BHP will spend a further $US345 million ($510 million) on its polarising Canadian potash project, saying the spending is required to help it decide whether to go ahead with a full development of the mine costing more than $US5 billion.

The extra money for the Jansen potash project came as BHP retained its full-year production targets for all major product groups, despite making a slow start to the year in its Australian iron ore and coking coal divisions.