Geology
The country rock of the mine is granite. The large mining sett (about 3 by 2 miles (4.8 by 3.2 km)) is crossed by many tin-bearing lodes which are substantially vertical and trend east-north-east. Most of the mine's excavations were made into just three of these lodes and were relatively shallow. The formation of the lodes was accompanied by extensive metasomatism which converted much of the plagioclase feldspar in the surrounding granite into the soft mineral kaolinite, and made excavation easier than it would have been in unaltered rock.
The lodes varied in width up to a maximum of around 2.4 ft (0.73 m) and were, at least in the early years of the mine's operation, sometimes of very high quality ore, uncontaminated with other unwanted metalliferous ores. The existence of these high quality ores near the surface led the miners to believe that even better ore existed deeper down, but the history of the mine suggests that this is not the case and the mineralisation becomes patchy at depth.
Read more about this topic: Eylesbarrow Mine