Diagenetic alunite in clastic sequences, Kuwait, Arabian Gulf



Diagenetic alunite occurs with calcrete, gypcrete and silcrete deposits in a Mio-Pleistocene clastic sequence at several locations in southern Kuwait, Arabian Gulf. Based on their physical properties and textural characteristics the alunite deposits were divided into (1) chalky quartzitic alunite, (2) chalky quartz-free alunite, (3) hard pink alunitic sandstone. The chalky alunite is composed mainly of hydronium-alunite (H3O)Al3(SO4)2(OH)6, while the hard pink alunite is composed solely of well developed potassium alunite KAl3(SO4)2(OH)6. These minerals resulted from the action of sulphuric acid on clays and K-feldspars in the muddy sandstone and mudstone host sediments. The sulphuric acid is most probably produced by the oxidation of hydrogen sulphide that might have seeped in from the oil fields of this area. Four diagenetic stages are suggested for the genesis of the studied alunites: gypsification, sulphuratization, silicification and alunitization. In oil field areas, the occurrences of alunite would serve as an indicator for the presence at depth of hydrocarbons.