Not wanting to be a smartass on you Graham, but..
From the BLK OP:
I suspect the OP has cloned BLK and now wants to mine the first blocks. So my advice would be to use poolers cpuminer to get his chain moving.
I found it
https://bitcointalksearch.org/topic/rads-radium-decentralized-identities-custom-assets-elections-and-more-1333026
and it
https://bitcointalksearch.org/topic/annpayah-crypto-pay-hubtech-support-apps-and-more-1345321
and it
https://bitcointalksearch.org/topic/warp-something-different-vpn-wallet-beta-release-bittrexyobit-1329494
how these altcoins mine first blocks and for pos?