LITHOLOGICAL AND GEOCHEMICAL SILICA LEVEL VARIABILITY IN THE ARCHAEOLOGICAL SITE “CASA MONTERO”, COMPARED WITH THAT OBSERVED IN OTHER MADRID BASIN SITES
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Abstract
This work compiles mineralogical, petrological and geochemical data from silica deposits of the “Casa Montero” Neolithic mine. The objetive of the work is to determine intrinsic variability in the silica deposits to distinguish them from other deposits potentially used as source rock for lithic tools. The archeological site of “Casa Montero” is located in a región with silica deposits (nodules, nodular beds, and lenticular beds), formed by silicification of dolomites and mudstones in surficial environment (Miocene of the Madrid Basin). The majority of the initially formed silica phases (opaline phases) were unstable and transformed to quartz by a process of aging. Petrological and geochemical data were obtained by XR diffraction, Micro-Raman, optic microscopy, emission and mass spectrometry (CP-ES and ICP-MS respectively). The results indicate that the rock types present in the site are chert, opal and opaline chert. They also allowed determining the textural characteristics and fabric of the silica deposits from the “Casa Montero” site. The statistical analysis of the geochemical data indicates that the Casa Montero silica rocks. Constitute a characteristic group. Their differentiation is due to the pres- ence of dolomite and mudstone host rock inclusions. The recorded clay minerals and rare earth element contents are the main distinguishing factors of the silica deposits from the “Casa Montero” site.