## 4 Discussion  
### Statistical Evaluation of Geochemical Data  
Although there is a remarkable difference in concentrations of several studied elements between the deep and shallow samples, considering the whole database, each element exhibits a unimodal distribution (histogram). Most distributions are close to normal, while some of them (Mg, K, Rb, Hf) are highly asymmetric and suggest lognormal distribution. As most applied multivariate statistical methods presume normal distribution, these variables were log-transformed in a common way. In the first step of the multivariate statistical evaluation, principal component analysis for all studied elements was fulfilled what resulted in five components (eigenvalue \(>\) 1) (Table 2). All these components can be interpreted geochemically as an accumulation process of the corresponding sets of elements. The first component (PC1-1, \(\sim\)38% of the total variance) has high correlation coefficients with the REEs as well as Ti, Al, and Fe among many other elements. As there are elements of significantly different geochemical behaviours, this set probably suggests the cumulative effect of more REE-accumulation processes. Interpretation of the second component (PC1-2, \(\sim\)23% of the total variance) is much more straightforward. Here Cu, Pb, Zn, As, Cd and Fe appear, a set of elements of similar geochemical behaviour. Most of them, but Fe prefer to bond with sulphur and so define the chalcophile elements based on the classical Goldschmidt classification [8]. In fact, Fe also commonly occurs as sulphide (e.g., pyrite) and so is familiar with other elements of PC1-2. Even if no single sulphide mineral grain was identified in the red muds by any phase analytical method, the common behaviour of these elements is typical even in bauxites [9]. Nevertheless, the accumulation tendency of these elements is suggested to be totally independent of that typical for the REEs (Table 2). The third component (PC1-3, \(\sim\)9% of the total variance) contains the high field strength elements (HFSE--Zr, Nb, Ta, Hf, Ce), which are known to behave in a similar way in numerous geochemical processes both under igneous and sedimentary conditions. Among the mineral phases of the studied red mud samples zircon, monazite and apatite are the major containers of the HFSE elements. All these refractory phases usually represent the igneous and/or metamorphic source rocks of the original bauxite. Their common behaviour in the red mud suggests that this set of elements could remain immobile not only during lateritic weathering that is the formation of the bauxite but also during the industrial treatment (Bayer process) and under diagenetic conditions inside the pitfalls. The only rare earth element in PC1-3 component, Ce represents the ancient igneous and/or metamorphic source, \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Principal Component**} & \multirow{2}{*}{**Total Variance\%**} & \multicolumn{2}{c}{**Elements with a Correlation**} \\  & & **Coefficient \textgreater{} 0.5** & **Geochemical Process** \\ \hline \multirow{3}{*}{PC1-1} & & \multirow{3}{*}{37.7} & La, Ce, Nd, Sm, Eu, Gd, Tb, Dy, \\  & & Ho, Er, Tm, Yb, Lu, Sc, Ni, Fe, V, \\  & & U, Th, Sr, \(\sim\)Ca, Ti, Al \\ \cline{1-1}  & & Cu, Pb, Zn, As, Cd, Fe \\ \cline{1-1}  & & Zr, Nb, Ta, Hf, Ce \\ \cline{1-1}  & & Mg, K, Rb \\ \cline{1-1}  & & As, P, W \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Results of the first principal component analysis (PCA). as well. Because Ce appears not only in a trivalent ionic form, like all other REEs, but also can form a smaller sized, 4+ ion, its compatibility to two different groups of trace elements (and minerals) is reasonable. On the other hand, numerous observations suggest that the major REE minerals in bauxites of diverse origins are zircon, monazite and apatite [9; 10], which is not the case for the Almasfuzito red mud. Here, the REEs but Ce have no genetic relationship with these phases as shown by their low correlation coefficients with PC1-3.