The carbonate and silicate mineralogy of the Zhilingtou gold-silver deposit, Zhejiang Province, south-eastern China

Abstract

The large Zhilingtou Au-Ag ore deposit is situated in the Zhejiang Province, NEE of the Suichang County Town, SE China. It is bound to Mesozoic volcanism and magmatism. Ore mineralization consists of electrum, minor argentite and native silver with traces of native gold. A local accumulation of silver tellurides and silver-bearing sulfosalts occurred only once. Sphalerite-rich veins are separate from the Ag-Au mineralization. Silicification, pyritization, and generations of hydrothermal carbonates and silicates are widespread. Hydrothermal rhodonite has 74 to 86 at.% Mn and 5 to 21 at.% Ca calculated from the sum of cations. Rare Mn garnet is spessartine with about 20 mol.% hydrogrossular component. Carbon- ates represent (a) a siderite – rhodochrosite solid solution, (b) rhodochrosite – kutnohorite solid solution with important Fe and Mg contents, (c) kutnohorite – dolomite/ankerite solid solution, and (d) manganoan calcite; between (a) and (c) tie-lines could be established. Low-Fe, Mn-Mg double-cation carbonates exhibit compositions exceeding 50 mol.% of the CaCO3component, up to mol 60 % contents. Pure kutnohorite appears missing and exsolution between Mn-rich and Mg- rich double-cation carbonates was observed. We indicate how changes in solution chemistry caused zonation, decomposi- tion and replacement of older generations by new ones, and formation of rhodonite by replacement of carbonates.