MINERALIZACJA KRUSZCOWA W SKAŁACH ULTRAMAFICZNYCH PASMA MNICHA W ZACHODNIEJ CZĘŚCI MASYWU BRASZOWICE–BRZEŹNICA (DOLNY ŚLĄSK)

Abstract

ORE MINERALIZATION IN ULTRAMAFICS FROM THE MNICH RIDGE FROM WESTERN PART OF THE BRASZOWICE–BRZEŻNICA MASSIF (LOWER SILESIA)

Abstract. Ultramafic rocks of the Braszowice–Brzeznica massif consist of harzburgites, dunites and lherzolites that are serpentinised in various degree. These rocks are regard as upper part of ultramafic sequence of the Sudetic ophiolite complex. Ultramafic rocks of ophiolite sequences are often associated with important mineral deposits like chrome, nickel, cobalt and PGE. EPMA analyses show that the most aboundant ore minerals are oxides like chromite, ferrichromite, magnetite. Sulphide ore minerals are mainly Fe-Ni sulphides. Documented sulphides are: heazlewoodite (Ni₃S₂), pentlandite(Ni,Fe)9S8, millerite (NiS), godlevskite (Ni₇S₆). In some sulphide grains occur nickel arsenides inclusions. Ore mineral are dispersed, forms xenomorphic grains from several μm to 4 mm in size. Primary ore minerals like chromite, pentlandite, pyrrhotite and chalkopyrite were affected by fluids, which results in precipitation of secondary mineral phases: Fe-Cr spinel, four generations of magnetite, Fe-Ni sulphides and Ni arsenides. During serpentinisation Cr, Al, Mg in chromite strutcutre were replaced by Fe. Result of this alteration is Fe-Cr spinel and magnetite Ia. Magnetite Ib crystalized in pseudomorphs after olivines and pyroxenenes. Magnetite II precipitate simultaneously with sulphides.