The Nayongzhi Zn-Pb deposit, located in the southeastern margin of the Sichuan-Yunnan-Guizhou (S-Y-G) Zn-Pb metallogenic province, China, has been recently discovered in this region and has an estimated resource of 1.52 Mt of metal at average grades of 4.82 wt % Zn and 0.57 wt % Pb. The ore bodies are hosted in the Lower Cambrian Qingxudong Formation dolostone and occur as stratiform, stratoid and steeply dipping veins. The predominant minerals are sphalerite, galena, dolomite, calcite with minor pyrite, and barite. In this paper, the inductively coupled plasma mass spectrometry (ICP-MS) technique has been used to investigate the concentrations of Fe, Cd, Ge, Ga, Cu, Pb, Ag, In, Sn, Sb, Co and Mn in bulk grain sphalerite from the Nayongzhi deposit, in an effort to provide significant insights into the element substitution mechanisms, ore-forming temperature and genesis of the deposit. This study shows that those trace elements (i.e., Cd, In, Sn, Sb, Fe, Mn, Cu, Ga, Ge, Ag, and Co) are present in the form of isomorphism in sphalerite, and strong binary correlation among some elements suggests direct substitution as Zn²⁺↔Fe²⁺ and coupled substitutions as Zn²⁺↔Ga³⁺ + (Cu, Ag)⁺ and Zn²⁺↔In³⁺ + Sn³⁺ + □ (vacancy), despite there being no clear evidence for the presence of Sn³⁺. Sphalerite from the Nayongzhi deposit is enriched in Cd, Ge and Ga and depleted in Fe, Mn, In and Co, which is similar to that of the Mississippi Valley-type (MVT) deposit and significantly different from that of the Volcanogenic Massive Sulfide (VMS) deposit, Sedimentary-exhalative (Sedex) deposit, skarn, and epithermal hydrothermal deposit. Moreover, the ore-forming temperature is relatively low, ranging from 100.5 to 164.4 °C, as calculated by the GGIMFis geothermometer. Geological characteristics, mineralogy and trace element contents of sphalerite suggest that the Nayongzhi deposit is a MVT deposit. In addition, according to the geological characteristics, Ag content in sphalerite, and Pb isotope evidence, the Nayongzhi deposit is distinct from the deposits associated with the Indosinian Orogeny in S-Y-G Zn-Pb metallogenic province (e.g., Huize, Daliangzi, Tianbaoshan and Tianqiao deposits), thus, suggesting that multi-stage Zn-Pb mineralization may have occurred in this region.

The Laochang Ag-Pb-Zn-Cu deposit, located in the southern margin of the Sanjiang Tethys Metallogenic Belt (STMB), is the typical Ag-Pb-Zn-Cu deposit in this region. Its orebodies are hosted in the Carboniferous Yiliu Formation volcanic-sedimentary cycle and occur as stratiform, stratoid and lenticular. Whether or not the stratabound ore belong to the volcanogenic massive sulfide (VMS) deposit remains unclear and controversial. In this paper, the whole rock geochemistry, trace elements in sphalerite, U-Pb zircon chronology and Pb isotopes were investigated, aiming to provide significant insights into the genesis and geodynamic setting of the Laochang deposit. Lead isotope ratios of pyrite and sphalerite from the stratabound ore are 18.341 to 18.915 for ²⁰⁶Pb/²⁰⁴Pb; 15.376 to 15.770 for ²⁰⁷Pb/²⁰⁴Pb; and 38.159 to 39.200 for ²⁰⁸Pb/²⁰⁴Pb—which display a steep linear trend on Pb-Pb diagrams. This indicates a binary mixing of lead components derived from leaching between the host volcanic rock and mantle reservoir. Sphalerite from stratabound ores is relatively enriched in Fe, Mn, In, Sn, and Ga—similar to typical VMS deposits. Moreover, the Carboniferous volcanic rock hosting the stratabound Ag-Pb-Zn-Cu ores has a zircon U-Pb age of 312 ± 4 Ma; together with previous geochronological and geological evidences, thus, we consider that the stratabound mineralization occur in the Late Paleozoic (~323–308 Ma). Collectively, these geologic, geochemical, and isotopic data confirm that the stratabound ores should be assigned to Carboniferous VMS mineralization. In addition, volcanic rocks hosting the stratabound ore exhibit elevated high field strength elements (HFSEs, Nb, Ta, Zr and Hf) abundance, slight enrichment of light rare earth element (LREE), and depletion of Ba and Sr with obvious Nb-Ta anomalies. Such characteristics suggest that their magma is similar to typical oceanic island basalt. In addition, the oceanic island basalt (OIB)-like volcanic rocks were formed at Late Paleozoic, which could be approximately synchronous with the VMS mineralization at Laochang. Thus, it is suggested that the Laochang VMS mineralization was generated in the oceanic island setting prior to the initial subduction of the Changning-Menglian Paleo-Tethys Ocean.