Abstract: The skarn-type scheelite deposit is an important type of tungsten deposits in eastern Jilin and Heilongjiang of Northeast (NE) China. The large-scale Cuihongshan Wo-polymetallic deposit in Xunke area of Heilongjiang Province and medium-scale Baishilazhi scheelite deposit in Wangqing area of Jilin Province are two representative skarn deposits. To determine their ore-forming fluid characteristics and metallogenic mechanism, scheelite single minerals were selected from these two representative deposits for in-situ LA-ICP-MS trace elements analysis. The results show that the scheelite in Cuihongshan deposit was formed in a Na- and Nb-rich ore-forming fluid system with left-dipped rare earth element (REE) distribution patterns and weak positive Eu anomalies. The substitution of REE3+ for Ca2+ in scheelite from Cuihongshan deposit can be accounted for the substitution mechanism: 2Ca2+ = REE3+ + Na+ and Ca2+ + W6+ = REE3+ + Nb5+. The scheelite in Baishilazi deposit was formed in a Na- and Nb-poor ore-forming fluid system with right-dipped REE distribution patterns and positive Eu anomalies. The substitution mechanism of REE3+ for Ca2+ in scheelite of Baishilazi deposit is 3Ca2+ = 2REE3+ + □Ca (where □ is a site vacancy). The obvious correlation between EuN and Eu*N and the high Mo content in scheelite samples indicates that the ore-forming fluids in two skarn-type tungsten (-polymetallic) deposits in eastern Jilin and Heilongjiang are oxidizing fluids. The Eu anomalies of scheelite in these two deposits are higher than those of their ore-forming intrusions, indicating that water-rock reaction occurred during the fluid evolution. The obvious correlation of Y and Ho contents between the scheelite in different deposits and their ore-forming intrusions, as well as the differences between Y/Ho and La/Ho, reveal that their initial ore-forming fluids are derived from magmatism, and water-rock reaction and fluid mixing occurred during the fluid evolution. Due to data from this studies and previous references, it can be concluded that the water-rock reaction and fluid mixing during ascending of the magmatic hydrothermal are major mechanisms of scheelite mineralization in the skarn-type tungsten (-polymetallic) deposit in eastern Jilin and Heilongjiang.

Key words: ore-forming fluid, metallogenic mechanism, in-situ trace elements, scheelite, skarn-type tungesten deposit, Cuihongshan Wo-polymetallic deposit, Baishilazhi scheelite deposit, Eastern Jilin and Heilongjiang Provinces