Cassiterite from a quartz-tourmaline rock at Nanjizal Bay, ca. 1 km from the Land’s End visitorcentre in Cornwall, was analysed using optical microscopy, SEM-BSE, SEM-CL, EBSD, andEPMA. Large (100 - 800 μm), euhedral grains grew simultaneously as tourmaline and quartz intolocal low-pressure zones or cavities. Cassiterite is typically observed as lining on clusters offine-grained tourmaline, which appear to have acted as the nucleation point (Figs. 1a and 1b).Coarse-grained quartz grow around cassiterite, and fine-grained, acicular tourmaline, typicallyassociated with cassiterite in SW England [1], occur as inclusions in both cassiterite and quartz. Inplane polarised light, cassiterite is colourless to light brown, with patchy zoning of darker brown.The dark brown patches are clearly linked to W-content (Figs. 2a and 2d), showing up to 6,000 μg/gin dark brown zones, and mostly below detection limit (~800 μg/g) in colourless zones.Cathodoluminescence (CL) textures reveal concentric growth zoning around the c-axis. A generalcorrelation between trace elements and cathodoluminescence zoning is not straightforward.However, a weak positive correlation between Ti and CL intensity (Figs. 2c and 2f), and a negativecorrelation between W and CL intensity can be observed (Figs. 2c and 2d). This is in disagreementwith Farmer et al. [2], who found W to be an CL activator. Particularly, the Ti-CL relationship isinconsistent, and other defects are likely to be the controlling CL activators. Nevertheless, Ti andNb follow the same concentric growth zones that can be observed in the CL maps.
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