JOHANNESBURG (Reuters) - Harmony Gold Mining , South Africa's third-largest gold producer, on Thursday said most striking workers were back at work, a positive sign that the strike at its Kusasalethu mine was over.

Spokeswoman Marian van der Walt said while the company was still confirming the numbers, the turnout was positive.

Harmony had given workers until 12 a.m. EDT to return to duty or face sacking. Van der Walt said those who did not show up would be immediately dismissed.

The 23-day strike at its Kusasalethu mine has cost the company about 13,000 ounces in lost production.

Harmony is the latest case where the hardball negotiating tactics have succeeded in getting substantial numbers of strikers back to work.

Gold Fields has ended strikes at its three mines after issuing an ultimatum. AngloGold Ashanti reported the return of at least half of the striking workforce at its South African mines.

(Reporting by Sherilee Lakmidas; Editing by Helen Nyambura-Mwaura)