Study On Combination Method Of Open Stope And Sublevel Caving For Steeply-inclined Thin Orebody Of Gongchangling Underground Mine

The underground ore resources of Gong Changling Underground Mine are sedimentary metamorphic magnetite deposite,containing two iron zones for a total of six orebodies that have stable to unstable ore rock between hanging and lower walls.For thickness greater than 8 meter ore bodies,non-pillar sublevel caving method was used and less than were abandoned leading to massive losses of ore.Therefore,we used "three laws of mining" adaptability high-efficient mining theory including bulk movement,collapse of rock mass and ground pressure activities,analyzing ore-rock stability,attitude and the characteristics of impact earth pressure and so on,systematically studied a safe and efficient mining method for steeply-inclined thin orebodies in Gong Changling underground mine.Firstly,according to stability grading evaluation results of the deep rock mass and the characteristics of ground pressure in underground mine,the mining method was designed as "route mining".Secondly,the best choice have determined to use the way of mined-out area ore drawing since the angle of ore body footwall was greater than the drawing-out angle of the fragmented ore/rock bulk under the stope and less than under the overlaying rock.Thirdly,the same equipment for mid-deep holes blasting and scraper for ore drawing were applied based on convenience of the near-by thickness ore bodies with non-pillar sublevel caving method.Fourthly,depending on the demand that ore rocks of mined-out area created by caving should be reclaimed at next sublevel and the overburden is easier to form because of surrounding rock falling when its area reaches a certain quantities,a recovery level of ore at the bottom of stopes was proposed.Therefore,the open stope and caving combined method was presented characterized by the mid-deep hole caving and face-end ore-drawing.And on this basis,according to geological conditions of steeply-inclined thin orebody in Gong Changling underground mine,an instability model was built to analyze the instability conditions of the rock surrounding rock around the open stope,and the estimating methods for open-stope sizes were achieved.At the same time,the impact waves induced by the falling rock were discussed by experiment.For doing that experiment,we developed the hanging thick iron plate falling model and an automatic measurement method for wind speed of impact waves.And then the rules of a sudden and sharp falling of the roof and how the wind speed of the impact waves with initial height and terminal distance of the falling body were simulated and analyzed.We also set up a calculation model,for testing the impact wave,to provide evidence for certain structure parameters and safeguards in the stopes by open stope and caving combination method.The open stope and caving combination method was carried on the industry test in-220-meter level.According to the results of an instability model and falling impact model,one transportation level was designed once every two mining levels.It was to remain some blasted ore to block the drift outlet and just show the goaf at the second mining level to prevent the impact of air flows induced by the rock falling.Through the trials in recent three years,the surrounding rocks were naturally and expectably falling after being minied completely as plan,when the second transportation level was completely mined.During the caving mining period,the ends of the routes were never empty.impact waves never affected the mining face in the whole process.The recovery was 78 percent and dilution was 10.63 percent and good technical and economic indexes were attained.The result of experiment shows that the computation precision for an instability model of surrounding rocks and a model for impact waves presented in this paper has satisfied the requirement of the open stope and caving co:mbination scheme design and production management.We thus built the open stope and caving combined method that met the conditions of steeply-inclined thin orebody in the underground of Gong Changling underground mine and can be used to excavate thickness less than 12 meters blind ore bodies,obtaining safe and high effective production results.