stripes
The Seligdar apatite ore field was formed during the Proterozoic and developed in a zone 6-7 km wide and 20-25 km long; Fig. 227 only depicts part of this field. The country rocks are Archaean quartzites, schists, granites and gneisses with remnants of the platform cover, represented by Cambrian dolomites and sandstones, also preserved in the region. The ancient rocks are cut by a series of faults associated with which are serpentine-chlorite and quartz-chlorite-sericite metasomatites, as well as dykes of Mesozoic syenite porphyry, pseudoleucite porphyry, kersantite and dykes and small stock-like bodies of shonkinite, which are located both in the main complex and around it. Vasilenko et al. (1982) have reconstructed the original composition of the complex and have suggested that the following magmatic-metasomatic events were involved in its genesis. In the late Proterozoic era a basic potassic alkaline intrusive complex of central type was emplaced at Seligdar. Earlier peridotite-missourite phases of this complex contained on average 4-6% of P2O5 and in schlieren up to 20% P2O5. In the final stages of intrusive activity shonkinite dykes were emplaced. It is surmised that differentiation of the melt took place with the generation of an aqueous calcium carbonate pneumatolytic phase which initially, through the reaction of a carbonate-aqueous composition, led to the alteration of the rocks to greenstones. The mineralogy of these rocks is: orthoclase + plagioclase + biotite + apatite + magnetite + chlorite + phengite + hematite + carbonate or orthoclase + plagioclase + apatite + magnetite + albite + phengite + chlorite + hematite + carbonate + leucoxene or plagioclase + phengite + chlorite + epidote + quartz + carbonate + hematite. At lower temperatures (400-500˚C) carbonate autometasomatism brought about further dolomitization and subsequent calcitization of the rocks. During these metasomatic processes phosphorus was inert but carbonate, alkalis, silicon and magnesium were lost into the country rocks resulting in the formation of K-feldspar, quartz and wollastonite metasomatities. In the course of this process the apatite-carbonate rocks of Seligdar were generated. These rocks consist principally of apatite, dolomite and calcite with less hematite (martite), quartz and phlogopite and accessory monazite, zircon, rutile, tourmaline, orthite, topaz, pyrite, chalcopyrite, galena and magnesite. The proportions of the rock- forming minerals vary within very wide limits. There are a number of ideas as to the generation of the Seligdar apatite deposits. According to Entin (1966) the principal role belongs to high- temperature apatite-bearing carbonatites, and the igneous association is persued further by Entin et al. (1985). In contrast, Bulakh et al. (1985) conclude that the phosphate has been mobilised from the surrounding country rocks. A notable feature of the Seligdar apatite is the abundance of micro- inclusions of monazite, serpentine, carbonate, chlorite, titanite and mica. The apatite of the apatite-carbonate rocks is typically a red colour, which is due to hematite inclusions. The compositions of ores, rocks and some minerals can be found in the monograph by Vasilenko et al. (1982) and chemical data on apatite and C and O isotope measurements on carbonate rocks in Smirnov (1978).
BULAKH, A.G., ZOLOTAREV, A.A., BOBROVA, I.P., GULIY, V.N. and VANDE-KIRKOV, Yu.V. 1985. Fundamental mineralogic features and origin of the Seligdar apatite deposit (Aldan crystalline shield). International Geology Review, 27: 144-56.
ENTIN, A.R. 1986. High temperature mineral associations of apatite-bearing carbonatites of Seligdar type. In I.M. Frumkin (ed) Geology and geochemistry of the ore-bearing magmatic and metasomatic associations from the Maly BAM area. 90-105. Yakutia Branch of the Siberia Division of the USSR Academy of Sciences, Yakutsk.
ENTIN, A.R., BELOUSOV, V.M. and GALKIN, G.F. 1977. New data on the geology of the Seligdar apatite deposits. In. F.L. Smirnov (ed) Apatite of the Aldan Shield. 5-18. Yakutia Branch of the Siberia Division of the USSR Academy of Sciences, Yakutsk.
ENTIN, A.R., SOBOTOVICH, E.V., OL'KHOVIK, Yu.A., RUDNIK, V.A. and BELOUSOV, V.M. 1985. Conditions of formation of the Seligdar apatite deposit. International Geology Review, 27: 157-67.
KRASILNIKOVA, N.A. and ILYIN, A.V. 1989. Igneous Proterozoic-Cambrian phosphate resources in eastern Siberia, USSR. In A.J.G. Notholt, R.P. Sheldon and D.F. Davidson (eds). Phosphate deposits of the world. 2. Phosphate rock resources. 510-7. Cambridge University Press, Cambridge.
SMIRNOV, F.L. 1976. New genetic type of commercial apatite deposits. Doklady Earth Science Sections. American Geological Institute, 230: 86-8.
SMIRNOV, F.L. 1978. Geologic position and conditions of formation of the Seligdar apatite deposit. International Geology Review, 20: 1043-9.
SMIRNOV, F.L., ENTIN, A.R., UGR'UMOV, A.N. and BURNAIKIN, A.I.
1975. Precambrian apatite mineralisation at the fault zones of the central part of the Aldan Shield. In. Phosphorite of Yakutia. 53-74. Yakutsk.
VASEILENKO, V.B., KUZNETSHOVA, L.G., HOLODOVA, L.D., EGIN, V.I., ENTIN, A.R., SUCHKOV, V.I. and BELOUSOV, V.M. 1982. Apatite rocks from the Seligdar. Nauka, Novosibirsk. 215 pp.