Alkaline Rocks and Carbonatites of the World

Setup during HiTech AlkCarb: an online database of alkaline rock and carbonatite occurrences

Panda Hill (Mbeya)

stripes

Occurrence number: 
163-00-038
Country: 
Tanzania
Location: 
Longitude: 33.23, Latitude: -9
Carbonatite: 
Yes

Panda Hill is approximately circular, with a diameter of 1.8 km, and rises to about 350 m. A central complex of carbonatites is intruded into Precambrian gneisses of the Ubendian System, which are extensively fenitized, but some of the outer contacts are obscured by volcanic ash derived from the Rungwe volcanic field (No. 163-00-040). On the northern side of the complex, including Panda Hill summit, and in the southeast, are areas of agglomeratic rocks, while there are many small vents choked with feldspathic agglomerates and breccias. The carbonatite has a complex, lobed distribution. The principal type is sovite, but there are several areas of ferrocarbonatite and numerous dykes of beforsite which cut across the flow-banding of the sovite, although others are conformable to it. The sovite banding, which has a steep inward dip, is partly defined by apatite- and magnetite-rich streaks. Along the eastern margin, in particular, fenite xenoliths are numerous and often many metres in diameter. All the carbonatite types are cut by late carbonate veins. The sovite commonly contains pyrite, magnetite, apatite (up to 13% by volume) and pyrochlore, with less commonly quartz and fluorite, which sometimes forms veinlets, and tetraferriphlogopite, REE carbonates, celestite and barite also occur. The beforsites are sugary textured dolomite rocks with some calcite and accessory magnetite, apatite, pyrochlore, ilmenite and occasionally titanite and rutile; in places the rocks have been extensively silicified. The ferrocarbonatites comprise calcite with later stage streaks and patches of brown turbid carbonate with the calcite extensively impregnated with iron oxides. Accessories include quartz, magnetite, apatite, fluorite and monazite; pseudomorphs after pyrochlore are present, but not the fresh mineral. Small bodies, mainly dyke-like, of layered apatite-magnetite rock are referred to by Basu and Mayila (1986) as 'pseudo-phoscorite'; they lie within the sovite and are conformable to the banding. There is a little pyrochlore and quartz present. Most of the fenites are shattered and brecciated basement gneisses with little development of new minerals. These pass into rocks in which blue sodic amphibole is developed and phlogopite may form at the expense of garnet. Adjacent to the carbonatite are ultra-potassic fenites consisting essentially of K-feldspar, and the same rock type is found as dykes cutting the basement gneisses. The agglomerates and breccias consist generally of crystals, fragments and blocks of K-feldspar in a matrix which may be feldspar or carbonate. In some varieties the blocks are of K-feldspar fenites and only slightly fenitized basement gneiss. A list of the minerals identified at Panda Hill will be found in Heinrich (1966) and petrography and analyses of carbonates, apatite and phlogopite in Basu and Mayila (1986). Pyrochlore has been described in a number of papers (e.g. James and McKie, 1958; Fawley and James, 1955) and may be replaced by columbite or altered to fersmite (Veen, 1960); a hydrated Ba-Sr variety has been named 'pandaite' (Jager et al., 1959). Suwa et al. (1969) give petrographical descriptions of the carbonatites together with oxygen and carbon isotope data, which are also to be found in Suwa et al. (1975). Ziegler (1992) gives some trace element data on two sovites together with Rb, Sr, Sm and Nd isotopic values, and Bell and Blenkinsop (1987) isotopic data for a single carbonatite sample.

Economic: 
Pyrochlore is widespread in the carbonatite and with the aid of drilling 125 million tons averaging 0.3% Nb2O5 have been proved. Among richer ore zones one area of contact rock with pandaite, as well as pyrochlore, contains 3.8 million tons averaging 0.79% Nb2O5. A pilot mill was operated from 1957 to 1960 (Deans, 1966; Fawley and James, 1955). Extensive accumulations of phosphate, with up to 20% P2O5, occur in residual soils (van Straaten, 1989).
Age: 
K-Ar on mica separated from carbonatite gave 113±6 Ma (Snelling, 1965). Determinations by the U-Pb method on two samples of pyrochlore gave discordant ages from 68 to 273 Ma the samples probably having been chemically altered (Schurmann et al., 1960; Snelling, 1965).
References: 

BASU, N.K. and MAYILA, A. 1986. Petrographic and chemical characteristics of the Panda Hill carbonatite complex, Tanzania. Journal of African Earth Sciences, 5: 589-98.BELL, K. and BLENKINSOP, J. 1987. Nd and Sr isotopic compositions of East African carbonatites: implications for mantle heterogeneity. Geology, 15: 99-102. DEANS, T. 1966. Economic mineralogy of African carbonatites. In O.F. Tuttle and J.Gittins (eds), Carbonatites, 385-413. John Wiley, New York. FAWLEY, A.P. and JAMES, T.C. 1955. A pyrochlore (columbium) carbonatite, southern Tanganyika. Economic Geology, 50: 571-85.HEINRICH, F.W. 1966. The geology of carbonatites. Rand McNally, Chicago, 608 pp.JAGER, E., NIGGLI, E. and VAN DER VEEN, A.H. 1959. A hydrated barium-strontium pyrochlore in a biotite rock from Panda Hill, Tanganyika. Mineralogical Magazine, 32: 10-25.JAMES, T.C. and MCKIE, D. 1958. The alteration of pyrochlore to columbite in carbonatites in Tanganyika. Mineralogical Magazine, 31: 889-900.SCHURMANN, H.M.E., ATEN, A.H.W., BOERBOOM, A.J.H., BOT, A.C.W.C., CONWENBERG, G., DANCE, D.F., HURLEY, P.M., LEDENT, D., STAUFFER, H., STEENSMA, J.J.S. and SURINGA, R. 1960. Fourth preliminary note on age determinations of magmatic rocks by means of radioactivity. Geologie en Mijnbouw, 22: 93-104.SNELLING, N.J. 1965. Age determinations on three African carbonatites. Nature, London, 205: 491.SUWA, K., OSAKI, S., OANA, S., SHIIDA, I. and MIYAKAWA, K. 1969. Isotope geochemistry and petrology of the Mbeya carbonatite, south-western Tanzania, East Africa. The Journal of Earth Sciences, Nagoya University, 17: 125-68.SUWA, K., OANA, S., WADA, H. and OSAKI, S. 1975. Isotope geochemistry and petrology of African carbonatites. Physics and Chemistry of the Earth, 9: 735-45.VAN STRAATEN, P. 1989. Nature and structural relationships of carbonatites from southwest and west Tanzania. In K. Bell (ed.) Carbonatites: genesis and evolution. 177-99. Unwin Hyman, London. VEEN, A.H.VAN DER, 1960. The alteration of pyrochlore to fersmite in the Mbeya carbonatite. Geologie en Mijnbouw (Billiton issue), New Series, 22: 512-5.ZIEGLER, U.R.F. 1992. Preliminary results of geochemistry, Sm-Nd and Rb-Sr studies of post-Karoo carbonatite complexes in southern Africa. Schweizerische Mineralogische und Petrographische Mitteilungen. Zurich, 72: 141-8.

Map: 
Fig. 3_315 Panda Hill (after Basu and Mayila, 1986, Fig. 2).
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