January 24 Through February 4—TUCSON, ARIZONA: Annual show
Welcome to the GemologyOnline.com Forum
A non-profit Forum for the exchange of gemological ideas
It is currently Tue Mar 19, 2024 4:46 am

All times are UTC - 4 hours




Post new topic Reply to topic  [ 1 post ] 
Author Message
 Post subject: Deciphering the Enigmatic Origin of Guyana's Diamonds
PostPosted: Thu May 06, 2021 12:37 pm 
Offline
Site Admin
User avatar

Joined: Sun Oct 16, 2005 12:22 pm
Posts: 21600
Location: San Francisco
Here is the abstract to an article which is available on Researchgate, if you have a membership: I found this very interesting.
June 2020American Mineralogist wrote:
Deciphering the Enigmatic Origin of Guyana's Diamonds
Authors:
-Roy Bassoo, Baylor University
-Kenneth S. Befus
-Peng Liang, Zhejiang University
-Steven L. Forman

Diamonds have long been mined from alluvial terrace deposits within the rainforest of Guyana, South America. No primary kimberlite deposits have been discovered in Guyana, nor has there been previous studies on the mineralogy and origin of the diamonds. Paleoproterozoic terranes in Guyana are prospective to diamond occurrences because the most productive deposits are associated spatially with the eastern escarpment of the Paleoproterozoic Roraima Supergroup. Geographic proximity suggests that the diamonds are detrital grains eroding from the <1.98 Ga conglomerates, metamorphosed to zeolite and greenschist facies. The provenance and paragenesis of the alluvial diamonds are described using a suite of placer diamonds from different locations across the Guiana Shield. Guyanese diamonds are typically small, and those in our collection range from 0.3 to 2.7 mm in diameter; octahedral and dodecahedral, with lesser cubic and minor macle forms. The diamonds are further subdivided into those with abraded and non-abraded surfaces. Abraded diamonds show various colors in cathodoluminescence whereas most non-abraded diamonds appear blue. In all populations, diamonds are predominantly colorless, with lesser brown to yellow and very rare white. Diamonds are predominantly Type IaAB and preserve moderate nitrogen aggregation and total nitrogen concentrations ranging from trace to ~1971 ppm. The kinetics of nitrogen aggregation indicate mantle-derived residence temperatures of 1124 ± 100 ºC, assuming residence times of 1.3 Ga and 2.6 Ga for abraded and non-abraded diamonds respectively. The diamonds are largely sourced from the peridotitic to eclogitic lithospheric upper mantle based on both δ13C values of -5.82 ± 2.45‰ (VPDB-LSVEC) and inclusion suites predominantly comprised of forsterite, enstatite, Cr-pyrope, chromite, rutile, clinopyroxene, coesite, and almandine garnet. Detrital, accessory minerals are non-kimberlitic. Detrital zircon geochronology indicates diamondiferous deposits are predominantly sourced from Paleoproterozoic rocks of 2079 ± 88 Ma.



Attachments:
Screen Shot 2021-05-06 at 9.32.42 AM.png
Screen Shot 2021-05-06 at 9.32.42 AM.png [ 1.43 MiB | Viewed 9748 times ]
Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 1 post ] 

All times are UTC - 4 hours


Who is online

Users browsing this forum: No registered users and 5 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
Gemology Style ported to phpBB3 by Christian Bullock