Mejora en la interpretación de la mineralogía de vetas polimetálicas mediante una caracterización mineralógica detallada

Abstract

Interpreting the mineralogy of polymetallic veins macroscopically has many limitations, both in recognizing minerals and classifying box rocks and their different alterations. A detailed mineralogical characterization using transmitted and reflected light optical microscopy, electron microscopy, X-ray diffraction, and fluid inclusions thermometry will allow a better interpretation of mineralogy, alterations, rock classification, determination of associations and paragenetic sequences, and the formation temperatures of minerals. With this interpretation, it will be possible to reduce losses of economic minerals and predict the problems that arise in metallurgical processing and direct exploration projects. The samples studied in this investigation come from the Bienaventurada Vein and its box rocks at level 4230 of the South - West zone, Bienaventurada Subunit, of the Huachocolpa Uno Mining Unit, owned by Compañía Minera Kolpa S.A. and located in the Huancavelica region, Huancavelica province, Huachocolpa district. Studies included petrographic, mineragraphic, electron microscopy, fluid inclusions, and X-ray diffraction. The host rock samples have been classified mainly as porphyritic andesites with intense phyllic alteration, with some breccia by alteration minerals. Regarding opaque minerals, three generations of pyrite and sphalerite, two generations of chalcopyrite, fahlore, and marcasite, and one generation of galena, bournonite, seligmannite, lead sulfosalts, and silver sulfosalts were determined. The results obtained by scanning electron microscopy determined that silver is present in the chemical composition of fahlore (tetrahedrite-(Zn), tennantite-(Zn) and tetrahedrite- tennantite-(Zn) series) and silver sulfosalts (pyrargyrite, stephanite, and miargyrite), the latter to a lesser extent. Other copper sulfosalts, such as bournonite, seligmannite, and bournonite-seligmannite series, and lead sulfosalts, including jordanite, geocronite- jordanite, gratonite, and robinsonite, were also confirmed. Fluid inclusions studies were carried out on quartz, sphalerite, and barite crystals, resulting homogenization temperatures between 150°C to 300°C and salinities of 2 to 8% NaCl weight equivalent. The mineralogy and salinities recorded in the fluid inclusions suggest the deposit corresponds to an epithermal with intermediate sulphidation. The homogenization temperatures indicate a migration of the mineralizing fluids towards the SW sector of the Bienaventurada vein. High sericite contents from host rock would cause the generation of slimes that impair the flotation process, increasing the consumption of reagents and reducing the capacity of the foam to retain minerals of economic interest. Thus, it is advisable to reduce residence times in grinding operations to reduce the generation of slimes.