Japan's high-tech rubbish dumps - the vast “urban mines” of landfill outside every big city - have grown so huge that the country now ranks among the biggest natural resource nations in the world.

Tens of millions of defunct mobile phones, discarded televisions, PCs and MP3 players conceal a “virtual lode” of hundreds of tonnes of precious metals. An even greater seam may be lurking forgotten - but not yet discarded - in Japan's attics and garages.

According to new calculations by the National Institute for Materials Science (NIMS) in Tsukuba, Japan has unwittingly accumulated three times as much gold, silver and indium than the entire world uses or buys in a year. In the case of platinum, Japan's urban mines may contain six times annual global consumption.

The institute's leading urban mine expert said that if these electronics-rich treasure troves were properly tapped, supposedly resource-poor Japan would suddenly join the likes of Australia, Canada and Brazil in the top five producers of some elements.

The mines have been accumulated because of the extraordinarily high speed at which Japanese consumers replace gadgets. Of these, the 20million mobile phones replaced by the Japanese each year are especially attractive “ores” for urban miners. Only 13 per cent, about 550 tonnes a year, are recycled, with the remainder thrown away or stored in drawers and cupboards.

The circuit boards of each phone contain a smorgasboard of precious metals: in minute quantities there are silver, lead, zinc, copper, tin, gold, palladium and titanium.

Although other developed countries - particularly the United States and Britain - are thought to have very substantial untapped urban mines of their own, Japan leads the world as an assessor of what its dumps and attics contain in the way of metal resources. Koumei Harada, the director of the institute's strategic use of elements division, has pioneered the calculation of Japan's potential urban mine resources.

By comparing the quantities of metals imported over the past 60 years with what has left Japan inside its electronics, cars and other exported goods, Professor Harada arrived at basic reserves. From this were subtracted theoretical quantities of metal that remain in use.

According to the professor, decades at the forefront of the global consumer electronics industry had left Japan with a tantalising legacy: it has invisibly accumulated stocks of some metals to rival proven worldwide reserves in the ground, but it knows where only about half of it is. Worse, that half is difficult to process.

Now the Ministry of Economy, Trade and Industry is pushing for nationwide collections of old electronics from homes and for ideas about how best to excavate the landfill. Companies such as Asahi Pretec already run urban mines at various plants in Japan. One of its plants retrieved about 15 tonnes of gold last year from a variety of industrial waste.

Professor Harada is part of a team working on establishing “artificial ore” factories at Japan's waste dumps and landfill sites. By his estimates, a tonne of ore from a real goldmine might produce only five grams of actual gold, while a tonne of artificial ore made from reduced mobile phones would yield about 150 grams.

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