The characteristics of granitoid-related tungsten deposits hosted in siliceous (carbonate-free) rocks (e.g., Panasqueira, Cligga Head, Pasto Bueno) are reviewed and the ranges of physicochemical parameters of the ore-forming fluids are summarized. The two important tungsten minerals in these deposits are wolframite and scheelite, which were deposited mostly between 200º and 500ºC and 200 and 1,500 bars. The salinities of the mineralizing fluids were typically less than 15 wt percent but commonly were significantly higher (up to 55 wt %). The two predominant dissolved components are Na + and Clwith subordinate Ca 2+ , K + , and carbonate species (CO 3 2-/HCO 3 -). The contents of CO 2 are highly variable, but X CO2 values typically range from 0 to 0.1. Limited pH and f O2 estimates indicate a moderately acidic fluid with oxygen fugacities between those of the QFM and HM buffers. These parameters were used to guide solubility and speciation modeling of W in hydrothermal fluids in granitoid environments.Experimentally derived thermodynamic data for scheelite, ferberite, aqueous Ca, Fe, and W species, and other required aqueous species were critically evaluated and the most reliable data were adopted. Where necessary, missing data were estimated. The resultant thermodynamic database provides a basis for solubility and speciation calculations in the system Ca-Fe-W-Cl-O-H. The simultaneous solubilities of scheelite and ferberite in NaCl-HCl-H 2 O solutions were calculated at temperatures from 200º to 600ºC, pressures from 500 to 1,000 bars, pH from 3 to 6, and m NaCl from to 0.1 to 5.0 moles/kg H 2 O. The solubility model takes account of the species H + , OH -, Na + , Cl -, NaCl 0 , HCl 0 , NaOH 0 , H 2 WO 4 0
