Mineralogical and chemical characterization of the sepiolite / Mg-smectite deposit at Mara (Calatayud basin, Spain)
Mayayo, José; Torres-Ruíz, Jοsé; González-López, Jοsé Manuel; López-Galindo, Alberto; Bauluz, Blanca
European Journal of Mineralogy Volume 10 Number 2 (1998), p. 367 - 384
published: Mar 31, 1998
manuscript accepted: Nov 18, 1997
manuscript received: Jan 29, 1997
ArtNo. ESP147051002012, Price: 29.00 €
Abstract The sepiolite / Mg-smectite deposit of Mara is located in the marly-carbonate transitional facies of the Calatayud Tertiary lacustrine basin. The mineralized intervals consist of alternating levels of clays, marls and carbonates. The mineral associations are made up of detrital minerals (illite, interstratified illite-smectite, quartz, feldspars, dioctahedral smectite, chlorite and kaolinite); neoformed phyllosilicates (sepiolite, trioctahedral smectite and palygorskite); and carbonates (calcite and/or dolomite). Occasionally, heulandite-clinoptilolite, apatite, opal-A and opal-CT are also found. REE and trace element contents of the first transition series, on the one hand, and the F content, on the other, clearly distinguish sepiolite and/or Mg-smectite from the detrital aluminosilicates, suggesting that the two former correspond to primary phases originated by precipitation from basin solutions in a lacustrine environment, whereas palygorskite is derived from postdepositional processes from the transformation of detrital aluminosilicates. Oxygen isotope data from Mg-smectite and silex nodules suggest that these were formed in isotopic equilibrium with meteoric waters. Both oxygen and carbon isotope values and molar ratios of Sr, Na and Mg vs. Ca in carbonates indicate that the precipitating solutions were of meteoric parentage, being the main reservoir of carbon pedogenic in all cases. The apatite formation took place diagenetically from the decomposition of vertebrate bone accumulations.