Sfaleryt i chalkozyn w żyle kwarcowej Białe Krowy na zachodnim zboczu Ślęży (Dolny Śląsk)

Abstract

SPHALERITE AND CHALCOCITE IN THE “BIAŁE KROWY” QUARTZ VEIN ON THE WESTERN SLOPE OF THE MOUNTAIN (LOWER SILESIA)

Summary

Numerous quartz veins intersecting the granite are found on the western of the Ślęża Mountain (A. Majerowicz, 1963). A rock sample with sulphides, subject to detailed examinations, has been collected from the biggest vein known as “Białe Krowy” (Fig. 1).
The holocrystalline massive quartz rock of haphazard fabric contains numerous minute (> 2 mm) sulphide inc1usions and minute plain-faced pores formed due to leaching of weathered sulphides. One relatively sizeable sulphide accumulation (20 x15 x 8 mm) – black with a blue shade – has been found among the inclusions. Microscopic examinations in reflected light revealed the aggregate to be built of sphalerite, chalcocite, chalcopyrite, pyrite, covellite, and digenite that form a complex paragenetic association. The older paragenesis embraces sphalerite, chalcopyrite, and pyrite. Chalcocite that metasomatically replaces sphalerite is probably of ascending character and is younger in succession. The youngest mineral – covellite – that fills minute fractures in chalcocite and chalcopyrite is probably of descending character. Digenite closely related to covellite would be similar  in character and age.
In reflected light sphalerite shows an anomalous light brown colour with a rose shade and consequently more precise methods have been applied for its identification. Spectral analysis revealed the lack of As end Sb which excludes the presence of thiosalts often producing optical anomalies. Spot spectral analysis with laser excitation eliminated the occurrence of  bornite that could have resembled sphalerite by its anomalous colour. Sphalerite in the aggregate was positively determined by X-ray analysis, and its content was found by chemical analysis to be 50 per cent.
The present studies revealed three parageneses with sulphides to occur in the “Białe Krowy” quartz vein. The first – older –  paragenesis contains older quartz generation (W. Heflik, I. Smolarska,1962), sphalerite, chalcopyrite, and pyrite. To the second – younger – association  belongs the younger quartz generation and possibly chalcocite that  metasomatically replaces sphalerite. Quartz veinlets of younger generation intersect sulphides of the older paragenetic association. The third – and youngest – paragnesis contains minerals formed due to exogenic (weathering) processes. These are covellite possibly  digenite and iron hydroxides not discussed in this paper. Metasomatic processes  related to the late hydrothermal phase of vein formation could have been responsible for the anomalous colour of sphalerite and possibly also for the anomalous anisotropy of pyrite. Sulphide mineralization seems to confirm at least two phases in the formation process of the “Białe Krowy” quartz vein.