Smallcleugh mine is recorded to have been developed from 1770 for a short time, working a series of veins and strata-bound replacement deposits (flats) believed to have been first encountered in 1776 associated with the Handsome Mea and Smallcleugh veins. Although the mine does not appear to have gotten into its stride until 1787, several other veins and flat deposits were also developed before the mine closed in the early 1900s. In 1963 an abortive attempted was made to locate further ore reserves. The most well-known account is the dinner held underground by the Masonic Lodge in the so-called Ballroom Flats in 1901. The first amateur exploration of the mine may have been in the late 1960s.
Smallcleugh mine in the North Pennine Orefield is well known amongst British mineral collectors for good examples of galena, sphalerite, ankerite, and calcite, and to a much lesser extent quartz, all of which have been collected for many years since access was regained. Excellent specimens of single black complex sphalerite crystals to 1.5cm or so on white matrix were collected from a replacement deposit above the so-called Hydraulic shaft. Single galena crystals to 4cm could be collected from cavities in the strata-bound replacement deposits (flats) and veins. Less well known are the secondary species: secondary minerals mostly of zinc, copper, lead, and iron, rare nickel, and manganese have occasionally been found. Many of the secondary minerals from Smallcleugh would be only of interest to micro-mineral collectors. Many of the flat deposits now have modern names such as Wheel Flats (from a set of ore cart wheels found there, the old name may have been Browns Flat), while Whit Hudsons Flat and Hetheringtons Flat and cross-cut are possibly an original name. Other modern names are Incline Flats (an incline level leads into these workings), Old Fan Flats (parts of a ventilator fan found here), New Fan Flats (near the Old Fan Flats), North End Flats (?), Smallcleugh Main Flats (after the mine), The Ball Room Flat (named after a Victorian Masonic dinner party held there), Zinc Flat (from a high sphalerite content), High Flats (above the Smallcleugh Horse Level), Proud's Sump Flat (after the sump near these Flat workings), and Gullyback Flats (?). The rises and sumps appear to have mostly retained their old names, e.g. Spottiswood, Proud's, and Luke Halls.
