Published online by Cambridge University Press: 09 July 2018
Primary kaolins, related to Pliocene-Pleistocene volcanic rocks of acid to intermediate composition from the southern part of Kimolos island contain kaolinite and quartz ± cristobalite. Smectite is rarely present whereas alunite is common and more prevalent than baryte or gypsum. The kaolinites show structural disorder (Hinckley indices ranging from 0·6 to 1·1) and contain faults along the c*-axis. The elements Nb, Th, Ce and Sr, La, V constitute two groups with a strong intercorrelation and the kaolins are enriched in these elements compared to the parent rocks. K, Rb, Y and Ba are positively correlated with feldspar content and decrease with the intensity of kaolinization. The mineral assemblages suggest a zonal pattern which is thought to be related to different types of hydrothermal alteration. Starting from the triple point of the alunite-K-feldspar-K-mica-quartz association encountered in Kimolos, a tentative path is presented showing the approximate ranges in concentrations of K2SO4 and H2SO4 required for the formation of the various mineral assemblages.