The company now has until October 31 to conclude the deal that will see it take control of the AIM-listed miner's Nkout iron ore deposit in Cameroon in a £126mln deal.
It had already extended the date to the end of September.
Afferro shareholders vote on Monday to decide whether to give the takeover the green light.
"All other commercial details of the Arrangement Agreement remain unchanged," it added.
IMIC has been raising funds and strengthening its Chinese ties ahead of the acquisition.
Along with its partner African Iron Ore Group (AIOG), the company has struck an agreement with state-owned China Railways Materials (NYSE:CRM) to get its projects marketed in the People's Republic -the world's biggest importer of industrial metals.
Shares fell 2.4% to 30.5p each.
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