Auckland methamphetamine dealer Say Tsong Lu has had a 12-year jail term added to his current prison sentence for his part in a drug ring run from inside a Christchurch prison.

Lu, a 39-year-old kitchen hand, was already serving a 10-year prison sentence on other drug-related offending. He had denied charges of conspiracy to supply the class A drug methamphetamine but was found guilty at a trial earlier this year.

In the various hearings the courts were told of a woman making repeated trips to Auckland to buy shipments of methamphetamine at between $12,000 and $13,000 an ounce to bring back to Christchurch.

One hearing was told of $100,000 cash changing hands on one of these visits.

Judge Jane Farish today sentenced Lu to 12 years in prison and imposed a seven-year non-parole term.

She said the evidence given by Lu at trial had not stood up to scrutiny. He became involved in the drug supply "purely for economic benefit", she said.

Lu met Dean Waka Nathan in prison during an earlier prison term and the pair stayed in touch following Lu's release.

Nathan is already serving a life sentence for a gang murder in Christchurch. He has admitted running the drug ring from inside Christchurch Men's Prison using an illicit cellphone which has never been found.

Nathan is also due for sentence on July 30 after a hearing to decide the scale of the drug shipments involved.

The police eventually shut down the drug ring in February 2009 with their Operation Fudge surveillance and interception investigation.