Adapted from Evans 1997: Ore Geology and Industrial Minerals
They usually develop at the upper contact of granitic intrusions by metasomatic alteration of granite, quartz and sericite replacing the granitic feldspar and biotite. The mineralisation occurs as irregular/sheet like bodies with stockwork zones and can extend downwards for up to 100m before grading into a feldspathic alteration zone and then into fresh granite. Pegmatites often form at the margins of greisen bodies.