Abstract:

The Tongshan copper deposit is a super-large copper deposit in the Duobaoshan ore district of the Great Xing’an Range, with total identified Cu resources of 4.16 Mt. The newly discovered No.Ⅴ orebody, identified after 2020, contains 2.81 Mt of Cu resources and remains open at depth, indicating substantial potential for further resource expansion. Drilling has revealed zones of intense silicic-potassic alteration within the No.Ⅴ orebody at depths of approximately 1 700 m below surface. In addition, strongly silicified and potassic-altered tonalite has been identified in the deep southern part of the No.Ⅲ orebody at approximately 1 300 m depth. These features indicate that the hydrothermal center is buried at a depth of approximately 1.3-1.7 km. The quartz-sericite alteration zone south of the intense silicic-potassic alteration core is therefore inferred to have favorable exploration potential. To constrain the mineralization age, the source of ore-forming materials, and the genetic relationship between the No.Ⅴ orebody and the Duobaoshan copper deposit, we conducted Re-Os isotope analyses of molybdenite that coexists with Cu mineralization in the No.Ⅴ orebody. The results show that molybdenite Re-Os model ages range from 468.1 to 464.2 Ma, with an isochron age of (463.7±4.7) Ma (MSWD=0.37, n=4). The mineralization age of the No.Ⅴ orebody is slightly younger than the main mineralization stage of the Duobaoshan copper deposit (ca. 475 Ma), suggesting that the No.Ⅴ orebody may have formed from an independent hydrothermal center. The average Re content of molybdenite from the No.Ⅴ orebody is 1 026.98×10-6, significantly higher than that of the Duobaoshan deposit (467.58×10-6) and of the other orebodies in the Tongshan copper deposit (601.85×10-6). This indicates that the ore-forming magma source of the No.Ⅴ orebody had a stronger mantle-derived signature. Together with regional S and Pb isotopic data, these results suggest that the ore-forming materials in the Duobaoshan ore district were dominated by mantle-derived components, with only a limited crustal contribution.

Key words: Duobaoshan ore district, Tongshan copper deposit, No. Ⅴ orebody, molybdenite, Re-Os isotopes, source of ore-forming materials