Genetic Model Of Yanzigou Gold Deposit In Northwestern Margin Of Yangtze Craton

The process controlling the formation of orogenic disseminated-style and lode gold ores is the basis for understanding the complexity of the orogenic gold system.The Yanzigou gold deposit coeval include strata-bound disseminated-style and fault-hosted lode ores.The disseminated-style gold ores,which are enveloped by wide alteration zone with pervasive sericitization,silicification and sulfidation,are distributed along with bedding only in carbonaceous slate.The ores are dominated by assemblage?stage I?of sericite,quartz and pyrite(Py_dcc and Py_dr)with enrichment of lattice-bound gold.However,the lode gold mineralization with narrow alteration zone?sericitization,silicification and sulfidation?consists of sericite,quartz and Au-poor pyrite?Py_q?assemblage?stage I?and a later assemblage?stage II?of sericite,quartz,pyrite(Py_qp),other sulfides and native gold.Pyrite(Py_dr)exhibits Au-As rims that are attributed to overgrowth on preexisting pyrite(Py_dc)by hydrothermal events.In contrast,Py_qpp does not have the rims.Compared to the Py_dr,Py_qpp is enriched in Ag,Sb,Pb,Zn and Cu,but deplete in Co,Bi and Ni.The lode gold ores fluids have mean?³⁴S_sulfideulfide of 8.5–10.7‰and mean?¹⁸O_H2O2O of 9.0–10.1‰,together with the retrograde metamorphic gold mineralization timeing,imply a potential source from metasomatized mantle lithosphere.Relative to those of the lode gold ores fluids,the disseminated-style gold ores fluids(mean?³⁴S_sulfide=-1.3–0.8‰;mean?¹⁸O_H2O=10.6–10.9‰)are depleted in?³⁴S values but slightly elevated?¹⁸O values.Combined with no crosscutting relationship and similar alteration and mineralization between the two types of ores,these isotopic variations in disseminated-style gold ores can be explained by the reaction of the gold-rich mantle-derived fluids with the wall rock to precipitate gold-rich pyrite,while in contrast,the pyrite?Py_q?in lode gold ores produced from the stage I of fluids contain little gold due to the lack of fluid-wall rock interactions.