The pegmatites are elongate tabular dikes in Precambrian gneiss. Pre-tectonic spodumene-free pegmatites, containing accessory cassiterite, columbite, and microlite, are unzoned. Post-tectonic pegmatites have cassiterite, tantalite, and microlite, plus abundant spodumene. Some of these show rudimentary zoning, with stages classified as magmatic and hydrothermal. Others that contain nonzonal units of contrasting texture and grain size, but similar mineralogy, are interpreted as composite, representing two or more separate injections. Tin and tantalum minerals are washed from the weathered pegmatite.

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