---

August, 1944

---

The dip to the east is very slight and the surface relatively flat until, about two miles from outcrop, there is a range of hills and in a very short distance the overburden increases from about 40 ft. to over 100 ft. in thickness. Somewhere in this range, quarrying must give place to underground mining. At Frodingham, by present methods, 55 ft. is considered to be the maximum possible, since the material is very largely loose wet clay. Holding the water back from the face by trenching parallel to the face at a distance of from 50 ft. to 100 yd. in front of the face has resulted in improved conditions. The use of much bigger machines of the walking type, and the carting away of part of the overburden may help to solve the difficulty. In the Northamptonshire area, the overburden is hard Lincolnshire limestone and estuarine clay and cover of 83 ft. has been removed successfully near Corby to get 8 ft. of ironstone.

The method of working is to have a face stretching for lengths up to a mile or more, if the size of the royalty permits, and to take a "benching," usually about 30 ft. wide, along. The overburden is dumped where the ironstone has been taken out. Where there is a considerable thickness of overburden, the result is usually the formation of "hill and dale dumps", the cause of a recent Ministry of Health enquiry. With overburden up to about 10 ft., however, the original soil can be restored to the farmer on the top of the flat overburden. This has been done in large areas in South Lincolnshire and Rutlandshire, often within six months of disturbing the land.

At Frodingham, holes are drilled in the ironstone to its full depth after the overburden has been removed. A wagon hammer drill is used, and holes are drilled 10 ft. apart each way and 2¼in. in dia. Cartridges of "ammonal 704," a special explosive developed for Frodingham ironstone, are used. A few years ago, liquid oxygen was tried at Frodingham for blasting the ironstone, and was a highly successful method. But the liquid oxygen had to be transported daily a distance of over 30 miles, while loss of power in wet holes was a drawback. It is a very good blasting agent as shown by practice in Lorraine, where central liquid oxygen generating plants are financed by a local group of mines. Excellent results are obtained in ironstones similar to our Jurassic ones. At Frodingham, the average charge of "ammonal 704" is 1 lb. per ft. of ironstone, 6 to 7 ft. of stemming being used. About nine shots are fired at the same time and about a day's supply of ironstone is kept blasted in front of the digger while as much overburden as possible is kept "bared." Large outputs can be obtained with relatively few men.

Underground Cleveland

Cleveland ironstone occurs in the Eston, Brotton, Skelton, Skinningrove and Loftus area of north-east Yorkshire. Only the Main Band is now worked, but the other seams, the Dogger, the Pectan, the Two Feet and the Avicula have been worked at different places in the past. The main seam is 12ft. thick in the Eston area, but due to the presence of the Pectan seam immediately below it, there is a total thickness of 15 ft. The Pectan is separated by shale to the south and the east. In other parts the main seam is about 8 ft. thick. Present mining is around Skelton, Brotton and Loftus. Farther south, at Kilton and the now disused Liverton mine, a middle shale band which increases in thickness to the south hinders new development.

The ironstone is worked by the bord and pillar method. Both sets of roads are driven about 14 ft. wide at 40 yd. centres in the headways and 30 yd. centres in the bords forming pillars 35 by 25 yd. In the last century, the idea was to develop all the royalty into pillars and present workings are largely the robbing of these pillars. Most of the old roads have collapsed, making this work difficult. However, systematic robbery takes place according to plan, and ventilation is usually good. All mines are equipped with surface fans and upcast and downcast shafts. The airways are of large size, assisting good ventilation, except when falls have occurred. At Kilton, with a very good ventilating system embracing quite a number of well-made air-crossings, 76,000 c.f.m. of air are sent round the pit with a pit bottom water gauge of 0.83 in. and a surface water gauge of 1.30 in. The brick-lined downcast winding shaft is 702 ft. deep and 13 ft. dia., whilst the upcast shaft is the same depth, but is 14 ft. in dia. A single-deck cage, with two tubs per deck, is used at Kilton, the winder is an electric 370 h.p. straight a.c. machine, which winds in 50.5 sec. and decking takes 15.0 sec.

Pillars are robbed by splitting up one side, leaving a 2-yd. "rib" and then taking a series of "lifts" across, leaving 3 to 4 yd. ribs between. Most of these ribs are removed as robbery proceeds. It is often cheaper to drive a road in the solid up the side of a pillar than to open up the roadway developed half a century before, where the roof has collapsed and strewn rock of low or negligible iron content on the floor.

Stone is got by hand. Usually there are two miners in one place and they drill and load the stone. Holes are drilled to suit the type of face, with regard to "backs" etc., by ratchet drills, to various lengths, and ignited by compressed black powder in cartridges. Both percussive and rotary drills have been tried and also permitted explosives, but the best success has been achieved by these hand methods. Scraper loading has also been tried, but found to be of little economic advantage.

Since the Cleveland mines come under the Coal Mines Act, the use of black powder may come as a surprise. It is allowed even in safety lamp districts (i.e. where gas has been found) provided no gas is present at the time of blasting. Exhaustive experiments have shown that black powder is the only explosive by which satisfactory results can be obtained. In such districts the shots are fired by appointed shot-firers, who use fuse instead of squibs, and who ignite the fuse by means of Bickford igniters which are crimped on to the fuse with suitable pliers, to obviate any external sparks. Elsewhere, in naked light districts, the miners fire their own shots with squibs,

Exemption from systematic support of roof and sides is allowed by the Act, and timbering is done by deputies in addition to their examinations before and during the shift. Norwegian spruce or larch is used and problems of erection of bulky timber can be quite acute, especially at Eston. Here, a large amount of timber is used, especially in a "jud." In a finished "jud" as much timber as possible is withdrawn by means of a sylvester, but where this safety withdrawal appliance will not move the timber owing to the weight, at Eston a shot hole is drilled into each prop left and these props are blasted, so that the "jud" will collapse and the weight be taken by the surrounding pillars.

Large horses, up to 17 hands in height, are used for all haulage work except on main roads, where electric haulages (usually main and tail) are used. Rails, 2 ft. 6 in. gauge, of 41 lb. per yd. section, are used on main roads, and 27¾ lb. per yd. section to the faces. Tubs are mainly of steel, except at Eston, Loftus and Lingdale, where wooden ones are still in use. The steel tubs have a 11 cwt. tare and hold 36 cwt. of stone.

It is worth mentioning that there has never been a strike in Cleveland.

Northamptonshire

Whilst quarrying in South Lincolnshire, Leicestershire, Rutlandshire and Northamptonshire is carried on over a very wide area in the Holwell, Eston, Woolsthorpe, Tilton Buckminster, Cottesmore, Desborough, Wellingborough, Irchester, Corby and other districts, underground mining has also been carried on in the Finedon, Irthlingborough, Holwell and other districts. In 1937, some 3,369,312 tons of stone were obtained by quarrying and 474,393 tons by underground methods. The two mines of largest size working the Northamptonshire ironstone underground are at Finedon and Irthlingborough.

Finedon was one of the earliest Northamptonshire mining areas. The method of mining is very similar to that described for Cleveland except that 22 yd. square pillars are made. Very little pillar extraction has been done so far. Shots are fired by fuse using a No. 7 detonator and Nobels "704" explosive. Mechanical drilling here, as in Cleveland, has had little success. Entrance to the mine is by adits.

Haulage is by endless ropes fed by diesel locomotives. Rails of 35 lb. per yd. section are used and the gauge is 2 ft. 4 in. Tubs hold 27 cwt. of stone.

The biggest mine in Northamtonshire is at Irthlingborough, where there were 480 men employed in 1938. A main haulage road 14 ft. wide has been driven into the royalty. Robbery of pillars has been done for about 20 years and half the output is obtained in this way.

In recent years one shaft has been sunk to the Frodingham ironstone and underground mining started. In addition, a large area has been prospected by diamond drilling, which is still being carried on. Holes are placed as near as possible, so as to form equilateral triangles with sides 2,000 ft. long.

An interesting innovation at the Winn shaft at Frodingham was the temporary use of a steel tubular headgear. This was done in 1937, when there was a considerable delay in obtaining fabricated steel, and this measure enabled sinking to be carried on. Later it was picked up bodily by crane and removed and the permanent headgear soon erected. The shaft was sunk through the thin Pectan seam of ironstone and then mostly loose clay to the ironstone. It is of rectangular shape, wooden lined and is 12 ft. 3 in. by 6 ft. inside timbers and 208 ft. deep. The winder is driven by a 200 h.p. a.c. motor and is equipped for automatic skip winding with skips holding 6 tons of ore. The winder is designed for an output of 300 tons per hour.

Drawings and Photographs accompanying the article