U–Pb SHRIMP geochronology of zircon from the Catoca kimberlite, Angola: Implications for diamond exploration

Abstract

We present the first age determinations of zircon from the diamondiferous Catoca kimberlite in northeastern Angola, the fourth largest kimberlite body in the world. The U-Pb ages were obtained using a Sensitive High Resolution Ion Microprobe II (SHRIMP II) on zircon crystals A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT 2 derived from tuffisitic kimberlite rocks and heavy-mineral concentrates from the Catoca kimberlite. The SHRIMP results define a single weighted mean age of 117.9 ± 0.7 Ma (Mean square weighted deviation MSWD = 1.3). More than 90% of the results indicate a single age population. There is no evidence for variable ages within single crystals, and no diffusional profiles are preserved. These data are interpreted as the maximum age of the kimberlite eruption at Catoca. The U/Th values suggest at least two different sources of zircon crystals. These different populations may reflect different sources of kimberlitic magma, with some of the grains produced in U-and Th-enriched metasomatized mantle units. This idea is consistent with the two populations of zircon identified in this study. One population originated from a depleted mantle source with low total REE (less than 25 ppm), and the other was derived from an enriched source, likely from the mantle or a carbonatite-like melt with high total REE (up to 123 ppm).The tectonic setting of northeastern Angola is influenced by the opening of the south Atlantic, which reactivated deep NE-SW-trending faults during the early Cretaceous. The eruption of the Catoca kimberlite can be correlated with these regional tectonic events. The Calonda Formation (Albian-Cenomanian age) is the earliest sedimentary unit that incorporates eroded material derived from the diamondiferous kimberlites. Thus, the age of the Catoca kimberlite eruption is restricted to the time between the middle of the Aptian and the Albian. The new interpretation will be an important guide in future exploration for diamonds because it provides precise data on the age of a diamond-bearing kimberlite pulse in Angola.

LIMA U–Pb ages link lithospheric mantle metasomatism to Karoo magmatism beneath the Kimberley region, South Africa

“…However, U and Th concentrations in the zircon are much higher than that of most mantle zircons analysed to date Hamilton et al, 1998;Heaman et al, 1990;Katayama et al, 2003;Kinny and Dawson, 1992;Kinny and Meyer, 1994;Kinny et al, 1989;Konzett et al, 1998Konzett et al, , 2000Konzett et al, , 2013Liati et al, 2004;Robles-Cruz et al, 2012;Schärer et al, 1997;Simonetti and Neal, 2010;Spetsius et al, 2002;Zheng et al, 2006). The only exceptions are: i) zircons from mantle xenoliths studied by Rudnick et al (1999), which contained U and Th concentrations up to 3950 and 3300 ppm, respectively, and were assumed to be inherited grains from recycled crustal rocks; and ii) zircons in mantle pyroxenites from the Hannouba alkali basalts (China), which have U and Th contents up to 23 000 and 16 500 ppm, respectively, and were attributed to carbonate metasomatism (Liu et al, 2010).…”

Carbonatitic lavas in Catanda (Kwanza Sul, Angola): Mineralogical and geochemical constraints on the parental melt

“…Most of the Angolan carbonatites are distributed along this rift including Virulundo, Tchivira-Bonga, Bailundo or Longonjo (Torró et al, 2011;Calvo et al, 2011a;Calvo et al, 2011b), along with kimberlites including the Catoca pipe (Robles-Cruz et al, 2012;Korolev et al, 2014), which is one of the most productive diamond mines in the African continent.…”

Overview of Diamond Resources in Africa

“…At about 200 m the pipe has a transition zone marked by a pronounced breccia layer, below which are pyroclastic rocks of the diatreme zone. The pipe is dated at approximately 118 Ma (Robles-Cruz et al, 2012).…”