JOHANNESBURG, Feb 28 (Reuters) - Harmony Gold, South Africa's biggest gold miner by volume, says it will pay a record interim dividend after output of the precious metal jumped 14% in the six months through December.

The Johannesburg-based gold miner on Wednesday declared an interim payout of 147 rand cents per share, increasing returns to investors after its headline earnings per share soared 226% to 956 rand cents in the six months.

Harmony is among South Africa's few remaining gold miners squeezing profits from some of the world's most costly, ageing and deepest gold mines.

Gold output jumped 14% to about 832,000 ounces buoyed by a 30% increase in production from its Mponeng mine. Harmony said it also approved a plan to extend the life of Mponeng, the world's deepest gold mine, by 20 years from seven currently. (Reporting by Felix Njini Editing by Mark Potter)