Speciation of noble metals and conditions of their concentration in massive sulfide ores of the Urals

Abstract

The distribution of noble metals has been studied in ores and sulfide concentrates from the Gai, Uchaly, Uzel'ga, Aleksandrinsky, Degtyarsk, and Saf'yanovka deposits. The ores, technological products, and hand-picked monofractions were analyzed with INAA; PGE were determined with kinetic and chromatographic methods after their preliminary chemical separation. The ultraheavy fractions from Au-rich samples were used for examining minerals of noble metals. Phase relations and compositions of ore minerals were studied with an X-ray microprobe and electron microscope equipped with an energy dispersive X-ray analyzer. Gold is associated largely with Fe and Cu minerals (pyrite, chalcopyrite, fahlore) and has been detected as an admixture in Pb, Bi, and Ag tellurides. Pyrite-the major mineral of massive sulfide ores-is the main gold concentrator (up to 20 ppm, ~1 ppm on average). As follows from the results of rational analysis, the concentration of finely dispersed gold in sulfide ores from the studied deposits ranges from 0.8 to 5.0 ppm, i.e., is less than the bulk Au content in the respective samples (0.93-21.2 ppm). Formation conditions of Au-enriched massive sulfide ores were estimated from the homogenization temperature of fluid inclusions in minerals and on the basis of the electrum-argentite-pyrite-sphalerite and electrum-hessite geothermometers, taking into account the sulfur and tellurium fugacities. The appearance of visible gold and tellurides in ores is caused by recrystallization of their fine-grained intergrowths with ore-forming minerals and, likely, by release of isomorphic admixtures contained in sulfides during epigenetic hydrothermal alteration.

Vanadium Mineralization in the Kola Region, Fennoscandian Shield

“…Metamorphism of primary pyrite ores formed in oceanic basalts led to the mobilization of ore elements located in sulfides in the dispersed state and to their concentration in ore minerals up to the formation of their own mineral phases [86,88,89]. Secondary hydrothermal stages and local metamorphism of sulfide ores resulted in redistribution of base and precious metals, refining of common sulfides, the appearance of submicroscopic and microscopic inclusions of Au-Ag alloys, and segregation of trace elements into new, discrete minerals [88].…”

Coulsonite FeV2O4—A Rare Vanadium Spinel Group Mineral in Metamorphosed Massive Sulfide Ores of the Kola Region, Russia

“…The source of vanadium can be an organic suspension, which absorbs it from seawater and precipitates with sulfides captured by them [39]. After [40][41][42][43], the metamorphism and secondary hydrothermal stage of primary (where pyrite is the main mineral) massive sulfide ores led to the remobilization and redistribution of elements located in sulfides in the dispersed state and to their concentration in newly formed sulfide minerals or in their own mineral phases. The metamorphic recrystallization of sulfides can possibly form vanadium oxides containing coulsonite-I and coulsonite-III.…”

Vanadium mineralization in the Kola region, Fennoscandian Shield

“…The supracrustal section in the Bergslagen Province consists of mainly 1.90-1. 89 Ga felsic volcanics with subordinate sediments, including marble and basic volcanics that were accumulated in an island-arc environment and then were deformed and metamorphosed under conditions of predominantly upper greenschist to upper amphibolite facies [62]. The main mineral is pyrrhotite, in a smaller amount pyrite, chalcopyrite, and sphalerite are present.…”

“…Metamorphism of primary pyrite ores formed in oceanic basalts led to the mobilization of ore elements located in sulfides in the dispersed state and to their concentration in ore minerals up to the formation of their own mineral phases [85][86][87][88][89]. Secondary hydrothermal stages and local metamorphism of sulfide ores resulted in redistribution of base and precious metals, refining of common sulfides, the appearance of submicroscopic and microscopic inclusions of Au -Ag alloys, and segregation of trace elements into new, discrete minerals [88].…”