Statistical analysis of geochemical data: a tool for discriminating between kaolin deposits of hypogene and supergene origin, Patagonia, Argentina

Abstract

The numerous kaolin deposits located in Patagonia, Argentina, have been formed by hypogene or supergene processes. The primary origin has been established from O18 and D isotopic composition of the main minerals, kaolinite and/or dickite, and from the behaviour of certain elements during the alteration. The aim of this paper was to find if there is a tool, other than oxygen-deuterium data, to establish the origin of the Patagonian kaolin deposits. To handle the large number of variables per sample, a statistical multivariate study was used. The Principal Component method defines, on one hand the variables that better characterize each deposit and, on the other hand, the correlation between them. Fifty seven elements were considered and those that were not explained using these two components (which represent 75% of the total variance of the model) were discarded. As a result, the contents of Fe2O3, P2O5, LOI, Sr, Y, Zr, V, Pb, Hf, Rb, S and REE were used and the results show that the two components separate the deposits into two fields that are consistent with the process of formation. The first component indicates that Fe2O3, Y, Rb, U and HREE are more abundant in the supergene deposits, whereas, Sr, Pb, S and V are more abundant in the hypogene deposits. The second component shows that S, P2O5 and the LREE are enriched in the hydrothermal deposits, whereas Zr is more abundant in those formed under weathering conditions.

Geochemistry of Hydrothermal Alteration in Volcanic Rocks

“…Consequently, kaolin samples with high Ti and Zr contents point to a superficial environment of formation (Marfil et al 2005). Cravero et al (2010) compared kaolin deposit from hypogene and supergene origin from Patagonia Argentina. In the hypogene deposits, S, Sr, Pb, V, P 2 O 5 , and LREE are more abundant, whereas Fe 2 O 3 , Y, Rb, U, Zr and HREE predominate in the supergene (weathered) deposits.…”

“…The samples from Patagonia studied by Cravero et al 2010 have been taken as representative of the whole altered area, so the element contents do not come from a specific part of the weathering profile; therefore it can be considered that the conservative behaviour of the REE elements arises from the fact that they have fractionation could have occurred within the profile. Another characteristic of the REE that supports a supergene origin is the presence of a Ce anomaly, produced when Ce 3+ is oxidized to Ce 4+ .…”

“…illite and relict quartz and feldspars (Dominguez & Murray, 1997;Cravero et al, 2001;Dominguez et al, 2008). Table 1 synthesizes the geology and mineralogy of the deposits (Cravero et al 2010). …”

“…The deposits examined in this study are located in different areas of Patagonia in the Provinces of Río Negro and Chubut and they are studied by Cravero et al (2010), Maiza et al (2009) and Marfil et al (2005Marfil et al ( , 2010.…”

Late Cenozoic deep weathering patterns on the Fennoscandian shield in northern Finland: A window on ice sheet bed conditions at the onset of Northern Hemisphere glaciation

“…These views derive largely from observations that thick kaolins and bauxites of Palaeozoic to Palaeogene age are found today along shield margins. These intensely weathered rocks are, however, confined largely to locations beneath and close to sedimentary and volcanic cover rocks along shield margins (Kaye, 1967;Parham, 1970;Smith, 1987;Lidmar-Bergström, 1995;Mordberg and Nesterova, 1996;Sarapää, 1996;Lidmar-Bergström et al, 1997;Patterson and Boerboom, 1999;Cravero et al, 2010;Hall and Migoń, 2010). Pockets of intense weathering are not widely reported from shield interiors.…”