-59 caldera intrusion driving convective circulation of seawater and magmatic fluids through caldera-60 related fractures, leaching metals from the host rocks, and depositing metals at a late stage in the 61 evolution of the caldera. However, the link between the caldera-hosted mineralization and Caradoc 62 magmatism is based solely on their close spatial association and any genetic relationship remains 63 conjectural.…”

Section: Guillous-frottier Et Al 2000)mentioning

confidence: 99%

Volcanological and environmental controls on the Snowdon mineralization, North Wales, UK: A failed volcanogenic massive sulfide system in the Avalon Zone of the British Caledonides

Lusty

Lacinska

Millar³

et al. 2017

Ore Geology Reviews

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14The Snowdon caldera of North Wales is host to base metal sulfide-bearing veins and stockworks, 15 mineralized breccias, disseminated sulfides, and localized zones of semi-massive to massive sulfide, 16 with subordinate magnetite-rich veins. The late Ordovician host volcanic sequence accumulated in a 17 shallow marine, back-arc environment in the Welsh Basin, which forms part of the Avalon Zone of 18 the British and Irish Caledonides. New field evidence, sulfur isotopes, and U-Pb dating indicate that 19 the Snowdon mineralization is genetically and temporally related to Late Ordovician magmatism and 20 caldera formation. It is interpreted to represent volcanogenic pipe-style sulfide mineralization, 21 resulting from focused hydrothermal fluids moving along caldera-related faults and simultaneous 22 dispersal of fluids through the volcaniclastic pile. Sulfur isotope data suggest that, whilst a limited 23 contribution of magmatic S cannot be ruled out, thermochemical reduction of contemporaneous 24Ordovician seawater sulfate was the dominant mechanism for sulfide production in the Snowdon 25 system, resulting in a mean value of about 12‰ in both the host volcanic strata and the mineralized 26 veins. Despite the tectonic setting being prospective for VMS deposits, strata-bound sulfide 27 accumulations are absent in the caldera. This is attributed to the shallow water depths, which 28 promoted boiling and the formation of sub-seafloor vein-type mineralization. Furthermore, the 29 tectonic instability of the caldera and the high energy, shallow marine environment would have 30 limited preservation of any seafloor deposits. The new U-Pb dates for the base (454.26 ± 0.35 Ma) 31 and top (454.42 ± 0.45 Ma) of the host volcanic rocks, indicate that the Snowdon magmatic activity 32 was short lived, which is likely to have limited the duration and areal extent of the ore-forming system. 33 2 The absence of massive sulfide mineralization is consistent with the general paucity of economic 34 VMS deposits in the Avalon Zone. Despite the highly prospective geological setting this study further 35 illustrates the importance of volcanic facies mapping and associated paleo-environmental 36 interpretations in VMS exploration. 37

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Volcanogenic mineralization related to the Snowdon Volcanic Group (Ordovician), Gwynedd, North Wales

Cited by 27 publications

References 17 publications

Volcanogenic quartz-magnetite-hematite veins, Snowdon, North Wales

Volcanogenic quartz-magnetite-hematite veins, Snowdon, North Wales

Lead-Antimony Mineralization at Bwlch Mine, Deganwy, Wales

Volcanological and environmental controls on the Snowdon mineralization, North Wales, UK: A failed volcanogenic massive sulfide system in the Avalon Zone of the British Caledonides

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