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

Colman, T. B.

doi:10.1180/minmag.1991.055.379.14

Cited by 2 publications

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“…The deposits at Avoca and Parys Mountain are volcanichosted massive sulphide or Kuroko-type deposits, a typical style of mineralization associated with submarine volcanism at destructive plate margins. In the Ordovician (Caradoc) Snowdon Volcanic Group of North Wales a suite of quartz-magnetite-hematite veins occupies fracture networks within basaltic tuff and welded silicic tuff (Colman & Appleby, 1991). Magnetite commonly occurs as pseudomorphs after early bladed specular hematite.…”

Section: Comparisons and Discussionmentioning

confidence: 99%

“…Chlorite and a little pyrite and chalcopyrite locally accompany the ironoxide minerals. The Snowdon veins have a distinctive mineralogy and structure within the overall setting of the Snowdon caldera mineralization (Colman & Appleby, 1991). The mineralization predates the cleavage and is considered to have formed as a result of late-stage hydrothermal activity during caldera evolution (Reedman et al 1985).…”

Section: Comparisons and Discussionmentioning

confidence: 99%

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Pre-Acadian copper mineralization in the English Lake District

1999

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The Ordovician sedimentary and igneous rocks of the English Lake District host a widespread suite of epigenetic metalliferous veins dominated by copper sulphides with abundant arsenopyrite, pyrite and accessory galena and sphalerite. New field and microstructural evidence from examples of this suite at Coniston, Wasdale, Honister, Newlands and Borrowdale shows that the veins were strongly cleaved during the Early Devonian (Emsian) Acadian orogenic event. The principal evidence includes the continuity of wall-rock cleavage fabrics with pressure solution seams in the veins and consistently orientated cleavage through enclosed, rotated wall-rock fragments and chloritic mats. There is also widespread complex intracrystalline deformation in quartz, cataclasis of arsenopyrite and pyrite, fracturing and/or buckling of bladed hematite, and growth of quartz or mica-fibre strain fringes. Chalcopyrite was partially or totally remobilized, enabling it to migrate along quartz crystal boundaries, and invade brecciated pyrite. Previous K-Ar Early Devonian age determinations for the mineralization are considered to have been reset. The pre-Acadian age of this mineralization, its style and relationship to the volcanic rocks permits a genetic link with the final phases of Caradoc magmatism.

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Section: Comparisons and Discussionmentioning

confidence: 99%

Section: Comparisons and Discussionmentioning

confidence: 99%

Pre-Acadian copper mineralization in the English Lake District

1999

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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 quartz-magnetite-hematite veins, Snowdon, North Wales

Cited by 2 publications

References 4 publications

Pre-Acadian copper mineralization in the English Lake District

Pre-Acadian copper mineralization in the English Lake District

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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