The discovery and significance of the Presinian Ma'anshan Formation in the central part of the Kang-Dian Axis, southwestern China

The discovery of the Presinian Ma' anshan Formation in the Huidong region, Sichuan marks an important progress in the research on the Presinian strata in the central part of the Kang-Dian Axis, especially in the prospecting and exploration of the Lala-type copper deposits in Huili, Sichuan. The Ma' anshan Formation consists of a suite of metamorphic sodic volcanic rocks-spilite associations, and may be correlated with the Palaeoproterozoic Hekou Group in Huili, Sichuan and Xiaoliukou Formation in Dongchuan, Yunnan. The volcanic rocks in the Formation that are assigned to the alkaline basalt series are characterized by:(1) higher contents of sodium and calcium and lower contents of potassium and iron; (2)REE association Cu-Au-U-Zn-As-Sb-Fe-Cr-Co; (3) relatively low ΣREE and relatively high LREE/HREE ratios indicating a LREE-enriched type of the rocks; (4) Eu and Ce depletion and a slightly rightward-dipping V-type distribution pattern.