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Mining activities and tectonic ripples

Sand Mining

Sand Mining

For so many years, illegal and unregulated mining activities have gone on in Nigeria to the disadvantage of the country and now, it is beginning to look like mother nature is whispering its disagreement for our indiscretion in this regard. Residents of Saki in Oke Ogun areas of Oyo State, recently experienced vibrations at Medinat, Veterinary and Ogbooro settlements. The most recent tremor was in Koi community in Southern Kaduna. A lot more needs to be done concerning tremors occurring in some parts of the country lately. Geophysical surveys have identified a fault line that runs from Ifewara in Osun State and Zungeru in Niger State.

This column, this week attempts to look at what could trigger such tectonic activity in an otherwise tectonically inactive region. What is mining and what is a tremor? Is there any relationship between mining activities and tremors? If there is, what can be done to reduce the losses if not avoid it entirely? Mining is the extraction of valuable minerals or other geological materials from the earth from an ore body, lode, vein, seam, reef or placer deposits which form the mineralised package of economic interest to the miner. Tremors on the other hand, are a relatively small or short-lived movement of the earth’s surface caused by the same forces that produce earthquake.

According to the journal, Analysis of Impact of Mining Tremors on Surface Sunsidence, mining tremors characterises the dynamic phenomena which is similar in its nature to earthquakes. However, they are localised and related to mineral deposits exploitation. Disturbed equilibrium of geo-mechanics by mining operation produces this type of phenomenon. Mining activity induces mechanical stress occurring in the rock mass. The effect of high pressure on the rock mass results in tremors.

As a result of vibration caused by the mining tremors, there could be destruction of facilities located in the zone of influence of the tremor. Mining tremors generate elastic waves that can cause deformation, displacement , vibration and usually have an adverse effect on the inhabitants. Induced mining tremors waves may also lead to the damage to buildings and infrastructure in the area of the epicenter (the point where the tremor originates). In a research article by Messers A, McGarr, J Bicknell, E Sembera and R.W.E Green titled, Analysis of Exceptionally Large Tremors in Two Gold Mining Districts of South Africa, the researchers were able to establish the direct relationship between Mining and earth tremors in areas along fault planes and areas with no fault planes.

In the journal of Natural Resources and Development, Serbia’s unabated quest for coal causes tremors among mining communities was extensively discussed. In the journal was the direct relationship between mining for coal in Serbia and earth tremors that happened in Radljevo, a village South West of Belgrade, Serbia. The Vitomir Simic who works in the nearby Kolubara coal mine tells the story of how the relentless quest for coal has expanded the boundaries of the mines, threathening whole villages and causing the landslides and tremors that have destroyed homes like his.

Like many others from the villages in the Kolubara basin, Simic has been displaced by the very mine he works for. Tensions between the inhabitants of the mine areas and government reached a peak in 2011. According to the president of the village council and a community activist with the Ecological Society Vreoci, a local non governental organisation, Zeljko Stojkovic, “Our demands was first, they give us a plan for collective resettlement including public infrastructure and not first, the graveyard and leave people here with all these pits.”

To mitigate against future reoccurrences, at least in the area of limiting the damage done to the environment within the mine area, microseismic systems could be installed as is done in South Africa. This is done by assembling an array of geophones around the mining operational areas. The geophones listen to the primary and secondary waves arrivals from the naturally occurring vibrations. This helps in determining where the highly stressed zones are in the hanging wall or in the pillars and from there, it is easier to predict where the next burst or tremor will occur which thereafter helps in making a quick decision on de-stressing and/or evacuation.

Another area where the effect of the tremor on inhabitants can be reduced as seen in the case of Serbia, earlier discussed, is the need to relocate whole village(s) and town(s) from areas where active mining is being practiced. Again, illegal mining which is the direct cause of what is presently being experienced in some parts of the country should be discouraged with the sector structured and regulated. That way, practitioners will be well aware of the rules of engagement and must adhere to such but of course with eagle-eyed oversight.

It has been established that mining triggers of tremors. it is therefore, incumbent on the Federal Government of Nigeria to incorporate in its mining roadmap measures to reduce the losses posed by mining at a time when solid minerals is looking more like the next cash cow. As we are excited about new discoveries in the sector and are eager to quickly turn such discoveries into sustainable revenue stream, we must find ways to reduce if not avoid the tectonic ripples associated with mining activities!
.Kayode Adeoye is an energy expert in Lagos.

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