Ore-forming material sources of the Pb-Zn-(Ag-Fe-Cu) deposits in the northern Gangdese belt, Lhasa terrane: Constraints from geology, geochronology and S-Pb isotopes

Many new skarn Pb-Zn-(Ag-Fe-Cu) deposits have been identified in the northern Gangdese polymetallic belt (NGPB). The NGPB comprises skarn deposits with different metal associations: Pb-Zn-(Ag), Pb-Zn-Fe-Cu, and Fe-Cu. The sources of ore-forming materials and whether intrusions contribute materials to these deposits, remain debated subjects. This study focused on zircon U-Pb dating and S-Pb isotopes of metal sulfides, oreforming rocks, and wall rocks from the typical deposits in the three systems. Zircon U-Pb dating indicates that the biotite granite in the Longmala deposit was emplaced at 54.6 & PLUSMN; 0.6 Ma, which is consistent with its metallogenic age. The & delta;34S values of sulfides from the Pb-Zn-(Ag) deposits (Yaguila: -2.1%o to + 6.0%o, Mengya'a: -0.8 %o to + 4.6 %o) are similar to those from Pb-Zn-Fe-Cu deposits (Longmala: +1.6%o to + 3.6%o, Lietinggang-Leqingla: -8.3 %o to + 2.0 %o), suggesting a magmatic source of sulfur. The Pb isotopes of sulfides in Pb-Zn-(Ag) deposits (206Pb/204Pb = 18.4804-18.6935, 207Pb/204Pb = 15.6637-15.7331, and 208Pb/204Pb = 38. 0164-39.2612) are similar to those of the contemporaneous intrusions, as are those of Pb-Zn-Fe-Cu and Fe-Cu deposits, suggesting that the intrusions provided metals for the three systems. In comparison, the sulfides from the Pb-Zn-(Ag) deposits have higher 207Pb/204Pb values (15.6637 to 15.7331, mostly > 15.70) than the Fe-(Cu) deposits (15.6186 to 15.6848) and the Pb-Zn-Fe-Cu deposits (15.6163 to 15.7197), indicating that the metals of Pb-Zn-(Ag) deposits were derived from the upper-crust magma, whereas the metals of Fe-(Cu) and Pb-Zn-Fe-Cu deposits originated from the deep magma that required the involvement of mantle-derived components. Combined with previous research, we propose that the metals of Pb-Zn-(Ag) deposits originated from Stype granites, whereas those of Pb-Zn-Fe-Cu and Fe-(Cu) deposits were derived from I-type granites in the NGPB.