Aspects of the Geochemistry of Kimberlites From the Premier Mine, and Other Selected South African Occurrences With Particular Reference to the Rare Earth Elements

Fesq, H.W.; Kable, E.J.D.; Gurney, J.J.

doi:10.1016/b978-0-08-018017-5.50049-3

Cited by 10 publications

(15 citation statements)

References 23 publications

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“…The absence of any negative Eu anomalies is important in that the majority of kimberlites analysed by reliable methods do not exhibit such anomalies in their whole-rock REE distribution patterns (Mitchell, 1986). Although minor to significant negative Eu anomalies are found in some kimberlites (Fesq et al, 1975) it would appear on the basis of the present data unlikely that these are related to the presence of perovskite.…”

Section: Ree Abundances and Distribution Patternsmentioning

confidence: 52%

“…The effects of this process are to decrease the slope of the distribution pattern from Tb to Lu and hence to reduce La/Yb ratios. Fesq et al (1975) and Cullers et al (1982) have provided data for the Premier and Bala kimberlites which clearly demonstrate such effects. Perovskites from the Chomur diatreme analysed in this work, are unlike all of those from hypabyssal kimberlites studied, in that their La/Yb ratios are low and their heavy REE abundances are relatively high.…”

Section: Ree Abundances and Distribution Patternsmentioning

confidence: 94%

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Ion Microprobe Determination of Rare Earth Elements in Perovskite from Kimberlites and Alnöites

Mitchell¹,

Reed²

1988

Mineral. mag.

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Ion microprobe analysis ofperovskite from kimberlites and aln6ites permits the accurate determination of La, Ce, Pr, Nd, Sin, Eu, Gd, Dy, Er and Yb at the part per million level. Other rare earth elements (REE) are subject to interferences in the mass spectrum caused by matrix-derived molecular ions and cannot easily be determined with comparable precision. Chondrite-normalized plots of the ion probe BEE data are smooth curves, confirming the superiority of this technique over electron microprobe methods at the levels of REE abundance found in these perovskites. The perovskites analysed contain between 2.8 and 7.1 wt. % REE oxides and are highly enriched in the light REE, having La/Yb ratios of 577-3229. These La/Yb ratios are not representative of the parental magmas but result from REE fractionation during crystallization of the perovskite. Parental magma La/Yb ratios are estimated to be of the order of 120 650. The lower La/Yb ratios (80-200) found for whole-rock kimberlites are considered to result from contamination by relatively heavy REE-enriched crustal material.

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Section: Ree Abundances and Distribution Patternsmentioning

confidence: 52%

Section: Ree Abundances and Distribution Patternsmentioning

confidence: 94%

Ion Microprobe Determination of Rare Earth Elements in Perovskite from Kimberlites and Alnöites

Mitchell¹,

Reed²

1988

Mineral. mag.

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“…Recently, Kjarsgaard et al () evaluated the Contamination Index (CI) and concluded a need to use it in conjunction with other geochemical screens. Here we combine two contamination indices, CI and Si/Mg (whose value of >1.2 implies crustal contamination; Fesq et al , ), to understand the samples under study (Figure ). Our data, together with the data for the same pipes reported by Paton et al (), show that some of the samples (NKF‐4, NKF‐10, NKF‐29–32 and NKF‐65) have clearly undergone crustal contamination and are excluded from petrogenetic evaluation.…”

Section: Whole‐rock Geochemistrymentioning

confidence: 99%

“…Variations in contamination index (CI; Clement, ) and Si/Mg ratios (Fesq et al , ) for the samples under study (black circles). Data of Paton et al () for the same pipes are also included (shown as x).…”

Section: Whole‐rock Geochemistrymentioning

confidence: 99%

Origin and diamond prospectivity of Mesoproterozoic kimberlites from the Narayanpet field, Eastern Dharwar Craton, southern India: insights from groundmass mineralogy, bulk‐chemistry and perovskite oxybarometry

2011

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The Mesoproterozoic Narayanpet Kimberlite Field (NKF) is located~200 km north of the well-known Wajrakarur Kimberlite Field (WKF) in the Eastern Dharwar Craton, southern India. Whereas a majority of the WKF occurrences are diamondiferous and contain mantle xenoliths and xenocrysts, their paucity is a characteristic feature of the NKF. This has been attributed alternately to the derivation of NKF magmas from a shallower depth, or to variability in thickness of the Sub-Continental Lithospheric Mantle (SCLM) beneath the Eastern Dharwar Craton. Recently, exploration by De Beers resulted in the discovery of a number of new kimberlite occurrences from the NKF, with some of their geochemical features and radiogenic isotope systematics subsequently becoming available. In this paper, we present detailed petrography, groundmass mineral composition and new bulk-rock geochemistry data for a number of NKF rocks and attempt to further constrain their origin. We also investigate the influence of redox conditions on diamond prospectivity by estimating oxygen fugacity ( f O 2 ) from Fe-Nb oxybarometry on NKF groundmass perovskites. We identify for the first time in the NKF the presence of volcaniclastic (fragmental textured) facies kimberlite belonging to the diatreme portion of the intrusion. Rarity of olivine macrocrysts and the presence of diopside are hallmarks of the NKF kimberlites, in contrast to archetypal kimberlites of southern Africa. Mineral components of the groundmass display features that are characteristic to both archetypal kimberlites and to orangeites, and it is not straight forward to apply conventional mineral-genetic schemes in the nomenclature of the NKF pipes. Low f O 2 of the NKF magma (ΔNNO (nickel-nickel oxide) = −1.9 to −3.2), indistinguishable from that of diamondiferous kimberlites world-wide, indicates that redox conditions were favourable for diamond prospectivity, and that magmatic emplacement could, instead, have played a major role in their low diamond potential.

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“…and concluded need of its utilization in conjunction with other geochemical screens. Fesq et al (1975) shown that Si/Mg values of >1.2 implies crustal contamination. The Si/Mg values for aphanitic samples are within range (i.e., <1.2) while macrocrystic samples shows values close to ~1.2 signifying the crustal contamination to be not a significant factor.…”

Section: Crustal Contamination and Deuteric Alterationmentioning

confidence: 99%

Petrogenesis of macrocrystic and aphanitic intrusions in Mesoproterozoic diamondiferous pipe 2 kimberlite, Wajrakarur kimberlite field, eastern Dharwar craton, southern India

2014

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Mesoproterozoic Pipe 2 kimberlite intruding granitic gneisses in the Wajrakarur kimberlite field (WKF) of Eastern Dharwar craton, southern India, is one of the first discovered pipes from this field. The two different intrusions belonging to coherent facies are observed in this kimberlite which are texturally distinct i.e., macrocrystic (with abundant macrocrysts) as well as aphanitic (devoid of or very fewer macrocrysts). Petrographic observations give evidence of presence of veined metasomatic mantle in the source region. Distinct geochemical variation is observed between macrocrystic (Mg# 75.4-76.6, SiO 2 : 34.3-35.4 wt%, MgO: 18.7-20.4 wt%) and aphanitic samples (Mg# 74.7-75.5, SiO 2 : 30.4-31.8 wt%, MgO: 21 wt%), furthermore aphanitic samples are relatively more enriched in trace and rare earth elements. Geochemical studies point out that aphanitic and macrocrystic varieties of Pipe 2 kimberlite to be products of the same mantle source but have experienced different evolutionary histories. The inferred primary magma of Pipe 2 kimberlite (for both aphanitic and macrocrystic) is suggested to have a composition of ~33 wt% SiO 2 , Mg# ~ 75.6 and ~460 ppm Ni. Pipe 2 primary magma can be derived by using forward melting model assuming ~1% partial melting of a source enriched in light REE by a factor of ~11 x chondrite and almost chondritic heavy REE with 2% residual garnet. Differences between aphanitic and macrocrystic varieties in their chondrite normalized REE abundance patterns can be explained by about 5% crystal fractionation of primary magma and not by variations in the degree of partial melting. The primitive mantle normalized trace element patterns exhibit significant negative K, Sr, P, Ti and Hf anomalies that are interpreted to be characteristic of the primary magma. Combined petrology and whole rock geochemistry including compatible and incompatible element abundances and their ratios confirm that Pipe 2 kimberlite intrusions are archetypal Group I kimberlites similar to other kimberlites of EDC and not lamproites.

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Aspects of the Geochemistry of Kimberlites From the Premier Mine, and Other Selected South African Occurrences With Particular Reference to the Rare Earth Elements

Cited by 10 publications

References 23 publications

Ion Microprobe Determination of Rare Earth Elements in Perovskite from Kimberlites and Alnöites

Ion Microprobe Determination of Rare Earth Elements in Perovskite from Kimberlites and Alnöites

Origin and diamond prospectivity of Mesoproterozoic kimberlites from the Narayanpet field, Eastern Dharwar Craton, southern India: insights from groundmass mineralogy, bulk‐chemistry and perovskite oxybarometry

Petrogenesis of macrocrystic and aphanitic intrusions in Mesoproterozoic diamondiferous pipe 2 kimberlite, Wajrakarur kimberlite field, eastern Dharwar craton, southern India

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