Ore-forming Fluid Evolution And Sb-Au-W Metallogenesis In The Central Hunan-Northwestern Jiangxi,South China

There are at least three superlarge deposit,the Xikuangshan,Woxi and Dahutang,have been discovered in the area of the Central Hunan and Northwestern Jiangxi,South China.The Xikuangshan antimony deposit is the largest antimony deposit in the world,with totle Sb reserves more than 2.00Mt.The Xikuangshan antimony deposit is a terminal mineralization of the crustal-scale ore-forming fluid.The Woxi Sb-Au-W deposit is an initial mineralization of the crustal-scale ore-forming fluid.The Dahutang tungsten deposit formed from a highly fractionated magma.How the crustal-scale fluid movement from basal?the cap rock of the Central Hunan basin,what is the critical factor,which controlling the fractionation of ore-forming elements mineralization,and how it works.In this study,author describes in detail the geology of the ore deposit and the features of alteration and mineral of the the Xikuangshan,Woxi,and Dahutang deposit:(a)author examine the Re-Os isotope of the Molybdenite and Pyrite from those deposit,and the U-Pb isotope of the Zircon from the dike of the Cental Hunan.(b)Author examine the microthermometry of fluid inclusion from the ore mineral and gangue mineral.(c)Author examine the detailed gains/losses of ore-forming elements during the alteration processes from the petrography and geochemistry of fresh and altered specimens.(d)Author using the EMPA and La-Icp-Ms?examine the detailed geochemistry of the stibnite and scheelite respectively.(e)Author examine the detailed geochemistry of scheelite and hydrothermal calcite,and the genetic connections?the crustal-scale fluid movement.Re-Os isotopic dating of pyrite samples from the Shixiangli carbite deposit yielded a precise isochron age of 127.8±3.8Ma at the Cental Hunan province.The Re-Os isotopic dating of pyrite restrict geochronology of the crustal-scale ore-forming fluid movement at the Central Hunan-Northwestern Jiangxi.Re-Os isotopic dating of molybdenite samples from the Dahutang tungsten yielded a precise isochron age of 137.9±2.0Ma,Northwest Jiangxi province.Based on the existing research results,we made a constructive process of the crustal-scale ore-forming fluid movement and mineralization at the Central Hunan-Northwestern Jiangxi.Firstly,initial enrichment of the ore-forming element(Sb,Au and W)by sedimentary processes at the Proterozoic.Secondary,enrichment of the ore-forming element(Sb,Au and W)by the multiple magma crystallization differentiation and crustal-scale fluid leaching wall rock(most the Proterozoic strata),from Jinningian?Yanshanian periods(800?150Ma).Thirdly,Sb,Au and W metallogenic explosion at the Yanshanian period(150?130Ma).The pyrite is enriched in the radiogenic 187Os/188Os(7.469?13.343)from the Shixiangli carbite deposit.The(187Os/188Os)initial is 1.03±0.24,and the from 571.8?755.1,which indicate that the ore-forming element(Au and Sb)came from the Proterozoic strata,the basal of the Cental Hunan basin.The molybdnite is enriched in the radiogenic 187Os/188Os(0.4829?79.69)from the Dahutang tungsten deposit.The(187Os/188Os)initial is from-0.22?0.022,and the ?Os from-435.97?10.31,which indicate that the ore-forming element came from the interfusion of HIMU and lithospheric mantle,at the Northewest Jiangxi.The(187Os/1880s)t is from-0.964?0.271,and the ?Os from-865.6?115.1,which indicate that the ore-forming element came from the interfusion of HIMU mantle,lithospheric,and the Proterozoic strata at the Northewest Jiangxi.The Tianlongshan fine-grained biotite granite is a syn-collision granite and shows characteristics of high SiO2 from 68.51?69.62 wt%,peraluminous,high-k,calc-alkaline,with a diagenetic age of 226.1±1.1Maby the U-Pb isotope of the zircon.There are at least three stages of dike identified in the Wanyunshan-Tianlongshan composite batholith at the Cental Hunan province.Firstly,it's a fine-grained biotite granite dike with the diagenetic age later than the biotite granodiorite(224.3±2.4Ma).Secondary,it's a fine-granited biotite granodiorite with a diagenetic age of 216.5±1.8Ma.Thirdly,there are aplite and pegnatite dike with a diagenetic age of Yanshanian from 162.2±2.1?163.7±6.4Ma.Which is corresponding?antimony mineralization age of 155.5±1.1Ma at the Xikuangshan deposit.Both the Xikuangshan antimony deposit deposit from the the cap rock of the Central Hunan basin,are characteristics of low formational temperature from 192 to 177.8?.The deposit from the basal of the basin is characteritics of higher formational temperature than the deposit from cap rock of the Central Hunan basin,souh as the Longshan Au-Sb deposit(mean=185?),the Longwangjiang Au-Sb deposit(mean=182.7?),the Xi'an W-Au deposit(215.3??195.9?),and the Dahutang tungsten deposit with early stage(240?360?),secondary stage(190?250?),and latterly stage(150?200?).The characteristic of ore-forming fliud temperature decline is possible the reason of ore-forming element fractionation.The element W mineralization at the temperature above 250?.While the elment Au start mineralization lower 250?,and the Au precipitation is completely at 200?,but the element Sb just start mineralization at 200?It's characteristics of highly enriched in the element W(mean=2922.75ppm)at the superposition alteration(Biotitization+greisenization)than the single alteration or unaltered rock,such as the unaltered rock(mean=9.65ppm),biotitization(mean=70.3 ppm),Phyllic(mean=119.62 ppm),Weak greisenization(mean=46.24 ppm),and silicification(mean=558ppm).The effect of superposition of alteration is the possible reason of forming super large deposit.The Woxi Sb-Au-W deposit also characteristics of highly enriched in the element Au and Sb(14.57ppm and 10697ppm respectively)at the superposition alteration(phyllic+silicification),and the Xikuangshan antimony deposit is the silicification+carbonatation.The ?REE of hydrothermal calcite is characteristics of increasing from Heqing(2.14ppm)?Xikuangshan(10.62ppm)?regional calcite veins(28.54 ppm)at the Cental Hunan basin.All the ?REE of hydrothermal calcite lower than the unaltered rock(marlstone=218.51 ppm;limestone from 235.1?218.5ppm).Both the marlstone from basal and the limestone from cap rock of the Cental Hunan basin,have been leached out the REE by the ancient fluid,and later the fluid formed the lower ?REE regional calcite veins,also the altered reginal rock(20.31 ppm).The Firstly satge scheelite just after the wolframite formation is characteristics of negative En anomaly(0.17?0.85).While the secongdary stage scheelite is characteristics of positive En anomaly(1.16?9.51)in the Dahutang tungsten deposit.The secongdary stage scheelite probablely formed from a fliud with reducing oxygen fugacity from the Firstly stage.The ore-forming fliud oxygen fugacity possibly decending?form the wolframite while increasing?form firstly scheelite and decending again?form the secongdary stage scheelite and the sulfide.Which is probablely the genetic of forming the ratio of wolframite/scheelite?1 at the Dahutang tungsten deposit.The crustal-scale fluid movement are probablely have experienced at least three stage at the Central Hunan-Northwestern Jiangxi.Firstly,the palaeocurrent leaching the element(W,Sb,Au,Pb,Zn,and Si else)from the Proterozoic formation?formed the ore-forming fluid in the basal of Central Hunan basin.Secondary,the ore-forming fluid in the basal been heated for the deep magmatism,while moved up?the shallow crustal at the depths of the basal as the early W-Au and Au-Sb deposit formed from Caledonian?indosinian.Thirdly,the ore-forming fluid accumulated and metallogenic explosion at the Yanshanian in the cap rock of the basin,and then the super-large Sb and Au-Sb deposit formed.The crustal-scale fluid movement and Sb-Au-W fractionation?form different types of deposit.All the ore-forming element origined from the Proterozoic formation,can be accumulated by the heated palaeocurrent.At the same time,the remelting and crystallization differentiation of Proterozoic formation at the basal(deep)of the Central Hunan basin probablely have experienced the same magmatism procees of Northwestern Jiangxi and?formed the super-large tungsten deposit.It is the Crustal-scale magma fluid movement genetic deposit at the basal of the Central Hunan-Northwestern Jiangxi.Under the whole work we have make a genetic model about the Crustal-scale fluid movement and Sb-Au-W fractionation in the Central Hunan-Northwestern Jiangxi.