By Bloomberg MINING companies in Zimbabwe said a central-bank requirement compelling them to surrender more foreign exchange earned from mineral exports will push their operations to the brink. The Reserve Bank of Zimbabwe on January 8 announced that exporters must now hand over 40% of their foreign currency earnings, up from 30%, which is then paid out in the local currency. The country’s mining body said the move would create “a viability crisis” for the industry as members already face increased demand for payment in hard currency from various government agencies, suppliers and service providers. “On average, 60% of gross export proceeds are now taken by government departments and agencies, leaving inadequate forex resources for the mining firms to sustain operations,” the Chamber of Mines of Zimbabwe said in a letter to the central bank dated Jan. 19 and seen by Bloomberg.