胶东寺庄金矿床成因:流体包裹体与石英溶解度证据  

Genesis of Sizhuang gold deposit,Jiaodong Peninsula:Evidences from fluid inclusion and quartz solubility modeling

作　　者：卫清[1,2] 范宏瑞[1] 蓝廷广[1,3] 刘玄[1] 姜晓辉[1,4] 文博杰 

机构地区：[1]中国科学院地质与地球物理研究所矿产资源研究重点实验室,北京100029 [2]中国地震局地壳应力研究所,北京100085 [3]中国科学院地球化学研究所,贵阳550002 [4]中核集团核工业北京地质研究院地质矿产研究所,北京100029

出　　处：《岩石学报》2015年第4期1049-1062,共14页Acta Petrologica Sinica

基　　金：国土资源部公益性行业科研专项项目(201411024-5)资助

摘　　要：寺庄金矿床位于胶北地体西北缘,招远-莱州金矿区焦家金矿带南段。矿体赋存于焦家主断裂寺庄段下盘的玲珑花岗岩中,以蚀变岩型矿石为主,石英脉型矿石为次。成矿流体可分为石英-钾长石(成矿前)和石英-黄铁矿-金(主成矿期)两个主要阶段。流体包裹体测温结果表明,主成矿期石英中流体包裹体均一温度为133~310℃,盐度为0%~12%NaC leqv,成矿流体属于中低温、中低盐度的H2O-CO2-NaC l体系。根据氢、氧同位素测试结果并结合前人数据发现,石英δ18O石英值变化于9.7‰~14.2‰,δDH-2O变化于77.7‰^-55.0‰,经计算获得的石英包裹体的δ18OH‰2O值落在-0.5‰~6.1之间,因此推测寺庄金矿床成矿流体为岩浆水与大气降水的混合,且主要为岩浆水,演化到后期可能有部分大气降水参与。硫同位素研究表明,寺庄金矿床与矿带中段的焦家和新城金矿床具有类似的硫同位素组成,其黄铁矿的δ34S值为7.5‰~9.4‰。这一范围与玲珑花岗岩和胶东群变质岩的硫同位素组成相近,可能暗示寺庄金矿床成矿物质来自中生代花岗岩。利用最新提出的适用于H2O-CO2-NaC l三元混合流体的石英溶解度模型,计算发现寺庄金矿床成矿流体中石英溶解度为0.015mol/kg,这与胶东地质事实相符。成矿期热液中的SiO 2含量极低,其对热液物理化学条件的改变极为敏感。随着成矿流体演化到后期可能有部分大气降水的加入,或是流体迁移至容矿构造压力下降导致的沸腾作用使得成矿流体温度下降,造成SiO 2的大量沉淀,改变了残余流体中Au-S络合物的稳定保存条件,进而发生大规模的金矿化事件。这可能是寺庄乃至整个胶西北金矿都发育有强烈的硅化蚀变带以及石英脉型矿体的一个主要原因。The Sizhuang gold deposit,located at the northwestern border of Jiaobei terrain,lies in the southward extension of the Jiaojia gold belt. Ore bodies primarily occur as sulfide disseminates and sulfide-bearing quartz veins,and they are hosted in Linglong granite,consisting the footwall of the Jiaojia main fault at Sizhuang. The ore-forming fluids can be divided into two generations,represented by the quartz-K-feldspar veins（ pre mineralization period） and quartz-pyrite veins（ main mineralization period）.Microthermometric investigation reveals that fluid inclusions from quartz in the quartz-pyrite veins homogenized at a temperature range of133 - 310℃,with salinity of 0% - 12% NaCleqv. This suggests that the ore-forming fluids are of medium-low temperature,mediumlow salinity H2O-CO2-Na Cl system. Results of hydrogen and oxygen isotope studies and previous data suggest that ore-forming fluids were a mixture of magmatic and meteoric water with δ^18OH2Obetween- 0. 5‰ to 6. 1‰,and δDH2Obetween- 77. 7‰ to- 55. 0‰.Magmatic water is suggested as the dominant component,which was added by meteoric water in later period. δ^34S values of pyrite range from 7. 5‰ to 9. 4‰,which are close to the Linglong granites and metamorphic rocks of Jiaodong Group,and this suggest that the oreforming materials（ Au,S etc.） of Sizhuang gold deposit might have sourced from Mesozoic granites. We computed quartz solubility in the ore-forming fluids of Sizhuang gold deposit,using our newly established model of quartz solubility in H2O-CO2-Na Cl system up to1000℃ and 1. 5GPa,and revealed that quartz solubility is 0. 015 mol / kg; this is conformed to Jiaodong geological phenomenon. The quartz solubility of ore-forming fluid is very low in the main mineralization period,and it is very susceptible to the physicochemical conditions of the fluid. The Si O2 will precipitate when the ore-forming fluids evolved in later stage with meteoric water adding or when it transferred to the host structure accompanying pressure droppi

关 键 词：流体包裹体 稳定同位素 石英溶解度 寺庄金矿 胶东 

分 类 号：P618.51[天文地球—矿床学]