loose contact = Heat as others have noted
Three most likley causes:
1) Though it does look more like an arc to me in your photo -- like maybe the GPU became partially unseated under power
(always unplug PSU and discharge the capacitors before removing any MB component, with PC "off/ shutdown" there is still power to MB)
2) Could also be the PCIe contacts are not squeezing the GPU firmly for an unknown reason
3) Way too much amperage tried to go through those contacts
If your still under warranty I would contact EVGA ---> and NOT touch it
Check warranty status by serial number
https://www.evga.com/support/guestregister.asp If your not under warranty, you could try the pink eraser cleaning
--> however I use a standalone eraser stick - pencil eraser are mounted in metal tube, which "could" cause damage if it strikes something
Then I'd test in a different PCIe slot if your MB has one.
There is no easy way to clean the contacts inside of the slot if it looks as bad as the card. Industrial contact cleaners exist, my experience says your beyond what that could do - try if you want to - just make sure it is Dry before testing
If the GPU card is faulty, you are taking a risk that if the MB is not already damage -- and the GPU is the cause of the issue -- that you could cause damage/ more damage to your MB