Every token holder in Proxima is a “miner” of sorts. Yet it is not a mining as known in PoW.
They receive inflation proportional to their token holdings for their contribution to the consensus and cooperation with others. It is achieved by running so called sequencer chains on the ledger.  Details in WP.
Initially, supply will be premined and distributed to bootstrap token holders via ICO. Then supply will inflate along the activity on the network with halving rules.