Peloids in stratabound Zn-Pb deposits and their genetic importance

Peloids from sediment-hosted Zn-Pb deposits in Belgium, Ireland and Poland are composed of Zn-calcite, siderite, smithsonite, silica, pyrite, melnikovite, sphalerite, galena, thiosulphates and Zn-As-bearing limonite. The size of peloids is between 7 and 60 m. The core and the shell of peloids are composed of different minerals and the shell is usually coarsely crystalline. Peloids are present in collapse breccias of karst cavities, stromatactis cavities, debris-flow breccias, and fractures cross-cutting carbonates hosting the mineralization. In places peloids form a major microtexture of the sulfide mineralization. Peloids are cemented and replaced by sulfides. Organic acids extracted from sulfide peloids are composed of amido-acids considered to be characteristic of bacterial origin. The size and specific texture of peloids are independent of mineralogy, location and age of the mineralization. Therefore the peloids disussed are considered as forms induced by bacterial activity rather than forms precipitated inorganically.