云南易门狮山铜矿床的喷气沉积成因

ON VOLCANIC EXHALATIVE-SEDIMENTARY GENESIS OF SHISHAN COPPER DEPOSIT, YIMEN, YUNNAN

本文讨论了云南易门狮山铜矿床的地质背景、含矿建造、火山岩及矿床地质地球化学特征。成矿地质背景为中元古代后期的裂陷槽。含矿建造为火山沉积黑色页岩碳酸盐含铜建造。胶状、变胶状黄铁矿及黄铜矿砂状碎屑构造是矿床同生成因的新证据。建立了海底喷气沉积矿床成因模式,论述了狮山铜矿床的成矿作用。

Shishan copper deposit, Yimen, Yunnan province, is one of the famous copper deposits in China. The copper deposit is formed in Central Yunnan Aulacogen in Middle Proterozoic subera. Ore-bearing horizons belong to Shishan member of Luzhijiang Forma-tion of Middle Kunyang Group of Middle Proterozoic suberathem. The Shishan Member is a set of spilite-keratophyre volcanic-sedimentary rocks and may be divided into three horizons i.e. violer, variegeted (mainly greyish-green) and black horizons in the ascending order. The orebodies are confined to the variegated (greyish-green) and black horizon. The ore-bearing formation belongs to volcanic-sedimentary black shale-carbonate copper-bearing formation. The orebodies appear as bedded or stratoid bodies which are conformable with the wall rocks. The main ore minerals are chalcopyrite and bornite and a small amount of arsenic cobalt. The ores have bedded, metacolloidal, concretionary and sandlike clastic structures . and framboidal texture showing characteristic of sedimentary origin. The metamelnikovite contains Co 100ppm, Co/ Ni>10, As>100ppm, Se>0.1%. The δ34S Values of the sulfides show characteristics volcanic exhalative-sedimentary sulfide deposits. The present paper suggests a new genetic model for volcanic exhalative-sedimentary deposits which may be used to explain the metallogeny of Shishan copper deposit. According to the model, the copper of Shishan deposit was derived from keratophyre magma and the violet horizon acting as a source-bed both of which were derived from the upper mantle and lower crust. The hydrothermal solutions consist of magma water, and meteoric water, sea water and connate water heated by volcanism. Sulphur of the deposit was derived from SO42-in sea water, partly from the upper mantle. The copper-bearing hydrothermal solution erupted to the seafloor discharged ore-forming elements under the reduction environment in the closed deep-sea trough and formed shishan copper deposit.