Large veins of gold in the Pacific island country of Papua-New Guinea may have been deposited in a relative blink of time, geologically speaking.
With an estimated 1,300 tons of gold, the Ladolam deposit is one of the largest and youngest gold fields in the world, according to researchers led by Stuart F. Simmons of the University of Auckland, New Zealand.
The gold precipitated from hot volcanic water rising up from below.
Ladolam, on Lihir Island, is the only known active hydrothermal gold deposit and could have been built up in 55,000 years or less at the current rate of deposit, Simmons reports in Friday's issue of the journal Science.
Simmons and Kevin L. Brown of GEOKEM, a New Zealand-based geochemical company, sampled water in deep wells below the gold deposit.
"Our results indicate a steady upward flux of gold, as a consequence of geothermal heat and mass transfer ... were critical in forming the Ladolam deposit in a compact volume of rock in a short period," the researchers said.
They sampled water from deep beneath the gold field and found gold, sulfur compounds and other minerals dissolved in the hot fluids. The minerals are deposited when the water rises toward the surface where the pressure is less and it cools.
The gold is deposited as the water cools from about 480 degrees Fahrenheit to about 300 degrees, they reported. About 50 pounds of gold is deposited per year, they calculated.
Christoph A. Heinrich, of the Swiss Federal Institute of Technology in Zurich, noted that deposits from water circulating in the Earth's crust have produced valuable deposits of not only gold but also such minerals as zinc and copper.
An understanding of this process is key to finding and developing these deposits, said Heinrich, who was not part of Simmons' team.
He suggested that the Ladolam deposit might have formed even more quickly than suggested by Simmons. The deposit is located in an extinct volcano and might have formed when the mountain erupted causing a sudden release of pressure on the mineral-rich water beneath.
The study was funded by New Zealand's Foundation for Research Science and Technology.
