As China warmed up to the Taliban regime by stepping up aid and diplomatic support for Taliban's global recognition, Chinese firms are busy exploring contracts to exploit resource-rich Afghanistan's mineral deposits, official media in Beijing reported today.   Representatives of several Chinese companies have arrived in Afghanistan on special visas and are conducting on-site inspections of potential lithium projects, while others have made contacts about such projects, Yu Minghui, director of the committee, which has been helping Chinese companies explore business opportunities in Afghanistan, told China's state-run Global Times.