Nothing in life is more certain than death, taxes and speculation that Rio Tinto might acquire the 49 per cent of Turquoise Hill Resources (TRQ) that it does not already own.
The full takeover has been regularly mooted since Rio took control of the company, which used to be called Ivanhoe Mines, in 2011.
So when Bloomberg terminals showed that Rio had increased its stake in TRQ by about 6 million shares on Thursday morning, there was no shortage of raised eyebrows and racing pulses.
Rio has good reason to want the remainder of TRQ, given the Canadian company owns 66 per cent of one of the world's most exciting new copper mines; the giant Oyu Tolgoi mine in Mongolia.
Oyu Tolgoi is Rio's most exciting growth project, yet because of the ownership structure through TRQ, Rio effectively owns just 34 per cent of the copper, gold and silver that comes from the mine.
Many observers, including Deutsche's respected mining analyst Paul Young, have opined in recent years that it would make sense for Rio to own more of Oyu Tolgoi, particularly given copper prices are tipped to rise over the next three years.
Rio's debt situation is healthy enough to handle an acquisition, and there are few safer takeovers than buying more of something you already own.
So was the creep up the TRQ register this week a sign Rio is set to launch a full raid on TRQ?
That remains unclear; some party-pooping sources believe the 6 million shares were linked to a share issue conducted by a small company that both Rio and TRQ own shares in; Entree Gold.
Entree owns much of the land around Oyu Tolgoi and has in recent weeks split itself into two companies named Entree Resources and Mason Resources. Some believe that process of issuing shares in Mason has inadvertently led to Rio's small, and innocent rise up the TRQ register.
Others reckon it is a more deliberate creep by Rio and the start of a full takeover play for TRQ.
Rio is expected to clarify the situation on Friday, and either way, Rio is now a small step closer to taking out the remainder of TRQ.
The biggest dilemma for Rio is whether to strike now, before copper prices start rising around 2020, or to wait until the $USUS5.3 billion underground expansion of Oyu Tolgoi is built and fully derisked.
Don't be surprised if, by the time Oyu Tolgoi reaches peak production in 2025, Rio has taken out both TRQ and Entree.
