大平掌铜多金属矿床火山岩构造环境的地球化学证据

大平掌铜多金属矿床是滇西目前发现的最重要海相火山岩块状硫化物矿床,其主要含矿建造为大凹子组火山岩系。大凹子组火山岩系主要岩性为中酸性火山熔岩及其火山碎屑岩夹细碧岩,其次还含多层硅质岩、凝灰质粉砂岩、沉凝灰岩、碳质或钙质页岩及碳酸盐岩等。通过结合已有的地球化学数据和最新的地球化学数据,对该区域的火山岩构造环境进行比较系统的研究。矿区细碧岩、英安岩等明显地Na2O>K2O;而凝灰岩和蚀变流纹岩则相反。矿区主要火山岩均以相对富集U、Th、La、Nd、Hf、Sm和相对亏损Rb、Ba、Nb、Sr、Ti、P为特征。火山岩的稀土元素总体上具有LREE>HREE的特点,LREE略微富集。综合大平掌火山岩主量、痕量元素岩石地球化学特征,表明大凹子组火山岩系形成于消减作用环境下的火山岛弧与弧后裂陷盆地的过渡带,并具有裂陷带双峰系列火山岩组合的特点。

Geochemical Evidence For Tectonic Setting of Volcanic Rocks in Da pingzhang Copper-polymetallic Deposit, Western Yunnan

Copper-polymetallic deposit of Dapingzhang which was discovered up to now has been the most important the volcanogenic massive sulfide deposit of marine facies.Ore-bearing formation of the deposit mainly occur in Dawazi Formation.The volcanic series of Dawazi Group mainly consist of medium acidic volcanic lava and volcanoclastic rocks,with locally developed basic lava(spilite),some siliceous rocks,tuffaceous siltstone,tuffite,calc and carbonaceous shale and carbonatite and others.The orefield spilite and dacite obviously possess the characteristic of Na2O>K2O via combining the stop-press and departed geochemical data analyzed systematically tectonic setting of the mining volcanic rocks.The tuff and altered rhyolite are the opposite.The characteristics of the mining area is that the main volcanic rocks of this mining area is generally relatively enriched with U,Th,La,Nd,Hf,Sm and lack of Rb,Ba,Nb,Sr,Ti,P.REE of the volcanic rocks of this area totally show that LREE>HREE which means LREE is reacher.The comprehensive analysis based on he characteristics of rock geochemistry of major elements and rare earth elements shows that Dawazi Formation of volcanic series is formed along the the transition zone of volcanic island arc and retroarc chasmic basins in the environment of subduction,and the characteristics of bimodal volcanic rock series in chasmic zone.