Geochemistry and Origin of Banded Ore of Manganese Belt, Eastern Carpathians, Romania.

Abstract

The Manganese Belt has a great mineralogical diversity and rarity contining more than 350 minerals and mineral varieties, of which 182 are new for Romania, being one of the most complex deposit in the world. The manganese ores are of carbonate-silicate type with a few oxides and sulfides. The chemical composition of many manganese carbonates, silicates, and oxides have high Mn/Fe ratios. The all manganese ores/manganiferous rocks have well-developed laminations/bandings, that appeared in hand samples and thin sections, representing distinct lithologies/petrographic types. The folowing types were established: metachert, quartzite with alkali pyroxenes and amphiboles, tephroite, Mn-humites, spessartine, pyroxmangite, rhodonite, mangancummingtonite, nambulite and natronambulite, pyrosmalte, and vein type (bannisterite, ganophyllite, and stilplomelane), all host by Tulgheş Series 1 (TG1) rocks. Each type was geochemical analysed. All lithology types show low concentrations of Ni, Co, Cu, Zn, U, Th, and REE trace elements, being similar to the trace element concentrations reported from sediments which are forming in hydrothermally active regions on the present sea floor. The metachert shows similar, but in low concentrations of trace elements, as the type ore. The metachert and manganese ore have high Li concentrations as trace element. The association of the manganiferous lithologies with metachert and meta-igneous rocks of TG1 is consistent with deposition of the original sediments in a rifting envronment, such as a back-arc basin. The current tectonic and structural setting of Mn ore correspond to their development and evolution in a subduction/rift zone, a narrow and long active paleotrench area, reflected in their line development as belt.