(Ph) 2. Geology
Phalen Colliery was situated in Nova Scotia near the the town of New Waterford. It occupied a position close to the centre of the Sydney Coalfield. The Sydney Coalfield is located along the northeastern coastline of of Cape Breton Island. It is predominantly a submarine coalfield and all remaining coal resources are located beneath the floor of the Atlantic Ocean. The most productive coal seams are found within the Sydney Mines Formation of the Pictou Group. The seams are Westphalia to Stephanian in age, and formed during the Carboniferous Period. Eleven major coal seams are present, and range from 0.8 to 3.7 m in thickness. Total insitu coal resources are estimated to be about 2,4 billion tonnes. The estimated recoverable reserves are about 550 million tonnes. The coal measures strata bear the characteristics of deposition in a fluvial environment on a slowly subsiding coastal plain. Full marine influence is not evident at Sydney, but locally restricted marine transgression occurred as suggested by brackish fauna.
At Phalen Colliery, the Phalen coal seam was the main target of exploitation. Mine workings were located about 138 m stratigraphically below the Harbour Seam which had been extensively worked, and became flooded in the past. The interburden between the Phalen and Harbour Seams contains two thin unmined coal seams and two major units of sandstone. The remaining strata is composed of Mudstone, Siltstone, Limestone, and thin beds of sandstone. Rapid vertical and horizontal changes in roof lithology is common. The Upper Sandstone Unit is about 90 m above the Phalen seam. The Lower Sandstone Unit is within 30 m of the roof of the Phalen seam. The 30 m of roof strata immediately overlying the Phalen seam is composed of three prominent stratigraphic facies:
(i) Backswamp Facies (less than 1 m) and
(ii) Flood Plain Facies (7 ~ 15 m thick),
(iii) Channel Facies (up to 10 meters thick).
Where fully developed, these facies occurred above the seam in the sequence indicated. Occasionally one or both of the first two facies may have been absent due to non-deposition or have been removed by erosion.
The Flood Plain Facies and Backswamp Facies are well laminated with natural bedding planes and listric surfaces. These facies were very prone to bed separation and as a result displayed stand-up times of less than an hour. The thin, intercalated, sandstone beds that generally occurred in the Flood Plain Facies frequently exhibited core disking. Where these two facies were encountered on longwalls, caving was good.
The composite thickness of mudstone and siltstone varied from 3.5 to 8.3m across much of Phalen. Along the topgate of #7 East panel, this strata was generally thin because of the increased thickness of the Lower Sandstone Unit. Locally, the sandstone contained lithic clasts and coal shards (but not clearly defined weak planes).
(Ph) 2.2 Geological Structures
The mining operations within the Sydney Coalfield has been spared the effects of tectonic faulting. Major faulting is only known along the eastern and western margins of the coalfield. The main structural features of the coalfield are its folds, which plunge gently to the northeast and fan out beneath the floor of the Atlantic Ocean. The gradients on the flanks range from 2 to 50 degrees, but generally do not exceed 10 degrees.
No major faulting was encountered at Phalen Colliery during its operation. Bedding planes and discontinuities were the major geological structures that had to be dealt with regarding the roof strata.
In regards to the hydrogeology of Phalen Colliery, the sole source of insitu water was the pore spaces within the sandstone strata. Water inflows at Phalen Colliery (up to 1500 gallons per minute) were derived from Harbour Seam Workings (flooded, abandoned workings 138m above the Phalen Seam). The water from these overlaying flooded workings entered Phalen Colliery through a series of fractures and bed seperation cavities that formed during longwall mining.
Within the mining property, the Phalen Seam dips to the north at an average inclination of 10 degrees. ( Figure Ph1). Seam thickness averages 2.4 meters, but increased to 3 m, where a prominent stone split thickened near the roof of the seam. The coal posesses a high volatile "A" bituminous rank, and an average methane content of 10 m3 per tonne. The sulphur, and ash contents of the seam average 2% and 7.5% respectively. Phalen Seam coal is considered to be a high grade thermal coal, but also posesses good metallurgical coal characteristics.
Phalen Seam coal is bright banded and contains several distinct durain bands that serve as excellent marker beds for coorelation. Fusain lenses are common throughout the seam, and commonly contain pyrite. The coal is moderately soft and has a very well developed cleat system.
List of Figures
Figure Ph1: Phalen Seam and Hub Seam in a vertical plane.
Figure Ph2: Gently dipping strata in Sydney Coalfield.
Figure Ph3: Typical longwall setup.
Figure Ph4: Mine map of the Phalen Colliery.
Figure Ph5: Sketch of a retreating longwall panel.
Figure Ph6: Lithology of the immediate roof in #7 East Panel.
Figure Ph7: Interpreted roof strata in #7 East Panel.
Figure Ph8: Cutter roof along rib side of longwall gate.