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Unusually high sub-microscopic gold and arsenic contents of pyrite from the Emperor gold deposit, Fiji
Published in Adam Piestrzyński, Mineral Deposits at the Beginning of the 21st Century, 2001
D.W. Pals, P.G. Spry, S. Chryssoulis
Ahmad et al. (1987), in a study of lodes in the central part of the mine, proposed eight stages of hydrothermal vein mineralisation. Quartz gangue dominates the first seven stages while the major gangue mineral in the eighth stage is calcite. The second, third, fourth, and eighth stages are gold-bearing. Stage II consists predominantly of pyrite, sphalerite, chalcopyrite, and tetrahedrite, as well as tellurium-bearing minerals (sylvanite, calaverite, krennerite, native tellurium, empressite, melonite, altaite, and coloradoite). Stage III is composed almost entirely of quartz but it also includes rare sylvanite and petzite. Stage IV contains essentially the same minerals as Stage II but the precious metal minerals consist of petzite, hessite, and native gold. Stage VIII contains plates of native gold (up to 5 mm in length) that coat calcite. Arsenian pyrite has been identified in Stages II, III, and IV in association with tellurides, chalcopyrite, sphalerite, and tetrahedrite group minerals (As/(As+Sb) = 0.35 to 1; Ag/(Ag+Cu) = 0 to 0.83; n = 60) throughout the deposit.
Solstad, a Co-Se-bearing copper ore in the Västervik quartzites, Sweden
Published in GFF, 2022
Kjell Billström, Johan Söderhielm, Curt Broman, Krister Sundblad
All samples carry substantial amounts of chalcopyrite and locally bornite. Other abundant phases include Co-rich pyrite, and nickel-bearing linneite (Co3S4) (Table 1). Digenite (Cu9S5) and covelline (CuS) are locally replacing bornite and chalcopyrite. The bornite paragenesis contains a number of more unusual phases carrying Ag, Bi, Se and Te that have not been described previously from this deposit. Such phases include native bismuth and native tellurium, bismuthinite (Bi2S3), clausthalite (PbSe), wittichenite (Cu3BiS3), hessite (Ag2Te), sylvanite (Ag,AgTe2) and krennerite (AuTe2) (Table 1; Fig. 3). From a textural point of view, the main mineral of economic interest, i.e., chalcopyrite, occurs as fracture fillings in quartz and disseminated in the more massive ore. Bornite, which is the dominating copper mineral in sample G2878, often shows a basket weave texture and is locally replaced by covelline and digenite along crystallographic planes and grain boundaries. The relative crystallization order of the copper minerals shows that chalcopyrite formed as the first phase, followed by bornite, and finally covelline and digenite. Co-free pyrite is abundant in practically all specimens and forms euhedral to subhedral (≤10 mm) grains, sometimes with goethite-filled fractures (as a result of recent weathering). Co-bearing pyrite is less common and is often fine-grained and sometimes replaced by chalcopyrite. Nickel-bearing linneite is also common and forms up to 30 mm large grains showing rather well-developed crystal surfaces. Galena is abundant in massive ore zones but also occurs sparsely as up to 0.3 mm anhedral grains or in cracks between pyrite grains.
Oxidative Decomposition of Silver Telluride (Ag2Te) Using Hypochlorite in Different Acid Environments
Published in Mineral Processing and Extractive Metallurgy Review, 2022
V.M. Rodríguez-Chávez, J.C. Fuentes-Aceituno, F. Nava-Alonso
The depletion of easily leachable gold and silver deposits has forced the mining industry to explore new processing alternatives to recover the precious metals from different ores. Among the most important silver phases, it is possible to find pyrargyrite, proustite, stephanite and silver telluride (Paterson 1990). The most common mineral phase of silver telluride is hessite (Ag2Te), and it is frequently associated with some gold tellurides, e.g. calaverite (AuTe2), petzite (Ag3AuTe2), krennerite (AuTe2), montbrayite (Au2Te3) and kostovite (CuAuTe4) (Adams 2016). However, according to Celep et al. (2014), these important silver mineral phases present a very low leaching kinetics in cyanide solutions. Furthermore, Wang and Forssberg (1990) reported that gold and silver telluride and selenide species are stable in the presence of cyanide, which suggests that direct leaching of gold and silver with cyanide is probably ineffective. The reported results demonstrate that the leaching kinetics is very slow compared to native gold and electrum (Cornwall and Hisshion 1976; Henley, Clarke and Sauter 2001; Jayasekera, Ritchie and Avraamides 1991; Johnston 1933; Marsden and House 2006; Padmanaban and Lawson 1991). As can be seen, the refractoriness of these type of minerals becomes an important challenge for the scientific and engineering viewpoint. Jha (1987) and Zhang et al. (2010) mentioned that refractoriness of some minerals including the telluride species can be usually solved by modifying the cyanidation conditions or providing an oxidation pretreatment. Roasting prior to cyanidation was the almost universal practice in old days; however, severe environmental regulations related to the toxic emissions have motivated the researchers to develop alternative leaching systems (Hiskey and Atluri 1988). In the case of gold telluride cyanidation, Haque (2007), reported the possibility to accelerate its dissolution using pre-treatments such as: thermal oxidation, roasting, chemical oxidation, (such as acid leaching, alkaline or acid pressure leaching or biological oxidation). In the case of the chemical oxidation of refractory ores, various types of oxidants have been studied e.g. ozone, hydrogen peroxide, permanganate, chlorine, bromine cyanide, Care`s acid, perchlorate, hypochlorite, ferric ion in acid media and oxygen (Canning and Woodcock 1982).