They've struck gold near Cromwell again - in the middle of the 150-year celebrations of its initial discovery.

Yesterday, an excited tourist and his family left the Goldfields Mining Centre, 10km upstream from the claim of miners Hartley and Reilly, with a 4.5g gold nugget worth about $500.

Goldfields guide Brian Henderson said the man, his wife and two children were thought to be from Christchurch.

"It's funny... his grandfather worked the [gold] dredges here at the turn of the century."

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Mr Henderson, who's worked at the centre for 15 years, said staff had seen the odd nugget turn up but the finds were usually just gold flakes.

A guide had once found a couple of small nuggets when demonstrating how to pan, he said.