SEM-CL and LA-ICP-MS trace element analysis of cassiterite in Gejiu tin district, SW China

Scanning electron microscope-cathodoluminescence images of cassiterite from various ore deposits in the Gejiu tin disrict, SW China reveal microstructures that differ among samples from different mineralizing environments. Cassiterite grains derived from granites and granite-proximal skarns and greisens are commonly larger in size, with clear euhedral oscillatory growth zones. In vein, stratiform oxidized and stratiform semioxidized samples, which are distal to the source granites, cassiterites are generally smaller, anhedral, and zonings are less evident. LA-ICP-MS trace element analyses indicate Ti, Fe and W are the most abundant trace elements in the samples of this study and Al, Sc, V, Ga, Zr, Nb, and Sb are commonly in lower concentrations. V, Nb, W and U have significant variations in concentration in a single sample. The skarn, greisen and tin granite samples have higher Ti, V and Al concentrations than vein-hosted, stratiform semioxidized and stratiform oxidized cassiterite. Trace element variations may reflect the distance between the granite-derived source fluids and the hydrothermal orebodies. In a tin granite cassiterite grain, the concentrations of Nb, U, Sb, W, Sc, V, Ti and Fe increase from core to rim of the crystal, but the greisen cassiterite does not show the same element zonation