Mineralization in the Isle of Man
|From: Stone, P, Millward, D, Young, B, Merritt, J W, Clarke, S M, McCormac, M and Lawrence, D J D. 2010. British regional geology: Northern England.
Fifth edition. Keyworth, Nottingham: British Geological Survey.
Epigenetic mineralisation within the Isle of Man comprises a range of vein deposits (P916090). The most significant of these are associated with steeply inclined faults in the Tremadoc to Arenig, turbiditic strata of the Manx Group, although some veins in the Foxdale area pass into granite at depth. Relatively little mineralisation is known from the Upper Palaeozoic rocks of the island. Despite a long history of base metal and iron production extending back to the 13th century or perhaps even earlier, the mineral veins of the Isle of Man are still poorly understood. They appear to have a close similarity to some of the Lake District mineral vein assemblages.
Most of the island’s veins carry dominant lead–zinc mineralisation, with galena and sphalerite as the principal ore minerals. Copper is locally common, mainly as chalcopyrite, though with some tetrahedrite in places. Unlike the nearby Lake District, there is insufficient evidence to distinguish a separate suite of copper-dominated veins and it seems likely that the island’s copper production came from copper-rich portions of veins dominated by lead–zinc mineralisation. Other ore minerals include pyrite, pyrrhotite and some jamesonite. Gangue minerals include quartz, calcite, dolomite, siderite and locally some baryte and fluorite.
The recorded silver contents of Manx galena varies enormously from as little as 3 ozs per ton of lead (84 ppm) to as much as 400 ozs (11 160 ppm) in rare instances at the Foxdale mines where, in addition, tetrahedrite rich in silver has been reported. A comparatively high uranium content is present in solid hydrocarbons within some lead veins, notably those at Laxey and Snaefell.
Although extremely limited, evidence for the age of the island’s lead–zinc mineralisation is consistent with late Carboniferous or Permian vein emplacement. This is similar to the likely age of the suites of veins dominated by lead–zinc mineralisation that are seen in the Lake District and northern Pennines.
A small group of veins dominated by haematite, with only very minor amounts of quartz, dolomite and calcite, are almost certainly counterparts of the Cumbrian haematite mineralisation. They have been worked from Manx Group wall rocks near Maughold Head (SC 486 924). Siderite, a scarce mineral in the Cumbrian haematite deposits, appears to have been common locally.