Will China break the Japan mould after Rio deal?

Others argue China's motives are more predatory, and that Beijing-backed companies are less likely than Japan's more independent operators to find satisfaction in minority or passive stakes, given long-term double-digit growth projections for its economy.

The Rio investment brings with it two board seats and no guarantee Chinalco will not pursue a larger stake later.

"The Chinese have a long-term plan that differs from old mining houses so there's a question about influence and control," said Warren Staude, investor adviser at Taurus Funds Management.

Through Aluminium Corp of China (Chalco), Chinalco is the largest producer of alumina and primary aluminium in China, but it hasn't made much of a splash anywhere else.

Rio ships a lot, but not all, its iron ore to Chinese steel mills, its copper turns up in dozens of countries and its aluminium is produced and sold almost universally.

It has amassed nearly 28 billion pounds in debt since 2007 by buying Canada's Alcan at the top of the commodities market, which has since crashed, and must repay 12.7 billion pounds in the next 18 months.