【作者】 敖冬；

【导师】 孙国胜；

【作者基本信息】 吉林大学 ， 岩石学、矿物学、矿床学， 2012， 硕士

【摘要】 奈林沟金矿位于赤峰－开源深大断裂北部地槽区一侧，是目前正在勘探、开采的小型金矿床。由于该区中、大型金矿都位于地台区一侧，而地槽区一侧的金矿床发现甚少，规模小，因此，在金矿的找矿勘查及理论研究等方面均未引起前人的重视。由于奈林沟金矿是区内分布于侏罗系地层中唯一具有工业意义的金矿床，对其开展成因机制等方面的研究，对赤峰－开源深大断裂以北地槽区一侧的新的矿化类型及新的资源地的找矿勘探具有重要指导意义。在奈林沟金矿成因机制方面，前人未做过实地专题研究工作，部分学者根据该金矿赋存于侏罗系张家口组火山岩地层中，而将该矿床归属于“火山热液型”金矿；有的学者则根据区域金矿成矿规律，认为是“岩浆热液型”。本文通过野外地质调查及室内观测表明，矿区石英脉带共有140多条，按分布方向可分为三组：即NE向、NW向、NNE向，个别矿脉近EW或SN，控矿断裂特征表明含矿断裂性质为张性；矿石矿物组合及组构均显示出典型的低温矿床特征。奈林沟金矿床石英的流体包裹体均以气、液两相为主，气、液比多集中在10%～30%之间。均一温度为157.2～279.6℃，属于中-低温热液的范围。盐度变化范围5.02%～13.88wt%NaCl，平均10.37wt%NaCl；第一世代致密粒状石英包裹体的盐度变化范围大（6.92～12.61wt%NaCl），平均11.00wt%NaCl，与高温高盐度岩浆热液与低温低盐度的大气降水混合有关；第二世代粒状石英包裹体的盐度变化范围（11.36～13.88wt%NaCl），平均盐度较第一世代石英高（12.54wt%NaCl），可能与成矿流体的沸腾作用有关；第三世代梳状石英包裹体的盐度变化范围也较大（5.02-10.27wt%NaCl），平均盐度最低（7.35wt%NaCl），可能与低盐度的大气降水等混合有关。根据计算奈林沟金矿床的包裹体捕获压力在14.8～30.4Mpa，成矿的深度在1.48～3.04km左右，属于浅成的范围。不同世代石英流体包裹体氢、氧同位素组成变化较大，早世代石英氢、氧同位素投点靠近岩浆水一侧，晚世代石英投点更靠近雨水线一侧；同一世代投点由上向下呈线性排列，说明了早期的热液是以岩浆热液为主与大气降水的混合水，晚期是以大气降水为主的混合水。方解石的碳、氧同位素分析结果表明，δ¹³C（‰PDB）变化范围在-4.158‰～-4.868‰之间，平均-4.54‰，与地幔δ¹³C值-5.5‰接近；δ¹⁸O（‰SMOW）值变化范围在7.025‰～8.595‰之间，均值为7.86‰，与花岗岩δ¹⁸O‰的变化范围+7～+13‰相吻合，而与安山岩类δ¹⁸O‰的组成具有一定的差别，为成矿流体是花岗岩体衍生的提供了有利的证据。与奈林沟金矿成矿有关的岩体为早白垩世克力代花岗闪长岩体，岩石化学及岩石地球化学的研究表明，该岩体为高钾钙碱性花岗岩类，属I型花岗岩；在花岗岩R1-R2构造环境判别图解上，投影点主要落入晚造山期。表明克力代花岗闪长岩体是在早白垩世区内构造活动由北西－南东向的挤压作用变为北西－南东向的伸展作用构造环境下，地壳减薄、岩石圈拆沉、地幔上涌和地壳重熔，造成壳幔混熔岩浆上侵形成的。上述综合研究表明，奈林沟金矿为燕山期浅成中低温岩浆热液型金矿床。更多还原

【Abstract】 Located in the north geosynclinal side of the large and deep Chifeng-Kaiyaun fracture,Nailingou Au deposit is a small Au deposit currently explored and exploited. Since medium-and large-size Au deposits in this area are all located in the platform side, the geosynclinalside with few or small-scale Au deposits hasn’t received enough attention in terms of oreexploration and theoretical research. Moreover, as the only Jurassic deposit with industrialsignificance in this area, the Nailingou Au deposit plays an important role in studying geneticmechanism, and in exploring new types of mineralization and new areas of resources in thegeosynclinal side north the Chifeng-Kaiyuan fracture.In terms of its genetic mechanism, there hasn’t any special field investigation. Based onthe fact that this deposit was hosted in Jurassic Zhangjiakou-Group volcano strata, someresearchers defined it as "volcano hydrothermal"; others classified it as "magmatichydrothermal", according to its metallogenic mechanism.Through geological field investigation and indoor observations, over140quartz-veinbelts were identified, which can be divided into three groups according to their distributionaldirections: NE, NW and NNE; some individual veins were close to EW or SN; thecharacteristics of the ore-control fracture revealed tension fracture; the mineral compositionand structural fabrics both displayed the properties of a typical low-temperature deposit.The fluid inclusions in the Nailingou Au deposit were dominated by gas and fluid phases,with gas/fluid ratios mainly between10%and30%. The homogenization temperatures were157.2～279.6℃, all within the range of medium and low-temperature hydrothermal fluids. Interms of salinity, it generally ranged from5.02%～13.88wt%NaCl （average10.37wt%NaCl）;in G1compacted grainy-quartz inclusions, it had a wider range （6.92～12.61wt%NaCl,average11.00wt%NaCl）, and was in relation to the commixture of the high-temperaturehigh-salinity magmatic hydrothermal fluids and the low-temperature low-salinity atmosphericprecipitation; in G2grainy-quartz inclusions, it ranged11.36～13.88wt%NaCl, with a largeraverage （12.54wt%NaCl） than G1, probably due to the boiling metallogenic fluids; in G3pectinate-quartz inclusions, it ranged5.02～10.27wt%NaCl, with a low average （7.35wt%NaCl）, possibly because of their isothermal blending with the low-salinityatmospheric precipitation. The capture pressures of the inclusions in this deposit ranged14.8～30.4Mpa, and the metallogenic depth was1.48～3.04km, indicating hypabyssal type.The hydrogen and oxygen isotopic compositions varied greatly among differentgenerations of quartz fluid inclusions; the hydrogen and oxygen isotopes fell close to themagmatic water side in early generations, to the precipitation-line side in young generations;and to linear arrangement from top to down in the same generation, indicating that themixture of magmatic hydrothermal fluids and atmospheric precipitation was dominated by theformer in early generations, but by the latter in young generations. The analyses of carbon andoxygen isotopes in calcite indicate that, δ¹³C（‰PDB） ranged between-4.158‰～-4.868‰（average-4.54‰）, close to the value in mantle （-5.5‰）; δ¹⁸O（‰SMOW） varied between7.025‰～8.595‰（average7.86‰）, consistent with the range in granite （+7～+13‰）, butdifferent from andesite, and thus providing favorable evidence that the metallogenic fluidswere the derivates of granite.The rocks related to the formation of Nailingou Au deposit were Early CretaceousKelidai granodiorite, in petrochemistry and petrogeochemistry, were indicated high-K andhigh-Ca alkaline granite, belonging to type I; in the R1-R2tectonic discrimination diagram,the projection points mostly fell into late orogenic phase. These results indicate that theKelidai granodiorite rocks were formed under the setting of Early Cretaceous tectonicactivities turning from NW-SE extrusive action to NW-SE extensive action, and due to theupward intrusion of crust-mantle mixed magma caused by the thinning of crust, thedelamination of lithosphere, the upwelling of mantle and the remelting of crust.In general, our study indicated that the Nailingou Au deposit was hypabyssal Yanshanianmedium-low-temperature magmatic hydrothermal Au deposit.更多还原