According to a regulatory filing, Kerimov bought a 2.86 percent stake or almost 37 million shares on April 29, when that holding would have been worth roughly 100 million pounds ($156 million).
He raised that to 2.96 percent the following day, according to a filing on Wednesday, buying an additional 1.3 million shares at just over 271 pence each.
A Kremlin-connected tycoon from Russia's southern province of Dagestan, Kerimov is a major investor in a range of Russian companies, with holdings including the single largest stake in Polyus Gold, Russia's biggest gold miner, and holdings in fertiliser group Uralkali and homebuilder PIK .
He has also been an opportunistic investor in stocks outside Russia.
ENRC shares are trading close to their 2008 lows after being buffeted by cooling metals prices, corruption investigations and boardroom scuffles. The were trading at just under 268p by 1120 GMT, down 2.5 percent on the day.
Kerimov's investment vehicle, Nafta, declined to comment. ENRC's trio of founders said last month they were considering a buyout of minority shareholders in the group. They have until May 17 to declare whether or not they intend to bid.