Gold in Quartz Pebble Conglomerates

Over 40% of the gold in the world is produced in the Witwatersrand of South Africa that is an ancient bed of conglomerate. It is only been in the past year that the source of the school's been discovered proving it to be a fossilized placer deposit formed when the gold a eroded from even older mountains where it was deposited in an ancient sedimentary basin. Today is the Witwatersrand is the home to some of the deepest mines in the world that either approach or exceed 13,000 feet in depth. Ancient conglomerate deposits are not limited to South Africa as some of the deposits in the area around Timmins, Ontario are hosted in conglomerate too.

Conglomerate rock in as natural setting.
Photo by Daniel Case

Although gold was discovered in just about any type of rock that is found on Earth prospecting in quartz conglomerates is a pretty good bet. In the eastern United States quartz pebble conglomerates are commonly found in the Queenstown Delta as exemplified by the Schwangunk Ridge of New York and New Jersey. There have been reports of sparse gold deposits associated with this ridge in both states.

There are two different ways that gold can be deposited in conglomerate. One of the ways is by direct precipitation from hydrothermal waters where it forms a primary deposit. The second way gold can be deposited in a conglomerate is as a fossilized placer deposit where the gold has eroded from ancient mountains.

Closeup of conglomerate that sometimes is called "Puddingstone."
Photo ny Roy Parkhouse

Although gold is not found in every conglomerate it is a good idea to check them all for the presence of gold especially if the quartz pebbles show any sign of staining either yellow or green. This is a sure sign that metal bearing hydrothermal waters have penetrated the conglomerate. There are several other interesting minerals found in conglomerate like uranium, thorium and rare earth metals. Conglomerates can also be the host of other metals such as iron, copper, lead and zinc.