Gold nugget worth $300,000 discovered in Australia

(CNN) -- One Australian gold prospector has hit pay dirt.

The man, described as an amateur explorer who wants to remain anonymous, unearthed a 5.5 kilogram golden nugget 60 centimeters in the ground outside Ballarat, a city about an hour and a half drive west of Melbourne.

Experts say the value of the find is at least $300,000.

"He came in to my shop at 12:30 p.m. on Wednesday and had a grin from ear to ear," Cordell Kent, owner of The Mining Exchange Gold Shop, told CNN. "His eyes were sparkling."

The 47-year resident of Ballarat says that gold has been continuously found in the region since 1851, but technology has recently become an essential aid for modern prospectors.

"In the last 10 years it's gotten very, very hard to find nuggets over a kilo, so this (5.5 kilogram) one is extremely rare," says Kent. "In the old days miners could only see or feel gold - but now with detectors they can hear it."

A Minelab GPX Model 5000 metal detector was used to find the nugget, Kent says. In Australia, the machine retails for nearly $7,000, according to Gary Shmith, Minelab's General Manager for the Asia Pacific.

Shmith expects collectors may already be eyeing a potential purchase of the Ballarat nugget because of its rarity.

"My guess is that it would sell at 20% or 30% above its weight in gold. A nice, small nugget would already sell for 10% to 15% above its weight in gold."

Kent says the lucky prospector is back at work, "detecting right as we speak."

"He doesn't want anyone to know his bit of ground. There are only four people who know that he found it -- he and his wife and me and my wife. And he's hoping the one he found this week is a small piece and that there are bigger ones still out there."

While many people in the region have been searching for gold for decades, Kent's friend only started last year.

Other prospectors - old and new - will hope that they will be as lucky.