甘肃霍勒扎德盖超大型金矿床成矿作用研究

The temporal-spatial-genetic relationship between epithermal mineralization and porphyry mineralization is a hot research issue of the mineral deposit geology. It not only helps improving the hypabyssal/super hypabyssal magmatic-hydrothermal fluid metallogenesis theory, but also affect the international mineral exploration direction. The discovery of the Herzhadegai super-large gold deposit is an important exploration breakthrough in the Beishan metallogenic belt. The present comprehensive studies show that the Herzhadegai gold deposit possesses some typical geological-geochemical characteristics of epithermal gold deposit in the shallow mining area as well as porphyry gold deposit in the deep mining area. In this project, we choose the Herzhadegai deposit as research target, take the ore-forming fluid system as key point and integrate the studies on diagenesis chronology, metallogenic chronology and geochemistry, in order to investigate the ore deposit geology, geochemical characteristics, find out the source of ore-forming fluid and its spatial and temporal evolution, then construct the geochronological framework in the deposit area, confirm the tectonic background, and finally establish metallogenic model. The expected achievement can offer a research paradigm for other porphyry/epithermal ore belt, provide a key basis to improve and perfect the hypabyssal/super hypabyssal magmatic-hydrothermal fluid metallogenic theory, then improve the research level of LS epithermal-HS epithermal-porphyry metallogenesis system. Besides, this study also can guide the next exploration work in Herzhadegai ore district, furtherly expand the prospecting thought in East Tianshan and Beishan orogen.

浅成低温热液型和斑岩型矿化的时空和成因联系是目前矿床学的研究热点问题之一，不仅影响浅成/超浅成岩浆-流体成矿理论的完善，而且关系国际矿产勘查的方向。甘肃霍勒扎德盖超大型金矿床是北山地区近年找矿勘探的重大突破，浅部显示浅成低温热液型矿化特点，而深部显示斑岩型矿化的特点。本项目选择霍勒扎德盖超大型金矿床为研究对象，以成矿流体系统研究为重点，结合成岩、成矿年代学和地球化学研究，解剖矿床地质、地球化学特征，查明成矿流体的性质、来源及时空演化规律，构建矿区年代学格架，厘定成矿构造背景，从建立该矿床的成矿模式。本项目预期成果不但可以为其他斑岩型/浅成低温型成矿带提供研究范例，为完善浅成/超浅成岩浆-流体成矿系统的成矿理论提供关键依据，从而提高低硫型–高硫型–斑岩成矿系统的研究水平；而且可以指导霍勒扎德盖金矿床的找矿勘查工作，拓宽东天山-北山地区的找矿思路。

北山造山带黑鹰山弧内的霍勒扎德盖金矿床是区内目前发现的首例超大型Au-Te矿床，已探明金金属量142吨。绝大多数矿体赋存在花岗闪长岩体中，个别赋存在下石炭统白山组浅变质火山碎屑岩地层中。矿石类型为含金石英脉型，首次发现金银矿物主要以碲化物形式产出，包括碲金矿、针碲金银矿、碲银矿等。确定了霍勒扎德盖金矿床成矿流体属于低温（峰值160–220°C）、低盐度（峰值2–9 wt.% NaCl equiv.）、贫CO2的盐水溶液体系，H-O同位素特征显示流体主要源自岩浆热液，成矿晚期大气降水显著加入。碲化物的发现、S-Pb同位素等特征指示成矿物质主要源自深部岩浆物质、而白山组地层对赋存在其中的含矿石英脉有部分贡献。借助岩浆/热液锆石的LA-ICP-MS U-Pb、硫化物的Re-Os定年技术确定了矿区岩浆-热液-成矿事件序列为：花岗闪长岩-英云闪长岩侵位于340-341Ma、闪长玢岩/细晶岩等脉岩形成于332-334Ma、金碲矿化时间为334.1±5.1 Ma、成矿后热液活动在200Ma左右，认为霍勒扎德盖Au-Te矿床为形成于早石炭世俯冲背景下的低硫型浅成低温热液矿床。初步判断矿区内深部斑岩型矿化潜力有限，但区域上浅成低温热液型金矿化有良好找矿前景，且北山-东天山地区的碲矿化潜力值得关注。