## 2 Materials and Methods
### Materials
#### 2.1.2 Data Materials  
We collected a set of 1:200,000 stream sediments survey data matching the study area shown in Figure 1, which were provided by China Geological Survey. As the study area is situated in arid and semiarid regions, the sampling media include soil and stream sediments (10-40 mesh). The surface organic layer was avoided during the sampling process. There were 0.25 to 1 sampling points per km\({}^{2}\), and samples collected within 4 km\({}^{2}\) were combined into one composite testing sample. If the stream-sediment samples cannot be easily collected, the soil samples will be used instead. The sample collection, preparation, storage, chemical tests, quality control and data preprocessing adhered strictly to the \"criterion of regional geochemical exploration\" released by the Ministry of Land and Resources of China in 2006. For example, the general quality control flow involved the following steps: (i) analyses of the Geochemical-Standard-Drainage sediment samples; (ii) analyses of the coded Geochemical-Reference-Drainage sediment samples developed  
Figure 1: Generalized geologic map of the study area. Note: 1. Quaternary; 2. Baogedawula Formation, Pliocene Series, Neogene; 3. Manitu Formation, Upper Jurassic Series; 4. Manketouebo Formation, Upper Jurassic Series; 5. Sanmianjing Formation, Lower Permian Series; 6. Elitu Formation, Upper Permian Series; 7. Early Cretaceous alkali-feldspar granite; 8. Early Cretaceous syenogranite; 9. Early Cretaceous granite porphyry; 10. Late Permian granodiorite; 11. Middle Permian monzonitic granite; 12. Middle Permian quartz diorite; 13. Early Permian quartz diorite; 14. Early Permian monzonitic granite; 15. Late Ordovician-Middle Silurian monzonitic granite; 16. Neo-Archean Liushugou Formation; 17. fault zone; 18. syncline; 19. anticline; 20. W-Nb-Ta-F deposit; 21. U-mineralized deposit. The study area is located in Inner Mongolia, North China, as shown in the overview.  
by the provincial laboratory; (iii) duplicate analyses of the randomly selected and coded samples; (iv) rechecked analyses of the samples with anomalous values; and (v) rechecked analyses conducted by external laboratories, if necessary.  
Finally, we got 1325 composite samples, and 39 elements were accurately analyzed by multiple methods, including 32 elements and 7 oxides. In this article, we mainly focus on eighteen main ore-forming elements, which are Ag, As, Au, B, Be, Bi, Cu, F, Hg, Mo, Nb, Pb, Sb, Sn, U, W, Zn, and Fe\({}_{2}\)O\({}_{3}\). Elemental contents of each composite sample are determined mainly by the ICP-MS (i.e., inductively coupled plasma mass spectrometry) method [7]. The statistical parameters of them are given in Table 1.  
Previous studies [29] have indicated that the mineralization of Nb, Ta, Li, Be, REE, U, etc. in the study area is most related to highly fractionated peraluminous granitoids (S-type); while the mineralization of W, Pb, Zn, Ag, fluorite, tourraline (B), Au, Cu, etc. is mainly of quartz-vein type, often occurring within the syenogranitic wall rocks (highly fractionated I-type) surrounding the peraluminous granitoids. Based on these facts and according to the metallogenic specialization of granitoids [31], the relevant ore-forming elements can be divided into two groups: (1) Ag, Au, As, B, Cu, Hg, Mo, Pb, U, Zn, and Fe\({}_{2}\)O\({}_{3}\), which are closely related to magnetite series granites (I-type); and (2) Be, Bi, F, Mo, Nb, Pb, Sb, Sn, U, W, and Fe\({}_{2}\)O\({}_{3}\), which are closely related to ilmenite series granites (S-type) [29]. At the same time, in consideration of the extensive development of granitic complexes in this area and the complex mineral paragenesis [30] such as Cu-Mo versus W-Mo, Pb-Zn versus W, Sn-Pb, U-Pb versus Th-U, and pyrite versus Fe\({}_{2}\)O\({}_{3}\), we make Mo, Pb, U, and Fe\({}_{2}\)O\({}_{3}\) appear in both groups.