甘肃小柳沟含矿隐伏花岗岩稀土元素地球化学特征

Characteristics of REE geochemistry of the ore-bearing concealed granite in Xiaoliugou,Gansu province

小柳沟W,Mo多金属矿床为复控型矿床,矿区内隐伏花岗岩属复式岩体,REE分布模式表明小柳沟隐伏复式岩体具有明显成因联系或同源演化特点,属同源岩浆岩,δEu强亏损与弱δCe亏损,REE分布型式为富集LREE的右倾式折线,LREE的分异程度明显高于HREE.早期花岗岩REE分布模式一致性好,w(La)N/w(Yb)N值大(远大于10),δEu强亏损为特征,是有利的成矿母岩;晚期花岗岩以REE分布模式一致性较差,LREE分异好而HREE分异差为特征,w(La)N/w(Yb)N值小(远小于10),δEu较强亏损为特征.晚期岩浆进一步分异,成矿物质在岩体中进一步富集、迁移、活化形成石英脉型W,Mo矿,寻找花岗岩型Mo矿应在晚期小岩体中寻找.

The W and Mo polymetallic ore in Xiaoliugou is a compound control-type deposit,the concealed granite in the mining area belongs to the composite rock masses.The REE distribution pattern shows that the Xiaoliugou composite rock masses have an obvious origin relationship or a homologous evolution characteristics,and thus they originate the same magma,with the δEu strong loss and the δCe weak loss,the REE distribution pattern shows a broken line of the right deviation type of the LREE enrichment.The LREE differenti on degree is obviously higher than HREE.The REE distributed pattern of the early granite presents a good consistency,with a characteristic of high w（La） N /w（Yb） N ratio（much more than 10） and strong δEu loss,sug-gesting that the early granite is the favorable ore-forming parent rock.But the late granite in the REE distrib-uted pattern presents a bad consistency,which has a good differentiation in the LREE and a bad differentiation in the HREE,with the low w（La） N /w（Yb） N ratio（much less than 10）,and the δEu has the charateristics of stronger loss.The further differentiation of the late magma leads to that the part mineralization materials further enrich,migrate and mineralize in the rock mass,and that finally form the W and Mo ores of the arteries during the course of migration and activation,It concludes that seeking Mo ore in rock mass should mainly focus on small rock masses of the late granite.