**5. Conclusions**

*Trace Metals in the Environment - New Approaches and Recent Advances*

protoliths. In this glass, the authors of [41] found accumulations by factors of 10–100 for As, compared with the mean continental crust values and other incompatible trace elements (e.g., Be, B, Rb, Sn, Sb, and Ta), and by factors of 100–200 for Li, Cd, and Cs. In a second article [43], the authors of reference [41] state that remarkable concentrations of Cd (up to ~300 ppm) could be found in quartz-hosted fluid and melt inclusions in hydrous peraluminous systems (pegmatites and leucogranites) for the first time ever. A distinct number of the groundwater samples used for this study show detectable concentrations of Cd. Significant amounts of Li, B, Zn, As, and Pb were also found in quartz-hosted fluid inclusions from the Huanuni tin deposit in Bolivia (hosted in peraluminous granites with ASI ≥ 1.1) [44]. The indicative trace elements of leucogranites (Li, B, P, Mn, Zn, As, Sr, Pb, and U) are similarly detected in the ground water in Nawalparasi. The high concentration of Sr in groundwater can be based by the frequent occurrence of calcium carbonates in the soil hosting the groundwater. In study [45], the authors mentioned lithologies like rhyolite and shale

*The most noticeable trace elements in groundwater from Nawalparasi district (green triangles) compared with the few available data of the Macusani obsidian glass (peraluminous in composition, enriched in As-B-F-P). The data for comparison (purple stars) are taken from [41]. Note the logarithmic scale for comparison of concentrations.*

(greywackes) representing a greater risk of elevated As in groundwaters.

As frequently described in the literature, low-grade metapelites are often considered as protoliths of peraluminous granites (see, e.g., [22, 46, 47]) where concentrations of As, Sb, Be, B, Ba, and Rb by a factor of 5–10 higher than their average crustal abundances (2–5 ppm) [48–50] were not unusual. The leucogranites (two-mica or muscovite-tourmaline mica) found in the Himalayas of Nepal are undoubtedly peraluminous in composition (see, e.g., [22, 51, 52]) and coherently a comparison with the findings from [41] is warranted. Most of the leucogranites analyzed in [51] are peraluminous (ASI > 1.1) to strongly peraluminous (ASI ≥ 1.1). According to Ref. [53], lead represents one of the rare elements usually behaving incompatible during crustal melting. Pb can be significantly enriched in low T S-type granite melts, especially if the proportion of partial melting remains low. Moreover, muscovite, known as being a major mineral of metapelitic sources, can exhibit relatively high Pb contents. The leucogranites in the Nepal Himalayas are widely described to be of crustal origin and are derived from vapor-absent muscovite-dehydration melting of pelitic and psammitic protoliths during the Late

**56**

**Figure 2.**

Miocene (see, e.g., [47, 54–59]).

So far it was considered that As is mainly released from iron (hydr)oxides, but a major host for sorption and release of As are alumosilicates such as clay minerals (including micas) into groundwater. The apparent decoupling of the concentrations of Fe and As and the positive correlation between concentrations of Na, K, and As in the groundwater are a significant evidence that As cannot be released from Fe minerals predominantly—so silicates represent the fundamental source of As in sediments. Clay minerals preferentially lose Na and K from their interlayers during chemical weathering and hence become enriched in immobile elements such as Fe and Al. Moreover, the trace elements detected in the groundwater samples of Nawalparasi are well known to be contained in peraluminous obsidian glasses from Peru enriched in As-B-F-P. These glasses equal the leucogranites in the Manaslu area North of Nawalparasi in their geochemistry and represent the original host rocks of arsenic.
