Petrograficzna zmienność surowca dolomitycznego w złożu Ołdrzychowice

Abstract

Rozpatrywano problem petrograficznej zmienności marmurów dolomitowych w złożu Ołdrzychowice.

Podstawą oceny były profile odsłonięć oraz wierceń archiwalnych. Jakościową ocenę samych marmurów oparto na mikrometrycznych analizach mineralno-strukturalnych, oznaczeniach gęstości pozornej i nasiąkliwości oraz archiwalnych oznaczeniach składu chemicznego (800 analiz). Na tej podstawie przyjęto cztery grupy kryteriów: chemiczne, petrograficzne, litologiczne i surowcowe. Posługując się nimi zrekonstruowano syntetyczny profil złoża, wyodrębniając w nim trzy strefy o różnej petrograficznej pozycji surowca dolomitycznego. Stwierdzony obraz zmienności jakościowej surowca wiąże się ze strukturalno-tektonicznymi założeniami złoża Ołdrzychowice.

PETROGRAPHIC VARIABILITY OF DOLOMITIC RAW MATERIAL IN THE' OŁDRZYCHOWICE DEPOSIT

The paper deals with petrographic variability of marbles in section of the Ołdrzychowice deposit. The deposit is related to the Proterozoic structure of the Krowiarki and Śnieżnik Kłodzki Ranges, the Central Sudety Mts. The studied marbles form four structurally different zones in-supracrustal Stronie sequence. The zones are varying in width of outcrops (from a few to several hundreds meters) and composition (from calcitic to calcitic-dolomitic and dolomitic). The Ołdrzychowice deposit belongs to the zone III, named as the Romanów Górny syncline by J. Kuźniar (1960).

The deposit was analysed on the basis of results of detailed surveys of open cut works (Fig. 1), petrographic (mineral, structural-textural, and physical) studies on samples of marbles, and reanalysis of sections of 55 prospecting boreholes and 800 chemical tests of core material from these boreholes. The studies covered sections 3,150 m in total length. Petrographic position of marbles was established using four groups of criteria. The first group comprised chemical criteria - contents (in wt. %) of CaO, MgO, SiO₂, Al₂O₃, Fe₂O₃, FeO, and TiO₂ The criteria were used to differentiate (see Table 1): - eight (I - VIII) levels of content of noncarbonate components, - a continuous series of marble varieties differing in content of calcite and dolomite (K, K_d, KD, DK, D_k, D), - eight (I'-VIII') levels of content (in wt. %) of colouring oxides (Fe₂O₃ + FeO + TiO₂).

The group of petrographic criteria comprised results of micrometric determinations of content (in vol. %) of mineral phases: noncarbonate (I-VIII), carbonate (K, K_d ... D_k, D), and colouring ones (I'-VIII'). Moreover, the level, homogeneity and ordering of blastic deformations were determined. Apparent density and soakability were used as measures of mineral position and tightness of marbles.

The group of lithological criteria comprised: relative share of marbles in the section (U_M) and distribution of thickness shares of individual marble varieties (K, K_d ... D_k, D) and its median as lithological index of share of dolomites (L_dd). The last group comprised raw material criteria, i.e. requirements which should be met by dolomitic raw materials.

The petrographic studies showed presence of three major varieties of marbles in the deposit. The dolomitic variety (D) was found to be most widely distributed (Tables 3, 4). Rocks of this variety are white or, sometimes, light-gray or pinky in colour and medium- (4) to finely-blastic (5), homeoblastic, and occasionally slaty (e) or cataclastic (g) in structure. The second variety comprises dolomitic marbles with calcite (D_k), gray to white-gray in colour and medium-, finely-blastic (4, 5), homeo- or heteroblastic (a, b) structure. Calcite, present in fairly large amounts in these rocks (Table 3, 4), penetrates fine pore interstices in overhelmingly dolomitic groundmass. The third variety is represented by calcitic marble with high content of noncarbonate phases (Table 3).

The analysis of lithological (Fig. 2) and chemical (Fig. 3) cross-sections through deposit made it possible to differentiate three zones differing in petrographic position of marbles. Of these, the marginal southern zone represents the lowermost structural complex of the deposit. It is 15 to 20 m thick in northern and central parts of the deposit, thickening to 95 m in the southern part. Dark-gray or gray marbles occuppying an intermediate petrographic position (VIII D_k III' - Table 4) predominate in this zone whereas strongly contaminated dolomite-bearing calcitic varieties (K_d) and calcite-dolomite (KD) or dolomite-calcite (DK) ones occur in direct proximity of the cover.

The central deposit zone is varying in thickness from about a dozen meters in the southern part to 250 m in the central. It is built of white to pinky marbles with the composition III-IV D_k, D 1'. A complex of the purest marble varieties II D I' occurs in axial part of this zone, above marble packet 100-150 m in thickness.

The northern marginal zone, 10 to 50 m thick, represents the uppermost structural complex of the deposit. It is built of marbles highly varying in chemical composition (Table 4, Figs. 2, 3), with high share of slaty material (Figs. 1, 2).

The variability in raw material quality appears determined by petrographic position of marbles in the above discussed deposit zones (Table 5). The interscetion image of the deposit (Fig. 4) shows that the marginal and central zones are clearly separate. This indicates possibilities to obtain dolomitic raw material of high quality.

The analysis of cross-sections (Fig. 2) and sections (Fig. 3) showed structural symmetry of the Ołdrzychowice deposit. The symmetry and changes in distribution of the zones, consistent with the strike of the deposit, indicate synclinal character of framework of this structure.