Applying Cliffords Rule to Finding Diamonds
Clifford's Rule for finding diamonds:
Clifford's Rule won’t tell you where to find diamonds in diamond bearing rock at least it will eliminate a lot of rock where you can’t find look for diamonds. Clifford's Rule states that most diamonds are in Archean rocks that are over 2.5 billion years old. These are the rocks that make up the core of a craton that manifest themselves as deep rock in the earth's crust. They are literally a keel like a sailboat's keel that are seen on the bottom of a craton.
T.S. Clifford's Rule that was written in 1966 stated that diamonds and kimberlites were always found in with Archean crust that was greater then 2.5 billion years old formed in the stable cores of cratons. It also said that diamond prospecting should only be carried out in these places. More recent investigations have found however that there are exceptions to this rule. In the African nation of Gambia where diamonds are found associated with early protozoic rocks, and in eastern British Columbia diamonds are found in rocks that may be underlain by Archean rocks that are fragments of broken up continents that have been brought together in the form new continents.
Another exception to Clifford's rule is the Argyle Mine of Australia found in rock ranging in age from 2.5 to .542 billion years old mountain chain. The Argyle Mine is operated by Rio Tinto PLC with the highest yield of diamonds per ton of any mine in the world. This suggests that the younger rocks exposed at the surface are probably underlain by older Archean rock. A similar situation happens in Brazil where the Carolina kimberlite is found in rocks ranging from 1.8 to 1.2 billion years old.
Diamonds have been found in California at Cherokee Flat in Butte County and Placerville in El Dorado County. These diamonds were found while the miners were recovering alluvial gold with these discoveries made in stream gravel. In addition to California similar occurrences have been reported from North and South Carolina as well as West Virginia. Murfreesboro Arkansas and the borderland between Colorado and Wyoming are the only places that diamonds have been actively mined. Both of these areas are found above Archean age rocks.
This is theoretically the result of younger subduction zones where one plate dives beneath another causing abrasion on both plates. The lower of the two plates is carrying a load of sediment where some of it is calcium carbonate. Under the influence of heat and pressure the calcium carbonate is reduce into its components one of which is elemental carbon that in this regime is converted into the allotrope of carbon “diamond.” Because of the somewhat lower temperature caused by the water content in the subduction of marine sediments. You will end up with a low temperature, high pressure environment as found today in the Coast Ranges of the Pacific coast of North America.
At present there is a worldwide glut of diamonds on the market the overall demand for diamonds has historically been on the rise so that more exploration will be done for diamonds. It is expected that the prospectors will find diamonds in other places. You might be sure that they will continue finding diamonds close to Archean age rocks.
KIM Report, Bending Clifford's Rule (KIM), http://www.kimreport.com/bending-cliffords-rule/
Ancient Rivers of Gold, http://goldmaps.com/ancient_tertiary_rivers_of_gold.htm
A Worldwide Diamond Glut, http://www.associatedcontent.com/article/1634611/a_worldwide_diamond_glut.html?cat=3