Backscattered electron images of columbite-tantalite from the Separation Lake area. (a) Essentially homogeneous ferrotantalite with faint oscillatory zonation and patchy (relatively Nb-rich) ferrocolumbite near the upper margin. Fe-suite SW subgroup beryl pegmatite. (b) Euhedral oscillatory zoned (mainly) ferrocolumbite exhibiting irregular and discontinuous patterns indicating many episodes of dissolution that have led to truncated layers and angular unconformities. Fe-suite eastern subgroup petalite pegmatite. (c) Oscillatory zonation in subhedral crystals with ferrocolumbite cores and ferrotantalite margins. Note the rounded corners, embayments and general discontinuity of the zonation. SW subgroup petalite pegmatite; Big Whopper. (d) Manganocolumbite with poorly defined oscillatory zonation disturbed by later patchy zonation towards the margins. The right hand margin of the crystal shows a second phase of unusually regular oscillatory zoned manganocolumbite. Li mica-cleavelandite pod in Mn-suite eastern subgroup beryl pegmatite.

© A.G.Tindle