摘要
秦岭泥盆系及其喷流沉积铅锌矿床,位于扬子板块北部边缘的线型裂谷环境中。裂谷系的扩张演化伴随三组同生断裂活动:近东西向、北东向和南北向,它们具有继承性活动特点,对本区地质演化起着重要的构造调整作用。泥盆纪岩相古地理特征,是研究区统一的构造沉积环境下出现的,岩相变化往往与同生断裂平行,直接控制了泥盆系的沉积。在该环境下形成的铅锌矿和铁白云石硅质岩,具有海底喷流沉积岩的地质地球化学特征。可作为恢复构造沉积环境和同生断裂的重要标志。本区同生断裂及岩相与赋存于泥盆系中的喷流铅锌矿床之间的相互关系,表现为东西向的构造-岩相带控制着铅锌成矿带的分布,北东向和南北向构造-岩相带制约着一系列单个矿床的线形分布。
The Qinling Devonian rifted trench, which extends from Xihe-Chengxian of Gansu in the west through Fengxian-Taibai area of Shaanxi to Zhenan area of Shaanxi, is cut by NE-trending and nearly SN-trending second-order faults into a series of discontinuous fault basins, i. e. Xicheng basin, Fengtai basin and Zhenxun basin from west to east. Although the fault basins show some difference in Devonian rock associations, they are basically coincident with each other in characteristics of ore-bearing rocks and lead-zinc ore bodies as well as features of rocks and ores, suggesting that they were formed almost in the same ore-forming sedimertary environment.
There are three groups of syngenetic faults in this region: EW-trending, NE-trending and Sn-trending ones. Their synsedimentary expansion affected Devonian sedimentation and governed the division of metallogenic provinces, zonation of mineralization and linear arrangement of ore deposits.
Lithofacies variation is parallel to and consistent with syngenetic faults, spatially showing some directivity. The lithofacies zone controlled by syngenetic faults served as a favorable environment for exhalative sedimentary mineralization.
Lead-zinc ore bodies and host rocks occur at facies-changing position between Middle Devonian carbonate rock and fine clastic rock. Such abrupt change in lithology and lithofacies must have resulted from the unceasing elevation and subsidence of sedimentary basins and the rapid change in physicochemical conditions of sdedimentary environment.
Lead-zinc ore bodies and ankerite siliceous ore-bearing rocks occur discontinuously in stratoid and lenticular forms. Where they appear, the conformably overlying strata also crop out completely with fairly great thickness, implying deposition in deep depressions; where they are missing, the overlying conformable strata became thinner, and even the underlying formations are missing, suggesting deposition in comparatively shallow depressions or relatively uplifted positions.
It is known from the above discussion that stratiform lead-zinc ore bodies and ankerite siliceous rocks were formed in a sedimentary structural environment with constant generation of tensile syngenetic faults. The intersection or concentration place of two groups of syngenetic faults in such a tenso-fractu-ring belt, in particular, represents a structurally weak zone which might have served as a passage for upward migration and exhalation of hydrothermal solutions and therefore led to the appearance of exhalites and lead-zine ore bodies in groups or zones.
出处
《矿床地质》
CAS
CSCD
北大核心
1991年第3期217-231,共15页
Mineral Deposits
基金
国家自然科学基金
