In terms o f major element compositions,diffe rent Proterozoic groups and formations h ave no distinct differences and on th e whole are characterized by interme diate SiO 2 contents and K 2 O /Na 2 O ratios and relatively high Fe 2 O 3? +MgO contents.

• 中元古代冷家溪群和新元古代板溪群(包括下部马底驿组和上部五强溪组)地层在主元素成分上无明显区别,总体上以中等SiO2含量和K2O/Na2O比值以及较高的(Fe2O3+MgO)含量为特征。