Formation and composition of cemented layers in low-sulphide mine tailings, Laver, northern Sweden

Cemented layers (hardpans) are common in carbonate or sulphide-rich mine tailings and where pyrrhotite is the predominating Fe-sulphide. Laver, northern Sweden, is an abandoned Cu-mine where the tailings have low pyrrhotite content, almost no pyrite and no carbonates. Two cemented layers at different locations in the Laver tailings impoundment were investigated, with the aim to determine their effects on metal mobility. The cementing agents were mainly jarosite and Fe-oxyhydroxides in the layer formed where the tailings have a barren surface, whereas only Fe-oxyhydroxides were identified below grass-covered tailings surface. Arsenic was enriched in both layers which also exhibit high concentrations of Mo, V, Hg and Pb compared to unoxidised tailings. Sequential extraction indicates that these metals and As were mainly retained with crystalline Fe-oxides, and therefore potentially will be remobilised if the oxic conditions become more reducing, for instance as a result of remediation of the tailings impoundment.An erratum to this article can be found at     

Pyrite geochemistry in the Toarcian Posidonia Shale of south‐west Germany: Evidence for contrasting trace‐element patterns of diagenetic and syngenetic pyrites

Authigenic pyrite grains from a section of the Lower Toarcian Posidonia Shale were analysed for their trace‐element contents and sulphur‐isotope compositions. The resulting data are used to evaluate the relationship between depositional conditions and pyrite trace‐element composition. By using factor analysis, trace‐elements in pyrite may be assigned to four groups: (i) heavy metals (including Cu, Ni, Co, Pb, Bi and Tl); (ii) oxyanionic elements (As, Mo and Sb); (iii) elements partitioned in sub‐microscopic sphalerite inclusions (Zn and Cd); and (iv) elements related to organic or silicate impurities (Ga and V). Results indicate that trace‐element contents in pyrite depend on the site and mechanism of pyrite formation, with characteristic features being observed for diagenetic and syngenetic pyrites. Diagenetic pyrite formed within anoxic sediments generally has a high heavy metals content, and the degree of pyritization of these elements increases with increasing oxygen deficiency, similar to the degree of pyritization of reactive Fe. The highest gradient in the increase of the degree of trace element pyritization with bottom‐water oxygenation was found for the elements Ni < Cu < Mo = As < Tl. In contrast, syngenetic pyrite formed within a euxinic water column typically is enriched in As, Mo and Sb, but is low in heavy metals, and the geochemical variation reflects changes in sea water composition.     

Role of carbonates in mitigation of metal release from mining waste. Evidence from humidity cells tests

 Leaching of two contrasting types of sulphidic tailings in humidity cells has been performed. The release of heavy metals and the oxidation rate have been studied. Tailings from the Laver mine contain a few percent sulphides and lack carbonates, whereas tailings from the Stekenjokk mine are both sulphide- and carbonate-rich. The results showed that in the leachates from the Laver samples, the metal concentrations increased and pH decreased with time, indicating an increased oxidation rate. In the Stekenjokk samples, pH remained high during the experiment, thereby keeping the metal concentrations low in the leachates. The oxidation rate also decreased with time, probably due to Fe-hydroxide coatings on sulphide surfaces. The results show that addition of carbonates and the maintenance of a high pH not only reduce the solubility of heavy metals, but also decrease the oxidation rate of sulphides. Received: 20 January 1998 · Accepted: 2 April 1998