Field, mineralogical and geochemical characteristics of As-sarat laterite profiles, SW Saudi Arabia

الملخص EN

Complete laterite profiles were developed over a variety of rocks including serpentinites, amphibolites and gabbroic bedrocks that are transected in most by ignispumite in the form of dykes and sills.

The fresh bedrocks grade upwards into light gray saprolite, kaolinite, impregnated at its upper part by red iron oxides and capped by fluvial and slope-wash clastics laid over undulatory surface of recent erosion.

Ancient weathering profiles are well represented in East of Al- Wahaba, West of Al-Wahaba, Ash-Shara, Al-Qubal and Ad-Darama.

These occurrences show lateral variation in elements composition during ancient weathering along a line extended from the North to the South of As-Sarat area.

It points out to the excessiveness of K2O over Na2O values in the central part of the region and the excessiveness of Na2O over K2O values in the northern and in the southern parts.

The behavior of trace elements suggest that during the early phase of weathering, small quantities of Na- and K-sulfates and chloride salts are formed in the upper horizons by virtue of capillary action.

The weathering materials that originated from thermal alteration products are characterized by relative enrichment in oxides of Ti, Fe+3, Fe+2, Na and K, and depletion in Si, Al and Mg.

Collectively, modern weathering in dry semi-tropical weather indicates that enrichment of iron content occurs at the expense of Si, Al and Mg.

In addition, iron oxides (Fe+3 and Fe+2) are enriched in the transition horizon between the saprolite and the top soil horizon, and associated with gain in CaO.

Trace elements (namely Cr, Cu and Ni) are allied to the ferric iron in the weathered scree-debris and allied to alumina and ferrous iron in the weathered basaltic blocks.

The provided examples of modern weathering in dry semi-tropical weather deny the iron enrichment in laterite crust by capillary action and attribute it to subsurface laterite migration of ephemeral water, derived from rain and drainage streams, carrying soluble iron in the divalent state.