(ShareCast News) - Rare Earth Minerals, an investment company which focuses on lithium and rare element deposits, increased its stake in Bacanora Minerals to 19.8% with an 'on market' deal worth £4.5m.The AIM listed company agreed to buy a further 4.5m shares in the Mexican lithium miner for £4.5m, with payment due at the end of September.Rare Earth already held a 30% interest in two joint-ventures with Bacanora, Mexalit and Megalit, which held the latter company's concessions in the Sonora lithium project.Hence, due to the increased direct stake in Baconora it will now have an indirect interest of 19.8% in the La Ventana, La Ventana 1, and Megalit concessions.It will also have an increased total economic interest of 43.9% in Mexalit and its El Sauz, El Sauz 1 , el Sauz 2, Fleur and Fleur 2 concessions due to the increased Bacanora shares.The Buenavista and San Gabriel concessions, which are also held by Megalit and therefore Rare Earth has a 43.9% economic interest in Megalit.In early August, Rare Earth raised $15m through a loan note convertible into ordinary shares with $6.5m having been issued to date, with completion to be announced once all funds had been received, the company said in a statement.Bacanora was focused on concluding the Feasibility Study for the Sonora project in the first quarter of 2017.Shares in Rare Earth Minerals were down 1.27% to 0.78p at 1353 BST.