The total capital commitment amounts to $382,962,003.08 million between both miners. Among Blackrock's hundreds of mutual funds and ETFs, broad indexes like its iShares Russell 2000 ETF, and its iShares Expanded Tech-Software Sector own the crypto miner shares.

The disclosure comes after Fidelity Group recently revealed that it had taken similarly large stakes in the bitcoin miners. Valley Forge, PA-based Vanguard Group is currently the largest shareholder in Marathon Digital and Riot Blockchain with BlackRock leading behind after the disclosure of the recent filing.