The Mevaiela kaolin deposits are located in the northern part of the anorthositic-gabbro massif within the Cunene complex (southern Angola) and were formed by the alteration of basic anorthosites and gabbros. The Mevaiela area is part of an elevated region which is located between two extensive NNW-SSE fracture systems. Several kaolinite samples were collected from a quarry (main excavation) and from drill-holes as well as from surficial occurrences in the Cunene complex. Chemical analyses, X-ray diffraction, differential thermal analysis, scanning electron microscopy and isotope analyses were performed in order to model the kaolinite occurrences. The alteration of the anorthosite to kaolin approaching the main excavation is characterized by significant decrease in alkaline-earth and transition metals (Ca, Mg, Fe, Co, Ni and Mn) between the average anorthosite and the kaolin. The crystallinity indices suggest that the kaolin contains kaolinite with a reasonably well ordered structure and near the transition between T (triclinic) and pM (pseudo monoclinic).

Mineral exploration tools have been evaluated during this study to assist in future kaolin exploration in the Cunene anorthosite complex.

Isotopic analysis of O and D indicates that Ca-feldspar alteration is essentially due to meteoric fluids, over a different range of temperatures. Furthermore, the presence of quartz-feldspar veinlets in the kaolinite bodies could be the result of hydrothermal activity linked to post-anorthosite granite intrusions of the so-called ‘red granite’. Kaolinite from Cunene plots on or close to the kaolinite line into the ‘warm temperature in tropical region’ area (surficial samples). Samples from drill-holes plot on the left and show the largest displacement from the KS line; these samples also have a relatively reduced δD range of values (−65 to −98%). However, if supergene processes take place in the presence of waters of meteoric origin at temperatures similar to typical surface temperatures, the clays thus formed should plot either in the vicinity of the KS line or be displaced towards lower δO18 and higher δD, depending on both the temperature and relative proportion of clay to water.

This paper reports a previously unidentified paleoenvironmental record found in sand dunes of the Atacama Desert, Chile. Long-term aeolian deflation by prevailing onshore winds has resulted in the deposition of sand on the irregular surface of a Miocene-aged anhydrite outcrop. Two deposits ~25 km apart, along the prevailing wind trajectory, were hand excavated then analyzed for vertical (and temporal) changes in physical and chemical composition. Radiocarbon ages of organic matter embedded within the deposits show that rapid accumulation of sediment began at the last glacial maximum and slowed considerably after the Pacific Ocean attained its present post-glacial level. Over this time period, grain sizes are seen to increase while accumulation rates simultaneously decrease, suggesting greater wind speeds and/or a change or decrease in sediment supply. Changes in δ34S values of sulfate in the sediment beginning ~10 ka indicate an increase in marine sources. Similarly, δ2H values from palmitic acid show a steady increase at ~10 ka, likely resulting from aridification of the region during the Holocene. Due to the extreme aridity in the region, these sand dunes retain a well-preserved chemical record that reflects changes in elevation and coastal proximity after the last glacial maximum.