ИСТИНА

The Maimecha trap intrusion occur in the Maimecha-Kotui ргоvinсе. It is located at the region of the Tunguss volcanic basin. The Maimecha intrusion is poorly differentiated and uр to 60-100 m thick. It consists of taxitic olivil1e gabbro-dolerite, gabbro-dolerite, olivine-free gabbro-dolerite. The taxitic gabbro-dolerite is enriched in olivil1e and clinopyroxene, with irregular disseminations of pentlandite-chalcopyrite-pyrrhotite. The major part of the intrusion is layered gabbro-dolerite with varyil1g amounts of plagioclase and clil1opyroxene. Nodules of native iron from the Maimecha intrusion are globular or ellipsoidal in shape. The sizes of nodules range from 1 х 1,5 х 2 cm to 10 х 15 х 20 cm. As previously mentioned, the simplest shape is that of small globules. An increase in the size and amount of these globules results in changes to drop-shaped-interstitial and spongy textures. Iron nodules are framed by a magnetite-troilite rims on contact with the rock and Fe-Ni-Cu sulfides. In some cases, when observed in situ over large nodules of native iron gabbro-dolerite has poriferous texture. The pore volume reaches 60 vol. % Size ranges from 0.005 mm to 0.7 mm. The presence of such porous “caps” in the gabbro-dolerite indicates great role of gases and fluids in the formation and crystallization of native iron. Native iron forms eutectic graphic intergrowths with cohenite, the amount of which is 15-30 vol.%. Its precipitates are oriented predominantly in one direction in each grain of iron, and reach 100 μm. The chemical compositions iron and cohenite are close. Usually they contain (in wt.%): Ni 0.1–1.5; Cu 0.2–1; Co 0.4–1.7. Nickel iron - kamaсite is much less common, it forms isolated precipitates and cohenite-kamaсite eutectic aggregates in the marginal parts of the iron nodules. It contains (in wt.%): Ni 5–6; Cu 0,9–1,2; Co 1.4–1.7. Taenite forms small (10-30 μm) orbicular grains in magnetite which has replaced kamaсite. It contains (in wt.%): Ni 35–36; Fe 54–55; Co 6–7; Cu 2–2,2. Sperrylite, heazlewoodite, native bismuth are formed in magnetite which replaced of nickel iron and sulfides. The formation of native iron is probably caused by the introduction of a basic melt into the coal-bearing stratum, and the capture of carbonaceous xenoliths — sapropel. The interaction of the melt and xenoliths produced hydrocarbons. They reacted with silicate and sulfide melts with the formation of native iron and cohenite.