Sulphate mineralisations from the dumps of the former Emma and Hendrik collieries (southern Limburg, The Netherlands)

During excavation of the dumps of the former Emma (Treebeek) and Hendrik (Brunssum) collieries, sulphates have been found to occur commonly and comprise thenardite, gypsum and a jarosite-type of mineral. During dry periods, thenardite occurs locally as crusts and overgrowths; it originates from the continual removal of Na ions. In order to define jarosite, chemical as well as X-ray diffraction (XRD) analyses were made, which showed this to be a mixed Na, K, H20 jarosite, its crystal habit being comparable with K jarosite (Joint Committee of Powder Diffraction [JCPD] map 36-427). Amongst the waste products at the dumps, jarosite is found as crusts with spherical extensions, bright yellow to light brown in colour. Gypsum (occasionally associated with jarosite) occurs especially in welldeveloped euhedral crystals in the Carboniferous shales and on concretionary siderite nodules; its crystal morphology is described. Jarosite and gypsum are typical products of pyrite oxidation, which mineral is either finely distributed or occurs as larger-sized concretions in the rock. In addition to mineralogical data, the results of pH measurements are presented. Following a brief account of the structure of the waste dumps is a tabulation of all secondary minerals of the Dutch collieries known to date.