Geology and mineralisation at the Cleveland Mine, western Tasmania

The Cleveland tin-copper deposit lies within a sequence of mafic volcanics and clastic sediments with minor limestone, of probable Eocambrian-Early Cambrian age. The north-east trending sequence is near vertical to north-west dipping, and faces north-west. The probable shallow marine volcano-sedimentary succession consists of an older mafic volcanic sequence (the Deep Creek Volcanics) and a predominantly clastic sequence (the Crescent Spur Sandstone) which are separated by a transitional sequence of clastic sediments, mafic volcanics and limestone (the Hall Formation). The Deep Creek Volcanics is dominated by spilitic, tholeiitic basalt with intercalated and interbedded lapilli, litho-vitric and lithic tuff, argillite and volcaniclastic greywacke. The Hall Formation consists of interbedded argillite, limestone and turbiditic greywacke and minor chert, lithic and litho-vitric tuff and spilitic, tholeiitic basalt. It is conformably overlain by the Crescent Spur Sandstone which consists of turbiditic greywacke and interbedded mudstone with argillite, chert, volcaniclastic greywacke and minor spilitic basalt. High-titania, spilitic basalt in the Deep Creek Volcanics and the Hall Formation exhibits geochemical affinities to ocean floor basalt, and has whole rock ˜í¬•18O compositions similar to marine, hydrothermally metamorphosed basaltic rock. The volcano-sedimentary sequence is cut by regionally concordant, tectonically emplaced, older(?) low-titania, mafic-ultramafic ophiolitic complexes (e.g. the Whyte River complex), and is intruded by pre-mineralisation, high-titania basalt-dolerite dykes which are probably associated with the Deep Creek volcanism.