87% Owned by Implats, page-2

Ok, I found a 2002 article in the Fin. Rev. which explains why:

The transaction took Implats' holding to 30.16 per cent on a fully diluted basis. The South African company was not required to make an offer to remaining shareholders, as Zimplats was not covered by any takeover protection rules, including the 19.9 per cent takeover threshold applying in Australia.This was because Zimplats is registered in Guernsey in the Channel Islands but is managed in Zimbabwe, meaning the UK Takeover Code did not apply. As a foreign listed company on the ASX, the Australian Corporations provisions on takeovers also did not apply.