Monazite and Cassiterite Dating and Pyrite S Isotopes of the Helukou Tungsten-Tin Polymetallic Deposit of the Guposhan Ore District, Nanling Range: Implications for Ore Genesis

The Guposh an orefield within the western segment of the Nanling Range hosts a globally significant tungsten and tin metallogenic province whose formation is tied to the intense Middle Jurassic granitic magmatism. Nonetheless, critical ambiguities remain regarding the metallogenetic ages and origin of ore-related hydrothermal fluids for W-Sn polymetallic deposits in this orefield. Here, we integrate in situ U-Pb geochronology of monazite and cassiterite and sulfur isotope analyses of pyrite from the Helukou W-Sn polymetallic deposit to resolve this outstanding question. In situ monazite U-Pb geochronology yielded lower intercept ages of 164.4 ± 1.1 Ma and 162.0 ± 2.0 Ma for the fine-grained and medium- to coarse-grained biotite monzogranite phases of the Guposhan pluton, respectively, bracketing its formation during the Middle Jurassic era. The initial 207Pb/206Pb ratio of 0.85 for the monazite grains is within the range of crustal and mantle materials, likely indicating a mantle–crust mixing source for the magma. Cassiterite from skarn-type ores yields a lower intercept U-Pb age of 165.9 ± 3.2 Ma, confirming a genetic relationship between the Guposhan magmatism and Helukou W-Sn mineralization. In situ pyrite δ34SV-CDT values show a uniform range from −0.66‰ to +0.79‰, indicating a uniform magmatic-derived sulfur source for the ore-forming fluids. We further demonstrate that fluid-rock interaction, rather than fluid mixing, acts as a crucial factor in the ore precipitation of W-Sn metals of the Helukou deposit.