Zircon: A new indicator mineral for diamond exploration?

Zircon entrained within kimberlite deposits should have distinctive U-Th-Pb-He signatures compared to those found in the host terrane. To investigate the application of zircon double dating to kimberlite diamond exploration, we performed (U-Th)/He and U/Pb analysis of zircon from the Sacramore pipe located in the Merlin kimberlite field and of detrital zircon from a regional sample of the kimberlitic host, the Bukalara Sandstone. The Sacramore zircon U/Pb age (n=14) ranged from 1541-2433 Ma, consistent with the Mesoproterozoic formation of the North Australian Craton and indicating that the kimberlitic zircon is of xenocrystic origin. (U-Th)/He thermochronometry of these kimberlite zircon xenocrysts (n=33) yielded a mean weighted average age of 368 +/- 4 Ma (2 sigma), concordant with a previously determined phlogopite Rb-Sr age of 367 +/- 4 Ma for the Merlin field. The U/Pb age (1472-2939 Ma; n=41) of detrital zircon from the Bukalara Sandstone is statistically indistinguishable from that of the kimberlite zircon xenocrysts, while the detrital (U-Th)/He ages range from 459 to 1279 Ma. The consistently young (U-Th)/He ages of the kimberlite zircon xenocrysts distinguish them from surficial detrital zircon. Initial results from stream sediment sampling of Merlin drainages show a high proportion (similar to 40%) of detrital zircon with (U-Th)/He ages comparable to those obtained from the Sacramore pipe, indicating that zircon may have application in regional diamond exploration programs.