新疆西昆仑大红柳滩花岗伟晶岩型锂矿叠加改造成矿特征:来自矿石构造、3D成像技术与年代学的约束

Metallogenic characteristics of superimposed deformation and mineralization of Dahongliutan granite-pegmatite type lithium deposit belt in West Kunlun,Xinjiang:Constraints from ore structure,3D imaging technology and chronology

花岗伟晶岩型矿床是大陆演化的直接产物,这类矿床易受后期岩浆、构造、变质等地质作用影响,使得矿床自身发生改造变形导致叠加改造成矿。叠加改造成矿不仅可以活化原有矿体,还有可能带来新的成矿物质。聚焦花岗伟晶岩型矿床的叠加改造成矿过程解析有助于建立潜力矿集区勘查指标和部署找矿靶区。新疆西昆仑大红柳滩花岗伟晶岩型锂矿带是我国近年新发现的重要的稀有金属伟晶岩成矿带之一。我们通过细致的野外调查,发现了西昆仑大红柳滩花岗伟晶岩型锂矿带较好地保存了晚期韧性变形细粒锂辉石伟晶岩-细晶岩和岩脉截切早期粗粒锂辉石伟晶岩岩脉的现象。通过岩芯CT三维扫描技术,本文揭示了强变形带相对于粗粒锂辉石伟晶岩中锂辉石整体体积含量较大的现象,并且发现韧性变形的锂辉石伟晶岩主体由“书斜”结构的锂辉石、“云母鱼”结构的锂云母和重结晶的石英流动带组成。韧性变形的锂辉石伟晶岩中铌钽铁矿的U-Pb定年结果为~193±0.89Ma,具“云母鱼”结构的锂云母的原位Rb-Sr定年结果为~187Ma,指示区域上除了广泛存在的212~206Ma(铌钽铁矿U-Pb定年结果)的成矿事件,还存在193~187Ma左右的叠加改造成矿作用。结合区域上的大地构造背景,我们推测晚期岩浆穹窿造成的拆离断层是早期岩浆活动形成的伟晶岩和围岩发生二次韧性变形活化的可能成因,这对区域上的找矿勘查部署提供了一定的科学指导。

The granite pegmatite ore deposits are products from continental evolution,which are easily influenced by subsequent geological processes such as magmatic,structural and metamorphic activities that easily lead to a superimposed deformation and mineralization of them.This superimposed mineralization not only can reactivate the original mineral bodies but also might introduce new ore-forming materials.Analyzing the superimposed mineralization process of the granite pegmatite-type ore deposits can yield comprehensive exploration criteria and facilitate strategic mining deployment in potential ore cluster areas.The Dahongliutan granite pegmatite lithium ore belt in the West Kunlun of Xinjiang is one of the important rare metal pegmatite mineralization belts discovered in recent years.Through detailed field surveys,we have discovered that the Dahongliutan granite pegmatite lithium ore belt preserves detailed records of a late-stage ductile superimposed mineralization where fine-grained spodumene pegmatite veins crosscut early-stage coarse-grained spodumene pegmatite veins.By utilizing CT three-dimensional scanning technology on the drilling core,we found that the spodumene with significant overall volume contents occurred within the strongly deformed zone.The main body of ductilely deformed spodumene pegmatite consists of a ‘bookshelf' structure spodumene,a ‘mica fish' structure lepidolite,and recrystallized quartz flow bands.The U-Pb dating of the niobium-tantalum minerals in the ductilely deformed spodumene pegmatite demonstrated a late superimposed mineralization event at ca.193Ma.In situ Rb-Sr dating on the lepidolite with ‘mica fish' structure also indicated a similar age around 195Ma.The aforementioned evidence supports a superimposed alteration and mineralization event postdating the widely occurring 212~206Ma(U-Pb dating of niobium-tantalum-iron minerals) mineralization event in this region.Considering the regional tectonic background,we speculate that detachment faults caused by late-stage magmatic doming resulted in the secondary ductile deformation of earlier-formed pegmatite and surrounding rocks.Thus,it can provide a certain scientific guiding direction for mineral exploration deployment in the Dahongliutan region.