* Ban to hit exports to China, South Africa
* Zimbabwe exports 600,000 tonnes in 18 months to April
* Ban to help build internal refining capacity
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HARARE, April 19 (Reuters) - Zimbabwe has banned the export of chrome from Wednesday as it looks to build internal refinery capacity, the Ministry of Mines and Mining Development said on Tuesday.
Zimbabwe, along with South Africa, holds about 90 percent of the world's chromite reserves and resources, according to the U.S. Geological Survey, and the ban will affect exports to China and South Africa.
There are three large-scale ferrochrome miners in Zimbabwe, including Zimbabwe Alloys and Zimasco, which is owned by China's Sinosteel. Zimasco recently told state media it planned a $300 million investment in the second half of 2011 to ramp up output and build a new smelter.
Zimbabwe already has three smelters that have the capacity to handle 1.5 million tonnes of chrome.
The ministry in November 2009 allowed the export of chrome for another 18 months, a period which will expire on Wednesday.
"We wish to advise all exporters of lumpy chrome that with effect from this date, no more exports of shall be entertained", the ministry said in a notice published in the local newspapers.
Zimbabwe exported 600,000 tonnes of chrome in the 18 months from November 2009, mostly to China and South Africa, according to official figures.
(Reporting By Alfonce Mbizwo; Editing by Ed Stoddard and Jane Baird)