陕西铧厂沟金矿床中细碧岩的岩石学和元素地球化学特征研究

Petrological and Geochemical Characteristics of the Spilite in the Huachanggou Gold Deposit in the Shaanxi Province

细碧岩是陕西铧厂沟金矿床的主要容矿岩石之一.在野外观察的基础上,利用显微镜观察、电子探针扫描和主微量元素分析等综合分析技术对细碧岩的岩石学、元素地球化学特征进行了研究.结果表明,细碧岩具有由钠长石＋绿泥石＋绿帘石±阳起石、钠长石＋含铁白云石＋绢云母两种典型蚀变矿物组合特征;在火山岩TAS分类图解上主要落入玄武质粗面安山岩区,属于拉班玄武岩岩石系列;其稀土元素总量较低（27.53×10-6～58.46×10-6）,轻稀土略富集[（La/Yb）N均值为1.24],稀土元素配分曲线主体呈平坦型;稳定高场强微量元素特征表明其原岩形成于伸展的构造环境,可能起源于软流圈之上的原始尖晶石二辉橄榄岩稳定区域,在形成过程中遭受地壳物质混染,推断为泥盆纪中期勉略洋盆的初始洋盆阶段的产物.

The spilite is one of the main host rocks in the Huachanggou gold deposit. On the basis of detailed field geological survey and systematic laboratory study including microscope observation, electron probe scanning, major and trace element analysis, this article studied petrological and element geochemical characteristics of spilites. The result showed that two typical altered mineral assemblages of spilite are albite＋chlorite＋epidote±actinolite and albite＋Fe-dolomite＋sericite, and that the spilite samples fall into tholeiitic basalt series and basaltic trachyande site areas in the TAS diagram of effusive rocks, having low REE content （27.53× 10-6 -58.46 ×10-6）, low en richment in LREE [the average value of （La/Yb）N is 1.24], and a flat REE pattern. The analysis of stable high field strength elements （HFSE） suggested the splite was formed in an extentional setting, and possibly originated from a primitive spinel-lherzolite stability field above asthenosphere mantle. Crustal contamination also contributed significantly to the formation of the spilite. It can be inferred that the spilite was formed in the early stage of the development of the Mianlue ocean in the Middle Devonian.