## 5 Geochemistry  
### Analytical Techniques  
Fifty samples were collected from various locations within the Jabal Al Bayda area, representing the spatial variability of the granitic rocks. These samples were prepared for petrographic examination in the \"Laboratory for Rock and Thin Section Preparation\" at King Abdulaziz University. Once a small piece of a rock sample (2-3 cm in length) has been glued to a slide, it can be further cut, ground, and polished to achieve the desired thickness (typically around 30 microns), which can then be examined under a petrographic microscope. Based on the petrographic observations, 25 samples were selected for subsequent whole-rock geochemical analysis. We focused on the analysis of granitic rocks that had undergone only minimal changes in their chemical composition and mineralogy, i.e., samples that showed little or no replacement of the original minerals by secondary minerals due to alteration processes such as argillization or other hydrothermal changes.  
The selected samples were sent to the laboratories of ACME Analytical Laboratories in Vancouver, Canada, for geochemical analysis. The major element analysis was performed using X-ray fluorescence (XRF), with an accuracy of \(\pm\)0.01 wt%. In addition, the number of volatiles in the form of loss on ignition (LOI) was measured with an accuracy of 0.01%. Trace and rare earth elements (REE) were measured using the induced coupled plasma mass spectrometer (ICP-MS) method, with an accuracy of 0.01 ppm to 1 ppm. The obtained geochemical data are presented in Tables 1 and 2.  
\begin{table}
\begin{tabular}{l c c c c c c c c c c c c c} \hline \hline
**Sample** & **ST-56A** & **ST-56B** & **ST-61A** & **ST-61B** & **ST-62A** & **ST-62B** & **ST-63** & **ST-64** & **ST-65** & **ST-66** & **ST-67** & **ST-78** & **ST-79** & **ST-80** \\ \hline SiO\({}_{2}\) & 75.07 & 74.78 & 76.57 & 75.37 & 76.67 & 75.37 & 74.87 & 77.17 & 79.96 & 74.28 & 72.88 & 76.17 & 76.27 & 77.57 \\ TiO\({}_{2}\) & 0.16 & 0.11 & 0.08 & 0.11 & 0.12 & 0.09 & 0.15 & 0.11 & 0.13 & 0.15 & 0.06 & 0.14 & 0.11 & 0.10 \\ Al\({}_{2}\)O\({}_{3}\) & 11.84 & 11.24 & 11.48 & 11.97 & 11.34 & 12.01 & 12.20 & 11.30 & 10.19 & 12.24 & 12.24 & 11.56 & 12.12 & 10.99 \\ Fe-O\({}_{3}\) & 2.50 & 3.35 & 1.87 & 1.82 & 21.8 & 1.93 & 2.16 & 1.64 & 1.06 & 23.2 & 1.62 & 1.44 & 0.92 & 1.93 \\ MnO & 0.01 & 0.05 & 0.03 & 0.02 & 0.02 & 0.03 & 0.04 & 0.02 & -0.01 & 0.04 & 0.04 & 0.04 & 0.02 & 0.04 \\ MgO & 0.05 & 0.08 & 0.04 & 0.10 & 0.04 & 0.08 & 0.25 & 0.04 & 0.03 & 0.20 & 0.13 & 0.07 & 0.10 & 0.03 \\ CaO & 0.18 & 0.43 & 0.35 & 0.53 & 0.30 & 0.26 & 0.85 & 0.31 & 0.18 & 0.69 & 1.86 & 0.56 & 0.33 & 0.52 \\ Na\({}_{2}\)O & 3.64 & 4.22 & 4.03 & 4.11 & 3.81 & 4.19 & 4.05 & 3.71 & 3.27 & 4.07 & 3.36 & 4.00 & 3.84 & 3.66 \\ K\({}_{3}\)O & 5.06 & 4.27 & 4.61 & 4.60 & 4.44 & 4.65 & 4.25 & 4.74 & 4.26 & 4.74 & 5.24 & 4.28 & 4.61 & 4.59 \\ Fe\({}_{3}\)O\({}_{2}\) & 0.01 & -0.01 & -0.01 & 0.02 & -0.01 & 0.01 & 0.03 & -0.01 & -0.01 & 0.02 & -0.01 & -0.01 & -0.01 & -0.01 \\ Cr\({}_{3}\)O\({}_{3}\) & 0.03 & 0.03 & 0.01 & 0.01 & 0.02 & 0.02 & 0.02 & 0.01 & 0.02 & 0.01 & 0.01 & 0.01 & 0.01 \\ IOH & 0.47 & 0.57 & 0.39 & 0.65 & 0.52 & 0.38 & 0.42 & 0.44 & 0.49 & 0.46 & 1.97 & 0.85 & 0.81 & 0.43 \\ Sum & 99.02 & 99.12 & 99.46 & 99.31 & 99.45 & 99.02 & 99.28 & 99.48 & 99.59 & 99.22 & 99.42 & 99.11 & 99.13 & 99.87 \\ La & 110.27 & 23.13 & 44.37 & 59.24 & 41.28 & 38.86 & 40.98 & 58.62 & 62.61 & 62.91 & 16.95 & 59.62 & 164.41 & 58.03 \\ Ce & 207.48 & 48.95 & 95.81 & 116.15 & 98.04 & 80.86 & 88.13 & 121.04 & 137.29 & 132.30 & 35.49 & 124.13 & 94.91 & 127.22 \\ Pr & 25.58 & 6.05 & 12.16 & 12.66 & 12.19 & 11.22 & 10.59 & 14.34 & 16.50 & 15.34 & 4.52 & 16.32 & 34.58 & 14.87 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Major (wt%), trace (ppm), and rare earth elements (ppm) of selected alkali granites from the Jabal Al Bayda of Central Hijaz Region, Saudi Arabia.