The U content ranged from 2.04 �� 10?6 to 10.91 �� 10?6 (average = 4.42 �� 10?6), and was higher than that of typical crustal rocks with average U content of 1.30 �� 10?6 [77]. These geochemical characteristics agreed with those found in typical hydrothermal sedimentary siliceous rocks [78]. The Ba/Sr ratios ranged VEGFR from 5.84 to 110.17 (average = 33.34), which agreed with hydrothermal siliceous rocks with Ba/Sr > 1 [79]. The V/(V + Ni) values ranged from 0.10 to 0.90 (average = 0.51), which denoted a reductive environment with V/(V + Ni) > 0.46 [80]. However, the U/Th ratios ranged from 0.22 to 2.91 (average = 0.87), which were slightly lower than those of typical hydrothermal sediments [44]. According to this, the siliceous rocks were shown to be hydrothermal genesis, and this was supported by the plotting in Mn-10 �� (Cu + Co + Ni)-Fe discrimination diagram (Figure 10).

In addition, the samples deviated from the typical hydrothermal sediments (Figure 10), which possibly indicated the effect of terrigenous materials or volcanic input. So, the siliceous rocks were originated from hydrothermal sedimentation, which were possibly affected by the terrigenous materials or the volcanic input to some extent.Figure 10Major element discrimination diagram of siliceous rocks in Dongxiang area (after [81]).(b) The siliceous rocks deposited in a basin of marginal sea. The siliceous rocks have Sc/Th ratios ranging from 0.55 to 4.33 (average = 1.19), which were consistent with those of siliceous rocks of marginal seas (Sc/Th > 1) [44]. The U/Th ratios ranged from 0.22 to 2.

91 with an average of 0.87, and some of them were higher than those of siliceous rock of marginal seas [44]. The Sr/Ba ratios ranged from 0.02 to 0.17 (average = 0.07), which agreed with those of siliceous rocks formed in the basin of a deep ocean or a shallow ocean in retention with Sr/Ba < 1 [82]. According to V/(V + Ni) values averaged 0.51, the sedimentary basin was oxygen deficient, which denoted the Sr/Ba ratios should indicate siliceous rocks of a deep ocean basin. Additionally, the siliceous rocks plotted in Ti-V discrimination diagram (Figure 11(a)) indicated the depositional ocean basin circumstance and tended to be nearer to the basin of a marginal sea in the Ti/V-V/Y discrimination diagram (Figure 11(b)). This meant the siliceous rocks deposited in an ocean basin which was relatively far away from the continent itself.

So, the siliceous rock should have been formed in a limited ocean basin in its width, which had also been proposed by the literature [83]. In conclusion, the siliceous rocks were formed in an ocean basin with limited width.Figure 11Trace element discrimination diagram by formation environment for siliceous AV-951 rocks from Dongxiang (after [84]). (3) The rare earth elements of the siliceous rock from Dongxiang ore area were shown in Table 4 and could indicate the following information.