Abstract: According to the characteristics of mining converted from underground to surface, we studied the open-pit and underground developments in one mine, and put forward two combined developing forms in the mine with its mining converted from surface to underground, including the end slope combined developing and pit bottom combined developing. Additionally, combined with the actual mine production geology conditions, we demonstrated the expansion feasibility of the mine, and used relative payback period to evaluate the economic efficiencies of different developing forms from the aspects of investment and production costs, then selected out the combined developing method which is suitable for the mine converted from surface to underground mining. The results show that the end slope combined developing is accord with the production practice of the mine, which can not only make full use of the exiting production and transportation systems of the underground mine, reduce the construction investment, and accelerate the construction speed of open pit, but also can expand the mining scale and improve the economic benefits of mineral resource development. Thus, this developing form can provide support for the construction of high yield and high efficient mines, and has practical significance for the mines converted from underground to open-pit mining in the development process of China's coal resources.

Key words: mining converted from underground to surface, surface mines, development system, combined development, feasibility