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

摘要

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 skam 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 delta C-13(pDB) and delta O-18(SMOW) values of 1.0 to + 0.9%o and +10.3 to + 12.7%(0), respectively, suggestive of isotopic affinities to both granite and marble. 813,v, values of the fluid inclusions in the pre -ore rhodonite and the syn-ore quartz range from 81.7 to 68.8%o and 76.6 to 56.3%o, respectively; whilst the calculated delta O-18(H2O) values of the rhodonite, syn-ore calcite, and quartz are of + 5.4 to + 6.1%o, + 1.4 to +3.8%(0), and -5.3 to -2.0%(0), respectively. This indicates that the ore -forming fluids were sourced from both magmatic and meteoric waters. delta S-34 values of the syn-ore sulfides (+ 8.9 to + 12.0%(0)) are slightly higher than those of typical crustal-derived granites (delta S-34 = 4.0 to +9.0%(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.