I. Trace element characteristics of series II and I granites
1. Trace element characteristics of rocks
The samples of series H granites were taken from Xiaokeng, Fuxi, Dabaoshan, Fogang, Lianhe, Sihui, Huangtian, Wucun, Lunshui, Gangmei, Wubeiling and Shijie, and there were 22 rock samples. Samples of series I granites are taken from Xiaokeng, Zhuguangshan, Dadongshan, Guidong, Fogang, Xinpeng, Dawangshan, Xishan, Yingwuling, Xiaonanshan, Xinxing and Qikou, and 28 rocks include almost all series I granites, which are also relatively representative (Table 2-1). Twenty-nine elements were analyzed in the rocks. Although the analysis of trace elements in each sample is incomplete, the characteristics of trace elements in the two series of granites are obviously different from each other from the randomly obtained average value.
(1) transition elements (Cr, Ni, Co, V, Mn), the average value of most elements in series II granite is higher than that in series I granite, up to 1 to several times; Besides Pb, the average value of series ⅱ granite is obviously higher than that of series ⅰ. In the precious metal ore-forming element groups (As, Bi, Au, Ag), the average value of Au and Ag in series II granite is higher than that in series I, whereas As and Bi are opposite, and series II is lower than that in series I.. From the comparison of the average values of these three groups of trace elements, it can be generally seen that the trace elements characteristic of series II granite are transition element group, nonferrous metal ore-forming element group and precious metal group, such as Au and Ag, which reflect some characteristics of deep origin of series II granite and are similar to those of series II ore-forming series Fe→Cu(Au)→Mo(W)→Zn, Pb→Pb(Ag) (Wang Liankui et al., 1982).
(2) Rare-element metallogenic group (Nb, Ta, Be, Sn, W), volatile element group (B, F, Cl) and radioactive element group (Th, U), except for a few elements, series I granite is obviously higher than series II granite, so it can Be seen that the trace elements characteristic of series I granite are rare-element groups Nb, Ta, Be, Sn. It also reflects that the series I granite should be a shallow-source recycled crustal material source, and at the same time, these elements are also geochemical with the metallogenic series REE→Nb, Ta(Li, Rb, Cs)→Be, Sn, W, Mo, Bi→As, Cu, Zn, Pb→Sb, Hg, U (Wang Liankui et al., 1982) of the series I granite.
(3) In the pro-MagmaElemental formation (Rb, Sr, K, Ba, Zr, Hf), the average values of characteristic elements Rb, K and Hf of granite in series I are higher than those in series II, while the characteristic elements Sr and Ba in series II are higher than those in series I, which reflects some information about the origin of granite in different degrees. The characteristic elements in series I may be related to the geochemical enrichment of K and Rb in shallow recycled crustal materials.
Table 2-1 Trace Element Content of Granite in Wuchuan-Sihui Fault Zone (wB/1-6)
Ore-controlling conditions and metallogenic prognosis of copper and gold in Wuchuan-Sihui Fault Zone
Ore-controlling conditions and metallogenic prognosis of copper and gold in Wuchuan-Sihui Fault Zone
Continued table
Ore-controlling conditions and metallogenic prognosis of copper and gold in Wuchuan-Sihui Fault Zone. (2) Yichang Institute of Geology and Mineral Resources, polymetallic metallogenic conditions, structural rock-controlling and ore-controlling laws and prediction of concealed deposits in Baoshan and its surrounding areas in northern Guangdong, 1989; ③ Geological Brigade 76 of Guangdong Bureau of Geology and Mineral Resources, 1: 5, regional survey report of Shitan Shahe sheet; ④ Guangdong Bureau of Geology and Mineral Resources, 1988; ⑤ Regional survey report of 1: 5, Tanshui amplitude by Guangdong Bureau of Geology and Mineral Resources; ⑥ Geological Brigade 74 of Guangdong Bureau of Geology and Mineral Resources, 1: 5, Yangchun amplitude regional survey report; ⑦ Regional Survey Brigade of Guangdong Bureau of Geology and Mineral Resources, Guangdong Magmatic Rock, 1977; ⑧ Geological Brigade 719 of Guangdong Bureau of Geology and Mineral Resources, regional survey data, 1989.
(4) The ratio of some element pairs between series Ⅱ and series Ⅰ granites is more obvious. The w(Rb)/w(Sr) and w(F)/w(Cl) of series I granite are several times to dozens of times higher than those of series II, and the w(Ba)/w(Sr) of series I granite is also higher than that of series II. The w(K)/w(Rb) of series I granite is lower than that of series II granite. In Figures 2-7 and 2-8, it is also clear that series I and series II granites are thrown into different areas respectively, with series I granites thrown into high w(F)/w(Cl) and w(Rb)/w(Sr) ratio areas and series II granites thrown into low ratio areas (Figure 2-7); At the same time, the series Ⅱ granite is put into the high w(K)/w(Rb) ratio area, and the series Ⅰ granite is in the low ratio area (Figure 2-8). Therefore, the ratio of trace elements in the two series granites can be used as a sign to distinguish or discriminate the two series granites.
figure 2-7 series ⅰ (ⅰ) and ⅱ (ⅱ) granite w (Rb)/w (Sr)-w (f)/w (cl) figure
figure 2-8 series ⅰ (ⅰ) and ⅱ (ⅱ) granite w (Rb)-w (k)/w. Series Ⅱ is the opposite, with high TiO _ 2 and low Li2O, which are 4.9% and .5% respectively. The average contents of TiO _ 2 and Li2O in the two series of biotite are several times to dozens of times different, especially in W (TiO _ 2)/W (Li2O). The average of Series I is only 2.82, and the average of Series II is 96 (Table 2-11). The w(F)/w(Cl) of biotite in series ⅰ is high, reaching 3.23 (average, the same below), while that in series ⅱ is low, only 2.82. The above shows that the characteristics of biotite trace elements in the two series of granites are consistent with those in rocks, indicating that the series ⅰ granites are relatively rich in Li, F and poor in Ti and Cl. Series ⅱ is the opposite, but the geochemical characteristics of biotite in series ⅰ and ⅱ are more obvious than those in rocks.
The characteristics of Mg, Fe and fo2 of biotite are also obviously different from those of two series of granites (Figure 2-9 and Figure 2-1). The biotite of series I and II granites are put into different areas respectively, and most of series I falls in iron biotite area (Yang Wenjin et al., 1988) and low fo2 area, with an average of .18 (Table 2-12). This shows that the geochemical characteristics of biotite elements are similar to those of rocks, which can reflect that series I granite is relatively poor in Mg and formed in a relatively reducing environment. Series Ⅱ granite is the product of relatively rich Mg and relatively oxidized environment.
Table 2-11 Comparison of two series of granite biotite W (TiO _ 2)/W (Li _ 2O) and w(F)/w(Cl) in Wuchuan-Sihui fault zone
Note: ① Regional Survey Brigade of Guangdong Bureau of Geology and Mineral Resources, Guangdong Magmatic Rock, 1977; ② Gong Wenshu et al. (1989); ③ Guangdong Bureau of Geology and Mineral Resources (1988).
Figure 2-9 Composition Diagram of Series Ⅰ (Ⅰ) and Series Ⅱ (Ⅱ) Granite biotite
Figure 2-1 Diagram of Series Ⅰ (Ⅰ) and Series Ⅱ (Ⅱ) Granite biotite fo2-N(Mg2+)
Table 2-12 Oxidation Coefficient (fo2) of Granite biotite in Wuchuan-Sihui Fault Zone. Part of the data comes from Guangdong Provincial Bureau of Geology and Mineral Resources, Regional Survey Brigade and Geological Brigade 75 and 76, etc.
the average value of trace elements in granite, the ratio of elements, the geochemistry of biotite elements and diagrams all indicate that series ⅱ granite is rich in transition elements, nonferrous metal elements, precious metal elements and high w(K)/w(Rb), w(TiO2)/w(Li2O), fo2 and low w(F)/w(Cl) and Mg-bearing biotite. Series Ⅰ granites are rich in trace elements of rare-earth ore-forming elements, volatile elements (especially B and F) and radioactive elements, with high w(Rb)/w(Sr), w(F)/w(Cl), w(Ba)/w(Sr) and low w(TiO2)/w(Li2O) and fo2. They may also reflect that series ⅱ granites were formed in the environment of high relative temperature and oxidation, while series I granites were formed in the environment of low relative temperature and relative reduction.
discrimination of trace elements in the tectonic environment of two series of granites
According to Pearce's (1984) discrimination model of trace elements, most granites in this area belong to intraplate or post-collision tectonic environment.
in figure 2-11 and figure 2-12, the trace element model curves of granite series I in Xinpeng, Xiaonanshan, Yingwuling, Xishan and Dawangshan are characterized by * * * that K, Rb, Th, Ta and Nb are richer than those in mid-ocean ridge granite, and Rb-Ba-Th peaks and valleys are obvious. From Hf to Yb, it is close to normal mid-ocean ridge granite values. The feature of this area is that the Ba of series ⅰ granite is abnormally low, even lower than that of mid-ocean ridge granite, which may be related to the later metasomatism or regional geochemical background characteristics.
in figure 2-13 and figure 2-14, the series Ⅱ granite curves of Lunshui, Gangmei, Wucun, Huangtian and Lianhe are characterized in that K, Rb, Ba and Th are richer than those of mid-ocean ridge granite, while Zr, Sm, Y and Yb are relatively deficient, especially the losses of Y and Yb are similar to those of volcanic arc granite model curves, and are positive and abnormal from obviously high Rb. However, the United (H73-1) and Sihui (H71) rocks are close to normal from Ce to Yb and the anomalies of K, Rb, Th, Ta and Nb are high, which can be compared with intraplate granite. Therefore, the above curve indicates that the series II granite in this area is similar to volcanic arc granite or near post-collision granite, or intraplate granite type. Combined with other characteristics, the series II granite should belong to post-collision granite or intraplate (attenuated continental lithosphere) granite type.
iii. Comparison of trace elements between anatexic granite and migmatite (Table 2-1)
There are few trace element analysis data in these two constructions. There are only 3 samples of Guangning and Heshui rock bodies in anatexic granite construction and 6 samples of Shijian and Tiedong rock bodies in migmatite construction. The average contents of trace elements in the two formations are generally close, but there are some differences. The migmatite formation is slightly higher than the anatexic granite formation in transition element group, nonferrous metal ore-forming element group, precious metal element group and radioactive element group, while the rare element group and volatile element group are slightly lower. In the pro-MagmaElemental formation, the Sr and Zr of migmatite are slightly higher, while the K, Rb and Ba of anatexic granite are slightly higher. This difference may also reflect the different degrees of deep melting of the two formations. The deep melting degree of the deep-melting granite is relatively high, so it is relatively rich in K, Rb, Ba and rare and volatile elements, while the deep melting degree of the mixed rock is relatively low, leaving some solid residues of the source rock, which leads to the relative increase of trace elements in the transition element group and non-ferrous metal metallogenic element group.
the contents of trace elements in the two constructions are similar, and the ratios of elements w(Rb)/w(Sr), w(K)/w(Rb) and w(Th)/w(U) are almost equal. Similarly, on the standardized curve of mid-ocean ridge granite (Figure 2-15), the shapes of the two constructions are completely consistent. Both formations are rocks mainly formed by shallow recycled crustal materials (series ⅰ). According to the series, deep-seated granites should belong to Himalayan series (series ⅰ) and migmatites should belong to Yunkai series (series ⅰ) (Wang Liankui et al., 1989).
Figure 2-11 Discrimination Diagram of Trace Elements Tectonic Environment of Series I Granites (I)
It should be pointed out that the characteristics of the standardized curves of the two kinds of mid-ocean ridge granites in Figure 2-15 are similar to collision granite or volcanic arc granite; Judging from the enrichment of Rb and the relative loss of Ba, it is closer to collision granite.