Characteristics Of Ore-forming Fluids In Taoyuan Gold Deposit,Wanzai,Jiangxi

Taoyuan Gold Deposit is located in Wanzai County,Yichun,Jiangxi Province.This deposit is a quartz vein type gold deposit discovered in the polymetallic ore district of northwestern Jiangxi in the 1970s.Its geotectonic location is located in southwest Ping-Le depression in the northeastern part of Qinhang metallogenic belt.The deposit is controlled by northwest Yifeng-Jingdezhen Superimposed fault zone.The ore deposit is distributed in the Caledonian and Yanshanian compound small rock mass with thin veins and lenticular structures;the ore is mainly composed of euhedral-subhedral grain structure and metasomatic structure with disseminated structures,blocks structure,banded structure,etc.pyrite is the main gold-bearing mineral,and gold is mainly produced in the form of parcel.The country rock alteration is mainly of pyritization and strong silicification,followed by potassium feldspar alteration and chlorite alteration.Previous studies on the Taoyuan gold deposit are rare,which means the mineralization source,metallogenic environment and metallogenic mechanism of this deposit are still unclear,especially the research blank on ore-forming fluids characteristic and evolution.In this paper,the Taoyuan gold deposit was selected as the research field.Based on the field investigation,the fluid inclusion petrographic,micro-temperature measurement,the fluid inclusions composition of Raman spectral analysis and isotope composition characteristics were studied.We analyzed the characteristic and evolution of hydrothermal fluids in gold deposits,combining with isotope composition analysis,trying to further explore the sources and metallogenic processes of ore-forming fluids.In this paper,the metallogenic period of the Taoyuan gold deposit is mainly divided into four stages:I mineralization stage?early?,II metallogenic stage?middle?,III metallogenic stage?late?,surface oxidation stage.The inclusion type of hydrothermal period is mainly composed of CO₂-H₂O inclusions and gas-liquid H₂O inclusions;the ore-forming fluids are generally of low-temperature?120?340??,low salinity?2.77?11.33 wt%NaCl?,medium-low density?0.72?0.99 g/cm3?;the ore-forming pressure varies from 13.2×10⁵ Pa to 149.5×10⁵ Pa,the ore-forming depth is mainly concentrated between 75.5?563.3m,belongs to the shallow metallogenic environment;single fluid inclusion Raman spectroscopy analysis show that the inclusions in quartz are simple in each stage,the characteristic peaks of CO₂ and H₂O are obvious.In general,the CO₂ content in ore-forming fluids decreased from early stage to late stage showing the transition from the early NaCl-H₂O-CO₂ system to the late NaCl-H2O system of ore-forming fluids.The hydrogen-oxygen isotope composition analysis shows the value of?D_V-SOMW-SOMW of ore-bearing quartz vein is -66.28‰;¹⁸O_V-SMOW is around 12.72;the mean value of ?¹⁸O_H2O-V-SMOW is 3.45‰,with ?¹⁸O_H2O-?D illustrated the sources of ore-forming fluid of Taoyuan gold deposit can be multiple,which is most dominated by metamorphic fluid,followed by magmatic water in recrystallization stage.The results of sulfur isotope composition analysis show that?³⁴S is positive,and the?³⁴S value is between 3.61‰ to 4.04‰,with an mean value of 3.87‰.The comprehensive analysis shows that the ore-forming fluid source of Taoyuan gold deposit is from crust sulfur,the average sulfur isotope value?5.47‰? of the Fengshuling formation strata of Wannian Group is close to ?34S.So we speculated that the Fengshuling formation strata provides the main ore-forming fluid source for mineralization of Taoyuan gold deposit.The ore-forming process of the deposit is presumed to be as followed.The ore-forming fluid is derived from the multi-stage strong tectonic stress and under the thermal force of the emplacement magma.The metallized metamorphic hydrothermal fluid are extracted from country rocks,mixed with magmatic hydrothermal fluid.Mineral-rich solutions moves upward along the crushing zone,and with the change of temperature,pressure and other conditions,it is finally integrated into the secondary fracture zone derived from the compresso-crushed zone.