As with ore mining operations it is necessary to leave an underground mine in a socially responsible state when mining ceases because underground mining has a smaller foot print in surface mining this is generally a less onerous task. However, there are still a number of important issues that must be dealt with and some of these are specific to underground mines. We’ll have a look at these in our final topic. In module one, we looked the general issues related to mine closure with the specific emphasis on surface mining. Generally underground mines produce a flawless waste rock than surface mines and so issues related to final landforms are fewer. Unlike surface mining the volume of voids created during mining is greater than the amount of waste rock produced. So, it is usually possible to incorporate some or all of the waste rock produced into the void to create it underground. In fact, clever operational designs includes provision for back filling work out stopes as mining progresses. In this way, they may be little or no need for handling of waste rocks at closure. In some cases, tailings from the beneficiation process can be pumped directly back down the mine. But in other cases, it’s necessary to store tailings depositors at the surface, tailings damp as was described in module one. In these cases it is still necessary to keep the tailing damps to ensure long term containment of the deposited tailings after closure. It is very important that all entries into an underground mine are effectively sealed after closure as underground mines are even more dangerous environments when they are abandoned than they are when are operating. Depending on the topographic setting abandoned many fill up with water when operational pumping ceases. Flooded mines may produce sea pictures at the ground surface. The chemistry of the sea water will depend upon the chemistry of the minerals in the mine. Of particular concern are mined that contain sulphide minerals. If these are able to oxidize post mining, they will produce essence. Acidic waters seeping from abandon mines are known as acidic mine drainage. Acidic mine drainage must be addressed by limiting water entry into the mine preventing water egress from the mine or treating acidic waters to neutralize them. One of the undesirable legacies of underground mining is the potential for ongoing ground surface substances. The likelihood of substance depends upon the size and the arrangement of the stopes and the characteristics of the roof strata and the depth of the mining. While substance is more likely to occur soon after mining there is no time limit on when substance can occur. Due to ongoing damaging rocks and redistribution of stress, rocks left behind in an underground mine can fail at anytime. Inundation in an underground mine lead to weakening and degradation of the rocks in the pillars. The stall of substance very much depends on the geometry of the mine workings. Vertical stopes can collapse to create deep sink holes stall substances, room and pillar workings collapsed to form shallow sink holes and thorough. Long wall mining produces surface cracking and broad depressions relatively gradual surface coverages. In this course, we’ve introduced you to the role of the mining engineer through an overview of the mining process. As you may or may not have a technical background with prior exposure to maths, Physics, Geology and Mechanics we have necessarily tried to present technical issues of mining engineering without getting too technical. So, don’t be deceived into thinking that mining engineering is just a bunch of nice ideas and pretty pictures. Behind nearly all of the topics we have covered are forming equations that allow the mining engineer to quantify the issues that we’ve discussed and to apply them to specific situations in particular mining operations. Like all branches of engineering, mining engineering relies heavily on maths and science and is simply no way of avoiding this. We hope you’ve enjoyed our presentations. Please remember that mining engineering is a broad discipline with many many faucets and its very hard to do justice in four short modules.
https://youtu.be/7NyrE-jD4cM