The proposed takeover of London-based mineral miner Rio Tinto (NYSE:RTP) by its larger Australian rival BHP Billiton (NYSE:BHP) has taken a couple of direct hits in the past few days, leaving the megamerger's future in dire doubt.

On Friday, the Australian Competition and Consumer Commission expressed concern that the combination could interfere with the global seaborne supply of iron ore. The mineral is one of the key ingredients in the manufacture of steel. The commission's proffered opinion doesn't yet constitute a formal ruling; that'll come sometime between now and Oct 1. The commission will accept comments on BHP's offer until Sept. 5.

It's likely that some comments opposing the buyout are coming from China, where steelmakers have watched their iron ore costs jump in recent months. Indeed, it hardly seems coincidental that over the weekend, Aluminum Corp. of China (NYSE:ACH) -- Chinalco to its friends -- received permission from Australian authorities to increase the stake it acquired in Rio Tinto earlier this year from 9% to 11%. The original $14 billion purchase was accomplished with some help from Pittsburgh-based aluminum manufacturer Alcoa (NYSE:AA), which put up $1.2 billion of the price.

You have to believe that the lobbying is hot and heavy surrounding BHP's proposed purchase, which Rio Tinto has thus far spurned. It appears that Chinalco was a guest of BHP at the Olympic games in Beijing earlier this month. Obviously, size is the key issue: BHP and Rio Tinto follow only Brazil's Vale (NYSE:RIO) in importance in the iron ore market. Beyond that, a merger of the two companies would form a major player in the thermal and metallurgical coal market.

For Alcoa's part, the company's participation may signal its desire to scoop up any aluminum assets that Rio Tinto might be forced to divest as part of a merger with BHP. Alcoa's efforts to buy Canadian rival Alcan were trumped last year by a considerably higher offer from the British company.

In short, events in the mining sector remain fun to observe, and well worth Fools' attention.

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Fool contributor David Lee Smith doesn't own shares in any of the companies mentioned. He does solicit your questions or comments. The Fool has mined and manufactured a solid disclosure policy.