Features of tin mineralization in carbonate deposits,as in Eastern Siberia

The paper shows differences in character of tin mineralization in skarns which develop after dolomites (magnesial) and limestones (limy). Cassiterite is not deposited in the former, since because of the relatively high alkalinity and the high activity of boron (B₂0₃), tin preferentially enters the crystal structures of Sn-borates such as hulseite, ludwigite, and nordenskioldine rather than cassiterite. In limy skarns, tin is largely dissipated in garnets (up to 0.62%), axinites (up to 0.2%), and other minerals. It is only at the end of the appropriate stage, at relatively high acidity, that tin is deposited as cassiterite in magnetitic and amphibole-axinitic skarns. The latter are very favorable for development of economic ore bodies. Conclusions are made to the effect that a) tin is present in the postmagmatic solutions during each of the three stages, and also b) concerning optimum conditions for deposition of tin minerals in any stage (depending on magnitudes of Eh and pH environments and B₂O₃ and S^2- activities. -- Author.