Location, landform, climate and development of the region

The deposit of alluvial diamonds of the valley of the Molodo river is located in the north of the Republic of Sakha (Yakutia) in the territory of Bulunskiy ulus (administrative centre – city of Tiksi).
In morphological terms the project area is characterised by basic specific features of the northeast margin of the Middle-Siberian upland and has an undulating landform inherent to Leno-Olenekskiy plateau. Absolute marks average 270-300 m, more rarely 140-200 m.
The main waterway of the deposit area is the Molodo river (left tributary of the Lena river) with large tributaries: Usunku, Tit-Yuryague (left tributaries), Syungyude, Khastakh (right tributaries).
The rivers regime is extremely variable and depends upon the amount of atmospheric precipitation. Rivers break-up normally occurs in the end of May - beginning of June. Maximum water level rise reaches 7 m and happens in spring. The freeze-up begins in the second half of September.
The climate of the region is extremely continental, which is manifested by substantial seasonal differences of air temperature, rather small overcast and relative shortage of precipitations. Winter is very cold (reaching -64°C), long (7-8 months), summer is hot (air temperature reaches +35°C). Frosts sometimes occur in summer, in August frosts are quite often, and in the first half of September snowfalls are rather frequent.
The vegetation of the region is characteristic of the northern taiga zone. In the river valleys besides Dahurian larch one can see spruce, alder, birch (the latter is more typical for the Molodo river valley). The fauna is not rich. There are wild reindeers, elks, polar hares, polar wolfs, bears,  gluttons, etc.

Geologic background of the deposit area
 
Systematic prospecting of the region began in the fifties of the last century. Aerial survey of the entire territory of the Lena region was carried out; geological survey was performed; a 1:1,000,000 geological map was made up; geomorphological researches were conducted; by reference to pyrope content in washings potentially productive areas for diamond searches were determined.
The first diamonds in the channel alluvium of the Molodo river (2 crystals) were found during 1:200,000 scale geologic survey conducted by the All-Union Aerogeological Trust (VAGT) as early as 1957-1961 (R.A.Bidzhiev, 1958, L.M.Natapov, 1959).
Since that time and up to the end of the 80-ies various organisations carried out research, prospect evaluation, explorative, and thematic operations in the region including the Molodo river basin. As a result of these operations reserves of Molodo alluvial deposits (a detailed exploration was carried out) and Verkhnee Molodo alluvial deposits (a preliminary exploration was carried out) were revealed and reckoned. The stones of revealed deposits, as compared to other placer deposits of Northern Yakutia, are characterised by a higher quality. The content of jeweller stones is about 30%. In terms of diamond content alluvial deposits are referred to average ones with a low content of a useful component. For this reason the reserves of the first site reckoned by categories S1 and S2 recognised on the State balance were not transferred under industrial development. Verkhnee Molodo alluvial deposit reserves have not been considered by the Regional Reserves Committee.
The obtained results served as a basis for exploration, auditing and test-and-production operations at alluvial deposits Molodo and Verkhnee Molodo. The work was started by joint venture Yakutzolotonedra (1992-94), and has been continued (on the basis of the decree of the President of the Republic of Sakha (Yakutia) No. 765s of 29 March, 1994) to date by OAO Nizhne-Lenskoye.

Diamond content of the alluvial deposit

The Molodo river alluvial deposit has a common history of formation and a single bed-rock source with other alluvial deposits of the northwest part of the Republic of Sakha (Yakutia) – more than 100 placer deposits and occurrences of diamonds of a single type (in terms of crystallomorphological signs) were revealed in the area of about 250 thousand sq. m.

Hydrological conditions of the deposit
 
The valley of the Molodo river within the industrial part of the alluvial deposit has a width of up to 1-2 km with a floor of 150 - 1600 m. The river channel slightly meanders, rectilinear sections of 2-6 km prevail. It represents an alternation of shallow (0.2-0.5 m) natural bars and somewhat deeper (1.5-2.5 m, sometimes up to 6 m) reaches. The length of natural bars does not exceed 150-200 m, and length of reaches is up to 4-5 km. The width of the river bed in the low-water period varies from 30-40 m to 135-155 m, in the high-water period it reaches 250-300 m. The river flow rate varies from 0.5-0.6 km/s at reaches to 0.9-1.5 km/s at bars and substantially decreases during the low-water period. The river’s regime is extremely changeable and is mainly determined by atmospheric precipitations. The spring high water begins in the end of May - beginning of June (right after the ice drift). Maximum water rise is 6-7 m at a rate of 0.20-25 cm/h. The duration of the spring high water is about one month.
In the beginning of July a short summer low-water period sets on the river, occasionally interrupted by rain high waters. In low-water years, as it was in 1998, a very low water level occurs, the river bed shallows at natural bars and is decomposed in a number of small streams. In rainy years there is virtually no summer low-water period. In the beginning - middle of August the low period is usually replaced by an autumn water level rise by 0,5-2,5 m due to an intensive thawing of permafrost and prolonged rains.
The freeze-up on the river begins in the second half of September. By the end of winter the thickness of the ice sheet is usually 0.6-0.7 m, in places of ice built up it reaches 1.0-1.2 m. In December - January the continuous stream of the river bed is separated into a number of basins due to through freezing of shallow natural bars (especially at sections of shallow bedding rock), and since January the stream underflow also almost discontinues. This is evidenced by an ice built up in places of through freezing of the river bed, as well as development of a stagnation water regime in water bodies.