Kimberlitic zircons ? A possible aid in prospecting for kimberlites

An ion microprobe U-Th-Pb study of zircon xenocrysts from the Lahtojoki kimberlite pipe, eastern Finland

“…This value is within the range reported for zircon megacrysts in kimberlites (Kresten et al 1975, Belousova et al 1999. Zr/Hf is not indicative of zircon Group A grains (03,04) are shown.…”

“…These features, together with similar inclusions as in the old zircons, suggest that grain 09 represents a fairly advanced stage of resetting of old grains. The inclusion suite of Group C zircons, dominated by pyroxenes and amphiboles (Table 1), differs from inclusions identified in zircon megacrysts of kimberlites and zircons of metasomatised mantle xenoliths which host primary and metasomatic mantle minerals such as olivine, Cr-diopside, Cr-spinel, magnesian ilmenite, K-richterite, rutile, apatite, phlogopite, Ni-Fe sulfides and diamond (Kresten et al 1975, Lyakhovich 1996, Konzett et al 1998. Most likely, all Group C zircons were derived from deepseated Archaean rocks which have experienced variable U-Pb disturbance and recrystallisation processes in a thermal event at c. 1.8 Ga.…”

“…The most characteristic features of the kimberlitic zircons are their very low U, Pb, Th and REE abundances, unusual large grain size, colour and trace element compositions. In addition, many kimberlitic zircons contain mantle minerals, such as olivine, Cr-diopside, Cr-spinel, magnesian ilmenite, K-richterite and phlogopite, as inclusions (Kresten et al 1975, Lyakhovich 1996, Belousova et al 1999. Zircon has also been found as inclusions in diamonds (Meyer & Svisero 1973) and in metasomatised mantle xenoliths (Konzett et al 1998).…”

The Composition of Zircon and Igneous and Metamorphic Petrogenesis

“…Typical igneous zircon is between 20 and 250 µm in the longest dimension with subhedral to euhedral face development. Larger mm-sized rare crystals are reported in kimberlites and kimberlite-related rocks (MARID-suite xenoliths); these are usually anhedral but can be subhedral (Kresten et al 1975, Belousova et al 1998, Hoskin 1998, Konzett et al 1998. Large cm-sized colorless "gem-quality" crystals are found in the Mud Tank carbonatite (Hanchar and Hoskin 1998) although brown-colored imperfect crystals up to 30 cm-long from this carbonatite are displayed at the Australian Museum in Sydney.…”

Uranium-Lead, Rubidium-Strontium, Kimberlite

“…The occurrence of zircon (ZrSiO 4 ) in kimberlite has been known for a long time (Ahrens et al 1967;Kresten et al 1975), but the application of U-Pb mantle zircon dating to constrain the emplacement age of kimberlites can be attributed to the pioneering research of Gordon Davis and colleagues at the Carnegie Institute of Washington in the 1970s (e.g., Davis et al 1976;Davis 1977Davis , 1978. Mantle zircon occurs as a sparse but relatively large (cm-size crystals) accessory mineral in kimberlites ( Fig.…”