Johannesburg - South African platinum miner Impala Platinum Holdings Ltd said on Monday first-half profit likely plunged by as much as 79 percent, hit by rising costs and lower output.

The world second-largest miner of the white metal also said the results were weighed by a 603 million rand ($68 million) writedown on payments it is owed.

Implats said headline earnings per share would be between 120 and 138 cents, or 76 percent and 79 percent lower in the six months to end-December.

By 10:48 SA time, shares in the company fell 3.4 percent at 159.55 rand, lagging behind a flat JSE top-40 index.

Headline EPS, the main profit measure in South Africa, strips out certain one-time items. - Reuters