Study On High Efficient Mining Technologies Of Transition From Open-pit To Underground Mining In Xiaowanggou Iron Mine

Presently, china’s industrialization process is being in the high speed development and requires tremendous steels. But demand exceeds supply for many years, it is urgent to research high efficient mining technologies and to increase independent development of exploiting iron resources for keeping national economy development healthy. Currently, more than80%of iron ores are mined by deep open-pit mines which are being or will be transferred to underground. Therefore, it is significant to study on high efficient mining technologies of transition from open-pit to underground.Xiaowanggou iron mine is being transferred from open-pit to high efficient underground mining in recent years. Its production capacity of open-pit mining is annual300,000tons and underground mining is annual one million tons. Thickness and dip angle are small at the top of orebody and orebody trend is not enough long, which result in narrow free working space to underground and deficient stope in first mining section. So it is difficult to achieve annual one million tons of production capacity by general methods.According to ore deposit conditions, this paper study a high efficient mining technique based on three rules (granular rock flowing rule, rock mass caving rule and ground pressure activities rule), which solves two problems of output connection and high efficient underground mining well.Firstly, it is presented that based on easy-caving character of rock mass, the whole orebody is divided into three mining areas by continuous caving area. It makes production capacity of Xiaowanggou iron mine increase to annual2.2million tons from1million tons in original designed. Secondly, an improved sublevel caving method that retreating form foot wall to hanging wall and extending the mining area in foot wall by trench and inclined incise groove, effectively controls the rate of ore loss and dilution of gently inclined and inclined ore body. Thirdly, the method of making roof naturally caving to form overburden through controlling the shape and area of mined region in first mining section, reduces mutual influence scope between open-pit and underground and extends time of open-pit and underground mining at the same time, gains the expectant purpose of form overburden safely and efficiently.Besides, through optimizing open-pit and underground mining technologies, ultimate boundary is designed according to convenient for exploiting and benefit maximization, and assistant project are adopted to accelerate the underground mining process, therefore, the result is realization of output dramatically increased year by year at the transition time from open-pit to underground.In sum, these high efficient technologies presented in this paper include divisional mining method, forming overburden by induced caving, controlling ore loss and dilution in footwall, optimization of open-pit ultimate boundary, optimization of structure parameter and so on. Meanwhile, theoretical research and production practices show that these technologies not only are indispensable in safely and efficiently transferring from open-pit to underground mining and gaining huge economic benefits in Xiaowanggou iron mine, but also the valuable experience and all of these can be provided for increasing output, reducing cost, safely and efficiently mining in other iron mines which in transition period and other underground iron...