PILOTAŻOWE BADANIA PIERWIASTKÓW ZIEM RZADKICH W STREFIE KONTAKTU BLOKU MAŁOPOLSKIEGO Z BLOKIEM GÓRNOŚLĄSKIM

Abstract

PILOT STUDIES OF RARE EARTHS IN THE CONTACT ZONE OF THE MAŁOPOLSKA BLOCK WITH THE UPPER SILESIA BLOCK

Abstract. The paper presents the results of a pilot prospecting study on archived drill cores from boreholes in the contact zone of the Małopolska Block with the Upper Silesia Block, with a use of a Portable XRF spectrometer Delta 50 Premium (Olympus). A few hundred measurements of concentrations of La, Ce and other trace elements were made in selected boreholes from the prospective zones for the occurrence of Mo Cu–W ore mineralization. The maximum content for La (400 ppm) and Ce (600 ppm) measured by the Portable spectrometer has been found in the Ko-4 borehole (depth interval 450–550 m). In the depth interval of ca. 400–1300 in the other boreholes (Pz-36, RK-2 and Cianowice-2), the maximum La and Ce contents were approximately twice lower than in the Ko-4. The study also shows an interdependence of the occurrence of LREE with Sr, Y or Th. The most interesting samples were additionally analyzed by ICP-MS and electron microprobe (CAMECA SX-100). The sum of REE (ICP-MS) in four samples that reveal the highest contents of these elements varied from ca. 0.02 to 0.1%. Total REE contents for samples normalized to the upper continental crust are low (1–10). The highest REE concentrations in samples of hydrothermal breccia were found in the Ko-4 borehole (depth ca. 500 m). They reach for the Ce (305.1 ppm), Nd (266.9 ppm), La (258 ppm) and Sm (31.3 ppm). Other REE occur at low concentrations. This is clearly visible on the standard logarithmic charts of REE concentration in relation to their content in chondrite and in the upper part of the continental crust. Characteristic is the lack of negative Eu anomaly on both charts. In the microprobe study, calcioancylite-(Ce), synchysite-(Ce) as well as bastnäsite and zircon were also detected in addition to the unidentified minerals from the anhydrous phosphate group enriched with REE (mainly Ce, La, and Nd) and monazite. The form and composition of the REE mineralization indicate clearly that it is of hydrothermal nature. During hydrothermal processes, REE underwent redeposition and concentrated within breccia and tectonic zones in the metasomatic changed rocks. The data on REE concentrations, presented in this paper, are only of indicative significance. The REE contents are much lower than the most interesting results obtained within the framework of research projects carried out in other geological units in Poland and published in separate papers.