Primary tin deposits on Belitung, Indonesia, are spatially related to Upper Triassic granites that have a Rb-Sr isochron age of 213 + or - 5 m.y. The average K-Ar age of muscovite from two cassiterite-bearing greisens is 198 + or - 4 m.y., which suggests that the tin mineralization is not a simple late-stage event in the emplacement of the granitic plutons. Lead isotope data suggest that the source of lead in galena from the tin deposits is continental crust rather than oceanic crust. Such a source is also supported by an initial 87 Sr/ 86 Sr value of 0.7139 for the Rb-Sr isochron. The part of the shelf upon which Belitung Island is located is most likely continental shelf and not a thin continental cover over a primitive arc system.