CHARACTERISTICS OF A CALCITE “LIMESTONE”-MARBLE FROM MACEDONIA, USED AS FLUX MATERIAL

The phase characteristics of calcite “limestone”-marble from Banjany area village (near Skopje, Macedonia) were examined by means of XRD, SEM, microscope in polarizing and reflected lights, chemical, DT/TG-analyses. It was concluded as follows: calcite (CaCO3) is a major mineral component (cca 80-90 %) prevailing in the marble over the other minerals dolomite is generally of minor importance (cca 10-20 %) in the rock quartz, micas, graphite, pyrite represent typical accessories. As result of the mentioned phase characteristics, this raw materials was for a long time (more than 30 years) used as flux in the iron and steel metallurgy in Macedonia.


Introduction
In the metallurgical smelting process usually are included special raw materials as fluxes, the purpose of which is slag formation.The selection of the material as flux, depends of the gangue mineral composition.So, the basic fluxes (limenstones) are usually used in the smelting process for metals obtaining.
The preliminary geological investigations (M.Stojanovic, 1967) reveal that the limenstones-marbles deposits at the vicinity of Banjany village, Skopje contain a lot of reserves and quality characteristics as follows: -CaO (52-54 %) and MgO (0.37-2.89 %) contents are uniformly distributed and ranged inside mentioned limits.-SiO 2 (1-2.5 %) and R 2 O 3 (0.33-0.63 %) are of minor importance and also uniformly distributed.Since 1965, as flux materials have been used the limenstones near Banjany village, in the working process of the "Mining and iron works -Skopje" -Skopje, although the phase characteristics of these raw materials were not determined in details.

Experimental
The determination of the phase characteristics of the mentioned "limestone" from Banjany village were determined by means of complex analytical procedures using XRD, SEM, microscopic, DT/TG, as well as chemical analyses.

Macroscopic description
Brownish-white and grayish-white "limestone" samples are two distinct types treated in this work, although the first mentioned species is predominant in the mine.
The brownish-white and white samples show a finegrained structure and homogenous massive texture with grains ranged between 0.5-1.0mm., because this rock is treated as marble.Here and there these rock samples are cutted with brown-yellowish veinlets of limonite (to 1 mm. in thickness).
The grayish-white samples have also finegrained structure and slightly schistose texture.
Both rock samples show very intensive reaction with 10 % cold HCl due to the calcite predomination over dolomite.

Microscopic examinations
By means of a LEITZ SM-POL equipment, in transmitted and reflected lights were performed microscopic examinations on the treated marble samples.
In the both rock samples (brownish-white and grayish-white marble) calcite is a major mineral component against dolomite, which contents are of minor importance.
Calcite is presented by xenomorphic grains of cca 0.03 to cca 1.0 mm filled with submicroscopic inclusions of graphite substance.The graphitic substance is more encountered component in the grayish-white marble samples.(Fig. 1 and Fig. 2)

Figure 1. White "limestone"xenomorphic calcite grains (c) with rombohedral sections filled with superfine grained graphitic materials (black spots) Figure 2. Thin veinlets of limonite enclosed in calcite "limestone" associated with disperged graphitic material as well as pyrite in form of coarse-grained black spots
Here and there in rock samples can be encountered accessories of pyriteisometric forms of cca 0.005 -0.02 mm (Fig. 3).Accessories of micas (to 0.1 mm) can be seen also in the grayish-white marble samples.
Granulometric examinations of examined marble samples were preformed by means of direct optical measurements using an object-micrometer scale.The obtained results (Fig. 4) show that both marble samples are characterized with an average grain size ranged between 0.1-0.25 mm.

Chemical examinations
The chemical examinations were performed by complete chemical analyses of 12 randomly selected marble samples.
According to Table1, could be concluded as follows: -

Quantitative SEM -Analyses
Fine-grained (cca 0.005 -0.02 mm) pyrite inclusions in calcite grains of examined marbles were preliminary indicated by the methods of ore microscopy and more exactly determined by means of SEM-analyses.

X-ray powder diffraction phase analyses
The X-ray powder diffraction analyses of the examined rock samples were performed by the difractometer method, according to the working conditions as follows: -Philips X-ray difractometer equipment -Cu/Kα/Ni monochromatic X-rays obtained at 40 kV and 20 mA -working area 12-45 o 2θ.
On the basis of obtained X-ray powder diagram (fig.5) in the examined rock samples, these mineral phases were determined: Calcite (c) , dolomite (d) , quartz (q) Starting of the contributed X-ray diagram, could be concluded that calcite represents a major mineral phase, while dolomite and quartz are of minor importance what is compatible with chemical data.Table 3 Representative SEM-analyses of pyrite (%)

DT/TG -examinations
Thermal examinations were performed by means of DT/TG -analyses at conditions of 0.5 g weight sample, Vt -10 o /min.
According to obtained DT/TG -diagram (Fig. 6) can be seen that endotermal effects at 760 o C and 880 o C correspond to dolomite and calcite respectively.The most intensive endo-effect at 880 O C represents another proof, that calcite mineral component is quantitatively predominant over dolomite what's compatible with X-ray, chemical etc. data.TG-data of 44.5 % loss of ign.also show that calcite is major mineral component in the examined marbles.

Conclusion
The calcitic marbles from Banjany village region near Skopje, were for a long time period used as flux material in the iron and steel metallurgy in Macedonia, although the phase characteristics of these row materials were not examined in details.

Figure 4 .
Figure 4. Granulometric curve for white and gray marble

Table 2 .
Complete chemical analyses of a marble sample from Banjany area, Skopje (%)