South Africa's Impala Platinum's refined platinum group metal (PGM) output declined 4% in the year ended June 30, missing its production forecast amid persistent electricity cuts, the company said on Monday.

The production decline and weaker metal prices will see Impala's headline earnings per share (HEPS) decline by more than 20%, compared to the 38.53 rand ($2.07) reported last year.

Impala said in a production update its refined PGM output for the year was 2.96 million ounces, just missing out on its production guidance range between 3 and 3.15 million ounces.

"Regional power constraints provided a notable impediment to operational continuity and delivery," Impala said.

Production of about 101,000 ounces of PGMs was deferred as a result of frequent power cuts and the resulting delay in restarting a refurbished furnace in the April-June quarter, Impala said.

Power cuts had also impacted Impala's operations in Zimbabwe, where its operations include the 87% owned Zimplats and Mimosa, an equally owned joint venture with Sibanye Stillwater.

Impala, which has recently taken control of mid-tier producer Royal Bafokeng Platinum's shallow, high quality assets, will release its annual financial results on Aug.31.

($1 = 18.6352 rand) (Reporting by Nelson Banya Editing by Bernadette Baum)