Lithologic controls on mineralization at the Lagunas Norte high-sulfidation epithermal gold deposit, northern Peru

摘要: The 13.1-Moz high-sulfidation epithermal gold deposit of Lagunas Norte, Alto Chicama District, northern Peru, is hosted in weakly metamorphosed quartzites the Upper Jurassic to Lower Cretaceous Chimu Formation and overlying Miocene volcanic rocks dacitic rhyolitic composition. Dafne Josefa diatremes crosscut are interpreted be sources pyroclastic rocks. Hydrothermal activity was centered on four hydrothermal stages have been defined, three which introduced Au ± Ag mineralization. first stage restricted characterized by silice parda, a tan-colored aggregate quartz-auriferous pyrite–rutile digenite infilling fractures faults, partially replacing silty beds forming cement small hydraulic breccia bodies. δ34S values for pyrite (1.7–2.2 ‰) (2.1 ‰) indicate magmatic source sulfur. second resulted emplacement related diatreme features relatively impermeable core dominated milled slate from Formation, whereas only contains quartzite clasts. third bulk mineralization affected rocks, diatremes, Formation. In classic alteration zonation exhibiting vuggy quartz surrounded quartz–alunite quartz–alunite–kaolinite zone observed. Company data suggest that present solid solution or micro inclusions pyrite. quartzite, subtle manifested presence pyrophyllite kaolinite beds, former resulting high silica activities fluid. fracture network filled with coarse alunite, auriferous pyrite, enargite. Alteration breccias were controlled permeability, depends type composition matrix, cement, clast abundance. Coarse alunite main textural equilibrium enargite has 24.8–29.4 ‰ $$ {\delta^{18 }}{{\mathrm{O}}_{{\mathrm{S}{{\mathrm{O}}_4}}}} $$ 6.8–13.9 ‰, consistent H2S as dominant sulfur species mostly fluid constraining low pH (0–2) logfO2 −28 −30. Alunite–pyrite isotope thermometry records temperatures 190–260 °C; highest corresponding samples near diatremes. Alunite dated 40Ar/39Ar at 17.0 ± 0.22 Ma. fourth modest amounts massive alunite–pyrite fractures, barite, drusy quartz, native deposited IV vary between 11.5 11.7 ‰ magmatic, an interpretation also supported isotopic barite (δ34S = 27.1 33.8 ‰  = 8.1 12.7 ‰). Δ34Spy–alu 210 280 °C concentrated around diatreme. Norte oxidized depth about 80 m below current surface making exploitation heap leach methods viable.