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碧口地块夹持于秦岭造山带、松潘-甘孜造山带与扬子板块之间,伴随中国大陆印支期造山事件,在其内部及北缘产出有大量花岗岩类侵入体,其中北缘主要为花岗岩脉,由东向西可分为康县月照—琵琶寺、文县联合村—阳山等多个产出密集区,在密集区内先后发现了塘坝、水洞沟、阳山、联合村、甲勿池等多个金矿床,针对琵琶寺、阳山及甲勿池等地的花岗岩脉的地球化学研究表明,它们具有高的w(SiO2)67.65%~74.86%、w(Al2O3)13.68%~19.61%,A/CNK=1.11~5.46,稀土元素总量较低(24.22×10-6~97.26×10-6),LREE富集,HREE亏损,轻重稀土分馏明显(LaN/YbN=3.29~22.40),具有弱负铕异常(δEu=0.70~0.79),微量元素特征表现为大离子亲石元素(LILE)强富集和高场强元素(HFSE)相对亏损。对岩浆源区及成分进行判别发现岩浆源区为下覆的陆壳基底,成分以杂砂岩为主。综合分析认为碧口地块北缘花岗岩脉活动高峰为晚三叠世,属后碰撞构造环境,成因机制与碰撞造山过程中加厚地壳拆沉作用和幔源物质底侵作用密切相关,地壳增厚导致的减压增温和幔源热流的注入诱使中上地壳杂砂岩部分熔融形成花岗质岩浆上侵而形成;同时,碧口地块北缘在早侏罗世(190Ma~195Ma)发生大规模金成矿作用,晚于岩浆活动高峰期近20Ma,成矿流体与岩浆岩极可能共用一个通道,花岗岩脉密集发育区易于成矿流体的聚集从而形成诸如阳山世界级超大型金矿床。
The Bikou massif is sandwiched between the Qinling orogenic belt and the Songpan-Garze orogenic belt and the Yangtze Plate. With the Indosinian orogeny in mainland China, a large number of granite intrusions are produced in the interior and the northern margin. For the granite veins, from east to west can be divided into Kangxian moonlight - Pipa Temple, Wenxian United Village - Yangshan multiple output-intensive areas, in the dense area have been found in Tangba, water ditch, Yangshan, Geochemistry of the granite veins of Pipa Temple, Yangshan and Jiapechi shows that they have high contents of 67.65% -74.86% w (SiO2), w (Al2O3 ) Ranged from 13.68% to 19.61%, with A / CNK ranging from 1.11 to 5.46. The total REE content was relatively low (24.22 × 10-6 ~ 97.26 × 10-6). LREE enrichment, HREE depletion and REE fractionation were obvious (LaN / YbN = 3.29 ~ 22.40) with weak negative europium anomaly (δEu = 0.70 ~ 0.79). The trace elements are characterized by strong enrichment of LILE and relative loss of high field strength element (HFSE). Discrimination of the magma source area and its composition reveals that the magma source area is the underlying continental crust basement, and the composition is mainly composed of miscellaneous sandstone. The comprehensive analysis shows that the granite vein in the northern margin of the Bikou block has a late peak in the Late Triassic and belongs to the post-collision structural environment. The genetic mechanism is closely related to thickened crustal delamination during collision orogeny and to the underplating of mantle-derived materials. The pressure-induced increase of temperature and the influx of mantle source heat induce the formation of granitic magma by partial melting of the middle-upper crustal sandstone. At the same time, the northern margin of the Bikou block formed during the Early Jurassic (190Ma-195Ma) Large-scale gold mineralization occurred later than the peak of magmatic activity in the past 20Ma. It is probable that ore-forming fluids and magmatic rocks share a common channel. Granite vein-dense development zones tend to accumulate ore-forming fluids to form the Yangshan world-class superlarge gold deposit .