as said it depends on your local law. where i live, if you made profit with btc and you buy gold with it, you also should pay the tax.
but only if the bitcoin is considered as a legal currency in a state, if a state consider as illegal then it is also illegal to buy gold or silver with bitcoin. in fact in our country we are not going to pay tax on gold or silver while buying, here we buy gold and silver as we buy vegetable or meat or other stuff from store and we do not pay tax on these things similarly we buy gold and silver from shops and do not pay tax on that .
so this gold you buy with your vegetables, say you bought one ounce for $1200 Euro per oz. and in a year you sell that one ounce gold coin for $2000 Euro per ounce, right back to the same gold merchant. In the US you'd owe taxes on the $800 in gains. I think in most countries you'd owe income tax on those gains.
so if the OP is paying for his gold with btc (now worth $600/btc) and he bought these btc back when they were $200/btc - does he owe taxes (not sales tax on the gold) but income tax on the $400 per btc in gains?
in this thread we have 2 answers:
1) no because btc is a 'thing' like gold or silver, so btc for gold is just swapping commodities like buying gold with silver (but same question, your silver was $5/oz when you bought it, and now it's $35/oz, do you ow income on that $30/oz increase in value)?
2) yes, because his btc went from $200 to $600 per, regardless of what he bought with it when he realized the current $600/btc value.
(and then a bunch of terrible answers about "not really it's not real" or "as long as you don't get caught")
So, anyone actually use any of those "buy gold with btc" sites above?