西藏甲马铜多金属矿床夕卡岩的喷流成因

夕卡岩为西藏甲马铜多金属矿床的主要容矿岩石 ,具有独特的喷流沉积和喷流交代成因。研究表明该夕卡岩的主要特征为 :(1)呈层状、似层状赋存于碳酸盐岩和细碎屑岩接触带 ,产状与地层一致 ;(2 )被后期脉岩穿切 ,成因上与岩浆岩无关 ;(3)喷流交代夕卡岩具交代残余结构和假角砾状构造 ,而喷流沉积夕卡岩具微粒状结构、雏晶结构和层纹、条纹、条带状构造 ,反映了二者不同的喷流成因 ;(4)发育典型的低温夕卡岩矿物组合 ,其形成温度小于30 0℃ ;(5 )夕卡岩的稀土配分型式与围岩的一致。甲马铜多金属矿床的夕卡岩是同生断裂系统、海底热流体 +深部烃碱流体与碳酸盐岩 +细碎屑岩耦合的产物 ,其成岩和成矿作用密不可分。

THE ERUPTIVE ORIGINS OF COPPER AND MULTI-METAL DEPOSITS IN THE SKARNS IN JIAMA,TIBET

The skarn with special eruptive deposition and metasomatism is the main ore-bearing rock in Jiama deposits.The main characteristics of the skarn are as follows:(1)occurring as bedded,para-bedded in the contact zone between carbonate and microclastic rock,and its occurrence being accordance to the strata;(2)cut by later vein rock,so having no relation with the magmatic rock on genesis;(3)metasomatic skarn having replacement remnant texture,pseudobreccia structure,while depositional skarn,particulate crystallitic texture and ribbon,stratified structure.These reflect they are eruptive genesis;(4)typical low temperature (<300℃) mineral assemblage developing in skarn;(5)the same REE pattern of the skarn and the wall rock.The skarn in Jiama deposits is regarded as the coupled results of contemporaneous fault system,submarine hydrothermal+deep-rooted hydrocarbon and alkali fluids and carbonate rock+microclastic rock.The diagenesis of the skarn has close relationship with the ore forming process.