Alkaline Rocks and Carbonatites of the World

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

Arbarastakh

stripes

Occurrence number: 
136-01-027
Country: 
Russia
Region: 
Aldan
Location: 
Longitude: 131, Latitude: 56.75
Carbonatite: 
Yes

Lying within Precambrian gneisses, granites and schists the Arbarastakh complex has a striking concentric structure. It is a 7x5 km stock which is composed dominantly of micaceous magnetite pyroxenite. All younger rocks lie within the pyroxenite stock or within the enveloping fenite aureole. A sickle-shaped body of apatite-magnetite-forsterite rocks (phoscorite) is situated in the centre of the complex. In the outer parts of the stock and in the fenite aureole small arcuate bodies of syenite, ijolite and nepheline-pyroxene rocks are concentrated. A large number of arcuate sheets of carbonatite, which are concentrically arranged about the centre of the complex and younger than the syenites and ijolites, are present throughout. Vertical dykes of picrite are radially disposed. The pyroxenites are only exposed in a few places. They are generally much replaced by mica and amphibole and are permeated by a network of veins of differing ages. The contacts of the pyroxenites with the fenites are sharp. Fenite fragments, up to 3 m3, are found in the outermost pyroxenite zone and these blocks are surrounded by mica-pyroxene reaction borders. The pyroxenites are formed by diopside, titanomagnetite and accessory apatite. The fenite aureole is up to 0.8 km wide. Nepheline-pyroxene and albite-pyroxene rocks do not form substantial independent bodies but occur as large numbers of small veins, lenses and bands in a broad ring zone. Ijolite- melteigite, ijolite porphyry and kalsilite ijolite porphyry form dykes in pyroxenites and in fenites. Alkaline syenites form numerous veins amongst which two age groups can be distinguished: the earlier group are cancrinite alkaline syenites (cancrinite + alkali feldspar + pyroxene ± biotite) and the later group consists of biotite and pyroxene alkaline syenites which contain calcite impregnations (K-Na feldspar + pyroxene ± biotite ± calcite). Syenites containing what is considered to be primary magmatic cancrinite are described by Zhabin and Sveshnikova (1971). The central bodies of phoscorite conform to the concentric structure of the complex. Their composition is highly variable with wide variations in the modal contents of the four principal rock-forming minerals, that is forsterite, magnetite, apatite and calcite. Amongst the phoscorites three groups can be distinguished which were generated in the following sequence: (1) magnetite-forsterite, (2) apatite-magnetite-chondrodite, in which the chondrodite develops at the expense of forsterite, and (3) apatite-calcite with magnetite, mica and chondrodite. Between the pyroxenites and phoscorites a zone of pegmatitic pyroxene rocks with magnetite is observed. Carbonatites are represented by a number of varieties. The earliest group are calcite carbonatites with alkali feldspar, cancrinite and zircon, the silicates comprising up to 45-60% of the rock. They are found near contacts with the alkaline syenites. For the second group of carbonatites the order of emplacement is calcite, calcite-dolomite, dolomite, and ankerite carbonatites. The calcite and calcite-dolomite carbonatites comprise 90% of the carbonatites of the complex. Mineralogically they include forsterite (chondrodite), magnetite, apatite and accessory pyrochlore, baddeleyite and zirconolite. These are medium- and coarse-grained rocks with spotted and linear textures and structures. Dolomite carbonatites are fine- grained, massive rocks which contain a small quantity of phlogopite and alkali amphibole of the riebeckite type. They form small lens-like bodies and a series of small, gently dipping veins in fenites and fenitized gneisses. The ankeritic carbonatites contain burbankite, bastnaesite, parisite, huanghoite, strontianite, baryte, witherite, galena and sphalerite. They form narrow veins which cut the calcite carbonatites. Three groups of vein rocks are distinguished: (1) picrite porphyry, (2) syenite porphyry, tinguaite porphyry and cancrinite syenite porphyry and (3) ijolite porphyry, feldspathic ijolite porphyry and kalsilite ijolite porphyry.

Economic: 
There is a potentially economic apatite-magnetite deposit (Frolov, 1984).
Age: 
K-Ar determinations on phlogopite from pyroxene-mica rocks gave 690±28, on apatite-magnetite rocks 720±28 and on carbonatites 690±28 Ma (Glagolev and Korchagin, 1974). K-Ar on phlogopite from forsterite-magnetite rocks gave 625 Ma (El'anov and Moralev, 1961).
References: 

BORODIN, l.S., LAPIN, A.V. and CHARCHENKOV, A.G. 1973. Rare-metal camoforite. Nauka, Moscow. 176 pp. EL'YANOV, A.A. and MORALEV, V.M. 1961. New data on the age of the ultramafic and alkaline rocks of the Aldan shield. Doklady Akademii Nauk SSSR, 141:‚ 686-9. GLAGOLEV, A.A. and KORCHAGIN, A.M. 1974. Alkaline-ultrabasic massifs. Arbarastakh and Inagli. Nauka, Moscow. 176 pp. SEMENOV, E.I., ESKOVA, E.M., KAPUSTIN, Yu.P. and HOM'AKOV, A.P. 1974. Mineralogy of the alkaline massifs and their deposits. Nauka, Moscow. 247 pp. ZHABIN, A.G. and KHARCHENKOV, A.G. 1973. Arbarastakh carbonatite complex (south Yakutia province). In. L.S. Borodin (ed) New data on the geology, mineralogy and geochemistry of the alkaline rocks. 142-57. Nauka, Moscow. ZHABIN, A.G. and SVESHNIKOVA, Ye.V. 1971. Magmatic cancrinite. International Geology Review, 13: 1269-74.

Map: 
Fig. 2_233. Arbarastakh (after Borodin et al., 1973, Fig. 4.1).
Location: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith