Metallogenesis And Prediction Of Jiaojia Gold Deposits, Shandong Province

Jiaojia deposit is one of the most important typical gold deposit in the Jiaodong ore cluster, which belongs to super-large gold deposit in terms of resource reserves. Research on regional geology, deposit geology, geochemistry, and genetic mineralogy has been abundant respectly. Otherwise, in the field of metallogenesis, issues such as different kinds of wallrocks petrogenesis and its relationship with gold deposit, and material origin of the gold deposit have been unsolved. To detect the reasons, complication of metallogenesis, material origin similarity of different geology bodies and some isotope content homogenization between wallrocks and ore bodies may contribute to the clarification of rock-ore relationship.The dissertation tittled "metallogenesis and prediction of Jiaojia gold deposit", petrology, whole rock major and trace elements and zircon U-Pb isotope analysis of the countryrock like Jiaodong group plagioclase amphibolite, Linglong granite, Guojialing granite and intermediate-acidic dykes are conducted. Ore samples from 630 to 1100 meters under the ground of Line 112,128,136,152 profiles were selected and polished into slice to study its fluid inclusion. Combined with the previous data of stable and radioactive isotopes, ore-forming fluid features, development and material source of the deposit were discussed. Besides, at the base of the ore stone elements content data, relation analysis and factor analysis were accomplished, and determined the primary haloaxial direction sorting with the method of Grigron. The above research of Jiaojia gold deposit maybe vital to the study of metallogenesis and prediction, as well as basic geological datafulfillment.LA-ICP-MS zircons U-Pb dating of metagabbros from Jiaojia gold deposit suggested that zircons 206Pb/207Pb weighted age is 2484±16Ma, which is interpreted as the represent of the emplacement age of the origin rock. The result means Jiaodong area exists the about 2.5Ga mafic magma activity. Whole rock major,trace and rear earth elements geochemistry shows that metagabbros are characterized by middle potassium tholeiite calc-alkali, with weak fractionation between LREE and HREE((La/Yb) N=2.81～5.55), flat HREE distribution, and significant nagitive Eu abnormal(δEu=0.67～0.86), enrich in LILE(Th、U、Ba、 Pb), indicating that the metagabbro was form in the setting of tension condition indulged by the splitting of newly formed crust, and the deep mantle melt invasion.Newly gained zircons 206Pb/238Uweighted age of 154.3±1.7Ma,155.03±0.96Ma of the 2 Linglong granites, futher confirmed the cognition that Linglong granite was formed in late Jurassic(150-165 Ma). Raock geochemistry study indicate that Linglong granite is calc-alkaline shoshonitic "I-S" transitional type. The REE patterns show right deviation((La/Yb) N=6-25), no significant Eu abnormal,and has high Sr,low Y feathures of C-type adakites, thus it may formed by the melting of late Archean rocks which mainly composed of metagabbro. At the base of preview information,Guojialing granite is calc-alkaline-high potassium I type granite, with significant fraction between LREE and HREE((La/Yb) m=14.5-137.18), and positive Eu amnormal(δEu=0.81-2.57, averaged 1.26). Geochemistry result indicate Guojialing granite was formed by the partial melting of mafic low crust.Newly gained 2 diorites intruded into metagabbros zircons U-Pb age are 155.1±1.8Ma、164.9± 3.5Ma, indicating a new stage of dyke stage exquisite with the Linglong granite is revealed in Jiaodong area. Geological study reveals that the diorites are enriched in LILE, such as K、Ba、Rb, and depleted in HFSE,such as Nb% Ta, P et. Trace elements indicate that diorite was formed by partial melting of enriched mantle which was indused by the metasomatism of subducted Yangtze block silicate melt. Dolerite dykes of Jiaojia gold deposit geochemistry has low Si, high alkaline and MgO features, a dramastic fraction exists between LREEs and HREEs. Trace elements are characterized by Nb,Ta enrichment,and indicate that the rock was formed partial melting of ashospheric mantle metasomatised by subducted Yangtze block.Petrography, microthermometry and laser laman detection of fluid inclusion showed that fluid inclusions in main mineralization stage quartze are included H2O-CO2±CH4 two or three phases type (I type)、H2Ovapor-liquid two phases (Ⅱ type) and CO2 single or two (Ⅲ type).Microthermometry indicate the main mineralization stage is featured by middle-low salinity, low density, total homogenization temperature range between 160℃～320℃, which is mesotherm. Variation of temperature with the depth of ore body, that is, top of a single ore body is low temperature(averaged temperature of -652m is195℃), temperature of the main ore body is relatively high(averaged temperature of -706m～-820m is 263～275℃), temperature of the bottom of ore body is low(averaged temperature of -890m is 188℃), hereby a model of "ore body horizon-fluid total homogenization temperature" is set up, and attempt to conduct deep prediction work. Combined with the preview data, fluid of Jiaojia gold depost is mainly composed of magma water, and drifted to meteoric water. Radioactive Sr,Nd isotopes indicates that material source of the deposit is charavterized by crustal-mantle mixing, it is concluded that material source of Jiaojia gold deposit is direct link with Guojialing granite.At the base of the above research, and combined the preview achievements, preliminary summarized reginal crustal evolution and its coupling relationship with the evolution of mineralization.Prospecting of deep ore body with the method of primary halo. Calcated the elements axial zonality sequence of south sgment of Jiaojia gold depost(Sizhuang segment)256 line profile deep ore body(-1115～-1690m) as Hg-Sb-Au-Mo-Sn-Bi-Ag-As-W-Pb-Zn-Cu, north segment of deep ore body of 128 line as Pb-Zn-Ag-W-Bi-Cu-As-Sb-Sn-Au-Hg-Mo. Hereby, prediction model of south segment (256 line) deep ore body(-1115--1690m) and north segment 128 line deep ore body primary halo prediction model. A continuous extend of 400m of south segment orebody was predicted,and vertical depth can reach 1900m. the third bonanza may exists at the 530m deeper at the oriention of pitching direction(vertical depth may reach 1270m).