华北克拉通北缘安家营子金矿床成岩成矿耦合：单个流体包裹体成分与岩体热年代学研究

The large-scale gold metallogenesis around the North China Craton (NCC) is spatially and temporally coincident with intense magmatism, but whether the intermediate-felsic intrusion supplied the metal and ore-forming fluid for gold mineralization is still highly debated. Moreover, the quantificational research on metal deposition (such as the Au, Ag, Pb and Zn) during the evolution of ore-forming fluid is scarce. Thus, this application propose analyzing the liquid, solid and vapor components of single fluid inclusion in quartz of four major ore-forming stages, contemporaneous intrusion and metamorphic veins from the the Anjiayingzi gold deposit, northern NCC, using the laser ablation inductively coupled mass spectroscopy (LA-ICPMS), scanning electron microscope and Raman spectroscopy, respectively. Based on the detailed investigations of field geology, petrography and ore microscopy, we can distinguish the source of ore-forming fluid and metal exactly, and investigate the variation process of gold and associated metals in the ore-forming fluid during the whole ore system quantificationally, using some special parameters, such as the elemental contents, ratios between elements of fluid inclusion and so on. Furthermore, we can get the cooling ages of intrusion through the high-resolution geochronology, such as the LA-ICPMS U-Pb ages of monazite, sphene and apatite and 40Ar-39Ar ages of biotite and K-feldspar, and reconstruct the thermal evolution history of associated intrusion. According to comparison between the cooling ages and their corresponding closer temperatures of intrusion and the mineralization age and ore-forming temperature, it is easy for us to get more information about the contribution of magma cooling to the gold mineralization, and to understand the ore-forming process comprehensively.

华北克拉通周缘早白垩世大规模金成矿与岩浆作用在时空上具有一致性，但后者是否直接为金成矿提供了成矿流体和物质仍存在争议，且成矿流体演化过程中金及相关元素的沉淀缺乏定量评估。围绕这些问题，本申请拟以克拉通北缘安家营子大型金矿床作为研究对象，在细致的野外基础地质、室内岩/矿相学及流体包裹体热力学研究基础上，利用激光剥蚀电感耦合等离子体质谱,结合扫描电镜与激光拉曼光谱技术，对不同成矿阶段及同时代赋矿岩体、变质岩脉体石英内单个流体包裹体的液、固、气相组分开展原位精确测定。通过不同地质体和不同成矿阶段包裹体内元素含量及特征比值等参数的综合对比，准确查明成矿流体和物质来源，定量刻画流体中金及相关元素的变化情况。结合岩体独居石、榍石、磷灰石U-Pb及黑云母、钾长石40Ar-39Ar等高精度年代学方法，重建岩体热演化史，并与成矿年龄和温度对比，可探讨岩浆作用及冷却过程对金成矿的贡献，精细刻画成矿过程。

安家营子金矿床所有矿体均赋存于喀喇沁变质核杂岩下盘的鸡冠子岩体内部。矿区内矿体以高硫化物含量和低Au/Ag比值（<1）为特征，依次发育四阶段与金成矿有关的矿物共生组合：石英-粗粒黄铁矿、石英-细粒黄铁矿、石英-多金属硫化物、石英-碳酸盐。成矿流体为H2O-CO2-NaCl流体体系，成矿温度为245–358℃，盐度介于1.3–15.6 wt.%。流体捕获压力为50–110MPa，据此估算的静岩/静水压力对应成矿深度为2.5–7.5km，流体演化过程中混合与不混溶是导致载金硫化物快速沉淀的重要机制。成矿流体稳定同位素δD 为-80.3 – -96.5‰，δ18OH2O 为3.7–5.5‰，黄铁矿、方铅矿等硫化物的 (206Pb/204Pb)i = 17.088–17.591，(207Pb/204Pb)i = 15.367–15.578，(208Pb/204Pb)i = 37.167–38.091，与鸡冠子岩体中的钾长石Pb同位素相当。.安家营子金矿床成矿流体与金属应来源于矿区东部喀喇沁变质核杂岩主拆离断层深部的隐伏岩体：1）金成矿作用与基底变质作用存在大于20亿年的时差；2）矿石稳定同位素指示成矿流体来源于岩浆水与大气降水的混合；3）鸡冠子岩体中出现大量流纹质脉岩，暗示矿区深部隐伏岩浆房为成矿作用提供成矿流体、物质和热源；4）东部主成矿阶段流体均一温度平均值（322° C）和硫化物δ34S（2.4‰）明显高于西部（287℃，0.3‰），指示成矿流体的中心应在东矿区深部。因此，安家营子金矿床形成于133–126Ma之间，与鸡冠子岩体的快速冷却及喀喇沁变质核杂岩的迅速隆升在时空上一致。这一过程同时伴随着构造由韧-脆性向脆性转换，流体环境由超静水压力向静水压力转换。.根据磷灰石裂变径迹数据进行的热史反演确定安家营子地区成矿后的隆升/剥蚀过程可划分为三个阶段：1）126–97Ma之间的快速冷却与抬升阶段，隆升幅度约为6.09km；2）97–40 Ma缓慢抬升阶段，隆升幅度约为0.43km；3）40Ma以后，隆升幅度为0.86 km。自早白垩世126Ma金成矿作用至现今，该区累计剥蚀量达到7.3km。由于安家营子金矿床成矿深度介于5.6–7.3km，矿脉最多可能被剥蚀掉了1700m。参考我国胶东地区地表以下2700m左右的矿化深度，安家营子矿区地表以下的探矿空间仍大于1000m。