## 6 Discussion  
### Protolith Changes and Element Mobility  
Slight changes in the bulk major oxides are estimated from the (TiO\({}_{2}\) + MgO + Al\({}_{2}\)O\({}_{3}\) + Fe\({}_{2}\)O\({}_{3}\) + CaO + MnO + K\({}_{2}\)O + Na\({}_{2}\)O + P\({}_{2}\)O\({}_{5}\))/SiO\({}_{2}\) ratios [18]. The calculated sum oxides/SiO\({}_{2}\) ratio (1.08-1.46) is similar to those of [54]. The investigated rocks represent some of the metamorphosed Egyptian ultramafic rocks with variable amounts of serpentine, tremolite, and talc, and fewer chlorite minerals. The presence of antigorite and talc suggest high temperature [55]. REEs and HFS elements are considered immobile, especially during alteration, in comparison with LFSEs--such as Cs, Rb, K, Sr, and U--even during low alteration [18]. Serpentinites represent as an alteration products of low temperature of ultramafic rocks, making some changes of the protolith chemical composition by water addition [3; 18; 56]. In addition, some major oxides--such as CaO and SiO\({}_{2}\)[49]--can be remobilized during serpentinization processes. According to [49], the completely serpentinite rocks are more depleted in CaO relative to partially serpentinized rocks. Some physical properties of the protolith--such as density and magnetism--are also changed by serpentinization processes. Protoliths have higher density and lower magnetism than serpentinites [56], due to magnetite formation by serpentinization, as represented by the following equation:  
\[\text{(Mg, Fe)}_{2}\text{SiO}_{4}+\text{H}_{2}\text{O}\rightarrow\text{(Mg, Fe)}_{3}\text{Si}_{2}\text{O}_{5}\text{(OH)}_{4}+\text{Fe}_{3}\text{O}_{4}+\text{(Mg, Fe)}\text{(OH)}_{2}+\text{H}_{2}\]  
There are two types of serpentinites based on the major serpentine minerals: (1) chrysotile is formed by retrograde metamorphism of primary minerals (olivine, orthopyroxene, and clinopyroxene) at low temperatures (<300 \({}^{\circ}\)C), and (2) angiogenic serpentinites are formed by prograde metamorphism of lizardite and chrysotile at temperature ranges from 320 \({}^{\circ}\)C and 390 \({}^{\circ}\)C, and become stable above 390 \({}^{\circ}\)C [56]. Lizardite represents the most common serpentine mineral, whereas chrysotile is the least common [34]. They crystallize at identical temperature and pressure, but in different modes, where chrysotile precipitates a void  
Figure 9: (a) Trace elements of the examined ultramafics normalized to the primitive mantle; and (b) chondrite-normalized rare earth elements [51]. space from a liquid state, whilst lizardite precipitates from a solid state on the surface of olivine [56]. Transition of lizardite or chrysotile to antigorite within water-saturated open systems takes place according to the following equation:  
Lizardite (Chrysotile) + SiO2 (aq) \(\rightarrow\) antigorite + H2O  
Major oxides (Al2O3) and some trace elements--especially HFSEs (e.g., Zr, Th, Nb, Hf)--of serpentinites and serpentinized peridotites exhibit little change, tending to be immobile during the different metamorphic conditions, whilst LFSEs are expected to be mobile [13; 57]. Fluid mobile elements (FMEs), encompasses LFSEs (Rb, Sr, Ba, U & Cs) and semi-volatile elements (e.g., Pb) are enriched in serpentinites relative to other of the same compatibility either serpentinites developed at supra-subluction or MOR [29]--due to high concentrations of these elements as a result of fluid-rock interaction leverage [17]. S serpentinization of mantle rocks is achieved via the formation of serpentine minerals and the addition of H2O at theoretical contents of up to 12.38 wt.% \(\pm\) 2.99 wt.% [18]. For this reason, the degree of serpentinization can be assessed by LOI. According to [57], samples with LOI of more than 6 wt.% are considered to be altered. LOI reached up to 11.5 wt.% in the studied serpentinites, and 10.7 wt.% in serpentinized peridotites, supporting the role of hydrothermal alteration.