Abstract
The lower sill at Benfontein, South Africa, shows a high degree of magmatic sedimentation to kimberlite, oxide-carbonate, and carbonate layers. The iron-titanium oxide minerals are similar in the carbonate-rich and silicate-rich layers and are represented by titaniferous Mg-Al chromite, Mg-Al titanomagnetite, magnesian ilmenite, rutile, and perovskite. The spinel crystallization trend was toward enrichment in Mg and Ti and depletion in Cr; this trend is similar to that observed in many kimberlites. The ilmenite has Mg and Cr contents within the range observed in kimberlites and lacks the Mn enrichment observed in ilmenites from carbonatites. Perovskite in silicate-rich and carbonate-rich layers shows similar total REE contents and LREE enrichment and lacks the remarkable Nb enrichment observed in perovskite from carbonatites. These new data on the iron-titanium oxide minerals in the lower Benfontein sill do not support a genetic relationship between kimberlites and carbonatites.
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References
Andersen DJ, Lindsley DH (1979) The olivine-ilmenite thermometer. Proc Lunar Sci Conf, 10th, 1:493–507
Basu JV (1978) Origin of kimberlites and carbonatites explained by Nd isotopes (abstract). GAC/MAC, Abstr with Progr 3:364
Boctor NZ, Boyd FR (1979a) Oxide minerals in layered kimberlite-carbonate sills from Benfontein, South Africa. Carnegie Inst Washington Yearb 78:493–496
Boctor NZ, Boyd FR (1979b) Distribution of rare earth elements in perovskite from kimberlites. Carnegie Inst Washington Yearb 78:572–574
Boctor NZ, Svisero DP (1978) Iron-titanium oxide and sulfide minerals in carbonatite from Jacupiranga, Brazil. Carnegie Inst Washington Yearb 77:876–880
Boynton WV (1975) Fractionation in the solar nebula: Condensation of yttrium and the rare earth elements. Geochim Cosmochim Acta 39:569–584
Buddington AF, Lindsley DH (1964) Iron-titanium oxide minerals and synthetic equivalents. J Petrol 5:310–357
Cullers RL, Medaris LG (1977) Rare earth elements in carbonatites and cogenetic alkaline rocks: Examples from Seabrook Lake and Callander Bay, Ontario. Contrib Mineral Petrol 65:143–153
Dawson JB (1966) The kimberlite carbonatite relationpship. Mineral Soc India, IMA, 1–22
Dawson JB, Hawthorne JB (1973) Magmatic sedimentation and carbonatitic differentiation in kimberlite sills at Benfontein, South Africa. J Geol Soc London 129:61–85
Eggler DH (1976) Does CO2cause partial melting in the low velocity layer of the mantle? Geology 4:69–72
Eggler DH, Wendlandt RF (1979) Experimental studies on the relationship between kimberlite magmas and partial melting of peridotite. In: Boyd FR, Meyer HOA (eds) Kimberlites, Diatremes and Diamonds: Their Geology, Petrology and Geochemistry. Washington, DC, American Geophysical Union, pp 330–338
El Goresy A, Yoder HS Jr (1974) Natural and synthetic melilite compositions. Carnegie Inst Washington Yearb 73:359–371
Gittens J, Hewins RH, Laurin AF (1975) Kimberlitic-carbonatitic dikes of the Saquenay River Valley, Quebec, Canada. Phys Chem Earth 9:137–148
Haggerty SE (1975) The chemistry and genesis of opaque minerals in kimberlites. Phys Chem Earth 9:295–307
Haggerty SE, Hardie RB, III, McMahon BM (1979) The mineral chemistry of ilmenite nodule associations from the Monastery diatreme. In: Boyd FR, Meyer HOA (eds) The Mantle Sample. Washington, DC, American Geophysical Union, pp 249–256
Haskin LA, Frey FA, Haskin MA, Schmitt RA, Smith RH (1966) Meteorite, solar and terrestrial abundances of rare earth distribution. Phys Chem Earth 7:167–321
Mazzullo LJ, Dixon SE, Lindsley DH (1975) T-fO 2 relationship in Mn-bearing compositions (abstract). Geol Soc Am, Abstr with Progr 7:1192
McMahon BM, Haggerty SE (1979) The Oka carbonatite complex: Magnetite compositions and the related role of titanium in pyrochlore. In: Boyd FR, Meyer HOA (eds) The Mantle Sample. Washington, DC, American Geophysical Union, pp 382–392
McMahon BM, Haggerty SE. Bence RJ (1979) Oxide mineral chemistry and oxygen fugacities of the Benfontein sills, South Africa (abstr). Cambridge Kimberlite Symposium, Cambridge, England
Mitchell RH (1973) Magnesian ilmenite and its role in kimberlite petrogenesis. J Geol 81:301–311
Mitchell RH (1977) Geochemistry of magnesian ilmenites from kimberlites from South Africa and Lesotho. Lithos 10:29–37
Mitchell RH (1978) Manganoan magnesian ilmenite and titanium clinohumite from the Jacupiranga carbonatite, Sao Paulo, Brazil. Am Mineral 63:544–547
Mitchell RH (1979) The alleged kimberlite-carbonatite relationship: Additional contrary mineralogical evidence. Am J Sci 279:570–589
Mitchell RH, Clark DB (1976) Oxide and sulfide mineralogy of the Peuyuk kimberlite, Somerset Island, NWT, Canada. Contrib Mineral Petrol 56:157–172
Nickel EH (1962) Compositional variation in pyrochlore and niobian perovskite from a niobium deposit in the Oka district of Quebec. Dept Mines Tech Surv, Canada, Tech Bull TB-31:1–35
Pinckney LR, Lindsley DH (1976) Effects of magnesium on irontitanium oxides (abstract). Geol Soc Am, Abstr with Progr 8:1051
Prins P (1972) Composition of magnetite from carbonatites. Lithos 5:227–240
Wendlandt RF, Harrison WJ (1979) Rare earth partitioning between immiscible carbonate and silicate liquids and CO2 vapor: Results and implications for the formation of light rare earth enriched rocks. Contrib Mineral Petrol 69:409–419
Wendlandt RF, Mysen BO (1980) Melting phase relations of natural peridotite+CO2as a function of the degree of partial melting at 15 and 30 kbar. Am Mineral 65:37–44
Wyllie PJ, Huang WL (1975) Peridotite, kimberlite and carbonatite explained in the system CaO-MgO-SiO2-CO2. Geology 3:621–624
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Boctor, N.Z., Boyd, F.R. Oxide minerals in a layered kimberlite-carbonate sill from Benfontein, South Africa. Contr. Mineral. and Petrol. 76, 253–259 (1981). https://doi.org/10.1007/BF00375452
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DOI: https://doi.org/10.1007/BF00375452