SUPERGENE MINERALOGY OF THE LOJANE Sb-As-Cr DEPOSIT, REPUBLIC OF MACEDONIA: TRACING THE MOBILIZATION OF TOXIC METALS

Abstract

As part of a larger project on the environmental mineralogy and geochemistry of the Lojane SbAs-Cr deposit, Republic of Macedonia, which was mined for chromite and, later, stibnite until 1979 and is a substantial source of arsenic and antimony pollution, the supergene mineralogy of the deposit was studied. Samples collected on ore and waste dumps were used to identify and characterize the previously uninvestigated suite of supergene mineral phases by standard mineralogical techniques. The following species were determined (in alphabetical order): annabergite, arseniosiderite(?), gypsum, hexahydrite, hörnesite, pararealgar, roméite-group minerals, rozenite, scorodite, senarmontite, stibiconite, sulphur, tripuhyite and valentinite.Their occurrences are described and their local conditions of formation are discussed. High-resolution Raman spectra of hörnesite, hexahydrite and rozenite are provided and compared with literature data. The Mg arsenate hörnesite is by far the most common secondary arsenate (and immobilizer of arsenic), an observation attributed to the Mg- and carbonate-rich serpentinite matrix which buffers any acid weathering solutions. Antimony is efficiently immobilized in secondary Sb(III) oxides, but trace amounts are also incorporated into scorodite. Nickel, derived from primary Ni(-bearing) sulphide and sulpharsenide minerals, is mobilized and incorporated into annabergite and chemically variable roméite-group minerals. No mobilization of Cr was noted, in agreement with literature data on weathered Cr deposits.

Key words: Lojane deposit; Republic of Macedonia; supergene mineralogy; arsenic; antimony; chromium