How does it make any difference if the country is foreign owned or not ? The contracts are signed with South African companies which are subsidiaries of Billiton. Almost all SA major companies are foreign owned, they still pay taxes and employ most of the workforce.
Industrial buyers (such as the car industry which is a massive employer in SA) have long term contracts which are negotiated under the prices of the international markets because the buyer commits to certain quantities over a certain period.
Importing it would incur:
- Massive transportation costs (aluminium and metals in general are extremely expensive to transport which is why the big consumers are located close to the smelters
http://www.talco.com.tj/en/world-aluminum-industry/production-cost)
- Import duties
- Logistics and supply chain unreliable
Which makes that most likely the industrial buyers will not invest more in SA and will get out of SA after their plants lifespans.