RAPAPORT... Petra Diamonds is investigating allegations that security guards at its Williamson deposit in Tanzania carried out deadly violence against local artisanal miners.At least seven deaths and 41 assaults have taken place at the Williamson mine since Petra acquired it in 2009, according to a report UK-based nonprofit RAID released Thursday. Some of the alleged victims had entered land belonging to the vast Williamson site, while others were mining in adjacent areas, a RAID spokesperson explained."The shocking levels of violence and mistreatment at the Williamson mine clearly cast doubt on the ethical assurances so often repeated by Petra Diamonds," said Anneke Van Woudenberg, RAID's executive director.RAID based its findings on more than 14 months of research and 118 interviews with local residents, security personnel and other informants. In "almost none" of the interviews did anyone describe the alleged victims as being armed or threatening violence at the time of their injury or death, the organization claimed.Petra has formed an independent committee to look into the matter, and has hired an external adviser to oversee the probe, which the company expects to complete by the end of 2020. "The board of Petra Diamonds finds the allegations of human-rights abuses at the Williamson mine in Tanzania to be deeply concerning, and is taking the matter extremely seriously," Petra said in a statement. "Petra has been engaging with RAID since being made aware of the allegations, and has requested that RAID makes available to Petra the information at its disposal to allow Petra to investigate further."In September, UK law firm Leigh Day filed a legal claim against Petra and its local subsidiary, alleging similar abuses at Williamson. The UK court filing was on behalf of more than 30 Tanzanian nationals.Image: The Williamson processing plant. (Petra Diamonds)