Genesis of the superlarge Luziyuan Zn-Pb-Fe(-Cu) distal skarn deposit in western Yunnan (SW China): Insights from ore geology and C-H-O-S isotopes

Abstract The superlarge Luziyuan Zn-Pb-Fe(-Cu) polymetallic deposit is located in the southern Baoshan Block of western Yunnan (SW China). The deposit contains over 4.2 million tonnes (Mt) of contained Zn + Pb metal reserves at 5.09% Zn and 2.40% Pb, and 301 Mt of Fe ore resources at 30.02% TFe. The stratiform or vein-type orebodies are hosted in the Upper Cambrian Shahechang Formation. Similar to many major Zn skarn deposits worldwide, the Luziyuan deposit shows a distinct metal zonation pattern with depth, which correlates with the different calc-silicate mineral assemblages: From Zn-Pb (sphalerite + galena) ores in marble, through Zn-Pb-Fe-Cu (sphalerite + galena + magnetite ± pyrite + chalcopyrite) ores in pyroxenoid (± clinopyroxene)-bearing skarn, to Fe-Cu (magnetite ± pyrite + chalcopyrite) ores in garnet (± clinopyroxene ± pyroxenoid)-bearing skarn. The syn-ore calcite has δ 13 C PDB and δ 18 O SMOW values of −1.0 to +0.9‰ and +10.3 to +12.7‰, respectively, suggestive of isotopic affinities to both granite and marble. δD H 2 O values of the fluid inclusions in the pre-ore rhodonite and the syn-ore quartz range from −81.7 to −68.8‰ and −76.6 to −56.3‰, respectively; whilst the calculated δ 18 O H 2 O values of the rhodonite, syn-ore calcite, and quartz are of +5.4 to +6.1‰, +1.4 to +3.8‰, and −5.3 to −2.0‰, respectively. This indicates that the ore-forming fluids were sourced from both magmatic and meteoric waters. δ 34 S values of the syn-ore sulfides (+8.9 to +12.0‰) are slightly higher than those of typical crustal-derived granites (δ 34 S = −4.0 to +9.0‰), but are significantly lower than those of Cambrian seawater sulfates. This indicates that the source of S is correlated with both granite and seawater sulfates. We propose that the Luziyuan Zn-Pb-Fe(-Cu) polymetallic mineralization occurred in a distal skarn system, and was genetically linked to concealed Early Cretaceous granite intrusions.