Productive Versus Non-productive Porphyry Systems Surrounding The Peñasquito Diatreme-Porphyry System, Zacatecas, Mexico.

Abstract

ABSTRACTIntrusive systems surrounding the Peñasquito polymetallic deposit including the productive Peñasquito diatreme-porphyry complex are located in the northeastern portion of Mexico, within the central-western margin of the Mexican fold-thrust belt. These igneous intrusive systems are included within the Concepción del Oro intrusive belt (COIB), a set of plutonic complexes approximately west-to-east oriented. The COIB has been divided into two regions: (a) Late Cretaceous plutons of the eastern portion, and (b) Eocene-Oligocene plutons of the western portion. Igneous rocks were emplaced through Mesozoic marine sedimentary sequences that host several mineralization-styles. Associated mineralization to those igneous complexes is considered a metallogenetic area, especially at the western portion. Also, most intrusive systems have either mining districts or mineralized areas of interest.The current study includes six intrusive systems of the COIB that include Noche Buena (NBIS), Melchor Ocampo (MOIS), Terminal de Providencia (TPIS), Santa Rosa (SRIS), Camino Rojo (CRIS) and El Saltillito (ESIS). Outcrop-style geologic mapping, petrography, whole-rock major and trace element geochemistry, fluid inclusion analysis and radiometric age analyses of hydrothermal products were performed at each study site. The results were compared with the Peñasquito intrusive system by contrasting similarities and differences among them in order to provide key factors for further mineral exploration in the region.The NBIS consists of several intrusive phases classified as quartz-monzonite, quartz-monzodiorite and granodiorite. Hydrothermal alteration consists of moderate to pervasive potassic, pervasive phyllic, moderate propylitic, moderate calc-silicate, local advanced argillic and moderate carbonate-silica assemblages. 40Ar/39Ar ages of hydrothermal K-feldspar and biotite range from 35.51 ± 0.06 Ma to 36.32 ± 0.09 Ma, in good agreement with reported U-Pb zircon crystallization ages of ~36 Ma of quartz-feldspar porphyries. Quartz phenocrysts fluid inclusion homogenization temperatures (Th°C) range from 240°C to 595°C and salinities range from 13.94 to 30.62 equivalent wt. % NaCl. Associated mineralization includes Cu, Fe, Pb, Zn, Ag, Au, As and Sb localized within chimney-, manto-, replacement-, and vein/stockwork-types of ore deposits.The MOIS consists of hornblende-biotite dacite dikes. Hydrothermal alteration consists of moderate potassic, pervasive phyllic, moderate propylitic, moderate calc-silicate, moderate advanced argillic and moderate carbonate-silica alterations assemblages. 40Ar/39Ar ages of hydrothermal K-feldspar range from 36.16 ± 0.082 Ma to 36.7 ± 0.25 Ma. Quartz phenocrysts fluid inclusion homogenization temperatures (Th°C) range from 244°C to 595°C and salinity ranges from 14.87 to 43.85 equivalent wt. % NaCl. Mineralization is skarn-, disseminated-, lode- and stratabound-types of Cu-Au-Ag-Pb-Zn ore deposits.The igneous rocks at the Terminal de Povidencia District (TPD) include monzonite, quartz-monzonite and granodiorite. Hydrothermal alteration consists of moderate potassic, pervasive phyllic, moderate propylitic, moderate calc-silicate, pervasive advanced argillic and moderate carbonate-silica alteration assemblages. 40Ar/39Ar ages of hydrothermal K-feldspar and biotite range from 39.419 ± 0.057 Ma to 40.95 ± 0.11 Ma, in good agreement with reported U-Pb zircon crystallization ages of ~40 Ma of igneous intrusions. Mineralization within the TPD includes chimney-, lode-, stratabound/manto- and skarn-types of Cu, Fe, Pb, Zn, Ag and ±Au ore deposits.The SRIS consists of quartz-monzonite, monzo-granite and granodiorite. Hydrothermal alteration consists of moderate to pervasive potassic, pervasive phyllic, weak propylitic, moderate calc-silicate, moderate advanced argillic, and moderate carbonate-silica alterations assemblages. The 40Ar/39Ar ages of hydrothermal K-feldspar range from 43.2 ± 0.067 Ma to 43.39 ± 0.08 Ma, and younger than reported U-Pb zircon crystallization ages of ~45 Ma of igneous porphyries. Quartz phenocrysts fluid inclusion homogenization temperatures (Th°C) range from 178°C to 570°C and salinity ranges from 14.97 to 41.35 equivalent wt. % NaCl. Associated mineralization includes Au, Ag, Pb, Zn and Cu within replacement-, chimney- and disseminated-ore deposits.The CRIS consists of hornblende andesite and hornblende-biotite quartz-monzodiorite dikes. Hydrothermal alteration consists of weak to pervasive potassic, pervasive phyllic, moderate propylitic, weak calc-silicate and pervasive carbonate-silica alteration assemblages. 40Ar/39Ar ages of hydrothermal K-feldspar range from 68.31 ± 0.19 Ma to 70.3 ± 0.098 Ma, and the radiometric age-date of biotite is 79.16 ± 0.41 Ma. K-feldspar ages are younger than the reported U-Pb zircon ages of ~73 Ma of coarse-grained dike. Mineralization at the Camino Rojo deposit includes Au, Ag, As, Zn and Pb contained in vein/stockwork and manto ore deposits.The ESIS consists of quartz-monzonite, monzodiorite and granodiorite porphyries. Hydrothermal alteration consists of moderate to pervasive potassic, pervasive phyllic, moderate propylitic, pervasive calc-silicate, moderate advanced argillic and moderate carbonate-silica alteration assemblages. 40Ar/39Ar ages of hydrothermal K-feldspar range from 70.02 ± 0.13 Ma to 71.76 ± 0.16 Ma, in good agreement with reported U-Pb zircon crystallization ages of ~71 Ma. Associated mineralization includes Au, Ag, Cu, Pb, Zn, ±Mo with skarn-, vein-, disseminated- and stratabound-ore deposits.Based on major, trace and rare earth element signatures, the magma sources of all intrusive systems are related to partial melting of mantle wedge and assimilation of continental crust in a continental volcanic arc environment. However, chemical distributions, trends and patterns exhibited by samples presented in this study indicate that differentiation processes were extremely complex, not only in each system, but within individual intrusive phases.Comparisons of these intrusive systems with the productive Peñasquito diatreme-porphyry system provide similarities and differences that suggest that more evolved intrusive phases with high grade potassic and phyllic alterations were more productive. From the mineral exploration point of view, synclinal structures within the study area seem more favorable for major mineral concentrations (i.e Peñasquito and Camino Rojo deposits) due to magma interaction with most of the stratigraphic column. This relationship allowed magma differentiation by assimilation of host rock material that yielded an increase in the water content, a prime factor for metal-mineral transport and deposition.