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Geochemical processes and mineralogical transformations in the spontaneously combusting coal waste pile of the Kukla mine in Oslavany, Czech Republic, were investigated. The aims of the study were:(1) the characterization of secondary minerals; and (2) determination of processes which influence the mobility of elements in the pile. The pile burned from the late 19th century until the 1990s and has acquired a zoned nature, with original black material in the core of the pile, red material produced by burning close to the pile slopes and grey and white efflorescent salts precipitated on the pile top and slopes. Several mineral assemblages have been identified including (1) primary minerals in the black material including bituminous coal to anthracite, micas, pyrite and goethite; (2) hematite, spinels and corundum in the red material produced by pyrometamorphism; and (3) hydrated sulphates of magnesium including hexahydrite, konyaite and picromerite in efflorescent precipitates on the slopes of the pile. A conceptual model of geochemical processes in the pile includes seasonal changes with mineral dissolution during the wet season and precipitation of efflorescent salt minerals during the dry season. Formation of secondary minerals such as hematite, which is resistant to weathering and immobilizes hydrolysable Fe, may have a positive environmental impact in the long term.

Investigated were occurrences of magnetite-rich rocks (five of which are associated with garnetiferous rocks) situated in the Sobotín Massif (two localities) or in the adjacent gneisses of the Desná Group (six localities). As shown in previous literature, these rocks either belong to iron-formations (six localities) or are of magmatic origin (two localities). The investigations involved detailed petrographic studies supported by cathodoluminescence microscopy, whole-rock geochemical and mineral (amphibole, biotite, garnet, chlorite, magnetite, ilmenite, carbonate, feldspar and apatite) analyses. The minerals have compositions unknown to iron-formations. Instead they indicate that these may be genetically related to the basic rocks of the ?Devonian Sobotín Massif. Under late-stage and increasing oxygen fugacity conditions of the melt (of the Sobotín Massif), the Fe 3+ activity seems to have risen as well. This presumably led to progressive extraction of magnetite from the melt and its enrichment due to gravitational segregation. During this stage, apophyses, mainly composed of amphibole and magnetite, intruded in the gneisses of the Desná Group in the vicinity of the Sobotín Massif. These followed older generations of apophyses that are mainly composed of amphibole only. The garnet-rich rocks are definitely older than the studied magnetite-rich types and of the same age as the gneisses. The garnetites are inferred to represent original mixtures of precipitates from submarine exhalations and detrital material of continental-derived greywackes. In the absence of local volcanogenic activity, the sedimentary protoliths were composed exclusively of continental-derived material. During a first tectonometamorphic event, the greywacke-derived sediments were transformed into the host-rock gneiss and the mixtures into garnet-rich rocks (= granular iron-formations) identical to coticules. During a second tectonometamorphic event, all the mentioned rocks were overprinted (alignment and weak foliation of the rocks, chloritization of amphibole and biotite and the formation of actinolite from pre-existing tschermakite and magnesiohornblende, albite, carbonate and epidote). Finally, under retrograde conditions, silicification of varying intensity took place.

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