Featured Research

from universities, journals, and other organizations

Scientists Discover That 40 Percent Of The World's Gold Is 3 Billion Years Old

Date:
September 16, 2002
Source:
University Of Arizona
Summary:
Scientists have for the first time directly dated gold from South Africa's Witwatersrand gold deposits, source of more than 40 percent of all gold so far mined on Earth.

Scientists have for the first time directly dated gold from South Africa's Witwatersrand gold deposits, source of more than 40 percent of all gold so far mined on Earth.

An international team of geologists led by the University of Arizona has discovered that the gold is around 3 billion years old -- older than its surrounding conglomerate rock by a quarter of a billion years.

More, their state-of-the-art dating technique shows that the gold deposits formed along with crustal rock directly from the mantle beneath South Africa. The event at this magnitude appears to be unique in Earth's geologic history.

Jason Kirk, Joaquin Ruiz and John Chesley of the UA, John Walshe of Australia's Commonwealth Scientific and Industrial Research Organisation, and Gavin England of the University of Edinburgh report on it in the Sept. 13 issue of Science.

The Witwatersrand gold is found in a sedimentary basin. But the age and origin of the gold has been hotly debated. One theory argues that the gold was carried into the basin by sedimentary processes. A conflicting theory holds that the gold was emplaced by hydrothermal fluids -- the equivalent of hot springs -- from the upper continental crust.

The new results confirm that the Witwatersrand gold deposits are "placer" deposits -- that millions of years ago, ancient rivers carried gold particles, along with sand and silt, into the Witerwatersrand basin -- then a great lake -- possibly from granite mountains to the north and southwest.

Over time and under pressure, the gold-bearing sediments solidified into rock, forming the rich gold-bearing reefs of South Africa's 'golden arc,' which have been mined since their discovery in 1886.

The UA scientists' new findings confirm that the gold first formed in older rocks, rocks that formed when upwelling mantle formed a major piece of South African continental crust called the Kaapvaal craton. Cratons are areas of Earth's crust that have remained tectonically stable over time. The Kaapvaal craton is one of the oldest known.

Later, the gold was weathered and reconcentrated in the Witwatersrand paleolake sediments.

Kirk is studying the age and extent of gold deposits around the world for a UA doctoral geosciences degree. He uses a rhenium-osmium isotope gold-dating technique developed by Ruiz at the university's NTIMS laboratory.

Ruiz, dean of the UA College of Science and professor of geosciences, was instrumental in developing the Negative Thermal Ionization Mass Spectrometer (NTIMS) with a grant from the W. M. Keck Foundation. The laboratory is one of the few of its kind in the world.

"This is precisely the kind of research that I envisioned when I was building the laboratory," Ruiz said. "The analytical capabilities of the W.M. Keck Laboratory is such that we will continue to discover aspects of how the Earth worked, questions that previously we could only dream of."

Gold and other minerals contain a rare metallic chemical element called rhenium. Rhenium-187 is the radioactive form of the element. NTIMS directly dates minerals by counting the number of their rhenium-187 and osmium-187 atoms. Rhenium-187 has a half -life of 45 billion years, or about 10 times the age of our solar system. It decays into osmium-187. So by determining the ratio of radioactive rhenium-187 to daughter osmium-187 atoms, scientists can directly calculate when the minerals formed.

"One of the reasons I think our results are so significant is that the rhenium-osmium system can be used directly on gold, and can also tell us if the gold came from the mantle or the crust," Kirk said.

There is relatively more rhenium than osmium in Earth's crust, but relatively more osmium than rhenium in Earth's mantle.

"Witwatersrand has a clear mantle signature," Kirk said. "It's possible that this mantle signature is so big because at 3 billion years ago, Earth's mantle might have been hotter, and richer in gold at this particular spot, compared to more recent deposits."

People, understandably, are keenly interested in why South Africa has been so blessed with gold. The Witwatersrand gold fields have yielded a half-trillion dollars' worth of gold since 1886.

"Estimates are that there's another half-trillion dollars in gold still to be mined, and that's a lot of money," Kirk said.


Story Source:

The above story is based on materials provided by University Of Arizona. Note: Materials may be edited for content and length.


Cite This Page:

University Of Arizona. "Scientists Discover That 40 Percent Of The World's Gold Is 3 Billion Years Old." ScienceDaily. ScienceDaily, 16 September 2002. <www.sciencedaily.com/releases/2002/09/020916064654.htm>.
University Of Arizona. (2002, September 16). Scientists Discover That 40 Percent Of The World's Gold Is 3 Billion Years Old. ScienceDaily. Retrieved July 26, 2014 from www.sciencedaily.com/releases/2002/09/020916064654.htm
University Of Arizona. "Scientists Discover That 40 Percent Of The World's Gold Is 3 Billion Years Old." ScienceDaily. www.sciencedaily.com/releases/2002/09/020916064654.htm (accessed July 26, 2014).

Share This




More Earth & Climate News

Saturday, July 26, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Virginia Governor Tours Tornado Aftermath

Virginia Governor Tours Tornado Aftermath

AP (July 25, 2014) Virginia Gov. Terry McAuliffe toured the Cherrystone Family Camping and RV Resort on the Chesapeake Bay today, a day after it was hit by a tornado. The storm claimed two lives and injured dozens of others. (July 25) Video provided by AP
Powered by NewsLook.com
Europe's Highest Train Turns 80 in French Pyrenees

Europe's Highest Train Turns 80 in French Pyrenees

AFP (July 25, 2014) Europe's highest train, the little train of Artouste in the French Pyrenees, celebrates its 80th birthday. Duration: 01:05 Video provided by AFP
Powered by NewsLook.com
Goma Cheese Brings Whiff of New Hope to DRC

Goma Cheese Brings Whiff of New Hope to DRC

Reuters - Business Video Online (July 24, 2014) The eastern region of the Democratic Republic of Congo, mainly known for conflict and instability, is an unlikely place for the production of fine cheese. But a farm in the village of Masisi, in North Kivu is slowly transforming perceptions of the area. Known simply as Goma cheese, the Congolese version of Dutch gouda has gained popularity through out the region. Ciara Sutton reports. Video provided by Reuters
Powered by NewsLook.com
Bill Gates: Health, Agriculture Key to Africa's Development

Bill Gates: Health, Agriculture Key to Africa's Development

AFP (July 24, 2014) Health and agriculture development are key if African countries are to overcome poverty and grow, US software billionaire Bill Gates said Thursday, as he received an honourary degree in Ethiopia. Duration: 00:36 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins