The perspectives of the potential diamondiferriosity of the southern and southeastern territory of the Evenk autonomous region are rather optimistic in the light of the available geology-structural facts. Unfortunately these perspectives couldn't be transferred to the exact diamond deposits, mainly because of the small searching-exploratory work volume being limited by insufficient assignations.

At present the biggest perspectives of the exposure of the basic diamondiferrouosity are connected with Tychansk diamondiferrous region, situated in the southwestern part of the Siberian platform in the zone of its two big above-ordered structural elements - Baikitsk anteclise and Tungussk anteclise conjugation.

The Tychanskiy region Tectonic scheme

The northwestern and central parts of the Tychansk diamondiferrous region according to their structural-tectonic position are spacely timed to the hard consolidated part of the earth-crust-archean craton. Exactly all the diamondiferrous (kimberlite and lamprouite) provinces of the world including the Yakutsk diamondiferrous subprovince are connected with such cratonized elements of the ancient platforms, as a rule.

The systematic searching for diamonds in Evenkia were started by the Orlovsk expedition of the MinGeo USSR in 1946 and had been carried out for ten years. As the result the non-industrial alluvial diamond field with the length of 100 km was ascertained in the basin of the river Tychana. The erosion of the intermediate diamondiferrous collector formed the diamond field. The weight of the diamonds of this field is from the first mg to 3.5 carat, the average weight is 50.9 mg.

Further the intermediate (second) low-middlecarbon diamondiferrous collector was exposed and studied in some local parts in the Tychana basin during the search-surveying work in the period of 1985-1992.

The considerable contents of high chromic low-calcium crimson pyropes of the diamond association from 0.9 to 5.0% and more, along with diamonds, in the intermediate collector rocks indicate the undoubtedly their sources were partially erosed about 300-330 mln years ago, then buried by younger deposits kimberlite tubes of heightened diamondiferrouosity. Undoubtedly tubes with industrial contents of high qualitative jewelry diamonds can be found among them.

The diamond content in the rocks of the collector fluctuates in wide limits, from 0.1 to 2.0 carat/m3. Crystals fluctuatein the classes -4 +2, -2+1 and more rarely -1. The weight of the diamonds is from the first mg to 1 carat. According to the results of the special crystal-morphological researches the Tychansk diamonds form a complex, having no analogues among the Yakutsk deposits. Most of the diamonds are transparent (78%), the quality of the diamonds is high in the whole, jewelry crystals consist 63%. The peculiarity of the Tychansk diamonds is the higher content of nitrogen free and nitrogen insufficient kinds (24%), after studying the content of the admixtureous nitrogen and isotope carbon characteristics it was concluded that the Tychansk diamonds differ from the Yakutsk ones and possibly originate from several sources.

The Tychansk diamondiferrous region is covered with the geological survey in the scale of 1:200000 and one the third of it (the northern part) is covered with the survey in the scale of 1:50000, besides with the gravimetric surveys of 1:200000 and partially the scales are 1:50000 and 1:25000. Practically the aeromagnetic survey in the scale of 1:25000 has been made on all the area of the region. Besides the profile works of the DSS (Deep Seismic Sound) and other regional geophysical works have been carried out.

In the whole the structural-tectonic situation of the region is favorable for the localization of the kimberlite magmatizm. The additional corroboration to it is the results of the interpretation of the regional geological-geophysical data (Hydrogenous Seismic Sound - HSS) carried out by academician V.S. Surkov and professor V.S. Staroseltsev on one of the profiles situated in the northern part of the region in 1998.

Geologo-geophysical section along the Baikit-Boguchany profile of deep seismic probing

(According to V.S. Surkov and others, 1998)

The results of the fulfilled reconnaissance and search work and also the planned detailed search-exploratory works allow to expect with the greatest certainty the discovery of a new Evenkiisk diamondiferrous subprovince, possibly exceeding with potential reserve and diamond quality the known diamondiferrous subprovinces.

According to the results of the complex analysis of the structural-tectonic, lithological-stratigraphical, paleogeographical and mineragenic factors some perspective areas for the search of the basic diamond sources are localized in the region. Within these areas the carrying out of a wide complex detailed search-exploratory works is necessary. They must result in the discovery of the middlepaleozoic kimberlite tubes including those having industrial diamondiferrouosity.

The program of these works is expected to last 3-4 years and requires 20 - 25mln US $.