It is believed that the albite-potash-feldspar-greenschists in the middle Proterozoic Langshan Group in Tanyaokou District are synsedimentary potassic spilite (or poenite) based on the following facts and features: ( ⅰ ) they occur in beds and look blackish (or apple) green and compact; ( ⅱ ) they bear blasto-glomeroporphyritic and blastocrystalloclastic crystals which consist of (altered) albite laths with hollow skeleton crystal texture in which there are slender dark strips and minor pyroxene, and blasto-amygdaloid filled with pyrite, chlorite, magnetite, etc.; ( ⅲ ) the results of the petrochemical diagrams show that they are orthometamorphites; ( Ⅳ ) Sm-Nd isotopic age of them is 1 824 Ma (model age (t) is 2 006—2 132 Ma).
