The area north of the River Swale has been called the North Swaledale Mineral Belt. It is the most highly mineralized zone within the broad area known as the southern part of the Northern Pennine Orefield. The ore deposits mainly in veins (vertical) and flats (horizontal) and principally confined to limestone beds (Yoredale Group). The mineralsiation took advantage and was emplaced in a system of roughly east–west and east-northeast–west-southwest faults associated with the Stockdale Fault. The ore mined was galena, the major source of lead, although minor amounts of zinc and copper were locally exploited. More recently (in the last 70 years) some of the mines were reopened and fluorspar (fluorite) extracted. None are being mined at present, although the occasional reworking of the dumps and tailings heaps has taken place. The dumps are the best source of viewing any mineral samples.
The minerals commonly encountered in Swaledale and especially in the North Swaledale Mineral Belt are lead (galena, cerussite), iron (pyrite, pyrrhotite, marcasite), copper (chalcopyrite, azurite), zinc (sphalerite), fluorite, baryte and quartz minerals. A distinctive feature of the orefield is the close relationship between the geology of the sedimentary rocks and the potential of the fault to act as a mineralised vein. Hard, competent rocks such as limestone and to a lesser extent sandstone provided clean open fractures favourable for the deposition of wide mineralised veins. In weak, incompetent rocks such as mudstone, faults and fractures fissures are normally tightly closed and generally poorly mineralised. In Yoredale-type sequences, this relationship results in laterally extensive ore bodies focused in the limestones. Mineral vein widths vary from a few millimetres to over 10m, though most of the worked veins appear to have been less than 5m wide.