Luzonite and associated Cu-excess tennantite from the Levant Sn–Cu deposit,Cornwall,England: Evidence for a high sulphidation hydrothermal event

Abstract

Luzonite, partially replaced by tennantite, was identified in dump specimens from the historic Levant Mine, west Cornwall, in a paragenetic sequence comprising early cassiterite–quartz–pyrite–arsenopyrite overprinted by Cu–Fe sulphides and followed by luzonite and tennantite. Mineral chemical data indicates the luzonite is near-end member and the tennantite is so-called Cu-excess tennantite, the implication being its Fe content (2.01–4.04 at.-%) is present entirely as Fe³⁺ in the sulphide lattice. Both the luzonite and its replacement product, Cu-excess tennantite, indicate that at least one hydrothermal episode in the long-lived Levant mineralising system involved influx of oxidised, high-intermediate sulphidation fluids. The presence of fine bornite and covellite lamellae in Cu-excess tennantite are interpreted to be post-depositional exsolution products. The luzonite has a sulphur isotope δ³⁴S of 0 ± 0.3 ‰ and it is tentatively proposed that the luzonite–tennantite depositing event represented a pulse of essentially pure magmatic-hydrothermal fluid.