In situ studies of the influence of steeply dipping slaty cleavage on rock displacement caused by exploitation of vein deposits have revealed a protective effect of slaty zones. A mathematical technique is proposed for prognostic rock displacement evaluation allowing for this effect in terms of influence factors. The account of the protective effect can result in exploitation of additional ore reserves previously ascribed to losses in protective pillars. Advance forecast of rock displacement promotes the selection of proper mining technologies diminishing environmental damage.


Rock displacement is known to be one of the most essential factors affecting both steady pace and environmental safety of mining operations. This is why prognostic evaluation of rock displacement and surface subsidence caused by mining is a very important geomechanical problem at mine design as well as at exploitation stage. Geological features considerably complicate this problem owing to difficulties associated with the account of structural disturbances. Slaty cleavage is one of widely distributed forms of geological disturbances typical for nonferrous vein deposits of East Kazakhstan and the Altai Ore Region. Slaty zones are usually considered to be unfavourable factors strongly deteriorating mining and environmental conditions all over the zones affected by mining. However, an analogy with some of problems in physics (sometimes even not related with mining problems) allows us to suppose that this is not always true. Moreover, our special studies have proven the favourable role of steeply dipping slaty cleavage zones acting in some cases like protective screens. This conclusion was drawn basing on calculations and the analysis of in situ measurements conducted at vein ore deposits in East Kazakhstan and the Altai Ore Region.


In order to evaluate rock displacement and rock mass deformations caused by extraction of a vein orebody with varying dip angle and thickness, we divide the orebody into elements characterized by roughly invariable thickness and dip angle. Corresponding boundary mathematical problem for such an element can be formulated as follows (see Fig.1). Let the length of the orebody element on the dip be 2L, its mined thickness be m, and dip angle be α. It is convenient to introduce a local coordinate system OX1Y1 in the section across the strike so that OX1 axis would be directed to the rise of hanging wall and OY1 axis directed perpendicular to it. The account of structure can be achieved by means of special influence factors. To find these factors for slaty cleavage zones, long-term in situ measurements at different sections of Vasilievskoye deposit were conducted. Mining and geological conditions at the deposit are typical for vein deposits of East Kazakhstan and the Altai Ore Region. The studies have shown that the influence factor is equal to 1 Within a zone bounded by points of maximum inclination ix, to 0.5 in the neighbourhood of these points, and 0.25 outside the zone. This means that the slaty zone reducts the displacements (down to 1/4 of corresponding value in a continuous rock mass) at sites located at certain distance from stoping blocks, i.e. acts like a protective screen. The comparison of in situ measured data and calculated displacements obtained using adjusted solution (1)-(3) for orebody 2 of Vasilievskoye deposit is shown in Fig.2. The difference does not exceed 10 per cent.


In situ observations were carried out at Irtysh ore deposit (East Kazakhstan) located in the Vicinity of a 50 to 80 m thick almost vertical slaty zone (Fig.3).

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