Study On Metallogenic Regularity And Dynamics Of Mesozoic NonferrousMetal And Precious Deposits In Eastern Guangxi And Western Guangdong

Through detailed studies on the geological background, tectonic features, representativedeposits, spatial-temporal distribution characteristics of deposits and Mesozoic granite ineastern Guangxi and western Guangdong, the metallogenetic epoch of Taohua gold deposit,Dongtao lead-zinc deposit and Changkeng-fuwan gold-silver deposit was determined. Theauthor also sums up the regularity of spatial-temporal of deposits in the studied area,establishes metallogenetic series and discusses mineralization dynamic mechanism.According to Rb-Sr isochron age of quartz (Changkeng gold deposit: 128±3Ma; Fuwansilver 62±1.7Ma), the minerogenetic epoch of Chengkeng-Fuwan gold-silver depositbelongs to later Yenshan movent. Study on the ore-controlling tectonics indicates that the golddeposit controlled by early stretching during early Cretacceous (K₁), the silver depositcontrolled by latterly stretching during late Cretacceous (K₂). The gold and silver depositswere formed in the same epoch, but in different stages, the different structural pattern resultsin the separation between gold and silver bodies.Based on the studies of geological background, deposit characteristics, S, Pb, H, Oisotope geochemistry, rare earth and trace elements of Taohua gold deposit in Dayaoshanuplift, eastern Guangxi, the author points out the genesis of Taohua gold deposit belong tosedimentary enrichment-hydrothermal reformation type. Ore-forming process has undergonesedimentary enrichment during early Cambrian, magmatic hydrothermal mineralizationduring latterly Caledonian movement, and later hydrothermal rework which is the mainmineralization period. Rb-Sr isochron age of fluid inclusion in quartz formed in mainmineralization period is 148±10Ma, belong to early Yenshan movement. The experiment ofgold lixiviation indicates the gold of Taohua deposit mainly occurred as fine-superfine grain.The new point view of the ore genesis of Taohua deposit has a significant bearing on oreprospecting in Dayaoshan uplift.Field investigation and isotopic geochronology indicates the structural movement inDongtao lead-zinc deposit underwent early napping during Caledonian affiliation (Rb-Srisochron age of granite is 426±15Ma) and late stretching. The stretch fault betweenOrdovician sandstone and shale controls the distribution of orebodies. The Rb-Sr isochron ageof total ore is 152±3Ma, the age represents the minerogenetic epoch of latterly thermal fluidsuperimposed mineralization. The ore-forming process of Dongtao lead-zinc depositunderwent initial concentration during Ordovician and thermal fluid superimposedmineralization during early Yanshan movement. The type of ore genesis belongs tosedimentary reformation. The early napping and late stretching and stretch fault controllingthe distribution of orebodies have a widespread significance in eastern Guangxi and westernGuangdong.Through field investigation, a new type tin deposit was discovered in FuhezhongPalaeozoic sag (Guanyinshan tin deposit). The tin orebodies are strictly controlled by SNdirection faults, and contain minor amount of sulfide, belong to tectonic alteration tin deposit. The tectonic alteration tin deposit has shown a good prospecting potential Huanan area.Based on the age data analysis and spatial distribution characteristic of deposits, theauthor divides the area into two metallogenic units (Xianggui metallogenic unit, Hhuaxiametallogenic unit) and six mineralization belts or region (there are Fuhezhong W, Sn, Sb, Pb,Zn mineralization region; Sanshui Au, Ag, Cu, Pb, Zn mineralization; Dayaoshan-Huaiji Au,Cu, Pb, Zn mineralization belt; Bobai-Cenxi-Luoding-Guangning Au, Ag, Cu, Pb, Znmineralization belt; Xinyi-Lianjiang Au, Cu, Pb, Zn, Sn mineralization belt;Xinxing-Yangchuen Cu, Pb, Zn, Sn mineralization belt) in eastern Guangxi and westGuangdong. Early Yanshan movement and late Yanshan movement are the mainmineralization epoch in this area.The deposits of eastern Guangxi and western Guangdong can be classified as seven types(shear-zone deposit; tectonic alteration deposit; porphyry deposit; skarn deposit; hydrothermalvein deposit; micro-disseminated deposit; sedimentary-reformation deposit) and seven depositmetallogenetic series. In Xianggui metallogenic unit, there are:â… ) W, Sn, Sb, Pb, Zn depositmetallogenetic series, it is related to early Yanshan movement intermediate-acid granite;â…¡)W, Sn deposit metallogenetic series, related to late Yanshan movement acid granite;â…¢) Au,Ag, Cu, Pb, Zn deposit metallogenetic series, related to early Yanshan movementtectonic-thermal event. All of these three metallogenetic series can be merged as one group ofmetallogenetic series, i.e. precious metal and nonferrous metal metallogenetic series grouprelated to tectonic dynamic mechanism transform in Yenshan movement. In Huaxiametallogenic unit, there are:â… ) Au, Ag, Cu, Mo, W, Sn deposit metallogenetic series, it isrelated to early Yanshan movement intermediate-acid granite;â…¡) Au, Ag, Cu, Mo, Pb, Zn, W,Sn deposit metallogenetic series, related to late Yanshan movement intermediate-acid and acidgranite;â…¢)Au, Ag deposit metallogenetic series, related to ductile shear-zone;â…£)Audeposit metallogenetic series, it is related to late Caledonian tectonic-thermal event. All ofthese four deposit metallogenetic series can be merged as two groups of metallogenetic series,i.e. gold metallogenetic series group related to the lithospheric compression in LateCaledonian and nonferrous and precious metal metallogenetic series group related to thelithospheric tectonic transformation in Yanshanian epoch.The study on the petrology, mineralogy and geochemistry of the Mesozoic granite andanalysis on the features of tectonic transmutation in Eastern Guangxi and Western Guangdongindicate that lithosphere in the studied area has undergone three evolution phases: thecollision between 224～265Ma, the tectonical transformation from compression to extensionbetween 154～160Ma and the extension between 80～100Ma. The metallogenesis wasconcentrated in mid-Jurassic and Cretaceous, and controlled by the tectonical transformationof lithosphere in early Yanshanian and by the shear-extension in the late Yanshanianrespectively. The tectonic dynamics transformation is the first order of ore-controlling factorfor the Mesozoic massive mineralization in this area. The distribution and localization of thedeposits were controlled by the transformation of local dynamic system.According to granitic rock heat flow value (A) calculating, the average heat flow value(A) is 2.33μw/m³, 3.07μw/m³, 4.52μw/m³, 4.47μw/m³ in Hercynian-Indo-chinese epoch,early Yenshan and latterly Yenshan respectively. These data indicate regional heat flow value increased greatly in Mesozoic, and the heat flow value increasing results in magmaunderplating and lithosphere thinning. The geodynamic mechanism for the tectonictransformation is related to the increasing of heat flow value in lithosphere itself.