Magmatism And Mineralization Of Daheishan Area, Qinghai Province

The Daheishan district is located in the southern part of the amalgamation belt between the North Qilian orogenic belt and the central Qilian Proterozoic continental block,which is an important components of the Qilian orogenic belt of the Qin-Qi-Kun orogenic belt.The Daheishan skarn-type tungsten deposit is an important deposit in this area,but its research is insufficient.So based on detailed ore deposit characteristics,this study is focused on the geochronological and petrogeochemistrical data of the Baokuhe granite and fluid inclusion data of the Daheishan W deposit.Besides,the characteristics of inclusion in skarn-type W deposits of China were summarized through comparative study of skarn deposits in China.Our study leads to the following salient conclusions.?1?The Baokuhe biotite monzogranite and tonalite are enriched in SiO₂,Al₂O₃,K₂O+Na₂O.The two granite have low P₂O₅ concentration and there is a negative correlation between the P₂O₅ and SiO₂,and belong to the high-K calc-alkaline series.The REEs of the granites are characterized by low REE concentrations,obverious negative Eu anomaly,highly fractionated LREE and unfractionated HREE.The spider diagram show positive Th,U,Pb,Zr,and Hf anomaly and negative Ba,Sr,Nb,P,Ti anomaly.indicating that they are belong to fractionated-highly fractionated I-type granite.?2?Zircon LA-ICP-MS U-Pb data suggest that the Baokuhe biotite monzogranite and tonalite were formed at 450.5±2.8 Ma and 160±2 Ma,respectively.The biotite monzogranite were formed by partial melting of crustal materials in a volcanic arc setting,which may related to the north-trending subduction of the Nroth Qilian ocean plate.The tonalite have a similar source with the biotite monzogranite.?3?According to intersection relationships and mineral associatioin,the mineralization process of the Daheishan W deposit can be divided into four stages,such as skarn stage,retrograde stage,quartz-sulfide stage and carbonate-fluorite stage.?4?Microthermometric and Raman spectroscopy data indicate that the skarn-type Daheishan stungsten deposit were mainly formed at 270³30?,and the inclusions were mainly composed of H₂O,CO₂,CH₄ with little N₂ and H₂S.?5?The matel of tungsten in the Daheishan W deposit was leached and extracted from the strata and magma.Fluid immiscibility was the main mechanism for the deposition of the tungsten in the Dashanshan deposit,and subsequently,the filling and replacement of W-bearing magma and hydrothermal fluid result to the formation of the skarn-type scheelite deposit.?6?The characteristics of the inclusions from skarn-type W deposits in China were summarized by comparative study of the metallogenic characteristics and mechanism of W depositin north Qilian.