The Association of Mineworkers and Construction Union (AMCU) said the company failed to take precautions two avoid injuries at its mines earlier this week.
Zimbabwe has attracted intense interest from miners with a promise of favourable terms as it seeks to reboot its economy after veteran leader Robert Mugabe was ousted last year.
By mid-morning, Lonmin shares had lost 5.6% of their value in London, while Sibanye’s were down 4.9% in Johannesburg, even though the companies announced they had received the approval of the South African Reserve Bank (SARB).