Cobre (ASX:CBE) said its Chilean unit Sierra Cobre executed amendments and restatements of key agreements for Cobre's investment in the Sierra Atacama copper project to implement a further $12 million capital raise by Sierra Atacama to pay for certain debts, according to a Tuesday Australian bourse filing.

The company said Sierra Atacama will issue new convertible non-voting preference shares, which, subject to certain conditions, will convert into ordinary shares, with completion of the capital raise expected to result in Cobre Chile owning 54.38% of all issued share capital in Sierra Atacama, up from 45%, assuming Sierra Atacama's minority shareholder does not participate.

The amendments allow Cobre Chile to acquire a total 63.5% interest and enhance its rights to increase its interest beyond 63.5%, the filing added.

The purchase price if the control option is exercised is $12 million, up from $10 million, with the control option to be exercised by Dec. 31, it added.