Sunday, 14 December 2014

Searching for abandoned mines: breaking new ground, literally! ... by Kirstin Lemon

Ballylig in Northern Ireland is home to one of many abandoned mines found in Co. Antrim. Worked from as early as 1872 it was originally exploited for its iron ore before closing just after the First World War. As is the case with many abandoned mines, there are no mine plans for Ballylig, although a brief inspection during the Second World War led to the creation of a partial sketched plan indicating that the mine workings extended at a shallow depth under a public road.

Given the lack of knowledge about the site, it is not surprising that farmers living near by didn’t give a second thought to the dangers posed by underlying mine workings.  However, in  2013, disaster struck when part of the mine collapsed as a tractor and its slurry tank working on the overlying field, and fell in to the underlying void. The farmer was uninjured but quite shaken by the experience.

Kieran Parker on site at Ballylig
The Geological Survey of Northern Ireland (GSNI) work with the Department of Enterprise, Trade and Investment (DETI) to look after abandoned mines and survey work began immediately to try and find out whether there was the potential for further mine collapses. The results were conclusive; there was a strong possibility that this could happen again. A programme of works was put in place to stabilize the area, with the public road being the prime area of concern. However, with no mine plan and access through the mine deemed unsafe, this was going to prove difficult.

BGS scientist, Kieran Parker with responsibility for monitoring abandoned mines in Northern Ireland, had been looking after the site at Ballylig. The solution seemed to be to drill ‘blind’ holes into the approximate location of the mine and hope that it was found before the cost of the works escalated. But Kieran decided to bring in the help of BGS scientist, geophysicist Mohammednur Desissa, and use a potentially more effective method.

Results of the geophysical magnetic survey showing the proposed
location of mines /adits with suggested locations for drill sites
Kieran and Mohammednur conducted a geophysical magnetic survey on site to see if they could detect the shallow underground voids that would indicate the location of the mines. The theory behind this is well-known but this method of mine location had never been used in Northern Ireland. The results indicated a ‘room and pillar’ mining method with the extent of the mine roadways greater than previously thought. Confident in the results, targets were chosen to locate the mine location at the points either side of the road.

It was time to put this theory to the test and work began to try and locate the mine. Kieran Parker gave a brief update from the site:

The drill rig on site at Ballylig 
“Using the map produced using the data from the geophysical survey, drilling started on Monday 8th December 2014. The first target on the first day was a success with the mine roof encountered at 11m depth and mine floor at 12.5m. A further two boreholes had to be drilled and each of them was successful. Given the fact that the mine voids are no greater than 2m in width, precision was of utmost importance and was made possible by the geophysical survey beforehand.”

With the mine roadways now located, remedial work is currently ongoing to stabilize the public road.

By using this groundbreaking technique of mine location, a huge amount of time and money was saved, as the alternative was to drill ‘blind holes’.  In the current economic climate it is more important than ever to be innovative and makes the work at Ballylig an important example of the practical applications of geoscience. 

For more information on the abandoned mine work carried out by BGS scientists at the GSNI then please contact Kieran Parker at kieran.parker@detini.gov.uk 

1 comment:

Tim Archer - Reid Geophysics said...

Good job, Kieran and Mohammednur. Great to see mainstream geophysical techniques being used in an unconventional application!