*5.5.1 Major element concentration/distribution*

In general, the major element concentrations in the Pidong Lake decrease in the order Mg > Ca > K > Na (**Table 5**). The highest concentrations of Mg (30 to ≤40 mg/l), Ca (21–25 mg/l), K (15 mg/l) Na (8–11 mg/l) are observed during the dry season (January–April) while lowest concentrations of Mg (16–25 mg/l), Ca (10–15 mg/l), K (4–7 mg/l) in the rainy season (August–October). The intermittent change of color of the Lake from clear blue to brown has been attributed to the increase in Fe concentrations into the Lake.

#### *5.5.2 Rare earth element (REEs) concentrations*

**Figure 14** presents the REE patterns from the Crater Lake normalized to Chondrites. The REE concentrations are impoverished relative to Chondrite values (<1 Chondrite). There are significant variations in the LREE (0.03–0.18 Chondrite for La) relative to HREE (Gd-Lu). An important characteristic of the spectra is the similarities between the LREE patterns indicating similar source. The slight enrichment in LREE must have been influenced by fluid percolation through the host crustal materials (host granite basement) rich in these elements.
