Abstract:

The Tuanjiegou deposit, located in Jiayin County, Heilongjiang Province, is the largest epithermal gold deposit in Northeast China. This study systematically investigated the petrography, zircon U-Pb dating, whole-rock major and trace elements, LA-ICP-MS zircon in-situ trace elements and Hf isotopes of granodiorite porphyry and granite porphyry. Additionally, single mineral Pb-He isotope and LA-ICP-MS in-situ S isotope analyses of gold-bearing pyrite were conducted. The zircon U-Pb ages of granodiorite porphyry and granite porphyry are (105.9±1.1) Ma and (102.3±1.2) Ma, respectively, belonging to calc-alkaline to high-K calc-alkaline series. These rocks are enriched in light rare earth elements and large ion lithophile elements such as Rb and K, but depleted in P, Ti, Nb, Ta and other high field strength elements. The Ce4+/Ce3+ values of zircons in granodiorite porphyry range from 165 to 656 ℃ (mean 322 ℃), with Ti saturation temperatures ranging from 605 to 715 ℃ (mean 658 ℃). On the other hand, the Ce4+/Ce3+ values of zircons in granite porphyry range from 359 to 868 (mean 480), with Ti saturation temperatures ranging from 606 to 680 ℃ (mean 646 ℃). Zircon εHf (t) values of these two rocks are 6.9-8.1 and 5.6-8.2, respectively. The δ34S value of pyrite ranges from -7.8‰ to -0.2‰ with an average of -3.5‰, and the common Pb isotope ratios are 206Pb/204Pb=18.160-18.399, 207Pb/204Pb=15.538-15.590, and 208Pb/204Pb=38.135-38.340. The R/Ra values of fluid inclusions in pyrite range from 0.75 to 1.23. Comprehensive characteristics suggest that the mineralization-related magma is derived from the evolution of homologous crystalline magma, and the of magma emplacement occurred during the Early Cretaceous. The initial magma may have originated from the partial melting of the young lower crust material during the subduction of the Paleo-Pacific plate, with some mantle-derived materials mixed in during the formation process. The ore-forming fluid comes from deep magma and exhibits the characteristics of a mixed crust-mantle source (with the crust being the main source and mantle fluid accounting for 8.23% to 13.62%). The higher oxygen fugidity and lower magmatic crystallization temperature of granite porphyry provide favorable conditions for gold accumulation and migration, thus facilitating large-scale gold mineralization.

Key words: petrogeochemistry')">

petrogeochemistry, zircon U-Pb dating, Hf-S-Pb-He isotope, granodiorite porphyry, granite porphyry, pyrite, epithermal gold deposit,
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