By Melanie Burton MELBOURNE (Reuters) -Top global miner BHP's focus on expanding its own copper assets while it undergoes leadership change means it is unlikely to gatecrash the planned $53 billion tie-up of Anglo American and Teck Resources, investors and bankers said on Wednesday. London-listed Anglo American and Canada's Teck Resources announced a merger on Tuesday, marking the sector's second-biggest tie-up ever, to forge a new global copper-focused heavyweight. The deal came just over a year after ...