The deposits are expected to last at least a quarter of a century, and have between 1.2 and 1.5 million tons of ore, from which rough diamonds are extracted.
"The last time Russian diamond deposits of this size were found was 10 years ago," Alrosa's spokesman said.
The deposits are in the Sakha republic, where almost all of the country's diamonds are found. Alrosa controls 97 percent of all Russian diamond output and has operations in Angola. It mined around 50 million tons of ore last year.
The diamond monopoly's president, Sergei Vybornov, said in May that company still had plans for an initial public offering toward the end of this year, but declined to say where.
The Kremlin and the Sakha regional government each control around half the company.
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