Alkaline Rocks and Carbonatites of the World

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

Yaksha

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Occurrence number: 
136-03-007
Country: 
Russia
Region: 
North Baikal sub-province
Location: 
Longitude: 111.8, Latitude: 56.92
Carbonatite: 
No

From structural and morphological analysis and geophysical interpretation the Yaksha occurrence is apparently a plutonic dome built of alkaline rocks and granites and extending to a depth of not less than 10 km. The alkaline intrusion is in contact with Precambrian and Cambrian crystalline schists and marbles and granitoid domes of late Palaeozoic age. The area of alkaline rock outcrops is about 100 km2. The larger part of the massif is composed of alkaline syenites which consist predominantlyy of orthoclase and microperthite (60-80%), pyroene (5-15%), biotite (3-12%) admixtures of albite and nepheline and accessories including titanite, magnetite and apatite and occasionally quartz. Because of wide variation in the quantity of nepheline (up to 20%), the rocks vary from alkaline syenites to foyaites. Nepheline, nepheline-kalsilite and kalsilite syenites are intimately mixed. Two structural-textural facies of the rocks are distinguished: massive and banded gneiss-like. Nepheline syenites (frequently pseudoleucite syenites) have a rather simple composition of orthoclase (50-70)%, nepheline (15-30%), biotite (6-15%), pyroxene (up to 5%), albite (up to 3%) and accessory titanite, apatite, magnetite, garnet and zircon. Nepheline-kalsilite and kalsilit syenites (synnyrites) are rare. Usually leucocratic pseudoleucite rocks with a distinctly orientated assemplage of dark-coloured minerals are predominant. They comprise orthoclase (65-75%), kalsilite (up to 2%) biotite (3-10%) with a small amount of garnet, pyroxene, nepheline and albite. Mineral and rock compositions are available in Orlova (1990) and Kshirin (1971) gives modal and chemical data, including REE, for part of the complex called Daoksha.

Age: 
A Rb-Sr whole-rock isochron gave 313±11 Ma. K-Ar dating of amphibole in biotite-amphibole peralkaline syenite gave 310±7 Ma, on biotite 283±13 Ma, on feldspar 273±12 Ma, on muscovite from muscovitized nepheline syenite 297±15 Ma and on biotite 267±Ma (Zhidkov, 1990).
References: 

*KASHIRIN, K.F. 1971. Petrochemical and geochemical characteristics of nepheline syenites of northern Baykal highland. International Geology Review, 13: 1330-8.
ORLOVA, M.P. 1990. Mesozoic stage of magmatism. In G.V. Pol'akov and V.V. Kepezinskas (eds) Potassium alkaline magmatism of the Baikal-Stanovoy rifting system. 65-123. Nauka, Siberian Branch of the Academy of Sciences, Novosibirsk.
ZHIDKOV, A.Ya. 1990. Palaeozoic stage of magmatism. In G.V. Pol'akov and V.V. Kepezinskas (eds) Potassium alkaline magmatism of the Baikal-Stanovoy rifting system. 32-64. Nauka, Siberian Branch of the Academy of Sciences, Novosibirsk.

Map: 
Fig. 2_183. Yaksha (after Zhidkov, 1990, Fig. 18).
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith