西秦岭大水金矿的花岗岩成矿作用特征

西秦岭大水金矿是西秦岭造山带南缘三叠系浅海相碳酸盐岩中新近发现的一类独特的特大型金矿床。矿区侵入岩属花岗岩大类 ,δ <4,ASI >1,属中性—中偏基性过铝质钙碱系列岩石 ,具深源浅成的特征。岩石化学成分δ τ图解以及稀土元素的w(Rb) w (Yb +Nb)和w(Rb) w(Yb +Ta)图解显示其属造山带同碰撞构造环境。金矿石的碳、氢、氧、硅同位素测试结果显示成矿物质来源于深部。矿石为轻稀土富集型 ,配分模式与岩浆岩接近。全岩K Ar同位素年龄表明格尔括合岩体为 190 0～ 190 5Ma ,矿化脉岩为 182 6～ 184 7Ma ,说明成岩与成矿具同源性但主成矿期滞后于脉岩的形成。花岗岩的成矿作用主要体现为 :( 1)沟通深部矿源场和成矿场 ;( 2 )岩浆高热能和岩浆水参与成矿流体的循环 ;( 3)花岗岩的就位机制为“气球膨胀”式 ,并通过就位扩容压缩围岩产生的张性断裂构造控制金矿体的产出。

GRANITIC MINERALIZATION OF THE DASHUI GOLD ORE DEPOSIT IN WESTERN QINLING

The Dashui gold ore deposit is a super-large and special one found in Triassic carbonate rocks of neritic facies in the south of western Qinling orogenic belt.The compositions of the intrusive rocks show granitoid feature in the Q-A-P diagram with δ<4 and ASI>1.They belong to neutral-basic peraluminous calc-alkaline rocks showing characteristics of anatectic origin and hyabyssal localization and the Rb-Sr isotopic ags are 174.31—204.08 Ma.The δ-τ diagrams of petrochemical composition and the Rb-(Yb+Nb) and Rb-(Yb+Ta)diagram of REE show that the granitics occur in syncollisional environment of orogenic belt,which is the same as the tectonic setting of orogeny caused by the collision between the South and the North continents in late Indo-Chinese epoch.The isotopic contents of C,H,O and Si from Dashui gold ores show that the ore-forming material comes from the deep,the ores are rich in light REE,and the REE pattern resembles that of magmatite.The K-Ar isotopic age of Ge'erkuohe rockbody is 190.0—190.5 Ma and the age of mineralization vein is 182.6—184.7 Ma,which suggests diagenesis and metallization are of the same origin and metallization is a little late.The granitic mineralization mainly appears as:(1)building a feeder between deep-seated source field and mineralization field;(2)mineral fluids circulating with magmatic high thermal energy and magmatic water;(3)tensional fractures caused by compression of position volume expansion to wall rocks controlled the occurrence and spatial distribution of gold orebodies.