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7010576 
Journal Article 
Geochemical constraints on the genesis of the 'Montana de Manganeso' vein-type Mn deposit, Mexican Plateau 
Madondo, J; Vafeas, N; Canet, C; Gonzalez-Partida, E; Rodriguez-Diaz, AA; Nunez-Useche, F; Alfonso, P; Rajabi, A; Pi, T; Blignaut, L; , 
2020 
1 
Ore Geology Reviews
ISSN: 0169-1368
EISSN: 1872-7360 
ELSEVIER 
AMSTERDAM 
125 
WOS:000571099900001 
Manganese mineralization at Montana de Manganeso, San Luis Potosi state, consists of oxide ores that form sharp contacts with volcanic host rocks. The orebodies are generally in the form of veins and irregular masses, and locally as mineralized breccias. Petrographic analyses indicate that the mineralization is multi-episodic, with colloform and crustiform textures predominating. The X-ray diffraction and electron microscopy show that manganese oxides (todorokite, birnessite, pyrolusite, romanechite and cryptomelane) are the main ore minerals, while iron oxides (goethite and hematite) are accessory. The most common gangue minerals are calcite and quartz with subordinate amounts of barite.According to fluid inclusion microthermometry, the mineralization is associated with aqueous solutions of intermediate salinity (8-16 wt% NaCl equivalent) and temperatures between 101 and 140 degrees C. Stable isotope analysis of calcite (delta C-13(PDB): -7.76 to -6.32 parts per thousand; delta O-18(PDB): -8.01 to -4.71 parts per thousand) and barite (delta S-34: 7.9-13.6 parts per thousand) shows a contribution of magmatic volatiles to hydrothermal fluids dominated by meteoric water (calculated delta O-18(fluid): 6.58-13.14 parts per thousand, relative to SMOW). Argillic alteration is the most widespread hydrothermal alteration at Montana de Manganeso and indicates fluid temperature below similar to 150 degrees C and near neutral pH. Much more local, advanced argillic alteration, revealed by the occurrence of kaolinite, is interpreted as a steam-heated overprint, which in turn suggests a boiling process that must have happened at greater depths. The Mn ores formed through a process of mixing of: (a) boiled-off hydrothermal fluids, with (b) cold, diluted meteoric water. Our results support a hot-spring deposit model, according to which Montana de Manganeso corresponds to the shallowest portion of an epithermal system formed in a continental volcanic arc setting. 
Stable isotopes; Geochronology; Fluid inclusions; Epithermal; Manganese oxides; San Luis Potosi