Nickel pushed above the $13 mark early, and held there, poking above $13.50 just before the open and easing later to close at $13.4203/lb., up 45 1/3 cents. Zinc rallied sharply but came well off its intraday highs, ending at $1.0379/lb., a penny and a third. Aluminum had a very strong day, adding just short of 3 cents, to $1.368/lb., while lead tacked on a penny, to $1.2933/lb.

Copper vaulted to within spitting distance of its all time high on renewed evidence that China’s economic growth isn’t slowing much, raising the possibility that supply will not be able to keep up with demand. China’s first-quarter 2008 gross domestic product, the broadest measure of economic activity, climbed 10.6%, the national statistics bureau said yesterday.

“Chinese investment in new cities, urbanization and in infrastructure is dominating metals demand and driving prices higher,” said Tom Albanese, Rio Tinto’s CEO. “The demand for metals, materials and minerals is continuing to grow and the outlook, notwithstanding the U.S. slowdown, is very favorable.”

At the same time, supply worries loomed. Albanese’s own company reported that its first-quarter copper output fell 6%, year over year. Rio cited lower grades of ore from its Kennecott Utah Copper and Northparkes mines.

In addition, labor unrest in Chile, the world’s biggest source of the metal, threatens to disrupt mine output. Chile’s state-owned Codelco, the world’s largest copper producer, halted work at its Andina site after striking contract workers blocked the entrances of at least three mines.

The subcontractor’s strike will prevent Codelco union members from entering job sites, says the Confederation of Copper Workers, which represents some 30,000 workers, including the protesters.

The subcontract workers started a new strike on Wednesday at all of Codelco’s operations, over work conditions and pay. Fighting with police broke out, and Codelco was forced to close its Andina division.

Codelco reacted by releasing a statement saying that the company “is sorry that a small group of people, who lend their services through some subcontracted companies, are trying to affect its production activities through the use of violence and threats.”

There may be no quick solution. “We are calling for the intervention of the government, because Codelco has lied to the country, to the church and to the workers,” a union spokesperson said. “Our patience has run out [and we] will not lift this strike until there is an immediate solution.”