Tue Apr 12, 2011 1:58pm EDT
* Deal puts Mercator on path to becoming a mid-tier player
* Mercator shares fall 9.5 pct; Creston shares jump(Adds details on deal, background, share price move)
By Euan Rocha
TORONTO, April 12 (Reuters) - In a bid to expand its copper and molybdenum resource base in Mexico, Mercator Minerals (ML.TO), a junior Canadian base metals miner, said on Tuesday it plans to acquire Creston Moly Corp (CMS.V) in a friendly cash-and-stock deal valued at about C$195 million ($203 million).