ZIMPLATS, Zimbabwe's biggest platinum miner, has warned shareholders about operational uncertainties in the country.

Analysts also expect investment to be hit by revelations about a Zimplats court dispute with the state over backdated royalties.

Zimplats said the Reserve Bank of Zimbabwe had not returned $34-million it owed the company. Last August outgoing CEO David Brown said the state had given "no indication" when or if the money would be repaid.

"Royalties for the period dating back to January 2010 have been accrued for at a higher rate than that provided for in the company's agreement," the company said.

This was the "subject of a legal dispute between the company and the tax authorities now before the courts".

Last month, Zimplats bankers were ordered to pay $28.3-million from its funds for outstanding royalty payments. Zimra said Zimplats continued paying royalties in 2010 at a rate of 2.5 percent when this had been increased to 5 percent.

Zimplats urged shareholders to exercise caution because of these factors, uncertainty over the indigenisation law and looming elections.

Aquarius CEO Stuart Murray, whose company owns the Mimosa Platinum mine jointly with Impala Platinum, said on Thursday regulatory risks of mining in Zimbabwe had risen markedly.

Zimplats blamed factors like the royalties bill and September's 61 percent hike in power tariffs for its operating costs rising 8 percent in the quarter.

The December quarter's operating profit was 68 percent down on the September quarter's as revenue fell 27 percent to $97-million, partly due to "weakening" international metals prices.

But Zimplats contributed $22-million in direct and indirect taxes, a 38 percent jump on the previous quarter.

Mimosa's output rose 3 percent to 104254 ounces and revenue rose 1 percent to $146-million "due to higher metal prices achieved".