Genesis of the Dogankuzu and mortas Bauxite deposits, Taurides, Turkey: Separation of Al, Fe, and Mn and implications for passive margin metallogeny

Abstract

The Taurides region of Turkey is host to a number of important bauxite, Al-rich laterite, and Mn deposits. The most important bauxite deposits, Dogankuzu and Mortas, are karst-related, unconformity-type deposits in Upper Cretaceous limestone. The bottom contact of the bauxite ore is undulatory, and bauxite fills depressions and sinkholes in the foot-wall limestone, whereas its top surface is concordant with the hanging-wall limestone. The thickness of the bauxite varies from 1 to 40 in and consists of bohmite, hematite, pyrite, marcasite, anatase, diaspore, gypsum, kaolinite, and smectite. The strata-bound, sulfide- and sulfate-bearing, low-grade lower part of the bauxite ore bed contains pyrite pseudomorphs after hematite and is deep red in outcrop owing to supergene oxidation. Tile lower part of the bauxite body contains local intercalations of calcareous conglomerate that formed in fault-controlled depressions and sinkholes. Bauxite ore is overlain by fine-grained Fe sulfide-bearing and calcareous claystone and argillaceous limestone, which are in turn overlain by massive, compact limestone of Santonian age, That 50-m-thick limestone is in turn overlain by well-bedded bioclastic limestone of Campanian or Maastrichtian age, rich with rudist fossils. Fracture fillings in the bauxite orebody are up to 1 m thick and consist of bluish-gray-green pyrite and marcasite (20%) with bohmite, diaspore, and anatase. These sulfide veins crosscut and offset the strata-bound sulfide zones. Sulfur for the sulfides was derived from tile bacterial reduction of seawater sulfate, and Fe was derived from alteration of oxides in the bauxite, Iron sulfides do not Occur, within either the immediately underlying or overlying limestone.