Dartmoor is an area of raised moorland formed by the intrusion of granite, an igneous rock from the the earth's mantle. The semi-molten rock forced its way through the surrounding country rock; later mineral fluids emanating from the mantle flowed through fissures in the granite. These then cooled and crystallised forming mineral veins or lodes.

 

Narrow lodes containing workable quantities of ferric oxide in the form of micaceous haematite are found in the south east corner of the granite mass, running roughly E to W, and within about 10 or 20 degrees to vertical.  Micaceous iron ore (MIO) has a purple to dark grey colour in bulk, but readily forms very fine flakes that shine and sparkle, hence the local name 'shiny ore'.  MIO is found only in this area in UK, but occurs elsewhere, and is still mined for use in paints.

 

Mining was carried out by accessing the lodes from shafts, or more often adits, and extractng the MIO and waste by working along the lode, taking out the ore by stoping, usually upwards, where there were workable deposits of the mineral.  Sometimes a length of the lode would be barren, and the adit would be carried on in the expectation (or hope) of getting to a better section.

 

Kelly Mine today is much as it was in the period about 1920 to 1940, when mining was carried out in the north lode from three adits one above the other, offset by the dip of the lode away from vertical.  Ore from the bottom adit was pushed in trucks along the 18 inch gauge track to the foot of the incline and was winched up to the level of the washing strips and mill.  Ore from the middle adit was tipped down the ore chute to reach the rail track leading to the washing strips, while from top adit ore may have been tipped down an internal shaft (or winze) into middle adit to be pushed along to the ore chute.

 

Outside the mill ore was sorted and broken by hand into pieces of about  25 or 40 mm, the rubbish discarded, and the rest washed by hand under a water spray in the washing strips.  MIO flake particles would be released and carried by the water flow, and by throwing settled out material back against the flow most of the MIO could be washed out and the rubbish shovelled out and sent to the tip.  Although MIO is much more dense that other minerals in the ore, the shape of the  fine flakes and their hydrophobic nature get them carried along while less dense material settles out in the washing trough.  After washing, lumps that still looked promising were sent to the stamps, where they were broken down and any MIO washed onwards.

 

The water flow carrying the MIO went to a number of settling tanks.  After most of the water had run off or dried out, the MIO was dug out into a truck as sticky lumps and pushed to the drying shed where it was spread onto a heated floor, and when dry checked by eye and sent through a sieve system and packed into barrels for shipment.

 

Material would have been recycled though parts of the sequence to improve yield, and a jigger was used to treat fines left in the washing strips.  Kelly mine produced high quality MIO, but the process was not perfect, and there is a lot of MIO in the dumps around the site.  Over the 20 years from about 1920, when the mine site was much as it is now, output of finished MIO probably averaged about 150 tons per year, with perhaps 6 or 7 workers  of which half or fewer worked underground.  Employment and output at Ferrubron's mine at Great Rock were very roughly three times as much.

 

There are old workings up the steep hillside, on the north lode and on others more or less parallel to it.