The Middle Miocene (Badenian) celestite (sulphate) diamictites, genetically associated with Salt (Evaporite) Formation, occurs in the external last lineament of the Sub Carpathian Nappe.
The Middle Miocene is the stratigraphic correspondent of the early used term “Tortonian” of Vienna Basin and to present term “Badenian”. It has been firstly separated and described in Muntenia Sub Carpathians and comprises four lithobiostratigraphic horizons: the “Tuff and Globigerina Marls” horizon; salt breccias with salt bodies or “Upper Saliferous” horizon; “Radiolarian Schists” and “Spiratella Marls” horizon. These horizons have been recognized under the same name or under different names all over the Carpathians domain and moreover these “horizons” were recognized, with some exceptions, in the whole extra Carpathian area, Transylvania and Maramures.
In Vrancea area the “Salt Formation” or the “Evaporite Formation” is represented by gravelly-sandy, gipsiferous lithotype respectively the sulphate diamictite, by the haliticanhydritic lithotype and by the secondary carbonate lithotype, together being genetically related.
The components of gravelly-sandy deposits are bound by a brown-black, clayey matrix having with earthy appearance. The matrix is chiefly impregnated with bituminous organic matter and is considered to be an insoluble residue entrained from dissolving evaporite beds. Usually the matrix is dominating (matrix-supported texture) – ubiquitous feature observed especially in mines. In places the matrix could be absent (claste-supported texture), this being explained by removal due to meteoric leaching. Its high-degree of intercrystalline porosity makes it a potential subsurface reservoir for hydrocarbons or metalliferous solutions.
Referring to celestite-bearing ore on the Valea Sării-Andreiaşu lineament (Vrancea district) the author separated in outcrops and in the mine (along Valea Sării brook) three types of mineralizations – petrologically and mineralogically different, but displaying continuous transitions between them. These are:
Mineralizations having impregnation character (mudstone-celestite using Dunham’s, 1962 classification for carbonate rocks), in a matrix-supported fabric according to background/crystals ratio. This type is widespread, was separated in heavy minerals concentrates too. Also, it borders the massive type of celestite mineralizations and is characteristically closely related to gypsum and anhydrite. Also, it has been considered that the celestite appearing in evaporite sediments of an intertidal environment is primary or early diagenetic. It does not form accumulation of economic importance.
The second type is a massive mineralization of replacement character, a wackestone/packestone celestite, in a crystal-supported fabric. Other authors termed it as “blocky celestite” or “replacement-type celestite”. Under the microscope some peculiar euhedral to anhedral shape of turbid-like methasoms of celestite, with a lot of inclusions and syntaxial rims showing an “intersertal texture” evidently disturbed by lack of space could be seen. The hot-rock within multiangular space between crystals is subordinated. This type has been developed during diagenetic stage as a true irregular and concretionary celestite bearing ore by redistribution of materials within sediment (diagenetic metasomatism).
The third type is a secondary mineralization, known as “celestite infilling cavities and fractures”. This type has been developed in a free space, with syntaxial rims and without inclusions and no host rock. It is white colored, in large fan-like or fibrous or long prismatic crystals or in collomorphous aggregates associated with sulphides. During epidiagenesis stage involving uplift and sub aerial exposure of diamictites as is observed on Valea Sării and Reghiu brooks – the evaporite re-enter in active phreatic zone and a secondary mineralization may develop.