内蒙古达茂旗北部哈布齐尔金矿床石英闪长玢岩锆石U-Pb年龄、地球化学特征及其地质意义

    Zircon U-Pb age, geochemistry and geological significance of the quartz diorite-porphyrite in the Habuqier gold deposit of North Damao Banner, Inner Mongolia

    • 摘要: 哈布齐尔金矿床是近年来在内蒙古达茂旗北部地区新发现的一个金矿床。对矿区内与成矿密切相关的石英闪长玢岩开展了岩石学、LA-MC-ICP-MS锆石U-Pb定年和Lu-Hf同位素组成研究。锆石U-Pb年龄结果表明,石英闪长玢岩的锆石206Pb/238U年龄加权平均值为431.8±3.6Ma,代表其就位发生在早志留世。主量元素数据显示,石英闪长玢岩具有中等含量SiO2、低K2O、高Na2O、相对富镁等特征,属于低钾拉斑-钙碱性系列,A/NK值介于1.61~2.33之间,A/CNK值介于0.83~1.07之间,具有准铝质特征;微量元素含量以富集大离子亲石元素Ba、Rb、K、Sr等,亏损高场强元素Nb、Ta、Ti等为特征,明显亏损重稀土元素,但Eu异常不明显;Lu-Hf同位素分析结果显示,它们具有正的εHft)值(+6.4~+10.9)和年轻的二阶段亏损地幔模式年龄(1014~718Ma)。结合区域构造演化历史和矿床地质特征,认为哈布齐尔金矿成矿与早志留世石英闪长玢岩岩浆作用密切相关,初始岩浆可能源于俯冲洋壳脱水熔融产生的熔体与地幔楔交代的产物,成岩成矿环境为早古生代古亚洲洋板块向华北板块俯冲的岛弧环境。

       

      Abstract: The Habuqier gold deposit is a newly-discovered gold ore deposit in North Damao Banner, Inner Mongolia. In this paper, petrography, geochemistry, LA-MC-ICP-MS zircon U-Pb age and zircon Hf isotope compositions of the ore-related quartz diorite-porphyrite from the Habuqier gold ore district were studied. Zircon LA-MC-ICP-MS U-Pb dating shows that the weighted mean 206Pb/238U age of zircons from the quartz diorite-porphyrite is 431.8±3.6Ma, indicating a lower Silurian crystallization age. Geochemically, the quartz diorite-porphyrite has moderate content of SiO2, low K2O, and high Na2O, and magnesiumenrichment in composition (3.11%~4.79%), which indicate that it belongs to low K tholeiitic to calc-alkalineseries. Its A/NK ratios and A/CNK ratios range from 1.61 to 2.33 and 0.83 to 1.07, respectively, mainly belonging to metaluminous series. The trace element data of the rocks display enrichment of large ion lithophile elements (e.g., Ba, Rb, K and Sr) and light rare earth elements without significant Eu anomalies, and depletion of heavy rare earth elements, high field strength elements (e.g., Nb, Ta, and Ti). In situ Hf isotopic analyses show variable positive εHf(t) values ranging from +6.4 to +10.9, which correspond to relatively young two-stage Hf model ages ranging from 1014Ma to 718Ma. Therefore, based on these element, isotopic and geochronologic data, combined with data about the regional tectonic evolution and deposit geology, the authors hold that this gold deposit was associated with quartz diorite-porphyrite magmatic activities in the Early Silurian. The initial magma might have been derived from partial melting of a subducted oceanic crust which reacted with mantle wedge. Its tectonic setting was an island arc background that was produced by the Early Paleozoic underthrusting of the Paleo-Asian oceanic plate beneath the North China Craton.

       

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