Geology
The mine's lodes were located in an outer zone of coarse-grained biotite granite of Carboniferous age, intruded into surrounding Devonian age "killas" - a series of metamorphosed sedimentary and volcanic rocks, visible to the north west of the mine around the cliffs. As the influence of the granitic emplacement increases toward the contact zone, the killas becomes spotted with cordierite, then mica-rich phyllites and finally at the contact, banded hornfels and tourmaline schist.
The tin appears as cassiterite (with around 65-70% tin), within veins associated with quartz, tourmaline, metal sulphides and fluorite. The veins are predominantly in a north west - south east orientation and the cassiterite itself forms around 1% of the vein material.
Read more about this topic: Geevor Tin Mine