BUZZ-Sherritt International Corp: Lower mineral grades
** Canadian miner's shares down 10.6 pct at C$3.12
** Company says overall grades have decreased to 0.85 pct nickel from 0.94 pct and to 0.07 pct cobalt from 0.08 pct for proven and probable mineral reserves at its Ambatovy mine
** Says proven and probable mineral reserves have increased by an aggregate 20.5 million tonnes to 190.4 million tonnes from its 2011 report
** Sherritt owns 40 pct of the Ambatovy nickel mine in Madagascar, which has an annual design capacity of 60,000 tonnes of nickel
** Up to Monday's close, shares had fallen nearly 6 pct this year
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