Copper (gold) and non-metal deposits hosted in Mesozoic shoshonite and K-rich calc-alkaline series from Lishui in the Lower Yangtze region, China

Abstract The early Cretaceous volcanic sequences from the Lishui Basin in the Lower Yangtze region may be subdivided into K-rich calc-alkaline and shoshonite series. Geochemically, typical features of the shoshonite series are high total alkali, K 2 O Na 2 O ratio, A1 2 O 3 , Fe 2 O 3 FeO ratio, large ion lithophile elements (Rb, Ba, Th, U, LREE) and low TiO 2 and Fe contents. In contrast, K-rich calc-alkaline series have lower K 2 O, Na 2 O and Fe 2 O 3 FeO ratio, but are rich in Fe and Sr. The copper (gold) deposits are associated with the shoshonite series and occur within the Guanshan caldera, as a hydrothermal infill vein type with low to moderate temperatures of formation. Silicification and pyritization are in close relationship with Au mineralization. δ 34 S values for sulfide are −5.42 to 5.66%. and δ 18 O values of quartz range from 8.52 to 18.53%. The thermoluminescent characteristics of gangue quartz are considered as a possible exploration indicator of Au mineralization. A large Sr deposit is hosted in high-K andesitic volcaniclastic rocks of the K-rich calc-alkaline series at Aijingshan in the Lishui Basin. The deposit is a hydrothermal vein type with low to moderate formation temperatures and contains mainly celestite with lesser kaolinite, calcite, quartz and pyrite. δ 34 S values of celestite and associated pyrite are 20.9 to 28.5%. and 7.2 to 9.5%. respectively. The anomalies outlined by geochemical and biochemical exploration have provided an important prospecting criterion for Sr deposits. The germanium (iron) deposits are hosted in fluviolacustrine sedimentary rocks which were formed in periods of volcanic inactivity. The superimposed Ge, Mn and Fe primary anomalies are an effective criterion for Ge mineralization. The large Jiashan bentonite deposit is hosted in volcano-sedimentary rocks in the northern margin of the Lishui Basin,and is an alteration product of these rocks. There are 97 bentonite ore bodies in the mining area in which 70 are Na-bentonites. The Na-bentonite ore bodies extend about 750–2400 m along strike, with 400–1200 m wide and 1–30 m thick. The pH values and Na contents of groundwaters stored in the ore beds of bentonites in the area may be useful in exploring for the Na-bentonite deposits buried by the Ca-bentonite.