湖南锡矿山锑矿矿区煌斑岩的地球化学特征

Geochemical characteristics of lamprophyres in the Xikuangshan antimony ore deposits, Hunan province.

对湖南锡矿山矿区煌斑岩脉进行了系统的元素和同位素地球化学研究,来探讨煌斑岩的成因。本区煌斑岩形成时代大约为120Ma,早于锑成矿时间,并与锑成矿有密切相关。其微量元素MORB蛛网图,以富集高场强元素,Nb-Ta亏损和Ti不亏损,Th强富集和Ce弱富集为特征,具有岛弧型玄武岩微量元素分配模式,构造环境可能为大陆内部破坏板块边缘。稀土元素具有总量高,无明显的负铕异常,配分模式呈轻稀土富集的右倾型特征。同位素以高87Sr/86Sr、低143Nd/143Nd为特征。结合元素地球化学、同位素特征和地质发展史分析,煌斑岩可能为富含REE和高场强元素的俯冲带流体交代过的富集地幔部分熔融所产生的岩浆,在上升过程中同化和混合很少量的矿区隐伏花岗岩浆和灰岩的产物。

Element and isotope geochemistry of the lamprophyres veins in the Xikuangshan antimony ore deposits issystematically researched in this article, aiming at discussing genesis of lamprophyres. The lamprophyres studied were formed ca 120Ma ago, prior to mineralization chronology, and is considered to be closely related to antimony mineralization in the Xikuangshan area. The MORB-normalized spidergrams of samples studied are rich in high field element, with depleted Nb-Ta and non-depleted Ti, strong enrichment in Th and weak enrichment in Ce, being similar to spidergrams of volcanic arc basalt. Their tectonic setting probably is destructive plate boundaries of an inter continent. The rare-earth element of sample studied have characteristics of high total contents and non-distinct Eu anomalies. The chondrite-normalized REE patterns are right-inclined. The isotopic contents of sample have high 87 Sr/87 Sr and low 143Nd/144 Nd. Combining element and isotope geochemistry with geological history, the lamprophyres studied in the area result from partial melting of enriched REE and HSFE fluid related to subduction of metasomatic mantle, mixing with a little underlying granite and limestone compositions.