Study On The Rubidium-tungsten Mineralization Of The Shadong Deposit,Xinjiang,NW China

The Shadong rubidium-tungsten deposit is located in Hami,Xinjiang,with a total of 62,800 tons of WO3 resources,and is the only large tungsten deposit discovered in the Eastern Tianshan.In this paper,based on the study of orebody and ore characteristics,alteration and mineralization characteristics,intrusive rocks isotopic chronology and geochemistry and scheelite geochemistry.We have identified the process and mechanism of tungsten mineralization,determined the genetic types of ore deposits,and proposed a new understanding of tungsten mineralization.The main innovative achievements are as follows:The Shadong Rb-W deposit develops strong skarnization,which is characterized by magnesian skarn minerals such as forsterite,diopside,tremolite,phlogopite and zoidote.In the outer zone,scheelite is mainly coexisted with magnetite and replace diopsides and tremolites,or coexists with phlogopite and quartz and replace magnesium-rich calcites and dolomite;in the inner contact zone,scheelite is mainly coexisted with zoidote or diopside,fluorite and replace plagioclase,or in quartz sulfide veins that cut through carbonate rocks and the pluton.The mineralization process can be divided into five stages:dry skarn stage,wet skarn stage,oxide stage,quartz sulfide stage,and carbonate stage.The variation of Mo content(281.9?30793.4 ppm)and the characteristics of positive and negative Eu anomalies in each occruance scheelite indicate the variation of temperature,fo2,and p H during the precipitation;the rare earth elements have the typical right-dipping negative Eu anomaly,flat negative Eu anomaly,hump-shaped positive or negative Eu anomaly REEN patterns,and the higher Nb(96.9?864.5 ppm)and Na(0?54,051.8 ppm)contents,indicating that REEs enter scheelite lattice mainly by 3Ca²⁺=2REE³⁺+?Ca replacement mechanism and to some extent by Ca²⁺+W⁶⁺=REE³⁺+Nb⁵⁺and 2Ca²⁺=REE³⁺+Na⁺replacement mechanisms;this evidence suggests strong fluid-rock reaction and inherited primitive fluids are the key factors influencing the formation of scheelite.The zircon U-Pb-weighted mean ages of the potassic granite,quartz diorite and biotite monzogranite in the mine area are 243.3±0.9 Ma,238.8±0.9 Ma and 233±2.3 Ma,respectively,indicating that the intrusive rocks were formed in the early-middle Triassic;the biotite monzogranite has a close genetic relationship with the deposit,combining the main trace evidence and previous studies on whole-rock Sr-Nd isotopes and zircon Hf isotopes,the lithospheric thinning led to the upward intrusion of mantle-derived magma in the Triassic intraplate extensional tectonic setting,and partial melting of the early thickened middle crust due to collage accretion,and the formation of granitic rocks at the bottom of the mine area by the parent magma,which subsequently underwent crystallization and differentiation,and the mineralizing hydrothermal fluids rich in volatiles and complexes such as F,Cl,B,etc.enriched the W elements continuously,and with the strong pressure gradient between the rock and the stratum,the ore-forming fluids from the exsolution of the melting process moved up along the tectonic fracture system,while contacting and percolating through the granite body and the peritectic and Mg-rich carbonate enclosing rocks,and with the rise of the hydrothermal fluids and the fluid-rock reaction,the temperature,pressure,oxygen fugacity and p H changed drastically,thus precipitating the ore-forming elements and forming the Shadong magnesium skarn-type deposit.