Xishantou Fm

The conformable base of the formation marked by light gray green rhyolitic vitric tuff is distinguished from the underlying Gaowu Fm marked by gray purple rhyolitic vitric and crystal ignimbrite.

The conformable top is bounded by the appearance of dark purple red massive conglomerate of the overlying Chawan Fm.

The formation is distributed in the Nanlongquan-Shangyu and Wencheng- Fenghua areas. It is complicated in lithology and well stratified and varies in lithology laterally. In the Longquan-Shangyu area, it has a larger number of acid and moderately acid lava partings, and decreases in the amount of intermediate and basic lava. In Baiyangwu of Longyou and Wumen of Wuyi, the rhyolite partings are more than 200 m thick and in Zaoli of Jinhua, the cumulative thickness is up to 650 m. In Taling of Yongkang, intermediate and acid lava is up to 400 m thick, with sedimentary partings of 5-40 m in general. In Wumen and Simingshan, the sedimentary partings are in excess of 100 m in thickness. In the Dongyang and other areas, the Xishantou Formation is intercalated with marl and limestone lenses.

It generally ranges from 700 to 1500 m in thickness, 446 m at minimum and 3000 m at maximum (in Wumen of Wuyi). It possesses lead and zinc ore deposits behind Qingtiantang, Xiaosi, Kingxia of Wenzhou and Chakeng of Sanmen; and copper and zinc ore deposits in Fangzhouting of Linhai; magnetite deposit in Tiankeng of Linhai; and pyrophyllite deposits at the mouth of the Qingtian mountain. In the Wencheng-Fenghua area, it is dominated by acid pyroclastic rocks, with the exposed sedimentary partings varying from place to place. In Shuangqiao of Shengxian, it is intercalated with carbonaceous shale and coal streaks.