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Boletín de la Sociedad Geológica Mexicana Volumen 72, núm. 3, A270719, 2020 |
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The Velardeña Zn–(Pb–Cu) skarn-epithermal deposits, central-northern Mexico:
New physical-chemical constraints on ore-forming processes
El sistema skarn-epitermal de Zn–(Pb–Cu) de Velardeña, Durango (México): Nuevos datos
fisicoquímicos de los procesos de mineralización
Abigail Jiménez-Franco1,2,3*, Carles Canet4,5, Pura Alfonso6, Eduardo González-Partida7,
Abdorrahman Rajabi8, Edgar Escalante9
1 Departament de Mineralogia, Petrologia i Geologia Aplicada, Universitat de Barcelona, Marti i Franquès s/n, 08028, Barcelona, Catalunya, Spain.
2 Institut de Nanociència i Nanotecnologia, IN2UB Facultat de Química, Universitat de 8 Barcelona, Av. Diagonal 645, 08028 Barcelona, Catalunya, Spain.
3 Posgrado en Ciencias de la Tierra, Universidad Nacional Autónoma de México, Ciudad Universitaria, Coyoacán, 04510, CDMX, Mexico.
4 Centro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México, Ciudad Universitaria, Coyoacán, 04510, CDMX, Mexico.
5 Instituto de Geofísica, Universidad Nacional Autónoma de México, Ciudad Universitaria, Coyoacán, 04510, CDMX, Mexico.
6 Dept. d’Enginyeria Minera, Industrial i TIC, Universitat Politècnica de Catalunya, Av. de les Bases de Manresa 61-73, 08242 Manresa, Barcelona, Spain.
7 Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, 76230, Santiago de Querétaro, Mexico.
8 School of Geology, College of Science, University of Tehran, 16th Azar St., Enghelab Sq., Tehran, Iran.
8 Industrias Peñoles, prolongación Comonfort s/n, Col. Metalurgica, 27370, Torreón, Coahuila, Mexico.
* Corresponding author: (A. Jiménez-Franco) This email address is being protected from spambots. You need JavaScript enabled to view it.
How to cite this article:
Jiménez-Franco, A., Canet, C., Alfonso P., González-Partida, E., Rajabi, A., Escalante, E., 2020, The Velardeña Zn–(Pb–Cu) The Velardeña Zn–(Pb–Cu) skarn-epithermal deposits, central-northern Mexico: new physical-chemical constraints on ore-forming processes: Boletín de la Sociedad Geológica Mexicana, 72 (3), A270719. http://dx.doi.org/10.18268/BSGM2020v72n3a270719
Abstract
The Velardeña mining district is economically the most important of Durango state. The ore deposits occur in different skarn zones developed within the intrusive contact between Mesozoic limestones and Eocene granitic stocks and dikes. The most important ore deposits are related to the Santa María dike and Reyna de Cobre porphyritic stock (separated from each other by 10 km). They occur as irregularly shaped replacement masses developed near the intrusive contact and have a skarn paragenesis dominated by calc-silicates and sulfides. The mineral assemblages show replacement textures and are dominated by calcic clinopyroxene (Di97-53Hd42-02Jh04-01) and garnet (Ad100-57Grs43-00) in the exoskarn, with wollastonite particularly abundant in the endoskarn. Hydrous silicates are actinolite, epidote, and chlorite, whereas sulfides include pyrite, sphalerite, pyrrhotite, galena, chalcopyrite, and sulfosalts. Scheelite, hematite, quartz, and calcite are also present. According to sphalerite geobarometry, the skarns formed at hypabyssal depths (~3–4 km). They developed by a succession of replacive mineralizing events, including (a) a prograde stage at temperatures from ≥470 to 335 °C in conditions of low f (CO2), followed by (b) a retrograde stage from 335 to 220 °C. There was a general increase in f (O2), accompanying the temperature decline during the formation of the system, which accounts for a process of mixing with cooler, oxidizing, and dilute water. During the retrograde stage, wollastonite, calcic garnet and clinopyroxene formed. On the other hand, hydrous silicates, sulfides, sulfosalts, scheelite, and hematite crystallized during the retrograde stage. Skarn mineralization is crosscut by veins of calcite, fluorite, adularia, and sphalerite. The vein mineralization formed at temperatures below 200 °C. The different ore deposits of Velardeña constitute a telescoped skarn–epithermal mineral system.
Keywords: paragenesis, geothermometry, epitermal–skarn telescoping, geochemical modeling, massive sulfides.
