A HALF-CENTURY OF ENVIRONMENTAL MINERAL FORMATION ON A PYRITE-BEARING WASTE DUMP IN THE MATRA MOUNTAINS, HUNGARY

摘要

Intensive Zn-Pb-Cu mining took place for about 40 years in the Gyongyosoroszi-Matraszentimre region, Matra Mountains, Hungary. The last mine was closed in 1986 without remediation. In 2006, a large-scale project was launched for the complete remediation of the waste dumps (more than 20 sites) and for the proper sealing of the abandoned shafts and adits still releasing acid mine-drainage owing to the large amount of oxidizing pyrite in the walls. During the remediation, full profiles (up to 5-10 m) of old dumps were created, offering a unique opportunity for the systematic sampling of the products of mine-waste alterations. One of these accessible "natural laboratories", recording 40 years of environmental mineral formation, is the Banyaberc waste dump. Its volume reached 26,000 m3, and its bulk pH was around 3.7. We carried out XRD, SEM-EDX and Mossbauer spectroscopic (room temperature, liquid nitrogen) analysis of the minerals present in the altering waste-dump material. Minerals found are pyrite, gypsum, jarosite, hydroniumjarosite, plumbojarosite, anglesite, quartz, the feldspars, goethite, hematite, picker-ingite, alunogen, epsomite, hexahydrite, a smectite-group phase, galena, sphalerite, and trace calcite. Rhomboclase and copiapite were identified by XRD in only one <2 mu m sample. The water-soluble sulfates are not pure end-member phases: pickeringite and epsomite contain Zn (Zn:Mg atomic ratio from 1:5 to 1:4.5 for pickeringite, and between 1:5 and 1:2 for epsomite). Moreover, pickeringite contains Mn (Mn:Mg 1:9.5-1:9), and alunogen and epsomite contain Fe (alunogen: Fe:Al 1:15 to 1:8, epsomite: Fe:Mg 1:20). The jarosite-group minerals form euhedral crystals in the 0.1—3 mu m range. Goethite is superparamagnetic and only identified by Mossbauer spectroscopy at the temperature of liquid nitrogen. The mineral assemblage shows that even after 40-50 years, the chemical evolution of these waste materials is still in progress.