It is one thing sitting on big reserves of natural resources, it is quite another getting them out of the ground, as Caledon Resources, the Australian coalminer and explorer, is discovering.

Caledon’s shares fell further yesterday, by 8½p to 76½p, as the company said that technical problems in April and May with its revolutionary mining system at its Cook colliery in Queensland meant that it would miss an already delayed target of producing 100,000 tonnes of coal a month. The Magatar system is supposed to increase efficiency by using conveyor belts, instead of rail trucks, in the mine. Teething problems mean that its forecast for this year’s production has slipped from 1.5 million tonnes to between 600,000 and 700,000 tonnes.

The shares have halved in price in only a month, partly as spot prices of coal have fallen. However, there is value there. Caledon said that the technical problems had been resolved and its latest agreed selling price is $300 a tonne of coal. Polo Resources, a Mongolian coalminer chaired by Stephen Dattells, who founded Caledon, has built a stake of 25 per cent.

The Real Hotel Company fell 8½p to 7p as Dawnay Day, which had 21 per cent of the shares and is thought to be appointing an administrator, was forced by margin calls to sell down its stake.

Portland Gas, which is trying to develop underground salt caverns on the Isle of Portland as a gas store, fell 2p to 345p after Daniel Stewart analysts raised their target price to 200p but said that the company was still overvalued because it would struggle to find a partner to fund the £500 million costs.

Iofina, which is trying to extract iodine and gas from fields in the United States, rose by 3½p to 61½p after a positive trading update.

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