AIM-listed mining group Rear Earth Minerals (REM) has increased its stake in joint venture partner Bacanora Minerals to 11.27% from the previous 10.18%.The group upped its stake in Bacanora, its partner in the Sonora Lithium Project in Mexico, through further on-market purchases totalling £0.328m. Shares in REM jumped on Wednesday, after the firm reported that the mineral resource for the Sonora Lithium Project in northern Mexico had been increased by 37%, to a new total of 3.28m tonnes of Lithium Carbonate Equivalent, and has been upgraded from the inferred to indicated category. Chairman David Lenigas said: "We continue to steadily increase our strategic shareholding in Bacanora Minerals, as we seek to increase REM's exposure to the Sonora Lithium Project in Mexico."As of 13:23 the share price had risen 1.4% to 1.04p.WS