安徽铜陵矿集区杨冲里金矿岩浆岩地球化学特征与成因

Geochemical characteristics and genesis of magmatic rocks in Yangchongli gold deposit,Tongling ore concentration area,Anhui Province

杨冲里金矿是长江中下游成矿带铜陵矿集区舒家店矿区新发现的新型金矿床,属构造蚀变岩型金矿床,矿体主要赋存于二长闪长岩和志留纪地层的碎裂岩中,元素受构造作用影响明显。矿区出露岩体主要有辉石闪长岩和二长闪长岩,对辉石闪长岩进行全岩主微量元素分析,结果辉石闪长岩碱铝比(A/NK)在1.63~1.96之间,铝过饱和度(A/CNK)在0.58~0.68之间,属于钾玄岩系列和高钾钙碱性系列,近AM远离FM,有富碱趋势;富集大离子亲石元素(LILE)Ba、Sr、Th等;亏损高场强元素(HFSE)Nb、Y、Yb等;稀土总量在205~268 mg/kg之间,平均值为232 mg/kg,轻重稀土分异明显。岩石地球化学特征显示岩浆起源于岩石圈地幔的碱性玄武质岩浆,烘烤下地壳使之发生部分熔融形成深部岩浆房,直接侵位到浅部形成辉石闪长岩,在侵位过程中经历了不同程度的结晶分异和同化混染作用。

Yangchongli gold deposit is a new type of gold deposit discovered in Shujiadian metallogenic area of Tongling ore-cluster region in the middle and lower reaches of Yangtze River metallogenic belt.It falls into the tectonic-altered rock type gold deposit.The ore body mainly occurs in monzonite diorite and Silurian cataclastic rock,which is obviously affected by tectonic action.The exposed rock bodies in the mining area are mainly pyroxene diorite and monzonite diorite.The main and trace elements analysis of pyroxene diorite as a whole shows that its alkali-aluminum ratio(A/NK)is between 1.63 and 1.96,and its aluminum supersaturation(A/CNK)is in the range of 0.58-0.68,which belongs to k-basanite series and high k-calc-alkaline series.It is near AM,far away from FM,and tends to be rich in alkali.It is rich in large ion lithophile elements(LILE)including Ba,Sr,Th,etc.,while depleted in high field strength elements(HFSE)such as Nb,Y,Yb,etc.The total amount of rare earth changes from 205 to 268 mg/kg,with an average value of 232 mg/kg,and the difference between light and heavy rare earth elements is obvious.The petrogeochemical characteristics show that the magma originated from the alkaline basaltic magma of the lithospheric mantle,baked the lower crust and caused its partial melting to form the deep magma chamber,and directly emplaced to the shallow part to form the pyroxene diorite.During the emplacement process,it experienced different degrees of crystallization differentiation,assimilation and contamination.