The characteristics of ore-forming Fluids and ore-forming mechanism of the Diyanqinamu super-large molybdenum deposit, Inner Mongolia

Diyanqinamu deposit is a super-large porphyry molybdenum deposit found in recent years, it' s part of the Erlianhaote-Dong Ujimqin polymetallic belt, located in the north central part of Daxing' anling Mountains. This paper mainly studies the fluid inclusions and sulfur isotopes of the Diyanqinamu Mo deposit. Four hydrothermal stages of the Diyanqinamu deposit are recognized : quartz-K-feldspar, quartz-molybdenite, quartz-polymetallic sulphides and quartz-fluorite-carbonate satges. In the fluid inclusions at different stages of the deposit, gas-rich ( V-type) , liquid-rich ( L-type) and daughter-mineral-bearing ( S-type) inclusions coexist in large quantities. The results of microscopic temperature measurement show that the homogenization temperature of the first stage inclusions is 492 similar to > 600 degrees C , the salinity is obviously divided into two parts : 5. 36% NaCleqv ( L-type) and 32. 39% similar to 64. 90% NaCleqv ( S-type) ; The second stage inclusions homogenization temperature is 292 similar to 510 degrees C , the salinity is 4. 49% -19. 92% NaCleqv ( L-type) and 28. 43% similar to 70. 21% NaCleqv ( S-type) ; In the third stage inclusions, the homogenization temperature is 206 - 388 degrees C and the salinity is 2. 24% to 22. 71% NaCleqv ( L-type) and 28. 62% -54.64% NaCleqv ( S-type). The homogenization temperature and salinity of the fourth stage are 133 similar to 288 degrees C , 0. 88% 7. 86% NaCleqv respectively. The fluid has the trend of evolution from high temperature and high salinity to low temperature and low salinity. The L-type, V-type and S-type inclusions coexisted in the first three mineralization stages. The uniform temperature of the end-envelope inclusions was similar, and the salinity varied greatly, indicating that a strong fluid boiling effect occurred. The multi-stage boiling action of the ore-forming fluid seems to have been the dominant factor for metallic sulfide deposition. Sulfide isotope studies have shown that the delta S-34 value of the overall range of 1. 78% similar to 10. 41 parts per thousand, suggesting that ore-forming materials of the Diyanqinamu Mo deposit were mainly derived from the magma.