Petrográfica y Geoquímica de la dolomía hospedante de una mineralización de Zn y Pb. Puesto Gregor, Neuquén, Argentina

in neuquen basin, argentina, a zn-pb mineralization was first reported by garrido et al. (2000). the ore occurs in a carbonatic level located in puesto gregor, 50 km sse from the city of zapala at 39°11'34'' s, 69° 59'18'' w (fig. 1). the hosting bed, a dolostone, belongs to a carbonatic-siliciclastic sequence of lajas formation, which is part of the cuyo group, jurassic age. in the mineralization of pb-zn deposits associated to dolostones, the fluids that were involved in the ore precipitation process were also related to the dolomitization of the carbonatic rock (warren, 2000). in this contribution, field, petrographic and geochemical studies were carried out in order to determine the temperature and composition of the dolimitizing fluids. the obtained results were then compared to those obtained from carbon and oxygen isotopes (garrido et al., 2001) to discuss the dolimitization process. the mineralized bed, 0.90 m thick, outcrops for about 300 m along the strike (w-e) and 60 m in the dip direction (fig. 2). this bed pinches out toward the east and toward the west it is no longer visible, it is cover by scours. petrographic studies determined that the host rock is a dolostone with a breccia texture that becomes more siliciclastic towards the east grading thus to a fine sandstone with carbonatic cement. the hypogenic mineralization, mainly sphalerite, low quantities of galena, pyrite and marcasite is found within the small fractures. some ghosts of fossils are still visible, but pervasive dolomitization characterizes the horizon. two distinct dolomites are recognized by crosscutting relationships: a fine to medium grained crystalline dolomite, and a coarse grained crystalline dolomite related to the mineralization. the fomer shows dark-orange and white crystals which occur as patches or partially filled vugs. these crystals are 120-400 mm in size and exhibit subhedral to anhedral shapes (fig. 3). according to sibley and gregg (1987), the texture is no planar -a- u