MONTERREY, Mexico, Dec 10 (Reuters) - Mexico"s Cemex, one of the world"s largest cement companies, said Friday that the U.S. Department of Justice (DOJ) has closed an investigation against the company for a possible violation of anti-trust laws. Cemex (CEMEXCPO.MX) also reported that it was fined about 68 million euros ($77 million) by Spanish authorities following tax audits of its operations from 2010 to 2014. Cemex said it would appeal the fine. ($1 = 0.8841 euros)