Structural Deformation, Fluid Flow And Gold Mineralization In The Zhaoping Fault Zone, Shandong Province, China

The Zhaoping Fault Zone (ZFZ) is one of the most important gold-hosting fault zones in theJiaodong ore cluster area. The NNE-NE trending ZFZ is controlled by the contact faces of theLinglong granites and the Archean Jiaodong Group of amphibolites. Ore bodies are distributed inthe Linglong granites, the footwall of the ZFZ. Wall rock alterations are characterized byK-feldspar alteration, silication, sericite-quartz alteration, pyritization, carbonation and clayminerals alteration. Ore types include the altered rock type and the quartz vein type.Previous studies showed that the gold mineralization of the fault zone takes place in earlyCretaceous (135-100Ma), the ore-forming fluids are from multi-sources and thestructural-alteration zonations are clear. However, lots of field evidences indicated that thedistributions of different structural patterns and alteration styles were non-linear showing astrong coupling between deformations and alterations. Based on the thought oftectonic-fluid-metallogenic system and the first hand information of field survey and indoorsmicroscopic observations, this dissertation intended to investigate the coupling effects betweenrock deformation and fluid flow in the ZFZ and its contributions to the formation ofstructural-alteration networks and to gold mineralization integrating the methods of chronology,structural geology, altered rock geochemistry, fluid geology and mathematics statistics.Results showed that gold mineralization of the ZFZ occurred on the stage of regionaltectonic regimes transiting from compression to extension. The regional maximumcompressional stresses were NNE to NE trending and the ZFZ experienced dextral transtension.Microscopic observation, TEM analysis and fractal dimensions calculations of the dynamicrecrystallization quartz suggested that the deformation and alteration environment of ZFZ weremainly characterized by low greenschist facies(280-400°C) and some reached to high greenschistfacies(400-500°C). The paleo stress values varied significantly from39.8to180MPa accordingto the estimation of both the conjugate joints and the free dislocations in quartz. Statisticalanalysis of selected ore-forming related trace elements of the altered rocks suggested that fluidsflowed in the ZFZ consisting of crust-rooted magmatic hydrothermals and mantle-generatedfluids. Mass balance calculations of altered rocks revealed that ore materials were enrichedduring the sericite-quartz alteration and gold might be partly from the Jiaodong Group. Acomprehensive analysis of Ar-Ar chronology, microstructures, fractal dimensions of particle sizedistributions of the fault gouge, fluid inclusions compositions and mass balance calculationsindicated that gold mineralization during135to100Ma can be divided into two phases and thetransition time was about120Ma. The two phases of mineralization were significantly differentin the regional stress fields, magmatism, fluid and thermal originations and alteration styles.The structural-alteration networks were seemed to have the fractal characteristics by meansof the field work, microscopic observation, SEM and CL analysis. The self-similarity was shownby the multi scales of association of the hard and soft layers (altered rocks), which controlled thequartz vein type and altered rock type of mineralization. Moreover, the coupling of deformationand fluid flow (interactions among the faulting, the reaction hardening and softening and thehydraulic fracturing) caused the transitions of the hard and soft layers or the formation of newlayers and resulted in the superposition of mineralization and temporal-spatial association of thealtered rock type and quartz vein type ores. Numerical simulation of tectonic stress field showedthat the transition zones from NNE to NE directions of the ZFZ were extensional positions whichwere favorable for fluids flux and gold mineralization.