Al(Fe,Ti,Si)-mobility and secondary mineralization implications: A case study of the karst unconformity diasporite-type bauxite horizons in Milas (Mugla), Turkey

作者：Hatipoglu Murat^*

来源：Journal of African Earth Sciences, 2011, 60(3): 175-195.

DOI：10.1016/j.jafrearsci.2011.02.009

• Metamorphic remobilized reactions
• Submicroscopic paragenesis
• Diaspore (zultanite)
• Al-mobility
• Karst unconformity diasporite-type bauxite horizons
• Menderes Massif
• Turkey

The Paleogene aged metabauxite deposit in the Upper Cretaceous-Early Paleogene aged marble sequence within the southwestern Menderes Massif in the Ilbir Mountains of the Milas (Mugla) region of SW Turkey comprises many initially karst unconformity-type bauxite horizons with unusual Al-mobility. Thus, it displays singular geochemical and mineralogical implications.
The settling down of these horizons was syngenetic with limestone sedimentation, as evidenced by their lithologic associations. In the region, they are mainly found as karst unconformity diasporite-type upper bauxite horizons due to lower-graded burial metamorphism in the Kucukcamlik and Buyukcamlik hills, and also found as emery type lower bauxite horizons due to higher-graded burial metamorphism in the Menevis and Kure streams.
The main focus of this study was the upper bauxite horizons because they contain significant secondary Al- and Fe(Ti)-rich mineralization in the structurally-controlled open spaces (fracture zones) crosscutting the brittle bauxite horizons. This secondary mineralization is unique worldwide because the fracture zones contain coarse crystals of secondary minerals, such as gem-quality diaspore, muscovite, specular hematite, ilmenite, goethite, and chloritoid. These secondary metamorphic minerals were formed by high-temperature hydrothermal activity involving metamorphic remobilized reactions of extraction, mobilization, migration and re-crystallization, from the primary metamorphic mineral constituents in the metabauxite ore bodies. Thus, within the well known Mediterranean Bauxite Belt (MBB) in southern Europe trending from Portugal through Turkey, the metabauxite deposit in the Ilbir Mountains is noteworthy for the coexistence of two serial phases of metamorphic mineralization which occurred when the metabauxite deposit was modified by late-stage Alpine tectono-metamorphism in the Menderes Massif.
This study is mainly focused on the original primary metamorphic submicroscopic mineralization, including polycrystalline (overlapped) occurrences, and uses the comparative matching technique on X-ray diffraction patterns to confirm that the main constituents of the karst unconformity-type diasporic metabauxite (diasporite) ore were the main source for secondary metamorphic mineralization in the fracture zones. It was found that the submicroscopic mineral constituents in the original primary diasporite ore are diaspore, gibbsite, corundum, specular hematite, ilmenite, donbassite and chloritoid as major constituents, with goethite, ferroalluaudite and Fe-Mg-rich muscovite as minor constituents.
It was concluded that the composition of the primary fine-grained mineralization in the unaltered (original) bauxite ore was adequate to serve as a source for the much coarser later mineralization in the fracture zones.

• 出版日期2011-5