I always wondered about those provinces as well. My interpretation of the trade good placement is the following:
The gold in Tirol must be because of its rich silver (and especially copper!) mines, which fits perfectly well, as the posession of this region was a major reason for the rise of the Habsburgs in the 15th and 16th century. There were some gold mines in the Eastern Alps (Tauern) in Salzburg and Kärnten/Carinthia, but they were mostly controlled by the Archbishops of Salzburg, who have their eponymous salt ingame. Probably with regards to game balance (who wants a strong Salzburg?), this gold belongs to the nearby Lienz in EU3, whereas Kärnten/Carinthia has iron. Iron would probably be better placed in Styria though, where a lot of iron was mined until the 20th century (at the Erzberg = ore mountain). The gold in Görz could be a reference to the mercury, which was mined in Idria and contributed quite a bit to the Austrian finances in the 16th century. Lastly, I have no idea why Krain was chosen as another gold province. Austria should be strong enough, even without this additional bonus (2 gold provinces plus one nearby should be enough).
It's a bit strange that other major mining areas of the Habsburg empire produce completely different trade goods (no silver in Bohemia, no copper/silver/gold in Slovakia). But this can probably be explained with the same old reason - game balance. Austria apparently needs a strong core and those resources would maybe make Bohemia and Hungary too strong.