Zotac cards a sort of the bottom of the barrel from what I have heard. When you go with a lower-quality manufacturer you are bound to end up with a few issues. I would suggest grabbing yourself an EVGA the next time you plan on grabbing a card; or at least some other reputable and top-tier manufacturer.

Those temperatures are not bad at all. I'm almost positive most people would consider that light-usage when it comes to mining. Nothing to be worried about as far as I am concerned. Are you doing anything strange with the TDP, memory clock or anything like that?