static const int CUTOFF_POW_BLOCK = 220000;

if (IsProofOfWork() && nHeight > CUTOFF_POW_BLOCK)
     return DoS(100, error("AcceptBlock() : No proof-of-work allowed anymore (height = %d)", nHeight));

https://github.com/mintcoinproject/mintcoin/commit/dad79713d4172a569238de1b736abfbf307acfbd