Summary: Investigation of the mineralogy and paragenesis of the fluorspar flat at Masson Hill, Matlock, Derbyshire, shows the mineralization to be a combination of void infilling and metasomatic replacement. The main paragenesis is of the non-sulphides, fluorite, baryte, and calcite accompanied by a sequence of sulphides, bravoite, pyrite, marcasite, chalcopyrite, sphalerite, and galena. A wide range of secondary minerals occur in the oxidation zone.