Key Metallogenic Controlling System Of Fankou Pattern MVT Lead-zinc Deposits In The Northern Margin Of Quren Basin

Abstract:This study area is the northern margin of Quren Mesozoic rift basin being adjacent to Zhuguangshan-Jiufeng granite belt, in which Fankou and other lead-zinc pyrite deposits gathered. The research results of geological mineralization characteristics, genesis and mineralization model about Fankou deposit are very rich, and researchers mostly think that Fankou deposit is belong to MVT deposit, but some of them don’t come to agreement on the genesis. Regional prospecting of Fankou pattern MVT deposit in the study area is quite complex because of the complicacy of basin geological environment and evolution, controlling factors and prospecting technology application conditions. Through fusing progressive metallogenic theory and metallogenic system theory, from the dynamic evolution angle of basin geological and dynamic environment, the multi-factor coupling closely contacting with related factors of source, flow, transport and storage, and the critical conversion metallogenic mechanism are both explored. Meanwhile, the coupling mineralization effect between lead-zinc and pyrite deposits is revealed.Based on analysis of regional metallogenic background, ore structures, mineral paragenesis, generation of mineral formation, alteration, spatial-temporal distribution characteristics between Fankou deposit and other deoposits, Yangliutang deposit is considered to be Fankou pattern MVT deposit whose whole metallogenic evolution process can be divided into sedimentation diagenesis, the early, middle and late hydrothermal four metallogenic periods. The whole metallogenic evolution processes of Luocun and other pyrite deposits contain sedimentation diagenesis and early hydrothermal metallogenic periods.According to geological and geochemical research results of Quren basin, combining with the basin evolution process and dynamic environment evolution, the ore-forming material sources of Fankou pattern MVT lead-zinc deposit are discussesed. The results show that the source of ore-forming elements in pyrite deposit comes from carbonate strata combination which is rich in sulfur and formed in the specific Devonian-Carboniferous lithofacies paleogeographic environment, while the ore-forming fluid is single basin source fluid. The sources of ore-forming elements in lead-zinc deposits mainly come from basal clastic rock aquifer system, partly from early Yanshanian magmatic hydrothermal fluid and ore-bearing carbonate rock strata, and the mineralizer sulfur comes from Indosinian pyrite ores and its metallogenic carbonate strata, while the ore-forming fluid contains mixed sources including basal clastic rock and carbonate rock aquifer systems, magmatic hydrothermal fluid.On the comprehensive study on geological and geochemical information of ores and related geological body in the lead-zinc and pyrite deposits, combining with the basin evolution process and dynamic environment evolution, the mineralization evolution process and key metallogenic controlling system of Fankou pattern MVT lead-zinc deposit are confirmed. Fankou pattern MVT lead-zinc deposit has two key mineralizations. Although suffered different degrees of Yanshanian tectonic magmatic thermal event influence of reconstruction, but the pyrite deposit is mainly formed in Indosinian single source basin fluid mineralization, which key metallogenic controlling system includes the geothermal gradient, fold and interlayer gliding structures, basin hydrological geology and geochemistry environment pattern, clastic-carbonate transition interface and sedimentary diagenetic stage’s sulfur storage body.Although suffered varying degrees of transformation and superposition in the later Yanshanian tectonic magmatic thermal event, lead-zinc deposit is mainly formed in the early Yanshanian mixed source basin fluid mineralization, which key metallogenic controlling system includes geothermal anomaly, crust source remelting type granitic magma, deep brittle-ductile transition interface moving upward, deformation and interlayer gliding structures, basin hydrological geology geochemistry environment pattern, clastic-carbonate transition interface, Indosinian pyrite ores and sedimentary diagenetic stage’s sulfur storage body.On the study of mineralization evolution process, geological and geochemical metallogenic conditions and key metallogenic controlling system, applying progressive metallogenic theory and metallogenic system theory, the metallogenic system attributes of Fankou pattern MVT lead-zinc deposit is claimed to be the two-hydrothermal superimposed metallogenic system. In the metallogenic system, the geochemical barrier is composed of Hercynian sulfur storage body, which was formed in relatively stable sedimentary environment, and pyrite deposit which was shaped by basin fluid tectonic compression driven formation in the initial period of DIWA (Indosinian). In the violent period of DIWA with crustal high inflation and strong lateral extrusion "extension thinning" dynamic environment, the fluid in basal clastic rock aquifer system contains rich metal elements, while the fluid in carbonate rock aquifer system contains sulfur and early Yanshanian magmatic hydrothermal. These two fluids are transported through faults, interlayer sliding belts and lithologic interface, and then are mixed, aggregated in special hydrogeological geochemistry unit. Relying on Metallogenic system attributes, the two hydrothermal superimposed-transformation polygenetic metallogenic model of Fankou pattern MVT lead-zinc deposit is established when taking the sources of materials (including metals, mineralizing elements, ore-forming fluid), key controlling system, the ore-forming fluid transmission and aggregation mechanism, metallogenic elements coupling and the critical conversion mechanism as the main contents. This model is not confined to the collision orogenic events in the shallow basin, but emphasizes the key role of the geological environment evolution in the deep basin.According to comprehensive prospecting information obtained through coupled handling multiple prospecting information of Fankou pattren lead-zinc deposit in the area, metallogenic prediction is accomplished under the guidance of key metallogenic controlling system and metallogenic model. Four prospecting areas and twelve targets are delimited, of which Ⅰ-1, Ⅰ-2, Ⅰ-3targets are important, Ⅱ-2, Ⅲ-2, Ⅳ-2targets have some certain prospecting and are worthy of further study.