白垩系膏岩层序对铅锌矿床形成的贡献——以云南兰坪金顶超大型铅锌矿床云龙组为例

Contribution of the Cretaceous Gypsum Sequence to Zinc-lead Ore Formation:A Case Study of the Yunlong Formation at the Jinding Superlarge Zinc-lead Deposit in Lanping Basin,Yunnan Province

通过野外地质观察,结合勘探资料和前人研究,本次用K-Ar法对兰坪盆地金顶超大型铅锌矿床云龙组中的伊利石开展测年研究,并分析典型勘探线剖面的主要围岩、矿体及矿石结构构造特点,论述了矿区膏岩层序可能的时代及其在成矿过程中的作用和方式,形成如下初步认识:金顶铅锌矿区云龙组中黏土矿物伊利石的K-Ar法年龄为(105.7±1.4)Ma,与前人测得地层中黄铁矿Re-Os等时线年龄(114±13)Ma相近,表明该套膏岩层序的地层时代为白垩纪阿尔布期(Albian);膏盐岩呈似层状、透镜状、角砾状赋存于云龙组中上部,经后期成矿作用改造而形成呈似层状、角砾状、不规则状产出的铅锌矿体,并常与膏盐岩共存;铅锌矿体的就位空间既包括原膏岩层序的空间位置,也包括高孔隙度的景星组砂岩;巨量的云龙组膏盐岩在成矿过程中通过硫酸盐还原提供丰富的硫,使铅锌矿床达到超大型规模。因此,巨量膏岩层的消耗是金顶矿床巨量金属得以富集成矿的关键因素之一,这对特提斯造山带含膏岩层序内寻找类似矿床具有普遍意义。同时,该类膏岩层序的对比研究,对于“金顶式”的MVT型铅锌矿床的区域找矿潜力评判也具有重要的指示价值。

Based on field survey and geological observations and combined with exploration data and previous studies,the authors used the clay mineral K-Ar dating methods to conduct preliminary research on illites in the Yunlong Formation of the supergiant Jinding Zn-Pb deposit in the Lanping basin of Southwest China as well as the main orebodies,ores and host rocks in typical geological section along No.12 exploration line.An analysis of the textures and structures of the orebodies shows that the gypsum salt sequences in the deposit may have undergone sulfate reduction.The age of(105.7±1.4)Ma of K-Ar dating of the illites in the Yunlong Formation,which is similar to the previous Re-Os isochron age of(114±13)Ma,indicates that the gypsum sequence of the Yunlong Formation should belong to the Cretaceous Albian period.The salts in the Jinding Zn-Pb ore district occur in the middle and upper parts of the Yunlong Formation with stratoid,lenticular,and brecciated shapes.After the late mineralization transformation,the orebodies also exhibited stratoid,irregular,and breccia forms,with the lead-zinc orebodies usually coexistent with gypsum.The space occupied by the lead-zinc orebodies may be either the location of the original gypsum salt sequence or the pores of the Jingxing Formation sandstones with high porosity.The huge amount of gypsum hosted in the Yunlong Formation provided abundant sulfur through sulfate reduction during the ore-forming process,which caused the Jinding lead-zinc deposit to reach a superlarge scale.Therefore,the consumption of gypsum formation is one of the key factors for the formation of the Jinding supergiant Zn-Pb deposit.It has universal significance in the search for Zn-Pb ore deposits related to the gypsum sequences in the Tethys domain.The comparative study of such gypsum sequences of the Yunlong Formation is of great significance for the judgment of the regional prospecting potential of the“Jinding-style”MVT Zn-Pb deposits.