When BHP launched a $3.2 billion takeover bid for copper explorer Filo Corporation in July, it was a reminder that mergers and acquisitions don’t always involve the element of surprise.

Just as South32 had done with Toronto-listed junior Arizona Mining in 2018, BHP had conspicuously sat on Filo’s share register for more than two years before it pulled the trigger, and the smart money was always expecting the Australian company to launch a takeover bid for Filo’s Argentinian asset.