Interesting post:
Nikolaus Boroffka · Deutsches Archäologisches Institut
I joined ResearchGate much later, so I have seen your question only now, and it may be out of date.
I have been part of a research group which studied the tin question for several years (some of us are continuing still). One major result of our excavations and analyses was the discovery of the (at present) oldest known tin-mines in Tajikistan (Central Asia), which date to the late 3rd or early 2nd Millennium BC. Tin was already in use at that time in Mesopotamia, but we did not excavate all mines, so that possibly we missed the oldest ones. In any case, for the time we could prove close trade contacts are indeed documented between that region and Mesopotamia.
It is also interesting that the mine in Tajikistan (the site is called Mushiston) actually contains an extremely rare geological situation. The ore there is a mix of copper and tin - a unique case of a “bronze” ore, as our experiments with smelting also confirmed!
If the question is still acute, let me know and I can give publication references - much is available on my site at academia.edu.
http://www.researchgate.net/post/At_what_place_the_Copper-Tin_alloy_Bronze_may_be_invented
You probably don't mean Xray diffraction (crystal structure determination) for identifying the geographical origin.
You probably mean that Xray fluorescence of heavier metallic elements might help. But actually, straight-forward chemical assay ought to pinpoint the origin of an ore, by the elemental analysis.
And why would one use mass spectrometry for this purpose?