The Sierra de Cacheuta Vein-Type Se Mineralization, Mendoza Province, Argentina

Abstract

The Sierra de Cacheuta vein-type Se mineralization in the Mendoza Province predominantly consists of clausthalite, klockmannite, eskebornite, eucairite, and naumannite. These primary selenides formed in a fault zone, cutting through fine-grained trachytic host rock. Cross-sections perpendicular to the veinlets, polarized light microscopy, and scanning-electron microscopy, combined with electron-microprobe analysis, provide a record of the relationship between different crystallization and deformation events. Mineralization encompasses four episodes of fault formation (d1-d4): early zonal selenide crystallization (stage (I)); ductile deformation of the selenides (stage (II)); fault re-opening, fluid-mediated metal mobilization, metalliferous-fluid infiltration, and mineral precipitation (stage (III)); and subsequent alteration (stage (IV)). The Se vein originated from multiple injections of highly oxidized, metal-rich fluids. These low-T solutions (estimated max. temperature 100 • C, max. pressure 1 bar) possessed high to exceptionally high Se fugacities (log f Se2 between −14.5 and −11.2) that prevailed for most of the evolution of the deposit. The source of the Se and the accompanying metals (Cu, Ag, Pb, and Fe) is probably the neighboring bituminous shale. The deposition of Se minerals occurred when the oxidized metal-bearing solutions came in contact with a reductant, which caused the reduction of mobile selenate to immobile selenide or elemental Se. We identified several features that permit us to safely distinguish samples from Cacheuta from Argentinian Se deposits in the Province of La Rioja: (I) trachytic host rock fragments containing bitumen and TiO 2 pseudomorphs after titanomagnetite; (II) early Co-rich and Ni-poor krut'aite (Co < 6.7 wt %, Ni < 1.2 wt %) partly replaced by clausthalite, umangite, klockmannite, eskebornite, Ni-poor tyrrellite (Ni < 2.7 wt %), Ni-poor trogtalite (Ni < 1.2 wt %), and end-member krut'aite and petříčekite; (III) lack of calcite gangue; and (VI) Se-bearing alteration minerals comprising chalcomenite, molybdomenite, cobaltomenite, an unnamed Cu selenide (for which the ideal formula may be either Cu 2 Se 3 or Cu 5 Se 8 ), and possibly mandarinoite, mereheadite, orlandiite, and scotlandite as new species for this occurrence.

Selenium Minerals: Structural and Chemical Diversity and Complexity

“…Its crystal structure was solved by Hawthorne [67], who defined it as a hexahydrate. However, this conclusion was recently questioned by Holzheid et al [68], who suggested for mandarinoite the chemical formula The second most structurally complex Se mineral is mandarinoite, Fe 2 (SeO 3 ) 3 •6H 2 O, that was first described as an alteration product of penroseite, NiSe 2 , at Pacajake mine near Hiaco, Colquechaca, Bolivia [62], and later found at other localities worldwide [63][64][65][66]. Its crystal structure was solved by Hawthorne [67], who defined it as a hexahydrate.…”

A Bibliometric Analysis of Research on Selenium in Drinking Water during the 1990–2021 Period: Treatment Options for Selenium Removal

“…Although the selenium content of most natural waters does not threaten human health, the aquifers and the related surface water bodies in natural selenium-rich geological areas can present selenium concentrations that require further treatment to obtain safe drinking water. Chinese, Indian, American and Canadian seleniumrich regions have been deeply investigated [46][47][48], but other countries with localized areas characterized by high selenium contents can be mentioned, such as Argentina, Brazil, France, Ireland, Israel, Italy or Venezuela [49][50][51][52][53][54][55][56]. Nevertheless, anthropogenic activities account for a widespread selenium contamination as the result of some industrial activities, such as coal mining and combustion; gold, silver and nickel mining; metal smelting (especially pyrometallurgical copper, nickel and zinc production); oil transport, refining and utilization; and agricultural irrigation with selenium-rich waters [57].…”

Enrichment of Se-Te-Au in the Jilongshan Au-Cu Skarn Deposit, Hubei Province: Insight from Pyrite Texture and Composition

“…The occurrences of Se in all ore deposits can be divided into three types: (1) existing as independent selenium minerals, such as naumannite (Ag 2 Se), clausthalite (PbSe), etc. ; (2) substitute to crystal lattice (S 2− ) as isomorphism in sulphides (e.g., pyrite, sphalerite, and galena); (3) organic matter that adsorbs Se, which can occur in calcareous rocks [34][35][36][37][38]. The LA-ICP-MS ablation curves for Se in Py2 from the Jilongshan deposit are generally smooth, without a "peak" signal (Figure 7c,d), indicating that Se exists in the lattice of pyrite in the form of isomorphism.…”