金顶超大型铅锌矿床角砾岩分形研究及地质意义  

Fractal analysis of breccias in the super-large Jinding Pb-Zn deposit and its geological implication

作　　者：庄天明 宋玉财[2] 侯增谦[2] 张翀[3] ZHUANG Tianming;SONG Yucai;HOU Zengqian;ZHANG Chong(Yantai Gold College,Zhaoyuan265401,China;Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;Beijing Research Institute of Chemical Engineering and Metallurgy,Beijing 101149,China)

机构地区：[1]烟台黄金职业学院,山东招远265401 [2]中国地质科学院地质研究所,北京100037 [3]核工业化工冶金研究院,北京101149

出　　处：《地学前缘》2020年第2期320-331,共12页Earth Science Frontiers

基　　金：国家重点研发计划项目(2016YFC0600306);国家自然科学基金项目(91855214,41773043,41773042,41772088)。

摘　　要：前人研究提出金顶超大型铅锌矿床发育出了多种角砾岩,其成因与盐底辟作用有关。文章对这些角砾岩进行了分形分析,确定了不同角砾岩的角砾形态分维值D_r和粒径大小分维值D_s,来进一步探讨角砾岩的形成过程。其中,D_r表征形态复杂性,可指示角砾迁移距离长短或后化学作用改造情况,D_s表征角砾破碎情况,指示形成角砾的能量大小。研究表明,金顶矿床中一部分角砾岩为蒸发盐或膏砂近原位底辟、破碎灰岩围岩形成,它们具有较小的D_r和D_s值。与这些角砾岩空间过渡的层状砂质胶结灰岩砾角砾岩(或称层状含灰岩角砾砂岩),为蒸发盐而非水流体携带灰岩角砾流出地表,并进入含水沉积系统后形成,角砾未经历水流体搬运、磨圆,具有较小的D_r和较大的D_s值。另外一部分角砾岩为蒸发盐和砂泥质底辟破碎围岩,并共同迁移了一定距离而形成,但总体未发生长距离的迁移,随后进入地表沉积系统中。上述部分角砾岩还经历了形成后的流体交代溶蚀作用,导致D_r值变大。本研究显示,在盐底辟有关铅锌矿床内,赋矿围岩包含多种由不同底辟过程形成的角砾岩。Previous studies have determined that a variety of complex breccias in the Jinding Zn-Pb deposit are genetically related to the salt diapirism.In this paper,breccia fractal analysis is used to determine two fractal dimensions of these breccias:D_r(the morphology of clasts)and D_s(particle size distribution),in order to understand their formation process.D_r indicates the morphological complexity and migration distance of the breccias or the degree of modification of the chemical process.D_sindicates the degree of brecciation and amount of energy that forms the breccias.Small D_rand D_svalues imply that some of the breccias in Jinding were formed by diapirs of evaporite and gypsum-sand and near-in-situ brecciation of the host limestone.Bedded limestone-clast-bearing sandstone that is spatially transitional with these breccias have smaller D_rand larger D_svalues,suggesting that limestone clasts in the sandstone were transported by evaporite rather than water into detrial sediments in a depositional system on the surface.Other breccias were formed by evaporite-sand-mud diapirs in a process where the breccia clasts were transported a certain distance,but the distance is limited and the clasts were not transported to the surface to enter a depositional system.Some of the breccias mentioned above also experienced post-brecciation fluid alteration and dissolution,resulting in a large D_rvalue.This study shows that evaporite diapir-related Zn-Pb deposits may contain breccias formed by a variety of diapir processes.

关 键 词：角砾岩 分形分析 形成过程 金顶 

分 类 号：P618.42[天文地球—矿床学] P618.43[天文地球—地质学]