Abstract:

Jiulongzhang and Xiangshan volcano-intrusive complexes are the Mesozoic rhyodacitic volcano-intrusive complexes associated with uranium ores in southern China. Xiangshan volcano-intrusive complex is the wall rock of the biggest volcanic-rock uranium ore deposit in China, and the main body is rhyolitic porphyroclastic lava, accompanied by hypabyssal or ultra-hypabyssal intrusive rocks such as dacite-porphyry and granite-porphyry. Jiulongzhang volcano-intrusive complexes are dominantly rhyolitic welded tuff, accompanied by dacite.porphyry and quartz monzonite-porphyry, and so on, and the uranium resources are being assessed.The comparative studies of lithogeochemistry for the volcano-intrusive complexes both from Jiulongzhang and from Xiangshan reveal that the chemical compositions of the volcano intrusive complexes in the two areas are very close , and the trace element spidergrams and REE patterns basically coincide with each other.It is also shown that the two volcano-intrusive complexes have the same source features and the active continental margin tectonic settings. At the same time, it is found that, from early volcanic magma activities to later intrusive magma activities, the content of SiO₂ and the Rb/Sr ratio decreased, on the contrary, the content of MgO and the ratios of K/Rb, Ba/Rb and LREE/HREE increased. It is shown that the hypabyssal or ultra-hypabyssal intrusives are not the products of the volcanic magmatic differentiation.

Key words: lithogeochemistry, volcanic rocks, hypabyssal or ultra-hypabyssal intrusives, tectonic setting, Jiulongzhang, Xiangshan