Abstract: Thermometric and D-ICP analysis of fluid inclusions in calcite and fluorite show that the fluids responsible for extensive carbonate-hosted copper mineralization in the Ecton Hill area were low-temperature (< 100 °C), high-salinity (19.5 to 23 wt. % NaCl equivalents) brines strongly enriched in calcium (mean Ca:Na wt. ratio = 1.9). Compared with the fluids responsible for classical ‘Mississippi Valley type’ lead-zinc deposits elsewhere in the south Pennine orefield, the Ecton ore-fluids were of lower temperature and slightly more enriched in potassium. Despite these subtle differences, the data are consistent with a basinal brine model for ore genesis in this western part of the orefield similar to that envisaged for the remainder of the orefield. These Ca-Na-K-Cl, copper-bearing brines were most probably derived from the Cheshire basin located to the west of the Derbyshire Dome.