HYPOGENE Ba-RICH TODOROKITE AND ASSOCIATED NANOMETRIC NATIVE SILVER IN THE SAN MIGUEL TENANGO MINING AREA, ZACATLAN, PUEBLA, MEXICO

The mineralogical characterization of argentian cryptomelane from Xiangguang Mn–Ag deposit, North China

“…Nanometric native silver has been reported to be adsorbed on todorokite at the San Miguel Tenango Mn-Ag mine (Gómez-Caballero et al, 2010), but it was not observed in argentian cryptomelane during our TEM and Raman experiments. SEM-EDS maps also show the uniform distribution of silver in cryptomelane instead of local enrichment.…”

“…So far over fifteen kinds of manganese oxides have been identified in the worldwide Mn-Ag deposits, but the content results indicate only a few kinds such as cryptomelane, coronadite, todorokite and chalcophanite carry most of the silver (Radtke et al, 1967;Hildebrand and Mosier, 1974;Li et al, 1996). The complex occurrences and distributions of Ag associated with fine-grained Mn oxide minerals also contribute to the problems of low recovery in the metallurgical process despite high Ag grades (Gómez-Caballero et al, 2010;Tian et al, 2012). Cryptomelane (K x Mn 8−x O 16 , where 0.2 ≤ x ≤ 1), essentially potassium manganese oxide, is the most abundant mineral of supergene manganiferous ore (Post, 1999).…”

“…An argentian todorokite (3.9 wt% Ag 2 O) and unnamed silver bearing lead manganese oxide (1.2 wt% Ag 2 O) were also reported in these black calcite veins. At the San Miguel Tenango mine Ag was described by Gómez-Caballero et al (2010) to occur as nanometric particles of native silver adsorbed on the external surfaces of todorokite and of the amorphous phase.…”

Sunlight-Induced Reduction of Ionic Ag and Au to Metallic Nanoparticles by Dissolved Organic Matter

“…This is evidenced by the observation of AuNPs and AgNPs in ore deposits 16,17 and environmental waters. 18 It is believed that these nanoparticles play important roles in geochemical reactions, weathering processes, metal migration, and supergene enrichments.…”

“…Besides biogenic pathway, 55 the photogeneration of nanomaterials from dissolved metals could be a possible source of naturally occurring AgNPs or AuNPs, which provides further evidence of the difficulty of differentiating between natural and engineered nanoparticles. Moreover, the photogeneration of AuNPs and AgNPs might explain the wide occurrence of AuNPs and AgNPs in gold and silver deposits, 17,56,57 which possibly plays an important role in the biogeochemical cycle of Ag and Au. 16 In the deposition process, AuNPs and AgNPs could be initially formed through photoreduction by DOM, and further solar irradiation could induce the precipitation of these nanoparticles.…”