Statistical analysis of geochemical data. A tool to discriminate the origin of kaolin deposits un Patagonia

CRAVERO FERNANDA; MARFIL SILVINA; MAIZA PEDRO

Castellaneta Marina (Italia)

Conferencia; XIV International Clay Conference.; 2009

AIPEA

The numerous kaolin deposits located in Patagonia Argentina have been formed by either hydrothermal, metheoric or sedimentary processes. The primary origin has been established from O18 and D isotopic composition of the main minerals, kaolinite and/or dickite and, as defined by Dill et al. (1997), from the behaviour of certain elements during the alteration. Considering that in all the primary deposits, the fresh rocks are similar in age and composition, the purpose of this work is to determine which are the chemical elements that better characterize the kaolins and allow to differentiate their origin. To handle the great amount of variables per sample, a statistical multivariated study was used. The Principal Component method permits to define, one one hand the variables that better characterize each deposit and, on the other hand, the correlation between them. Once worked with all the elements, those that were not explained in the first two components (which represents 75% of the total variance of the model) were discarded. Doing so, the contents of Fe2O3, P2O5, LOI, Sr, Y,Zr,V, Pb, Hf, Rb and REE were used. The results show that the first two components allow a clear separation between the hydrothermal and metheoric-sedimentary deposits. The first component indicate that Fe2O3, Y, Rb, U y HREE are more abundant in the metheoric-sedimentary deposits, whereas, Sr, Pb y V are in the hydrothermal. The second component shows that P2O5 and the LREE are enriched in the hydrothermals and Zr in the metheoric- sedimentary. In the metheoric deposits and their transported products (sedimentary deposits), most of the elements show the same geochemical behaviour, emphasizing the idea that the sedimentary processes have little influence in the mobilization of the analyzed elements. Data suggest that there is an enrichment in Y-HREE during weathering and a depletion during hydrothermal processes. The obtained data can be plotted in binary diagrams (Ce+La vs Y+Yb+Lu), P2O5 vs Y, P2O5vsZr, P2O5+Sr vsZr) were the field of the hydrothermal deposits is well separated from the field of the metheoric ones. Dill H.G., Bosse R., Henning H. and Fricke A. (1997) Mineralogical and chemical variations in hypogene and supergene kaolin deposits in a mobile fold belt the Central Andes of northwestern Peru. Mineralium Deposita 32: 149-163.