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BOLETÍN DE LA SOCIEDAD GEOLÓGICA MEXICANA http://dx.doi.org/10.18268/BSGM2010v62n1a8 |
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Metalogenia del depósito de manganeso Santa Rosa, Baja California Sur, México
Metallogeny of the Santa Rosa manganese deposit, Baja California Sur, Mexico
Augusto Antonio Rodríguez–Díaz1,2*, David Blanco–Florido1, Carles Canet3, Fernando Gervilla–Linares4, Eduardo González–Partida5, Rosa María Prol–Ledesma3, Salvador Morales–Ruano4, Maite García–Vallès6
1 Posgrado en Ciencias de la Tierra, Universidad Nacional Autónoma de México, Ciudad Universitaria, 04510, México, D.F.
2 Facultad de Ciencias de la Tierra, Universidad Autónoma de Nuevo León, Ex–Hacienda de Guadalupe, Carretera Linares–Cerro Prieto km 8, 67700, Linares, Nuevo León, México.
3 Instituto de Geofísica, Universidad Nacional Autónoma de México, Ciudad Universitaria, 04510, México, D.F.
4 Departamento de Mineralogía y Petrología e Instituto Andaluz de Ciencias de la Tierra, Universidad de Granada, Avd. Fuentenueva s/n., 18002, Granada, España.
5 Centro de Geociencias, Universidad Nacional Autónoma de México, Blvd. Juriquilla 3001, Juriquilla, Querétaro, 76230, México
6 Departament de Cristal•lografía, Mineralogía i Dipòsits Minerals, Universitat de Barcelona, c. Martí i Franquès s.n., Barcelona 08028, Catalunya, España.
* This email address is being protected from spambots. You need JavaScript enabled to view it.
Abstract
The Santa Rosa Mn–Ba deposit is located southwest of the town of San Nicolás and south of the Concepción Peninsula in Baja California Sur (Mexico). It consists of a manganese oxide vein–breccia striking NNW with a subvertical dip to the ENE that is exposed discontinuously over 500 m. The deposit is hosted in conglomerates that belong to the Los Volcanes member of the Pliocene age San Nicolas Formation. The mineralization is characterized mainly by banded and brecciated structures with manganese oxides (romanèchite and pyrolusite), along with barite, opal, quartz, calcite, magnetite–maghemite and minor goethite.
The ore contains between 23.6 and 50.0 wt. % MnO, 13.3 and 32.4 wt. % SiO2, and 9.9 and 13.7 wt. % BaO. In addition, the ores are significantly enriched in Sr, Sb, As, Cu and Zn. The NASC normalized REE profles show a pronounced negative Eu anomaly and a more moderate negative Ce anomaly. The Fe/Mn and the Co/Zn ratios range between 0.01 and 0.16, and 0.17 and 0.34, respectively.
Microthermometry suggests two fluid inclusion populations: one with an average Th of 136.5°C and estimated salinity of 4.2 wt. % equivalent NaCl, and the other with an average Th of 136°C and estimated salinity of 11.4 wt. % equivalent NaCl.
The mineralogical and geochemical composition, together with the ore formation conditions and the geotectonic setting, suggest a genetic relation between the Santa Rosa deposit and the modern coastal hydrothermal systems of the Concepción Bay.
Keywords: Hydrothermal, vein, breccia, romanèchite, barite, opal, fluid inclusions, hot spring, extension tectonics.
