The effect of temperature of reaction on the extraction of tin from calc-silicate rocks by NH4I volatilisation

Extraction of lattice-bound tin from calc-silicate minerals in the determination of tin in skarn rocks by NH₄I volatilisation is reported. This analytical technique has previously been regarded as specific for cassiterite and stannite. Although the NH₄I volatilisation reaction does not decompose calc-silicate minerals there is an increase in the yield of NH₄I-volatilised tin when the volatilisation temperature is raised above 500°C. The temperature effect is only observed for whole-rock samples and the type of behaviour appears related to the mineralogy of the rock. For instance, magnetite-bearing rocks have a different temperature yield curve to pyrrhotite-bearing rocks. When concentrates of single minerals are reacted with NH₄I this temperature dependence is not observed, although there is an increase in tin yield with decreasing grainsize.