2013

The first data on petrology, geochemistry and mineralogy, unexplored, and the recently discovered occurrences of alkaline magmatism Kandalakshsky district

Akimenko MI, Kogarko NN., Sorohtina NV

Vernadsky Institute, Moscow, akimenko.alkaline@gmail.com

This work is devoted to the study of recently identified new occurrences of alkaline magmatism in Kandalakshsky district, represented by rare species of alkaline rocks of agpaitic series - malignites.

Geology. Dike of malignite locate in the south-western part of the Kola Peninsula, in the Kandalaksha district. In the middle reaches of the river Kanda. The strike of the dike east, north-east. Contacts with the host rocks clear. The host rocks are metamorphic of Archean (AR₂ mt), Proterozoic igneous complexes acid composition (γ₂PR₁), and igneous massif of ultrabasic  Sorkayokskoy Group (νσРR₁).

According to the drilling alkaline rocks can be traced in the range of 4.0 - 93.9 m dike parameters: stretch east, the length of about 1.0 km, the width in terms of an average of 160 m drop to the north at an angle of 60⁰-90 ° .

Mineralogy. The rock generally consist of mafic alkaline minerals, which makes up 70 vol. The main rock minerals are arfvedsonite, aenigmatite, lamprophyllite, barytolamprophyllite, astrophyllite, nepheline, feldspar. Minor mineral are shcherbakovite, aegirine-augite. Ore minerals are ilmenite, goethite. Of the group of secondary minerals are sodalite, natrolite.

Feldspar and nepheline usually form a mass of fine-grained leucocratic practically inseparable, occupying the interstices between the grains of mafic minerals.

Arfvedsonite represented by two generations which closely related to each other. Arfvedsonite I forms elongate major grain brown in color, with slight bluish tinge, longitudinal cross-section less frequently have a hexagonal shape (Fig. 1). Arfvedsonite - I forms an elongated, sometimes needle-like grains of blue-green color with an uneven color, with negative elongation. It develops in the earlier arfvedsonite.

Lamprophyllite represented by two species (Fig. 1, 2). Lamprophyllite I forms a yellow prismatic crystals in the interstices between the grains of amphibole. Lamprophyllite II (barytolamprophyllite) forms a scaly shapeless mass of yellow color in the interstices between the grains and I arfvedsonite lamprophyllite. According to their optical properties lamprophyllite II is different from the early lamprophyllite.

Astrophyllite forms a yellow-orange fine-scaled, micaceous mass units less needle-like crystals in the interstices between the grains of amphibole and lamprophyllite .

Aenigmatite (fig. 2) forms large tabular crystals with perfect cleavage and a very high relief. Aenigmatite often surrounded by a rim of light, yellow-orange astrophyllite and often replaced by lamprophyllite.

Geochemistry. Agpaite coefficient values ​​(according to Table 3) in the test unit malignites greater (mean 1.2).

Table 1. Chemical composition of maligmite (wt.%)

Conclusions. The studied rocks are rare species of nepheline syenite - malignite. It can be assumed that they are analogues of nepheline syenite, as described earlier in the largest alkaline massifs of the Kola alkaline province: the   Khibini and Lovozero [1]. Malignite rocks arise as a result of derivative the same tectonic and magmatic activity of Paleozoic age.

References:

Gerasimovsky VI, Volkov VP, Kogarko N. Polyakov, I., Saprykina T., Balashov, Yu A, Geochemistry of the Lovozero alkaline massif, M. 1966.