MINERALOGICAL AND CHEMICAL VARIATIONS, CASTELLANOS SHARE-HOSTED ZN-PB-BA DEPOSIT NORTHWESTERN CUBA

The shale-hosted Castellanos sedimentary exhalative Zn-Pb-Ba deposit o f Jurassic age in northwestern Cuba consists of pyrite, sphalerite, an d galena in a hydrothermal quartz-carbonate-barite matrix with very Li ttle elastic or shale matrix The northeastern end of the Zn-Pb-Ba lens overlies a transgressive Cu stringer zone which is interpreted as the vent or feeder channel for the exhalative mineralization. Abundance p atterns in the sulfide assemblage define layering within the deposit. In the southwestern part of the deposit sphalerite and galena increase and pyrite decreases stratigraphically upward within individual layer s. To tile northeast, near the vent, sphalerite and galena decrease up ward, parallel to pyrite. In the area of the vent the basal carbonate is exclusively dolomite; however, calcite abundance increases rapidly upward. Remote from the vent, dolomite is the dominant carbonate from the base to the top of the deposit. Carbonate and barite are the main gangue minerals near the discharge site; quart: is the major gangue mi neral in the southwestern section. These and other variations result f rom differences in a(Ca2+),f(O2) temperature, and Sigma S relative to sulfide-forming cations, especially Fe2+, at the discharge site and in the depositional basin some distance from the vent.