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Parys Mountain |
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Wales, UK |
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Cu Zn Pb Ag Au
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Super Porphyry Cu and Au
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The Parys Mountain volcanic hosted massive sulphide zinc-lead-copper deposit is located in northern Anglesey in northwestern Wales, UK.
The Lower Palaeozoic of northern Wales is composed of a thick sequence of predominantly marine sediments with intercalated volcanics of the Welsh Basin, overlying Precambrian continental crust made up of a series of volcanic arcs. These marine sediments were replaced with continental sequences by the early Devonian reflecting the onset of basin inversion which culminated in the Caledonian Orogeny.
The Parys Mountain deposit occurs at or near the contact between Ordovician shales and the overlying few hundred metre thick lower Silurian rhyolites, which are in turn followed by lower Silurian shales. The Silurian volcanics include massive and flow banded, flow brecciated, pyroclastic and volcaniclastic rhyolites and basalts, occurring as a thin sheet intercalated with the lower rhyolites.
The deposit area appears to represent an east-west trending synform with outer limbs of Proterozoic basement, overlain by the Northern and Southern Shales of early to middle Ordovician age, then by the Silurian Northern and Southern Rhyolite limbs, with a core of early Silurian shales, the Central Shales. Ages are based on graptolite faunas.
Copper bearing stockwork veins occur in the upper part of the Ordovician Northern Shales, while similar copper bearing stockwork mineralisation is also found in the Silurian Central Shales. Massive sulphides have been delineated at, near and just above the contact between the Ordovician Southern Shale and the Silurian Southern Rhyolite contact.
The massive sulphides of the Chapel/Engine Zone are within the basal Southern Rhyolites and comprise a 100 to 200 m wide zone traceable down plunge for 800 m. These sulphides are present as three lenses separated by thin rhyolite bands. The highest grade sections assay 15 to 25% Zn, 5 to 10% Pb, 1 to 4% Cu, 200 to 400 g/t Ag and 1 to 5 g/t Au over narrow intervals. These sulphides are overlain by Silurian rhyolites cut by polymetallic sulphide veins.
The Carreg-y-Dol Zone near the contact of the Northern Shales and the Northern Rhyolite contained 5 to 15 m of massive quartz rich rocks with chalcopyrite-pyrite rich veins and metre scale pods of semi-massive sulphide. The shallow part of this zone was mined in the 19th century, and passes down into silicified Northern Shale with centimetre scale quartz-pyrite-chalcopyrite veins which contain 27 Mt @ 0.7% Cu.
The White-Rock Zone is also found within the Northern Shales, near the Northern Rhyolite contact and coprises quartz rich (white) rocks and semi-massive sulphides and is more Zn and Pb rich than at the Carreg-y-Dol Zone.
Total estimated reserves in 1990 were: 6.45 Mt @ 2.34% Cu, 2.6% Pb, 5.35% Zn, 39 g/t Ag, 0.23 g/t Au.
For more detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 2001.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Selected References:
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Barrett T J, MacLean W H, Tennant S C 2001 - Volcanic sequence and alteration at the Parys Mountain volcanic-hosted massive Sulfide deposit, Wales, United Kingdom: applications of immobile element lithogeochemistry: in Econ. Geol. v96 pp 1279-1305
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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