Paper No. 35-3
Presentation Time: 8:30 AM-6:00 PM
GENETIC CONDITIONS OF THE LA CEMENTERA SKARN SYSTEM AND ASSOCIATED INTRUSIVE BODIES, SONORA, MÉXICO
La Cementera skarn in northwest of Mexico is formed mainly of paleozoic metasedimentary rocks intruded by 64.9 ± 1.33 Ma (K/Ar) to 60.5 ± 0.33 Ma (40Ar/39Ar) granitic to granodioritic bodies. The aim of this work is on the genetic aspects of the metamorphic and plutonic rocks of the La Cementera skarn. Field observations, petrography, geochemistry and termobarometric analyses were carried out in metamorphic and plutonic rocks. Petrographic studies shows that La Cementera skarn is composed of marbles, carbonate-silicate, calc-silicatites and silicate carbonate rocks with granoblastic to decusate fabrics with locally mylonitic-porphyroblastic fabrics. The marbles have calcite and wollastonites, the carbonato-silicate rock exhibit calcite-diopside-vesuvianite- wollastonite-garnet-quartz, calc-silicate rocks exhibit wollastonite-diopside-vesubianite-garnet-quartz paragenesis. Garnet-pyroxene skarn zone is mainly composed by garnet-vesubianite-diopside-wollastonite calc-silicate rocks with prograde phase paragenesis and calcite-quartz-epidote calc-silicate rocks as retrograde paragenesis. Geothermobarometry analyses was made to determinate genetic conditions of the La Cementera metamorphic and igneous rocks. Results obtained shows prograde metamorphism and intrusive cooling temperatures (600-700°C) and retrograde metamorphism temperatures (400-500°C). Pressures obtained shows low to mid values (2.9-4.0 Kbar), consistent with contact metamorphism conditions. Pseudo compound data indicates that the skarn paragenesis occurrence was mainly dominated by hydrothermal fluid composition. Paragenetic association of the La Cementera metamorphic rocks is stable under a hydrothermal activity with low CO2 (0.05-0.1%) values and high H2O (99.9-99.95%) under the obtained pressures and temperatures. Petrography, geothemorbarometry and pseudocompounds associate these rocks with a contact metamorphism and metasomatism phenomena that occurred at high temperatures-low to mid pressures and high H2O values- low CO2 hydrothermal activity, associated to a Laramidic-intermediate composition intrusive bodies within Hermosillo city and around.