Groundmass oxide minerals in the Koidu kimberlite dikes, Sierra Leone, West Africa

Tompkins, Linda A.; Haggerty, Stephen E.

doi:10.1007/bf00413351

Cited by 39 publications

(16 citation statements)

References 25 publications

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“…The spinels from the Blue Ball kimberlite analysed by Salpas et al (1986) occur in the first two types of the modes described above. Most spinels analysed by Tompkins and Haggerty (1985), however, differ in possessing higher Cr and Fe, and lower Mg and A1; and also they all belong to a finer grained population. The Spangar spinel is also different from the lamprophyric spinels (e.g.…”

Section: Mineral Chemistrymentioning

confidence: 97%

A newly discovered kimberlitic rock from Pakistan

Ahmed

McCormick

1990

Mineral. mag.

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This first report of the occurrence of a kimberlitic rock in Pakistan is supported by its field relations, textures and mineral chemistry. Linear dykes, lenses, conical and pipe-like bodies, plugs and sills intrude non-orogenic, early Jurassic limestone near the SW extremity of an Eocene-emplaced ophiolite on the transform-type Indian plate margin; far away from the stable Precambrian craton. The rock resembles 'micaceous kimberlites' petrographically and contains olivine, phlogopite, perovskite, chromian spinel, monticellite, chlorite, serpentine, calcite, apatite, pectolite, clinopyroxene, amphibole, nepheline, magnetite and titanomagnetite. The minerals and their microprobe analyses resemble those of kimberlitic rocks.

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Section: Mineral Chemistrymentioning

confidence: 97%

A newly discovered kimberlitic rock from Pakistan

Ahmed

McCormick

1990

Mineral. mag.

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“…On the other hand, spinel xenocrysts can be of any size but are generally coarser than the groundmass spinel and range in size typically in excess of 150 μm. Xenocrysts are also less commonly euhedral and seldom have sharp edges (Tompkins and Haggerty 1985;Mitchell 1995;Roeder and Schulze 2008).…”

Section: Petrography and Spinel Morphologymentioning

confidence: 99%

Diamond-facies chrome spinel from the Tokapal kimberlite, Indrāvati basin, central India and its petrological significance

et al. 2012

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Widespread and abundant spinel is the only primary mineral of petrogenetic significance preserved in the hydrothermally altered, crater-facies, Neoproterozoic (≥620 Ma) Tokapal kimberlite pipe that intruded the Indrā-vati basin, Bastar craton, Central India. Two distinct spinel populations occur: (i) finer-grained (<50 μm) microcrysts which are zoned from titaniferous magnesiochromitechromite to magnetite; and (ii) larger macrocrysts (>400 μm) with cores having distinctly chromium-rich (Cr 2 O 3 up to 63.67 wt%), and TiO 2 -poor (<0.68 wt%) compositions. Based on their morphology and chemical composition the macrocrysts are inferred to be disaggregated mantle xenocrysts and their compositional range extends well into the diamond stability field. However, the reported absence of diamond and other indicator minerals (such as pyrope garnet, chrome diopside and magnesian ilmenite) in the Tokapal pipe is intriguing since diamondiferous cratonic roots are indeed preserved in the Bastar craton, and also the kimberlite itself was derived from a similar source region(s) as that of the well-known diamondiferous Mesoproterozoic (ca. 1,100 Ma) kimberlites from Wajrakarur, Dharwar craton, southern India. Given the large areal extent (>550 ha) of kimberlite, there is a possibility that it contains diamonds but they were not recovered during the sampling. Alternately, highly oxidising conditions imparted by the metasomatic fluids/melts derived from (i) asthenosphere-lithosphere interaction, or (ii) the kimberlite itself might have played an important role in the destruction of diamond, and other indicator minerals.

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“…Most of these kimberlites are diamond bearing. This rock-magnetic investigation supplements a detailed study on the mineralogy, petrology, and geochemistry of the Koidu kimberlite complex , 1985. Its main purpose is to evaluate the magnetic properties of these kimberlitic rocks in terms of the detailed study of their opaque minerals.…”

Section: "mentioning

confidence: 99%

Oxide Mineralogy and Magnetic Properties of the Koidu Kimberlite Complex, Sierra Leone, West Africa

Haggerty

Hargraves

Tompkins

1990

Geophysical Journal International

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A good correlation between opaque mineralogy and rock magnetic properties has been established in a study of a small number of oriented samples from four kimberlite dykes and one pipe in the Koidu complex of Sierra Leone. The pipe sample is mineralogically distinctive, in that it alone contains deuteric titanomaghaemite after titanomagnetite, and haematite after chlorite. All of the kimberlites contain xenocrystic, upper-mantle derived ilmenite that has undergone sub-solidus reduction to form Mg-Ti magnetite. Three of the dykes contain serpentinized olivine with microscopic to sub-microscopic magnetite and identifiable metal Ni-Fe alloys, and finely textured Mg titanomagnetite and magnetite as atolls surrounding complexly zoned Cr-Mg-A1 spinels. Consistent with these observations, Curie and blocking temperatures range from 520 to 590°C and high alternating field (AF) coercivities imply single domain or pseudo-single domain particles as the bulk carrier of natural remanent magnetization (NRM). In the pipe sample, however, the remanence persisting above 600°C is comparatively strong. Preliminary remanent vectors, isolated by either thermal or AF demagnetization, from four of the five samples are moderately consistent, and yield a mean (n = 4) of D = 323", Z = -17", k = 18", and ag5 = 22".

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Groundmass oxide minerals in the Koidu kimberlite dikes, Sierra Leone, West Africa

Cited by 39 publications

References 25 publications

A newly discovered kimberlitic rock from Pakistan

A newly discovered kimberlitic rock from Pakistan

Diamond-facies chrome spinel from the Tokapal kimberlite, Indrāvati basin, central India and its petrological significance

Oxide Mineralogy and Magnetic Properties of the Koidu Kimberlite Complex, Sierra Leone, West Africa

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