El yacimiento de paligorskita de Bercimuel (Segovia)génesis y propiedades tecnológicas

Abstract

The palygorskite deposit of Bercimuel (Segovia) is studied. It is situated at the top of the Miocene filling of an cratonic SW-NE basin in the southeastern part of the Tertiary Duero Basin. The age of the bed is upper Miocene. A complementary study is also made for other sections and outcrops located in the neighbourhood of the Bercimuel deposit. The palygorskite can be 80% of the total rock, and it appear with quartz, illite and kaolinite are inherited minerals. The palygorskite is associated with smectites and interstratified of the type smectite-illite, these minerals are minerals of transformation. The filling of this basin has been made by two alluvial fans from the pre-Neogene rocks in the elevated blocks flanking the depresión. The Bercimuel deposit lies approximately over the meeting of the two alluvial fans over an extensive level of caliche, which together with its lithological, structural, textural and mineralogical characteristics allows one to propose an origin for the palygorskite based on the following: 1) alteration of the phillosolocates and quartz present in the profile; 2) the solutes dissolved in the runoff water originating from the weathering of the reliefs composed of pre-Neogene rocks (gneiss, schist, dolomite, limestone...) In view of the features of hydromorphosis observed in the profile it may be inferred that there is a fluctuating ground water table that is affected by existence of underground caliche that would have acted as an impermeable layer. This circumstance may have been crucial for the development of the alteration of the minerals in the profile and to achieve the chemical (cation concentrations, pH), and physical (climatic drainage) conditions required for the genesis of the palygorskite. Regarding the fluctuating ground water table, it has been observed that alteration decreases from the base to the top of the profile; in the other words, it is better developed in the more permanently waterlogged levels of the lower part of the profile. By the excelents thecnological properties of the deposit, it present a economic interest.