The main lead ore mineral within the Northern Pennine carbonate-hosted galena-fluorite orefield is silver-bearing galena. Numerous reliable assay and recovery records, from the heyday of lead mining during the eighteenth and nineteenth centuries, indicate that silver values in the ores then being mined were typically fairly modest, in the range 100–250 ppm Ag. Historical records from the area written during the eleventh and twelfth centuries, although very much less complete and more open to interpretation, indicate levels of silver production which could not have been sustained from such ores. It is suggested that lead ores with much higher silver content may have been available in these earlier times. A few scattered occurrences of galena with enhanced silver content may represent the vestiges of these ores.

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