ИСТИНА

Fe-Ti-V deposits related to basic-ultrabasic intrusions are widespread within the Eastern Siberia. The two largest of them are located in the Kodar-Udokan trough (Siberian Platform) and Taimyr Peninsula in the Chineysky and Dyumtaleysky massifs consequently. The problem of ore origin includes an estimation of parental melt composition and its evolution. To solve it we have studied the internal structure, composition of rocks and ores from these massifs. The first one (lopolith) has thickness 2.5 km and consists of four rock groups formed during different stages. These are the following: 1) coarse-grained anorthosite, 2) high-Ti gabbro and gabbronorite, 3) low-Ti gabbronorite and norite, 4) lamprophyre. Layering is a typical feature of the second group of rocks enriched in titanomagnetite. Disseminated ore consists of 10-80 vol% titanomagnetite and massive ore contains 80-100 vol% titanomagnetite. Orebodies occur as layers or irregular bodies. Economic Cu-Ni sulfide mineralization (Cu/Ni=10-100) concentrates within the lower boundary of the massif and includes the endo-and exocontact ore. The main ore mineral is chalcopyrite. Chineysky massif essentially consists of basic rocks with typical crustal characteristics (Ta-Nb negative and Pb positive anomalies). Dyumtaleysky intrusion represents tabular body of 600 m in thick. It consists of two groups of rocks – gabbro (upper zone, 300 m) and peridotites (lower zone, 300 m). It was suggested that they were formed at two stages. The upper zone is characterized by layering which is similar to the layering of the Chineysky massif. Concentration of titanomagnetite forms disseminated and massive ores. There is no massive ore of irregular form. Sulfides are concentrated within the massif (between upper and lower zones) and in the endocontact zone. The mineralization consists of chalcopyrite, pyrrhotite, pentlandite, millerite, cubanite; Cu/Ni= 1-0.5. In contrast to the rocks of the Chineysky massif the rocks of the Dyumtaleysky intrusion are characterized by patterns without Ta-Nb anomaly. Gd/Yb ratio demonstrates the origin of these two massifs from different magma sources: shallow for the Chineysky intrusion and deep (with garnet) for the Dyumtaleysky one. Thus, Fe-Ti-V deposits could be formed from different magmas but contain the same type of ores because the leading process of ore formation is multiple fractional crystallization.