内蒙古陈巴尔虎旗谢尔塔拉铁锌矿床成矿流体演化与成矿作用

内蒙古谢尔塔拉铁锌矿床位于大兴安岭中段华力西期、燕山期成矿带上,是一个大中型的火山喷发沉积-热液富集型矿床。在对谢尔塔拉铁锌矿床的物质组成分析的基础上,着重对流体包裹体和稳定同位素进行分析,以此来研究该矿床的成矿流体演化和成矿作用。研究表明,从热液作用早期到中期,具有成矿温度递减、盐度升高的趋势,两者呈负相关变化,指示流体发生了沸腾作用;从热液作用中期到晚期,具有成矿温度递减、盐度降低的趋势,两者呈正相关变化,指示流体发生了混合作用。S、Pb、C、H、O同位素组成表明,金属物质主要来自赋矿岩石和下伏地层,同时还有深部岩浆物质的参与。成矿热液为大气降水补给加热的循环地下水和岩浆水组成的的混合流体,后期又有大量的大气降水补充,使得成矿流体与围岩发生了强烈的同位素交换。矿化和蚀变作用是在水/岩比值比较低的体系中进行的。谢尔塔拉铁锌矿床的成矿流体总体表现为中低温、低盐度、低密度的热液。构造热效应、地热梯度和多次的岩浆喷气热是驱动流体活化迁移的主要因素。构造体制转换使流体稳定体系发生改变,压力释放发生沸腾作用,造就铁、锌在有利位置富集成矿。

Fluid evolution and metallogenic processes of the Xie'ertala Fe-Zn deposit, Chenbaerhu Banner, Inner Mongolia

Located in the Variscan and Yanshanian metallogenic belt in the middle of the Da Hinggan Mountains, the Xie'ertala Fe-Zn deposit is a large-medium-size Fe-Zn deposit of volcanic eruption sedimentation-hydrothermal enrichment type discovered in recent years. Based on an analysis of material composition, the authors investigated emphatically the fluid inclusions and isotopes so as to study the ore-forming fluid evolution and mineralization. Salinity had negative correlation with fluid temperature from early to middle stage, indicating a boiling event. From middle to late stage, however, salinity was positively correlated with fluid temperatures, suggesting a mixing event. S, C, Pb, H and O isotopic compositions show that the ore-forming materials were derived mainly from country rocks and underlying rocks and partly from deeper sources. The data obtained suggest that the ore-forming fluids were derived predominantly from an active meteoric groundwater system and magmatic water. Because of meteoric supplement in the late stage, strong isotope exchange occurred between ore-forming fluids and surrounding rocks. The amount of the hydrothermal fluids in the ore-forming and alteration system was relatively insignificant. All these data demonstrate a combination of ore-forming fluids with moderate to medium-low temperature, low salinity and low density. Structural thermal effect, geothermal gradient and magmatic exhalation heat might have played the dominant role in Fe and Zn activation, whereas structural transition led to the Fe and Zn precipitation at a favorable position through changing the conditions of the primary well-evolved fluids.