西藏甲玛铜多金属矿床中新世埃达克岩特征

Characteristics of Miocene Adakite in Jiama Copper polymetallic Deposit in Tibet

摘要:

埃达克岩与Gu、Au等金属元素的富集关系密切，并对深部造山构造作用具有重要的指示意义。受到碰撞造山作用，在西藏地区发育了一条成矿潜力巨大的斑岩铜矿带，甲玛铜多金属矿床就位于该铜矿带的东段。对甲玛矿床中酸性侵入岩进行地球化学测试分析，结果显示：SiO2（≥56%）、高Al2O3（≥15%）、低MgO（<3%），Na2O含量大于2.3%，K2O含量大于2.1%，K2O/Na2O为0.6~1.2；稀土元素和微量元素结果显示高Sr（>400×106），低Yb（<1.9×106)、低Y（<15×106），LREE富集，HREE亏损，无负Eu异常，具有埃达克岩地球化学特征，属于C型埃达克岩，为加厚下地壳或上地幔物质部分熔融所形成。

Abstract:

Adakite has close relation with the enrichment of metallic element, such as Gu and Au, and also has an important indicating significance of deep orogenesis. Because of the collisional orogeny, an enormous potential porphyry copper ore belt was formed in Tibet. Jiama copper polymetallic deposit is just located in the eastern section of the copper ore belt. The geochemistry test has been carried out on the intermediate acid intrusive rock of Jiama deposit. It is showed that the content of SiO2≥56%, Al2O3≥15%, MgO<3%, Na2O>2.3%, K2O>2.1%, and K2O/Na2O is between 0.6~1.2. As showed by rare earth element and trace element results, it is high in Sr content(>400×106), low in Yb content（<1.9×106) and Y content（<15×106）, LREE is enriched while HREE is deficiency, and without Eu anomaly. It has the same geochemistry characteristics with adakite, and belongs to C type adakite. It is considered that the intermediate acid intrusive rock was formed by the melting of extra heavy lower crust and upper mantle materials.