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You will get two turns: Primal Wellspring's mana is used to cast Nexus of Fate. This results in a triggered ability putting a copy of Nexus of Fate on the stack. The two Nexus of Fate on the stack resolve and the real card is put into the library and the copy. You get two full turns after this one (starting with the turn produced by the copy, just for information).
If you get lucky in those two turns and draw another Nexus of Fate then you can restart the process, but only if you draw/tutor it from your library.