CSN and its associated companies bought almost 4.6 million Riversdale shares from February 1 to 8.

Riversdale’s regulatory announcement revealed the purchases were made at prices ranging from $15.84 to $16 per share, with up to eight trades each day.

Many of the biggest trades were made at or within 1c of the $16 price Rio is offering for Riversdale shares.

CSN lifted its stake of Riversdale from 16.29% to 17.58%, but India’s Tata Steel remains the major shareholder with 24.14%.

Both steelmakers collectively hold 41.72% of the company at a time when higher metallurgical coal prices are soaring as a result of Queensland’s devastating wet season.

Riversdale’s flagship Benga mine (65% RIV, 35% Tata Steel) in Mozambique was officially opened in April last year and is expected to start premium coking coal exports in the second half of 2011.

At full production under stage 2 development, the Benga mine aims to export 6 million tonnes per annum of prime hard coking coal and 4Mtpa of export thermal coal by 2013.

Riversdale is also advancing a prefeasibility study for its nearby and bigger $2 billion Zambeze hard coking coal project, which holds more than 9 billion tonnes of resources.

Last year the company started investigating the long-term possibility that Zambeze could become a 90Mtpa run-of-mine operation.

China’s Wuhan Iron and Steel Corporation struck a memorandum of understanding with Riversdale over the project in mid-2010, but discussions have been put on hold since Rio’s takeover offer was launched before Christmas.

Under the proposed deal, WISCO aimed to gain a 40% stake of the Zambeze project for $US800 million, plus an option to purchase up to 8% of Riversdale’s shares at $A10 each.

Riversdale also owns the Zululand anthracite colliery in South Africa, which produced 185,912 tonnes of saleable output in the December quarter.

This morning Rio extended its $16 bid by 14 days to March 4.

Shares in Riversdale are down 2c to $15.83 this morning.