This paper reports the minerals in an argillized tuff from the Lvshuidong mine, Huayingshan Coalfield, southwestern China. The clay assemblages of the samples are mainly kaolinite, varying proportions of illite and trace chlorite. Other minerals include various proportions of pyrite, small proportions of carbonates (calcite and ankerite), anatase, rutile, hematite, florencite and rare analcite. The clay mineralogy of the tuff profile changes vertically due to the change in the depositional environment. Although illite is minor in the middle and lower parts of the profile, it is relatively abundant in a few topmost samples where the proportion of illite is comparable to that of kaolinite. This is probably because the original volcanic ash was mainly deposited in a continental environment, but marine water may have percolated to the uppermost layers of the ash bed during early diagenesis, leading to the formation of concretions of concentric rings of kaolinite and illite. The samples of this study are derived from alkali mafic volcanic ash with relatively high concentrations of critical metals, including Nb, Ta, Zr, Hf, rare earth elements and Y.

The Shuangwang Au deposit (with a gold resource of approximately 70 t Au), is located in the Fenxian-Taibai fore-arc basin in the West Qinling Orogen of central China. Igneous intrusions in the region include the Xiba granitic pluton and granite porphyry and lamprophyre dykes. The Xiba pluton is composed of granodiorite and monzonite granite. The granodiorite is typical I-type granite, and it yields a crystallization age of 221.1 ± 1.2 Ma and a two-stage Hf model age of 1432–1634 Ma. The monzonite granite shows a transitional characteristic between I-type and A-type granite, and it yields a crystallization age of 214.8 ± 1.2 Ma and a two-stage Hf model age of 1443–1549 Ma. The granitoid was derived mainly from a crust–mantle mixed source. The ages indicate that the granodiorite and monzonite granite formed during two different stages. The REE distribution patterns of the Xiba granitoid exhibit significant fractionation between LREE and HREE, showing right-dipping curves, with an enrichment of LREE and a deficit of HREE. The granodiorite displays a light negative Eu anomaly, while the monzonite granite displays an obvious negative Eu anomaly. The granite porphyry dikes are distributed in the No. I breccia and Jiupinggou granite porphyry, and they yield crystallization ages of 219.9 ± 1.5 Ma and 213.1 ± 0.89 Ma, respectively, and two-stage Hf model ages of 1382–1501 Ma and 1373–1522 Ma, respectively. The lamprophyre dikes in the deposit yield a crystallization age of 214.4 ± 2.7 Ma. After the collision event between the Yangtze and the North China Plates along the Qinling orogenic belt, at approximately 220 Ma in the Late Triassic, the detachment of the slab produced the upwelling of the asthenosphere material. Under conditions of mantle heat and tectonic stress, widespread partial melting of the subducted continental crust and the upper lithosphere mantle occurred, forming granitoids with various degrees of adakite characteristics.