Erin Keltie

B.Sc. (Honours) Thesis

DIAMOND DISSOLUTION IN Na2CO3, Na2CO3-NaCl, AND Na2CO3-NaF MELTS
AT 950ºC AND 0.1 MPa

(PDF - 10.2 Mb)

Kimberlites are the source of most natural diamonds, and despite extensive study many aspects of such magmas remain enigmatic. Their explosive method of emplacement indicates high volatile content, but the composition of these volatiles is still poorly constrained. Kimberlitic diamonds often show resorption features such as rounded morphologies and trigonal etch pits which develop from interaction between the diamond surface and fluids in the kimberlite melt. Experimental studies at high pressures have reproduced many resorption features of natural diamonds and indicated the effect of the composition of kimberlitic fluid on diamond resorption morphology. However, the extent and character of diamond resorption in a kimberlite body after the emplacement is not known. This study exposed unresorbed kimberlitic diamonds to melts of Na2CO3, Na2CO3-NaCl, and Na2CO3-NaF at 950ºC and 0.1 MPa. The developed resorption features were measured using atomic force microscopy (AFM). The study examines how the presence of halogens in the carbonate melt affects diamond dissolution kinetics and the morphology of positively oriented trigonal etch pits. The study confirmed that positive trigons can be produced by near-surface resorption. Comparison of the experimentally produced positive trigons to those present on natural diamonds from Snap Lake kimberlite allows us to shed more light on the process of emplacement of the Snap Lake dyke. Results of this study provide new insights into the mechanism of diamond resorption as well as the occurrence and evolution of etch pits on the diamond surface by observing how the same trigons change from consequent runs with AFM.

Keywords: kimberlite fluid composition, diamond dissolution, carbonate-halogen melts, AFM, experimental petrology
Pages: 63
Supervisor: Yana Fedortchouk