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What they all say pretty much. Theoretical temperatures for smelting oxides tend to be based on the pure product. Real temperatures for achieving the same vary according to what is going into the smelting equipment. Not only co-existing minerals as seen in hand specimen but micro inclusion-phases are important as they can affect (either positively or negatively) the process. You only need to look at the variability of ore mineralogy in just Cornish tin-bearing lodes to see that any gravity-produced concentrate will vary widely in its mineral chemistry from place to place and once you are into micro-inclusions the same thing applies to concentrates produced by more modern methods. Stream tin might well be closer to purity regarding SNO2 content - oxidation during the weathering/erosion/placer-forming process would see to a lot of the associated sulphides, arsenides etc etc. Cheers - John