东疆雅西371-西北坡铜金矿化带下石炭统火山岩地球化学特征与成矿背景

Metallogenic background and geochemical characteristics of Lower Carboniferous volcanic rocks in No.371-Xibeipo copper-gold mineralization belt in the Yaxi area,eastern Xinjiang.

新疆东天山雅西371-西北坡铜金化带中下石炭统火山岩属钙碱性系列。流纹岩类中SiO_2(73．96%～78．01%)和Al_2O_3(11．3%～14．63%)含量高,含Na_2O为2．04%～4．15%,K_2O为2．74%～3．74%,(Na_2O+K_2O)为5．34%～7．03%；流纹岩类属过铝质、中钾—高钾火山岩系列。微量和稀土元素分析结果显示：流纹岩类具有Ti、Nb、P和Ta明显负异常、Sr中等负异常,LREE明显富集,La/Nb值为0．4～2．3,La/Th值0．4～1,Th/Ta值高(6～36．5),具有明显δ_Eu(0．17～0．29)负异常,地球化学特征表明流纹岩类可能形成在活动大陆边缘上的陆缘岛弧构造背景中。本区(含矿)酸性火山岩特征对于寻找与长英质火山岩有关的金属硫化物矿床十分有利,因此认为本区具有较大找矿前景。

Rhyolites in Yaxi No. 371 to Xibeipo copper-gold mineralization belt in East Tianshan Mountain in Xinjiang, China, are defined as cal-alkaline volcanic rock series. Rhyolites are high in the concentrations of SiO2 （73.96% to 78.01% ） and Al2O3 （11.3% to 14.63% ） and they have the concentrations of Na2O from 2.04% to 4.15% and K2O from 2.74% to 3.74% with concentrations of （ Na2O＋ K2O） from 5.34% to 7.03%, which are peraluminous, high to medium potassium volcanic rock series. However, analytical results of their trace elements and REE shown that the rhyolite were characterized by obvious negative anomaly of Ti, Nb, P and Ta, moderate negative anomaly of Sr, obvious enrichment of LREE, noticeable negative anomaly of δEu （0. 17 - 0.29）, the ratios of La/Nb from 0.4 to 2.3, and the ratios of La/Th from 0.4 to 1, with high ratios of Th/Ta （6 to 36.5 ）. Therefore, based on their observed geochemical natures, it can be inferred that the rhyolite would possibly produced in the background of the continental margin arc zone in the active continental margin. Therefore, it may be quite favorable and in the high potential to find metal sulfides deposit related to the acidic volcanic rocks because the rhyolites occur in the area, and some of them are of copper mineralization.