The Cornubian Ore Field comprises a 180x40 km, south-west trending belt on the Cornish Peninsula of south-western England, UK which has been continuously exploited since the bronze age.
The ore field is related to a Permo-Carboniferous (295 to 270 Ma), s-type ilmenite series high heat, two mica, tourmaline bearing monzogranite batholith intruding a series of folded and thrusted Devono-Carboniferous mud-rocks, sandstones and mafic volcanics.
Base metal deposits generally take the form of steeply dipping lodes emplaced within the roof zone of the steep sided botholith and in the hornfelsed enclosing sediments. These lodes are generally tabular and less than 2 m thick. Some have been followed to depths of 900 m and persist over lengths of as much as 6 km. Most dip at beteen 60° and vertical and have a gangue of quartz, usually with chlorite, tourmaline, feldspar, hematite or white mica. The main metallic mineral is usually cassiterite with associated arsenopyrite, with or without chalcopyrite, chalcocite, specularite, sphalerite and wolframite. Late pyrite is common, as are fluorite and siderite. Grades range from 0.6 to 2% Sn, with variable copper from 0.25% Cu to more than 1%.
(Source: Porter GeoConsultancy, www.portergeo.com.au, 1990)
