From the aeolian landform to the aeolian mineral deposit in the present and its use as an ore guide in the past. Constraints from mineralogy, chemistry and sediment petrography

Abstract

Quaternary aeolian landforms (AL) can convert into aeolian mineral deposits of economic grade through concentration of metals (Ti, Fe, Zr, Sn, REE, Au, PGE), industrial minerals (silica) and gems (diamonds), purification (winnowing) of trash minerals (feldspar, mica) and the provision of accommodation space for uranium and base metals. Therefore, during the study of aeolian deposits (AD), emphasis is placed on the mineral assemblage, chemical composition and numerical data obtained from sedimentology to constrain the potential of accumulating mineral commodities. The physical–chemical regime of AL and AD is characterized by alkaline to neutral fluids and oxidizing conditions during the early stages of deposition. An acidic fluid regime evolves from it during late-stage supergene alteration when reducing conditions are created in fossil dunes and the likelihood of sulfide accumulation gets improved. The climate zones have a strong impact on the sorting of the AD causing different types of vegetation and degrees of wetness, more pronounced in the inland than coastal AL. This is also valid for grain sphericity, the chemical (Ti/Fe ratio) and mineralogical composition (carbonate/ silicate ratio). Chemical residues (e.g. carbocretes, sulcretes) in the fine-grained and clay minerals in coarser-grained fraction are more widespread in arid/semiarid and dry continental climate zones which are the aeolian active ones. Neighboring ones such as the wet-and-dry or humid-mid-latitude climate zones are typical of fossil inland AL and dominated by fluvial environments. With the aid of the trend analyses and composite x-y plots using HM, chemical markers, and sedimentological parameters the aeolian facies can be distinguished from fluvial and coastal environments. The source of the AD is related to the geodynamic setting and the tripartite subdivision into pre-mature, mature and supermature crustal section forms the basis for the classification of AL and AD. HM and chemical markers allow for a attribution of AD to mantle (Cu, Ni, Cr) and crustal (Zr) lithologies. In conclusion, mapping AL and investigating AD using the afore-mentioned parameters can be used as an ore guide and help delineate aeolian mineral deposits. The ore-forming aeolian processes may be subdivided into (1) concentration (light and heavy mineral placers), (2) purification (heavy mineral placers), (3) provision of accommodation space (uranium and base metal deposits).