Three general models have been proposed for cassiterite (SnO2) mineralisation in magmatic-hydrothermal environments: 1) magmatic crystallisation from granitic melt (Linnen et al. 1992), 2) late-stage magmatic partitioning of Sn into a vapour phase and subsequent cassiterite deposition (Sun & Eadington 1987), and 3) hydrothermal leaching of Sn from granite and/or country rocks and subsequent deposition (Lehmann & Harmanto 1990). Identifying a model that is most applicable to a particular Sn deposit is difficult due to the large and pervasive hydrothermal systems inherent in their formation that can overprint and destroy evidence of the primary metal and fluid source(s) and mode of deposition. Here we use tourmaline geochemistry to chemically fingerprint the mineralising fluids and identify the origin and any subsequent evolution of fluids that emanated from the Mole Granite, NSW, and that produced rich, polymetallic mineralisation. Tourmaline has been touted as an ideal passive monitor of melt and fluid chemistry due to its complex chemical structure, stability over a wide temperature and pressure range and its resistance to physical and chemical abrasion (see Dutrow & Henry 2011 for summary).