Morphogenetic types of ore bodies, ore textures and crystallization mechanisms in the hydrothermal madan deposits, central Rhodopes

In the Madan Pb-Zn deposits three morphogenetic types of ore bodies are recognized: (i) steep simple veins; (ii) complex disseminated stockworks and (iii) gently sloping marblehosted skarn-ore bodies. Their formation is structurally controlled by the fault systems, and lithological variety of the host Rhodope metamorphic complex. The replacement ore bodies reveal complex morphology according to the number, thickness and position of the host marble layers, shifts along the fault structures and local physicochemical parameters. Among the well presented morphological types – bed-like, mushroom-like, columnar or irregular, single or multilayered replacement bodies occur. The varied sulphide textures are formed by crystallization in open space or metasomatic growth in solid state. Infill ore textures like cutting veinlets, layered textures, druses, crustifications and breccias are indicative for crystallization in open space. Typical for the vein and stockwork mineralization, they are observed as well in the dissolution cavities formed by “hydrothermal karst” in the replacement ore bodies. In the latter, characteristic are the textural varieties inherited by the primary skarns in the processes of alteration and overprinting. Radiate and spherulitic, concentric, conical, massive, porous, rhythmic-banded textures typically occur. Ore impregnations and nests, pseudomorphs and interstitial formations complete the textural diversity. Certain zonal distribution in the mineral and textural characteristics is determined. The main mechanisms of ore deposition include boiling, intensive fluid/rock interaction, retrograde alteration of skarns, performed generally by convection and diffusion.