Drag folds in sedimentary rocks hosting kimberlites, West Yakutia

Drag folds were revealed in Lower Paleozoic sedimentary strata of Mirny, Nakyn and Syuldyukar diamondiferous fields, West Yakutia. They consist of minor anticlinal forms (3-5 to 15-20 cm thick) and cut marl, clayey limestone and dolomite bands located between monolith seams of carbonate rocks. Some folds as monocline, flexures and S- or Z-shaped folds reflect the degree of shearrelated interlayer offset. Drag folds are among shear zone occurrences including microfaults, slickensides with slip groove horizontal planes, and schistosity zones. Drag folds reflect local extension points while schistosity zones indicate compression points. For Syuldyukar field, detailed mapping results for drag folds and schistosity zones are provided at 3 scales: across 20 × 20 m observation grid within a local 2 km2 site; across 200 × 200 m grid within 20 km2 area; across 500 × 500 m grid within ~100 km2 territory. For all scales, drag fold halos are restricted to schistosity zones. Within a local site adjacent to kimberlites, drag folds mark ore-hosting fault controlling long axes of kimberlite areal projections. Within large areas, drag fold halos are 1,2-2 km, which compares with kimberlite group areal parameters. Drag fold halos reflect shear junctions, with some of them hosting kimberlites. Local occurrences of drag folds mark a major shear hosting a kimberlite body. Drag fold analysis combined with other evidence should be used as an indirect prospecting indicator of concealed shears and local extension areas controlling kimberlites.

Conditions of localization and criteria for kimberlites exploration (on the example of Igyatta diamondiferous region, Western Yakutia)

The main source of mined diamonds in Russia is the Yakutia diamond-bearing province (YAP). To date, all open areas within the prospective Vilyuy-Markha deep fault zone (VMZ) of the YAP, which is a mineragenetic and which hosted diamond deposits of Mir, International, Nyurbinskaya, Botuobinskaya, have been studied satisfactorily. It is unlikely to reveal new kimberlite fields within its' opened part. In this case, the presence of direct signs of new objects beneath the Mesozoic-Cenozoic strata indicates that the diamond potential of the territory is not exhausted. This was confirmed by the discovery in 2015 of a kimberlite body in the Suldyukar field, which confirmed the presence of the Igyatta diamondiferous region and allows us to view the overlapped areas of the VMZ as the most promising for discovering of the new deposits. However, the search for buried deposits requires improvement of the criteria.

Geological structure and material composition of the kimberlite body «Yanvarskoe» (Daldyn-Alakit diamond-bearing district)

The new kimberlite pipe «Yanvarskaya» has been discovered in the Alakit-Markha field by a complex of geological and geophysical methods. For its delineation and the study three profile of wells were covered: one profile is along the long axis and two are in the cross stretch at the network 40x40 m. In wells geophysical researches, and also testing works, were carried out, including the selection ot the nine core samples with a total weight of 1120 kg, at the wells which had opened kimberlite. Yanvarskoe kimberlite body has a dike-like form with the orientation of the long axis in a North-East direction (50—55°) with sizes under overlying rocks 90x45 m, with an area of 2836 m2, which allows reference of this body to the class of small bodies. The body is composed of porphyry kimberlites of greenish-gray and yellowish-brown colors, strongly altered, dissected by numerous differently oriented cracks filled with calcite. Based on the results of core testing, a diamond of class -2+1 mm weighing of 2.1 mg (0,01 car.) was found.