OR/16/053 3D Model of Spireslack surface mine
| Ellen, R, Callaghan, E, Leslie, A G, and Browne, M A E. 2016. The rocks of Spireslack surface coal mine and its subsurface data: an introduction. Nottingham, UK, British geological Survey. (OR/16/053). |
To add to the BGS knowledge of the structure of the Glenbuck area, a 3D model has been constructed, based on mine data of the strata at Spireslack (Figure 34). Geospatial data collected during the underground and surface mining phases at Spireslack provide an accurate point cloud of XYZ data, allowing a 3D reconstruction of the Carboniferous strata at depth. The model was constructed using Move, the 3D geological modelling software (designed by Midland Valley Exploration). The 3D model of Spireslack described in this report is the result of an initial phase of work to pull together relevant geospatial data into a single space, in order to gain an understanding of the broad subsurface structure. Future refining of this model is anticipated following further analysis of the higher resolution data, such as photogrammetry and Lidar data. This section of the report describes the data used to build the model, the techniques used, and recommendations for future work.
Model datasets
The following datasets were imported into Move:
- DTM (trimmed to area of interest based on major bounding faults)
- 10k standard fieldslips: NS72NW, NS72NE, NS73SW, NS73SE.
- - Linework, faults and dip data digitised within Move
- Shapefile of the Spireslack main void (3D point cloud)
- Aerial photographs of site
- Traces of faults and dykes digitised in Geovisionary. Photogrammetry and Lidar scans were carried out on the south-eastern main face and north-western limestone pavement respectively. The data was loaded into Geovisionary allowing a fully georeferenced 3D view of the Spireslack main void to be visualised. The data is of such high resolution that individual faults and dykes can be digitised.
- Georeferenced scan of Scottish Coal Spireslack Geological Plan
- - Contours of Muirkirk Six Foot Coal, Muirkirk Nine Foot Coal, McDonald Coal and Gill Coal digitised within Move from scan
- Abandonment Plans from underground workings (contours and spot heights):
- - Muirkirk Six Foot Coal
- - Muirkirk Nine Foot Coal
- Excavation model — seam data for base of individual surface mined coal seams (contours and spot heights):
- - McDonald Coal
- - Muirkirk Six Foot Coal
- - Muirkirk 30 Inch Coal
- - Muirkirk Nine Foot Coal
- - Muirkirk Four Foot Coal
- - Muirkirk Three Foot Coal
- - Muirkirk Ell Coal
- - Faults
Modelled surfaces/volumes/faults
| Name of Modelled Surface | Lexicon Code — RCS |
| McDonald Coal | MCDC-COAL |
| Muirkirk 6 Foot Coal | MSIX-COAL |
| Muirkirk 30 Inch Coal | MTIP-COAL |
| Muirkirk 9 Foot Coal | MNFC-COAL |
| Muirkirk 4 Foot Coal | MFFC-COAL |
| Muirkirk 3 Foot Coal | MTFC-COAL |
| Muirkirk Ell Coal | MKEC-COAL |
Model workflow
The data for the abandonment plan and excavation model were provided in .dxf format. This was imported into Move, and manually sorted to keep only the geological information (‘coal lines’, ‘contour normal’, ‘contour prominent’ and ‘fault lines’) from the files within the .dbf file.
These XYZ files were loaded into Move creating a 3D framework of the worked seams. The contours (polylines) were resampled within Move at 1 m spacing (retaining original control points) and converted into a point cloud. These points combined with spot height data were collected into Move’s surface building algorithm and used to construct a 3D surface using the Delauney Triangulation method, in order to honour all of the data. Erroneous points and spikes were manually removed where they represented mispicked points within the data.
To identify faults from the XYZ data, the surfaces were colour mapped for curvature to identify discrete surface dip changes which may represent faults or changes in orientations across dykes. The outlines of faults or dykes picked in this method were drawn using the 3D line drawing tool to represent the location of faults to be later checked and cross-referenced with faults observed in the field.
Method:
- Import .dxfs into Move, and separate by attribute
- Extract observation points, contours and fault lines from data
- Resample contour data to 1 m nodes
- Convert resampled contour data to point cloud
- Build surfaces (Delauney Triangulation) from the point cloud
- Clean up erroneous points and triangles
- Use curvature analysis to draw eye into bumps on the surface which are likely to represent faults/dykes
- Using the 3D line drawing too, trace on faults surrounding differences in curvature or individually select triangles composing possible fault trace.
Model assumptions and limitations
The 10k geology sheet is based upon data from the older underground mine workings, and as such, has no record of the significant fold structure to the north-east of the fault. It was therefore assumed that for the purposes of building this model, the more recent 20th/21st century surface mine abandonment data contains the more accurate XYZ positions, as it was acquired using differential GPS on the bases of coal seams during extraction. When comparing the XYZ positions of the older mine working and surface mine abandonment plans, there is a 5–10 m difference in the Z value between the Muirkirk Six Foot Coal seam subsurface positions, whilst the dip and XY position are similar. In addition, a mismatch was noted between the mapped 10k geology sheet line work and the projected positions of the surface mine abandonment coal seam data to the DTM. For example, the difference in distance for the Top Hosie (McDonald) Limestone is around 35 m and for the Muirkirk Six Foot Coal seam, 18 m. Conversely, the older mine workings data has a better match, consistent with the original 10k geology linework being based on the older data.
Future modelling
The model is currently a work in progress and requires further work to refine it. The steps necessary to improve the model are discussed below.
- Fault and dyke traces digitised from the Geovisionary Spireslack project should be incorporated with the interpreted faults and dykes digitised from the mine plan XYZ data — how do they compare, and how do the fault and dyke traces vary across the now empty void, using the mine plan XYZ data as a guide?
- Currently the model is composed of areas of surfaces where mining took place — it would be appropriate to extend these surfaces so as to have a more complete model which shows the broader synclinal structure of the area. This can be informed by the 10k geological line work.
- Some of the mine abandonment modelled surfaces overlap each other in areas where faults are presumed. This is geologically incorrect and will be fixed in future modelling.