MINERAL ASSOCIATIONS AND GENETIC MODELS OF NATIVE IRON FORMATION IN MAGMATIC ROCKS OF SIBERIA
M.O. Khmelnitskaya1, O.S. Vereshchagin1, A.G. Kopylova2, Yu.D. Gritsenko3,4, N.S. Vlasenko1, S.N. Britvin1
1Saint Petersburg State University, St. Petersburg, Russia
2Diamond and Precious Metal Geology Institute, Siberian Branch, Russian Academy of Science, Yakutsk, Russia
3Lomonosov Moscow State University, Moscow, Russia
4Fersman Mineralogical Museum Russian Academy of Sciences, Moscow, Russia
Keywords: Native iron, carbide, germanide, phosphide, sulfide, EBSD
Abstract
Native iron occurrences in Siberian magmatic rocks (gabbro-dolerites) have been known since the second half of the 20th century and are among the largest in the world. However, detailed data on minerals associated with native iron are lacking, and its genesis remains a subject of scientific debate. This paper examines native iron and associated anoxic minerals from magmatic rocks of Krasnoyarsk Krai (Dzhaltul, Khungtukun, Khininda, and Maimecha) and Yakutia (Aikhal), and summarizes data on accessory minerals and their genesis. In the studied samples, native iron is associated with oxides (ilmenite, magnetite, titanomagnetite, hercynite, wustite, rutile), native elements (taenite, copper, graphite, bismuth and lead), intermetallics (tetrataenite, awaruite, a compound of the Ni-Sn system close to Ni3Sn), carbides (cohenite and haxonite), germanide (olgafrankite Ni3Ge), phosphide (schreibersite), sulfides and their analogues (troilite, pentlandite, cobaltpentlandite, heazlewoodite, chalcopyrite, cubanite, chalcocite, bornite, mackinawite, weissite, orcelite, sphalerite, nickelite and sperrylite). Mineral association of native iron varies among the various massifs and is most diverse in the Dzhaltul intrusion, characterized by the presence of native mineral phases of nickel, germanium, and tin. The mineral association of native iron of the Dzhaltul intrusion is similar to those identified on Disko Island (Greenland). Based on the original and previously published results, it is suggested that native iron was formed under low-pressure near-surface conditions (pressure ~30-100 MPa) at initial temperatures typical of basaltic melt (~1000-1200 ºC), as a result of the interaction of silicate melt with sedimentary rocks rich in organic matter. Data on the geological position of the studied massifs and the established conditions of their formation indicate that igneous rocks containing native iron should be widespread within the margins of the Tunguska syneclyse.
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