Origins and Geochemical Signatures of the Amiangen Pb-Zn Deposit in Western Yunnan Province:Insights from Sulfur and Lead Isotopic Analysis of Sulfides and Trace Element Profiling of Sphalerites
The Luziyuan region,situated in the southern sector of the Baoshan Block,serves as a significant locus of iron,copper,lead,and zinc polymetallic ore concentration in southwestern China.Recently discovered within this vicinity is the Amiangen Pb-Zn deposit.Despite its newfound status,the deposit has been subject to limited scholarly inquiry,leaving questions about the origin of the ore-forming materials and the genesis of the deposit unresolved.This study employed meticulous geological field survey and microscopic characterizations to analyze the sulfur and lead isotopic compositions,as well as the LA-ICP-MS trace element profiles,of metal sulfides present in the metallogenic stage of the Amiangen deposit.These data were then compared with trace elements of sphalerite from disparate deposit types to elucidate the mineral's source and genesis.The δ34SV-CDT isotopic ratio of sulfides in the Amiangen deposit,ranging from 9.44‰ to 12.16‰,exceeds that of sulfides associated with magmatic processes but is marginally lower than that of surrounding seawater stratigraphy.These observations suggest the assimilation of both magmatic and stratigraphic sulfur.The primary Pb source is the upper crust.Sphalerite in the deposit is marked by elevated levels of Fe,Mn,Co,Cu,and Cd,while exhibiting a scarcity of Ga,Ge,As,Sn,Cr,and Ni.Elements such as Fe,Cd,Mn,Co,Ag,Sb,and Ga are integrated as solid solutions,whereas Cu exists in both solid forms and as inclusions.Notably,this study identified several coupled elemental substitutions:Zn2+↔Fe2+、Zn2+↔Cd2+、2Zn2+↔Ag++Sb3+.Moreover,the trace elemental composition of the sphalerite in the Amiangen deposit differs significantly from those in VMS,MVT,skarn,and epithermal deposits.The distinct ratios of Cd/Fe(0.02～0.04,mean 0.03),Co/Ni(15～1 019,mean 1 275),and Ga/In(0.11～1.10,mean 0.31),as well as the diminished Ge content,indicate that sphalerite formation is intrinsically linked to magmatic hydrothermal fluids.Crucially,the materials contributing to the genesis of the Amiangen deposit predominantly originate from deep concealed intermediate-acid intrusive rocks with a minor contribution from the surrounding lithology.When considered alongside its geological characteristics,the Amiangen deposit can be categorized as magmatic hydrothermal,filling-metasomatic Pb-Zn deposit.
LA-ICP-MStrace elementssphaleriteS-Pb isotopesAmiangenthe Baoshan Blockwestern Yunnan Province
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