Jeffries, who turned 32 on Tuesday, has spent the last 10 years in Super League in two spells with both the Bulls and Wakefield.
His 86th appearance for Bradford against Catalan Dragons in Perpignan on Saturday will be his last as a professional unless the Bulls make the play-offs.
Jeffries, who will return with his family to the Newcastle district, said: "I'll be playing for Kurri Kurri Bulldogs, which is more of a local competition but is pretty much classed as the best in New South Wales below the NRL and the Under-20s.
"Through that, I've been offered a job in the mines, which allows me to earn the same sort of money I earn now for the rest of my working life if I want to stay in that industry.
"It's a no-brainer really. I don't know what my exact role will be just yet but I'll be working in the mining industry and I know that when I get there I can diverse into certain categories of mining - I can be open-cut or underground.
"Coal mining is a massive industry in Australia and people are queuing up to get into that line of work so I'm grateful to have landed this job. I've loved playing for Wakefield and Bradford but starting a nine-to-five job and living in a country I've not lived in for 10 years represents a new challenge for me now."
Jeffries played in Sydney for St George Illawarra and Wests Tigers before joining Wakefield in 2002 and recently made his 250th appearance in the British game and scored his 100th try.
Bradford coach Mick Potter said: "He has given great service to both the Bulls and the Wildcats. I would like to thank him for what he has done for the club and wish him and his family every success in the future."
Jeffries is the second of 17 out-of-contract Bradford players to announce their departure from the club, whose Super League future remains uncertain as they wait for the Rugby Football League to ratify the takeover by local restaurant owner Omar Khan.
- Super League