Effect of T, fO2, volatiles and composition on the solubility of cassiterite (SnO2) inevolved granites
1*12Paras Bhalla,1 François Holtz, 2 Robert L. Linnen, 1 Harald Behrens and 1 Otto Diedrich

Institute of Mineralogy, Callinstrasse 3, University of Hanover, 30167 Hanover, GERMANY
Department of Earth Sciences, Faculty of Science, University of Waterloo, Waterloo, Ontario, N2L3G1 CANADA*Present Address: Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1
Ookayama, Meguro-ku, 152-8551 Tokyo, JAPANExperiments were performed at 600-850 °C, 2 kbar and at different fO2 (Ni-NiO to Co-CoO)
on F-bearing natural peraluminous melt and also on F-free and F-bearing synthetic granitic
melts of peralkaline, subaluminous and peraluminous compositions. Normative corundum
content in these melts varied from 1.0 wt.% to 3.2 wt.% C along with varying amount offluorine (from 0 wt.% F to 4.9 wt.% F in melt) and chlorine (from 0 wt.% to 0.4 wt.%) in themelt, in order to examine the cassiterite (SnO2) solubility in these melts as a function of T, fO2,
halogens and corundum content. A SnO2 crystal was placed in the granitic melt (glass). The
dissolution behavior of the SnO2 crystal was examined. All experiments were conducted incold seal pressure vessels for 5 hours to 24 hours. Bulk composition, F and Cl in the starting
glasses and in the run products (silicate melt or glass) were determined by electron microprobe
and ICP-AES. Concentration of SnO2 was analyzed using electron microprobe. The oxygen
fugacity of most of the experiments was measured using hydrogen sensor capsule technique ofChou (1987a). Various diffusion (concentration) profiles were analyzed from glass-crystal(SnO2) interface towards glass boundary. The SnO2 concentration calculated at the SnO2-glass
interface is the SnO2 solubility.
At Ni-NiO buffer, the solubility of SnO2 in peraluminous melts containing 1.12 wt.% Fincreases from 0.32 wt.% to 1.20 wt.% SnO2 with increasing temperature from 700°C to850°C, respectively. At Ni-NiO buffer, SnO2 solubility increases from 0.35 wt.% SnO2 to 0.55
wt.% SnO2 at 750°C and from 1.05 wt.% SnO2 to 1.10 wt.% SnO2 at 850°C, with an increase
from 0 to 1.12 wt.% fluorine in the melt. A significant increase in SnO2 solubility is noticed at
800°C and 2 kbar when the F-content in subaluminous melt is > 2.3 wt.%. At ~NNO, 800 °C
and 2 kbar, SnO2 solubility in a subaluminous melt increases significantly from 2.23 to 4.17
wt.% SnO2 with increasing F-content of the melt from 2.4 to 4.6 wt.% F, respectively. At thesame experimental conditions, SnO2 solubility in the subaluminous melt (with 2.4 wt.% F) inmelt can be predicted as log CSnO2 = 6.09 – 6.26.103/T, where CSnO2 and T are concentration ofSnO2 (wt.%) and temperature (K), respectively. At NNO, 850°C and 2 kbar, SnO2 solubility inperaluminous melts also increases from 1.05 to 1.25 wt.% SnO2 with increasing chlorine
content from 0 to 0.4 wt.% Cl in melt, respectively.
Our results, combined with those of Linnen et al. (1996), suggest that chlorine is at least
as important as fluorine for controlling SnO2 solubility. At reducing conditions (Ni-NiObuffer), tin is incorporated as Sn2+ and SnO2 solubility increased from 0.47 to 1.10 wt.% SnO2
with increasing normative corundum content (excess alumina) from 0.1 to 2.8 wt.%. At
oxidizing conditions (Ni-NiO+2 to +3), tin is mainly incorporated as Sn4+ and the effect ofexcess alumina seems to be significantly lower than at reducing conditions.
References: (1) I-Ming Chou (1987a): In: Ulmer, G.C. and Barnes, H.L. (Ed.), Hydrothermal ExperimentalTechniques. John Wiley & Sons Ltd., New York, pp. 61-99.
(2) R. L. Linnen, M. Pichavant, and F. Holtz (1996): Geochimica et Cosmochimica Acta 60, pp. 4965 – 4976.