Ore genesis of the Fule Pb Zn deposit and its relationship with the Emeishan Large Igneous Province: Evidence from mineralogy, bulk C O S and in situ S Pb isotopes

Abstract

Magmatic activity plays an important role in mineralization, but little is understood of its role with respect to carbonate-hosted stratabound epigenetic Pb-Zn deposits. The Fule Pb-Zn deposit (~10 Mt of sulfide ore with mean grades of 15-20 wt. % Zn + Pb), is stratigraphically placed in middle Permian strata and spatially (~1 m) associated with late Permian continental flood basalts of the Emeishan Large Igneous Province (ELIP). It thus provides an ideal case to investigate its genetic relationship with the ELIP. In addition, the Fule deposit is characterized by high concentrations of Ag, Cd, Ge and Ga, and contains a variety of Cu and Ni sulfide minerals. Syn-ore calcite (δ 13 C = +2.57-+3.01‰) and associated fluids (δ 13 C = +2.96-+3.40‰) have δ 13 C values similar to those of fresh limestone (δ 13 C = +1.58-+2.63‰), but the δ 18 O values of calcite (+16.83-+19.92‰) and associated fluids (+7.80-+10.89‰) are distinctly lower than those of limestone (δ 18 O = +21.85-+23.61‰). This means that C is mainly derived from limestone, whereas the O isotope signature may be related to water/rock (W/R) interaction between mantle and/or metamorphic fluids and limestone. δ 34 S values of sulfide minerals obtained by in situ NanoSIMS and conventional bulk techniques record a range of +9.8-+23.1‰ and +10.04-+16.43‰, respectively, reflecting the enrichment of heavy S isotopes in the oreforming fluids and thermochemical sulfate reduction (TSR) is the principal mechanism for the formation of S 2-. Cores of sulfide crystals have much higher δ 34 S values than their rims, indicating a probable mixture of multiple S reservoirs and/or a dynamic fractionation of S isotopes occurred during sulfide precipitation. The uniform femtosecond (fs) LA-MC-ICPMS in situ Pb isotopic data for galena plot in the field that differs from any of the three potential 3 sources in the region. Such signatures demonstrate that metal Pb was most likely derived from a well-mixed source of basalts, sedimentary rocks and basement rocks. We propose that (a) the enrichment in Ag, Cu, Ni, Cd, Ge and Ga, and the isotope signatures of hydrothermal minerals in the Fule region are related to fluids derived from or flowed through multiple reservoirs; (b) Emeishan magmatism provided heat, elements and associated fluids, and its basalts acted as an impermeable and protective layer; and (c) fluid mixing caused TSR, and then resulted in W/R interaction and CO2 degassing, all of which played a key role in the precipitation of hydrothermal minerals.

The giant Upper Yangtze Pb–Zn province in SW China: Reviews, new advances and a new genetic model

“…2b) (Zhou et al, 2002). The platform carbonate sequences constitute a key part of Ediacaran to Triassic marine strata, and are rich in evaporites and organic matters, as well as contain numerous Pb-Zn sulfide deposits and Au deposits (Huang et al, 2004;Jin, 2008;Cheng et al, 2015a;Zhou et al, 2014aZhou et al, , 2018aZhou et al, , 2018b. Tectonics that strictly control sedimentation, magmatism and mineralization in the western Yangtze Block are characterized by multi-stage activities (Hercynian, Indosinian, Yanshanian, and Himalayan orogenic events) .…”

“…1a) include the Pine Point in Canada (Powell and Macqueen, 1984), Upper Mississippi Valley in the United States (Leach and Rowan, 1986;Brannon et al, 1992), Irish Midlands in Ireland (Wilkinson et al, 2005), Upper Silesia in Poland (Heijlen et al, 2003), Lennard Shelf in Australia (Tompkins et al, 1994) and the Upper Yangtze in China (Zaw et al, 2007;Zhou et al, 2013aZhou et al, , 2018aWang et al, 2014;Zhang et al, 2015b). Although extensive research has contributed greatly to the understanding of ore genesis, however, as the carbonate-hosted Pb-Zn deposits are the products of various ore-forming processes in a variety of geological and tectonic settings (Wilkinson et al, 2009;Zhou et al, 2014aZhou et al, , 2018bDavidheiser-Kroll et al, 2014;Marsh et al, 2016), their mineralization is complex and the ore formation processes are still unclear.…”

“…2a), >400 Pb-Zn deposits have been discovered within the triangular domain (~0.2×10 6 km 2 ) of SW Sichuan, NE Yunnan and NW Guizhou provinces (Fig. 2b) (Zheng and Wang, 1991;Liu and Lin, 1999;Huang et al, 2010;Zhou et al, 2013bZhou et al, , 2018b, which constitute the giant Upper Yangtze Pb-Zn metallogenic province (Zhou et al, 2014b). The Upper Yangtze metallogenic province contains >2000 Mt reserves of sulfide ore, grading 10-35 wt.…”

“…2b and 3); (ii) sulfide ore bodies occur as stratiform, lentiform or scrotiform shape within fold bedding-planes or steeply-dipping veins along fault dip planes (Zheng and Wang, 1991;Zhou et al, 2001Zhou et al, , 2013dWu et al, 2013;Wei et al, 2015;Li et al, 2015;Zhu et al, 2016a;Bao et al, 2017;Tan et al, 2017); (iii) sulfide ores have high grade, averaging >10 wt. % Pb + Zn, with abundant Ag, Cu, Cd, Ge and Ga (Ye et al, 2011;Zhou et al, 2011Zhou et al, , 2018bZhu et al, 2017); and (iv) sulfide ores are precipitated from the mantle/metamorphic fluids of medium-low temperatures (<300 °C) and salinities (<20 wt. % NaCl equiv.)…”

“…However, most of these studies only focused on individual deposits and concerned with ore deposit geology, trace elements, isotopes, geochronology or fluid inclusions. Thus, the regional mineralization and ore formation processes are still lacking (Zhou et al, 2018b), which limits the overall understanding of such type of Pb-Zn sulfide deposits and regional exploration. Sulfide ores in Pb-Zn deposits mainly consist of base metal sulfide minerals (e.g.…”