Study On Metallogenic Regularities And Metatlogenic Prognosis Of Gold Deposits In Northern Zhaoping Fracture, Jiaodong Area, Shangdong, China

As one of the most import regions with rich gold pool in China, Jiaodong area ofShandong province possesses hundreds different sizes gold mines. The mostsignificant ore-controlling tectonic belt locates in Zhaoping fault at northwest of Jiaodong.However, north side is the major gold deposits producing area in the whole fault belt.Although researchers still have different definitions about north area of Zhaoping fault atpresent, they all admit the geological fact that this area is enriched with gold depositswhich are mainly controlled by fault activities.In this work, two branch faults with NE and NNE directions are unified as north sideof Zhaoping fault, which are Jiuqujiangjia fault and Potouqing fault respectively. Researchwas focused on five gold deposits controlled by the areas from their intersection part totheir ends. Aims of this research are to summarize the causes and metallogenic regularityof gold deposits, and further predict the gold deposits using digital geological simulationsoftware. North to south distributions of Jiuqujiangjia fault are Damoqujia gold deposit,Fushan gold deposit, and Jiuqu gold deposit separately. And for Potouqing fault, they areZhaojia gold deposit, Shuiwangzhuang gold deposit, and Dongfeng gold deposit fromnorth to south.Research turns out that alter rock type gold deposit/mineralization is the main type.And Jiuqu gold deposit, as part of the famous Linglong gold mineralization, belongs to alter rock type and quartz vein type transitional mineralization. In spite of the differencesin respective orebody output scales and spatial distribution, all the gold deposits werecaused by the impacts from different geological parts during the same geological processunder the same tectonic environment. Therefore, all the gold deposits share similargeological characteristics. The outside strata are mainly metamorphic rocks of originalJiaodong group. Magmatic rocks mainly consists of Goujialing granodiorite and Linglonggranite rocks which are closely associated with mineralization. Generally, the golddeposits in researching area or even Jiaoxi alter rock type gold deposits are divided intofour metallogenic stages which are pyrite-quartz, quartz-pyrite, quartz-polymetallic sulfide,and quartz-carbonate respectively.Systematic fluid inclusion studies indicate that characteristics of mineralizing fluidschange obviously during different mineralizing stages. The fluids for pre-andsyn-mineralization are typically characterized by low salinities, mesothermal condition,NaCl-H2O-CO2components and phase separation. The evolution of mineralizing fluidsstarts from initial immiscibility to intense immiscibility, following by decreasingimmiscibility. With the escape of volatile components (CO2, H2S) during the phaseseparation process, the physical and chemical conditions of fluids have changed. Theprecipitation of gold and gold compound is controlled by the stability of gold-bearingcomplex, which is affected by the changing fluid conditions.The extent of goldmineralization is directly controlled by phase separation process. Quartz-pyrite stage inour study area represents the strongest immiscibility, which is corresponded to the maingold mineralization stage. The fluids for post-mineralization, with the mix of meteoricwater, are characterized by low salinities and simple NaCl-H2O components. Because ofthe low concentration of gold in the post-mineralizing fluids, the precipitation of gold islimited.Fluid inclusion, H-O and C-O isotope studies indicate the mineralizing fluids arederived from magma. Comparing the geochemical data (gold components, S, Pb isotopevalues, etc) to Jiaodong stratum, Linglong granite and Guojialing granodiorite, the oreminerals mainly derive from Guojialing granodiorite.The molybdenite model suggests theages ranging from128.5±1.9Ma to131.1±1.8Ma for gold mine. The ages for Linglong granite are150-160Ma, following by the ages of126-135Ma for Guojialing granodiorite.With the constraint of the ages (119±7Ma) from post-mineralization veins, the ages forAu-mineralization are considered to be119～128Ma in our study area. The diagenesis andore-forming processes in our study area are controlled by the Pacific Ocean tectonic field.The lithospheric thinning situation, resulted from the subduction of the Pacific Ocean plate,is favourable for multiple magma activities in Jiaodong area at Yanshanian. The intrusionof the Guojialing granodiorite is responsible for the Au-mineralization in our studyarea.The cretaceous Au deposits formed after the intrusion of the early cretaceousGuojialing granodiorite. The deformation process and structural movement contribute tothe gold precipitation from magma differentiation in fracture zone.The locations, dimensions and ore minerals of gold deposits are directly controlled bythe texture, size and distribution of fractural alteration zone. The distributions of oredeposits and fractural zones are basically consistent.The ore deposits with the trend fromweak to decreasing distribution and to wedge out is following the NE-NNE strikes of twosecondary fractures.The structural control on gold deposits is characterized by multilevelore-controlling. The main fractures controlled the occurrences and distribution of maindeposits, and the secondary fractures controlled the occurrences and distribution ofsecondary deposits. The size of fracture is positively correlative to the dimension of oredeposit.This ore-controlling process contributes to the discontinued concentration of oredeposits. The existence of barren zone along the strikes of veins, showing end to endalignment structures, is correspond to the discontinuity.Our study area lies in the stream sediment with gold abnormity J13、J14area. Theregional gravity field, magnetic field and electricity abnormity all refer to the favorableore-forming conditions in this area. Based on geological setting of our study area, theOPIS ore-forming prediction model is used on Jiuqu Jiangjia and Potouqing fracture zonesin terms of the shape of fracture, grade of gold, thickness of the ore body and the alterationzone. The results indicate potential ore deposits in the deeper area of Jiuqu Jiangjiafracture zone. Even though the northeast Jiuqu Jiangjia fracture zone lies in the tip ofstructure, the fracture zone shows continuity with little destruction in late period. Thepotential ore deposits in our study lie within the No.104prospecting line and No.112 prospecting line, with the depth ranging from800to1200meters.The northeast Potouqingfracture zone lies in the tip of structure as well, and the fracture zone is crosscut byLuanjia River. The interactive relationship is not ideal for ore-forming even withindividual high values. Considering little ore-forming evidences were reported in recentlywork, further mining exploration is not recommended in the deeper part of northeastPotouqing fracture zone.Base on the geologic characteristic and engineering data, using OPIS System modelthe shapes of the ore-bearing vein NO.207in Fushan gold deposit and the ore-bearing veinNO.302in Damoqujia gold deposit and the ore-bearing vein NO.207in Fushan golddeposit respectively. Restrict the forecast scope from the superposition of everyOre-forming parameter.