Johannesburg-based Impala tabled an offer to acquire all outstanding RBPlat shares in January 2022, but was held back for over a year by a rival bid from Northam, which was terminated in April.

The sale of Northam's 34.5% holding will raise Impala's stake in the smaller platinum-group metals producer to 91%.

Shares in Northam, which said it will receive 9 billion rand ($505 million) in cash and about 30 million Impala shares for the transaction, were up 8.68% at 0713 GMT.

Impala spokesperson Johan Theron said the sale "represents the best possible outcome for all parties and our focus now shifts firmly to integrating the business and delivering value for our shareholders."

Impala now has a "clear path" to getting to 100% ownership of RBPlat, with its cash-and-shares offer open to other remaining investors, he added.

RBPlat has shallow and mechanized mines that both Northam and Impala wanted to gain control over.

RBPlat's mines are adjacent to Impala's own ageing, costly and deep-level shafts at the Rustenburg complex.

Citigroup analysts said the deal will remove an investor overhang and allows Impala to integrate RBPlat to its existing assets and fully realize synergies from it.

Northam said the stake sale could enable it to pay its first dividend, implement share buy backs and cut debt and offers the chance to significantly boost its balance sheet and liquidity position.

While Northam has sold the shares at a loss, the price it received for the stake is attractive due to the decline in platinum metal prices, RMB Morgan Stanley analysts said.

"We believe that Northam's balance sheet position has been an overhang into the (platinum price) downturn. This is now largely resolved," they said.

($1 = 17.8159 rand)

(Reporting by Felix Njini in Nairobi and Nelson Banya in Harare; editing by David Evans and John Stonestreet)

By Felix Njini