Neutron leakage flux spectra are simulated to explore whether the nature of volatile deposits residing within the permanently shaded craters near the poles of Mercury can be identified using state-of-the-art space neutron detection techniques deployed aboard a flyby mission to Mercury. The most sensitive method for discriminating between H2O (ice)-rich and S-rich deposits involves measurement of the flux of epithermal neutrons. We conclude that a single flyby over crater Chao Meng-Fu at an altitude of 200 km is sufficient to detect a circular deposit rich in elemental sulfur at the 2.6&sgr; statistical significance level, and that a similar deposit rich in H2O can be identified at the 7.8&sgr; level. Whereas identification of a S-rich deposit is not unique but compelling because of auxiliary physical arguments, that of an H2O deposit is unique.¿ 1997 American Geophysical Union