Hi,
I wanted to trade an iron ore +250 refill with a friend. When I created a direct trade (250+ iron ore refill for 300 iron ore) I couldn't complete the trade, the message stated that I needed to choose a different resource. It seems the trading logic treats an iron ore refill as if it were iron ore and won't allow the trade. I had to break the trade into 2 transaction (buy the refill for 1 fish, then buy back the fish for 300 iron ore). This is ok if trading with a trusted friend but not ideal.
The same might apply to gold ore but I couldn't test this.