Boiling and vertical mineralization zoning: a case study from the Apacheta low-sulfidation epithermal gold-silver deposit, southern Peru

被引：0

作者：

Anne-Sylvie André-Mayer

Jacques Leroy

Laurent Bailly

Alain Chauvet

Eric Marcoux

Luminita Grancea

Fernando Llosa

Juan Rosas

机构：

[1] UMR Géologie et Ressources Minérales et Energétiques,

[2] Université Henri Poincaré,undefined

[3] B.P. 239,undefined

[4] 54506 Vandoeuvre-lès-Nancy Cedex,undefined

[5] France,undefined

[6] BRGM,undefined

[7] REM/MESY,undefined

[8] Avenue Claude Guillemin,undefined

[9] B.P. 6009,undefined

[10] 45060 Orléans Cedex 2,undefined

[11] France,undefined

[12] ISTO,undefined

[13] FRE 2124,undefined

[14] Université d'Orléans,undefined

[15] Bât. Géosciences,undefined

[16] B.P. 6759,undefined

[17] 45067 Orléans Cedex 2,undefined

[18] France,undefined

[19] ISTO,undefined

[20] Université d'Orléans,undefined

[21] 8 rue Léonard de Vinci,undefined

[22] 45072 Orléans Cedex 2,undefined

[23] France,undefined

[24] Cedimin S.A.,undefined

[25] Luis Saenz 447–449 Jesus Maria,undefined

[26] Lima 21,undefined

[27] Peru,undefined

来源：

Mineralium Deposita | 2002年 / 37卷

关键词：

Epithermal gold-silver Peru Andes Boiling;

D O I：

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学科分类号：

摘要：

The Au-Ag (±Pb-Zn) Apacheta deposit is located in the Shila district, 600 km southeast of Lima in the Cordillera Occidental of Arequipa Province, southern Peru. The vein mineralization is found in Early to Middle Miocene calc-alkaline lava flows and volcanic breccias. Both gangue and sulfide mineralization express a typical low-sulfidation system; assay data show element zoning with base metals enriched at depth and higher concentrations of precious metals in the upper part of the veins. Three main deposition stages are observed: (1) early pyrite and base-metal sulfides with minor electrum 1 and acanthite; (2) brecciation of this mineral assemblage and cross-cutting veinlets with subhedral quartz crystals, Mn-bearing calcite and rhombic adularia crystals; and finally (3) veinlets and geodal filling of an assemblage of tennantite/tetrahedrite + colorless sphalerite 2 + galena + chalcopyrite + electrum 2. Fluid inclusions in the mineralized veins display two distinct types: aqueous-carbonic liquid-rich Lw-c inclusions, and aqueous-carbonic vapor-rich Vw-c inclusions. Microthermometric data indicate that the ore minerals were deposited between 300 and 225 °C from relatively dilute hydrothermal fluids (0.6–3.4 wt% NaCl). The physical and chemical characteristics of the hydrothermal fluids show a vertical evolution, with in particular a drop in temperature and a loss of H2S. The presence of adularia and platy calcite and of co-existing liquid-rich and vapor-rich inclusions in the ore-stage indicates a boiling event. Strong H2S enrichment in the Vw-c inclusions observed at –200 m, the abundance of platy calcite, and the occurrence of hydrothermal breccia at this level may indicate a zone of intense boiling. The vertical element zoning observed in the Apacheta deposit thus seems to be directly related to the vertical evolution of hydrothermal-fluid characteristics. Precious-metal deposition mainly occurred above the 200-m level below the present-day surface, in response to a liquid/vapor phase separation due to an upward boiling front.

引用

页码：452 / 464

页数：12