Global miner BHP Billiton said it expects to finalise its iron ore joint venture with Rio Tinto this year and took a swipe at a plan being considered by Australia to hike taxes on miners. “It is imperative that the impact of any policy and tax changes of governments around the world on sectors of economies should be well understood and do not hinder investment and the capacity of economies to grow,” outgoing Chairman Don Argus said in a farewell letter to shareholders on Thursday.