Indigenous diamond deposits, developed by the open method, or combined:
The upper horizons are open, and the deeper horizons are underground. In Russia, diamonds are mined only in the open way.
The open method of developing pipes is approximately the same in all fields. Consider it on the example of the pipe Fischi (South Africa).
The tube has an oval horizontal section and almost vertical contacts with the surrounding rocks. The zone of weathering of kimberlites extends to a depth of 60 m. A secondary phase, saponite, a swelling mineral that absorbs a large amount of water, occupies a significant amount in the composition of kimberlites. For this reason, the tube’s ore is hygroscopic and, when moistened, it quickly loses its strength properties, therefore special methods are used to isolate the surface of kimberlite from water, and when drilling wells dry dust collection is used.
The development of an open-pit tube began in 1966, and by 1990 the depth of the pit reached 423 m with an average annual decrease of 18-20 m. Over 97 million tons of kimberlite (about 5 million tons per year) were extracted and 55 million tons T of waste rock. The quarry area on the surface is 550,000 m2. This method of mining provided stable operation of the mine and good technical and economic indicators: a low overburden, a systematic transition to the underground method. An inclined trunk with a length of 1300 m at an angle of 12 ° from the surface to the quarry at a depth of 280 m was traversed in the enclosing rocks. It housed a conveyor for transportation of ore to the concentrating mill and an underground crushing plant, which made it possible to sharply reduce the number of working dump trucks.
Under the underground method, several systems of underground mining of diamond-bearing tubes are used.
The chamber system provides for the penetration of 8-meter chambers with a height of 12 m, separated by temporary 8-meter lobes, on each working horizon along the short axis of the tube. Kimberlite, taken out from the chambers and from the ends of the overlying horizon, under the influence of the weight of the collapsed rocks, falls on the bottom of the workhole, where it is loaded into trolleys and rolls back to the ore deposit located in the enclosing rocks, along which the kimberlite is fed to the main hauling horizon.
The method of slot development is used on the Premier tube (South Africa). As the tube was being developed on each working horizon, the main drifts ran parallel to the slit at intervals equal to half the distance from the gap to the boundaries of the ore body. At a depth of 270 m, the ore was discharged from the ore discharges into trolleys and transported along the haulage drifts. Further, the ore was fed into the crusher, crushed and transported to the surface. The most progressive method of development is a floor self-destruction; It provides high productivity (up to 5 million tons of kimberlite per year) at low cost and relatively small application of manual labor. Under this system, the destruction of kimberlite occurs under the influence of gravity, the number of working horizons and loading points is sharply reduced. The essence of the system consists in the fact that a scraper drift passes at a distance of 14 m from each other, from the gangway, oriented across the tube, at intervals of 3-5 m on both sides, square niches of 1-2 m in size are arranged in staggered order. The niches are rising up in the form of a funnel, rising to a height of 7.6 m above the level of the sole. The kimberlite blocks are then completely cut, and layers with a thickness of 18 m are produced in such a way that kimberlite breaks down and collapses into conical rebels. As a result, a compensating gap of 2.2 m in height is formed on the whole area of the tube. After that, a massless kimberlite mass is left above the compensation space, which gradually under the influence of its own weight collapses onto the outlet funnels. As the kimberlite collapses, it is partially discharged to restore the compensation space, so the level of the kimberlite that is falling is constantly rising until it reaches the rocks of the overlying horizon. After that, the ore output continues at a certain rate, until an empty rock appears in the scrapers. The development of this horizon ends here, after which they start working on the underlying one.
Placer deposits with a depth of occurrence up to 40-45 m are processed by the open method. In the Republic of Sakha (Yakutia), production is carried out in the summer by bulldozer-hydraulic method. Sands fed by bulldozers are washed on a grid of a hydrocrocker with a cell size of 30-50 mm. The surface material is removed by the jet of water, and the sub-slurry pulp is transported through the pipes by a distance of 20, -2.5 km to the seasonal stationary concentrating mill. From a valley of long placers, diamonds are mined in a dredging way. Draghi move from the bottom up the river valley in transverse or longitudinal strokes. After the depletion of the main reserves, the dredges are re-promoted from the top down, with a shift in the moves relative to the primary ones.