青海杂多打古贡卡印支期含矿斑岩体的发现及其地质意义

LA-ICP-MS Dating and Geological Significance of the Dagugongka Ore-bearing Porphyry in Qinghai Province

打古贡卡斑岩型铜钼矿位于青海省南部三江北段,属青海省重要的斑岩型铜钼矿成矿带中。本文对打古贡卡含矿花岗斑岩体进行了LA ICP MS U Pb测年,获得(240.1±0.89)Ma的年龄值,属中三叠世。含矿斑岩的SiO 2含量为65.18%~70.43%,K 2O为3.05%~6.76%,Na 2O为1.99%~3.47%,富SiO 2、K 2O、Na 2O为特点,相对贫Fe、Mg、Ca,里特曼指数为1.09~4.29,铝饱和指数ASI=1.01~1.23,总体表现为弱过铝质到强过铝质高钾钙碱性系列岩石的特征;微量元素配分曲线总体呈右倾型,大离子亲石元素(LILE)富集,高场强元素(HFSE)亏损,具有较弱的Eu负异常。通过岩体地质特征、岩石学及岩石地球化学特征结合区域构造演化特点初步确定打古贡卡中三叠世花岗斑岩形成于俯冲阶段。该岩体的发现具有较为重要的科学意义,为重新认识“三江”北段斑岩型矿床的成矿时代和形成背景提供了新的线索和依据。

The Dagugongka porphyry copper-molybdenum deposit is located in the northern section of Sanjiang,south of Qinghai Province,and it is the important porphyry copper-molybdenum metallogenic belt in Qinghai Province.The formation age of Dagugongka ore-bearing granite porphyry is 240.1±0.89Ma.The SiO 2 content of ore-bearing porphyry ranges from 65.18-70.43%,K 2O from 3.05%-6.76%,Na 2O 1.99%-3.47%,characterized by rich SiO 2,K 2O and Na 2O,relatively poor in Fe,Mg,Ca.Ritmann index is 1.09-4.29,and aluminum saturation index(ASI)is 1.01-1.23.Overall,it is a series of rocks from weak peraluminous to strong peraluminous high potassium calc-alkaline.The partition curves of the microelement are generally right-dipping,with the enrichment of large ion lithophile elements(LILE),the deficiency of high field strength elements(HFSE)and weak negative Eu anomaly.The geological,petrological and geochemical characteristics of the rock mass combined with the characteristics of regional tectonic evolution preliminarily determined that the Middle Triassic granite porphyry in Dagugongka was formed in the subduction stage.It indicates that the Indo-Chinese porphyry deposit is related to the subduction environment in the Sanjiang belt.