Noble Metal Speciations in Hydrothermal Sulphides

Abstract

A significant part of the primary gold reserves in the world is contained in sulphide ores, many types of which are refractory in gold processing. The deposits of refractory sulphide ores will be the main potential source of gold production in the future. The refractory gold and silver in sulphide ores can be associated with micro- and nano-sized inclusions of Au and Ag minerals as well as isomorphous, adsorbed and other species of noble metals (NM) not thoroughly investigated. For gold and gold-bearing deposits of the Urals, distribution and forms of NM were studied in base metal sulphides by laser ablation-inductively coupled plasma mass spectrometry and by neutron activation analysis. Composition of arsenopyrite and As-pyrite, proper Au and Ag minerals were identified using electron probe microanalysis. The ratio of various forms of invisible gold—which includes nanoparticles and chemically bound gold—in sulphides is discussed. Observations were also performed on about 120 synthetic crystals of NM-doped sphalerite and greenockite. In VMS ores with increasing metamorphism, CAu and CAg in the major sulphides (sphalerite, chalcopyrite, pyrite) generally decrease. A portion of invisible gold also decreases —from ~65–85% to ~35–60% of the total Au. As a result of recrystallisation of ores, the invisible gold is enlarged and passes into the visible state as native gold, Au-Ag tellurides and sulphides. In the gold deposits of the Urals, the portion of invisible gold is usually <30% of the bulk Au.

U-Th-He Geochronology of Pyrite from Alteration of the Au-Fe-Skarn Novogodnee-Monto Deposit (Polar Urals, Russia)—The Next Step in the Development of a New Approach for Direct Dating of Ore-Forming Processes

“…These stratified rocks are located in the roof of the Late Silurian-Middle Devonian comagmatic, multiphase gabbro-diorite-plagiogranite Sob' (Lagorta-Kokpela) batholith [38,41,[44][45][46][47][48]. The ore district is located in a long-lived tectonic zone forming a series of faults oriented in a north-west direction, which are recognized as some of the key conduits for various types of ore mineralization [46,[49][50][51][52].…”

“…%), however, if it is associated with cobaltite and Co-bearing pyrite and chalcopyrite, its fineness increases to 90.0-99.0 at. % [51].…”

“…These rocks are cross-cut by younger intrusions of the gabbro-diorite-plagiogranite Sob' complex (D 1-2 ) and the late-stage gabbro-dolerite dykes of the Musyur complex (C 1 ) [40,45,50]. The geological structure and ore deposits of the Novogodnee mineral field were studied from 1957 [46,51,52,54,58,59]. The U-Pb ages of zircons from diorites of the second (main) and plagiogranites of the third phases of the Novogodnee gold field are 410 ± 2 Ma [45] and 403 ± 4 Ma [40].…”

Gold and Arsenic in Pyrite and Marcasite: Hydrothermal Experiment and Implications to Natural Ore-Stage Sulfides

“…In Au deposits, pyrite is commonly associated with subordinate arsenopyrite and marcasite. These minerals host an important and dominant fraction of "invisible" gold (see [8] and references therein). The "invisible" gold content in ore minerals can reach a wt.% level in As-rich ones (arsenian pyrite, arsenopyrite), but usually ranges from a few ppm to a few tens ppm.…”

A Pretreatment of Refractory Gold Ores Containing Sulfide Minerals to Improve Gold Leaching by Ammonium Thiosulfate: A Model Experiment Using Gold Powder and Arsenic-Bearing Sulfide Minerals

“…Hence, the gold mining industry has been driven by the demand for gold to find ways to process lower grade and refractory gold deposits over the past 50 years [6,7]. In these refractory ores, gold commonly occurs as free particles of gold and electrum, with the inclusion of these phases in the sulfide mineral matrix [8]. The encapsulation of gold in sulfide matrices as well as its association with other minerals (e.g., arsenopyrite (FeAsS), chalcopyrite (CuFeS 2 ), and pyrite (FeS 2 )) renders these gold ores refractory.…”