Brief : Minato has no chakra nature

[Draxus]

Minato most likely had a nature element which is unrevealed

P.S. Wind cannot be his affinity - since Kakashi mentioned that Minato was unable to infuse his element into Rasengan [Which later on helped Naruto to perfect it and create rasen shuriken] .​

I think Minato's chakra nature is fire.. I think I saw him using some fire techniques...

Neither of these statements are accurate.

We already know you can infuse multiple elements into rasengan due to Naruto's STBR

You have never seen Minato use fire jutsu, you were probably just drunk.

 

[jiraiya nindo]

I could see minato with a lightening affinity...just seems to match his style. Plus, I'd like to think that minato helped kakashi develop his raikiri but who knows. It was never discussed in the manga. Would've been cool for kishi to at least have minato show one elemental type when he was brought back as an edo.