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The published and original data on the tellurium mineralization of gold ore deposits of the Aldan Shield are systematized and generalized. The gold content is related to hydrothermal-metasomatic processes caused by Mesozoic igneous activity of the region. The formation of tellurides occurred at the very late stages of the generation of gold mineralization of all existing types of metasomatic formations. 29 tellurium minerals, including 16 tellurides, 5 sulfotellurides and 8 tellurates have been identified. Tellurium minerals of two systems predominate: Au-Bi-Te and Au-Ag-Te. Gold is not only in an invisible state in sulfides and in the form of native gold of different fineness, but also is part of a variety of compounds: montbrayite, calaverite, sylvanite, krennerite and petzite. In the gold deposits of the Aldan Shield, three mineral types are distinguished: Au-Ag-Te, Au-Bi-Te, and also a mixed one, which combines the mineralization of both systems. The decrease in the fineness of native gold is consistent with the sequence and temperatures of the formation of Te minerals and associated mineral paragenesis from the epithermal–mesothermal Au-Bi-Te to epithermal Au-Ag-Te. The conducted studies allowed us to determine a wide variety of mineral species and significantly expand the area of distribution of Au-Te mineralization that indicates its large-scale regional occurrence in the Aldan Shield.

The Gaching high-sulfidation epithermal deposit in the Maletoyvayam ore field features a wide range of Se-containing minerals and selenides, as well as complex gold oxides, Au tellurides (calaverite, krennerite) and native gold typical for epithermal deposits. Pyrite included in quartzites and quartz-alunite rocks was probably formed during an early stage of the ore-forming process. During the following Au-rich stage, the $f_{{\rm S}{\rm e}_{\rm 2}}$/$f_{{\rm S}_{\rm 2}}$ increased with $f_{{\rm O}_{\rm 2}}$ being relatively high, resulting in the formation of very rare compounds that have not been previously described in nature. These include Au2Te4(Se,S)3, Se3Te2, AuSe and Au(Te,Se,S) phases. The Au2Te4(Se,S)3 compounds have some variations in composition: the complete isomorphic series between Au2Te4Se3 and Au2Te4S3 was observed. The gold and Au-minerals at the main ore stage can be stable within a range of log$f_{{\rm O}_{\rm 2}}$ of −27.3 and atmospheric oxygen (?); log$f_{{\rm S}{\rm e}_{\rm 2}}$ between −12.4 and −5.7; log$f_{{\rm T}{\rm e}_{\rm 2}}$ between −10.5 and −7.8; and log$f_{{\rm S}_{\rm 2}}$ between −12.8 and −6.8 (at 250°C). The increasing oxygen fugacity during the final stage of mineralization resulted in the formation of complex Sb,As,Te,S-bearing Au oxides. Gold-oxide formation occurs due to oxidation of Au-tellurides. The final products of this process are newly-formed secondary mustard gold and Te–Se solid solutions.

The crystal structure of the first thallium-bearing gold telluride, honeaite Au3TlTe2, is reported and its topological novelty discussed. Honeaite is orthorhombic, space group Pbcm and unit-cell parameters a = 8.9671(4), b = 8.8758(4), c= 7.8419(5) Å, V = 624.14(6) Å3 (Z = 4). Its structure has been refined to R1 = 0.033, wR2 = 0.053, Goof = 1.087. The structure is based upon a corrugated double-sheet comprising two sub-sheets, each composed of six-memberedrings of corner-linked TeAu3 pyramids in which the Te lone pair is stereoactive. Rows of thallium atoms lie in the grooves between sheets and provide the only inter-sheet connectivity via Tl-Au bonds. There is extensive Au-Au bonding linking the two sub-sheets of the double-sheet.The structure is distinct from those of the 1:2 (Au,Ag)-tellurides: calaverite AuTe2, sylvanite AuAgTe4 and krennerite Au3AgTe8, which are based upon sheet structures with no connecting inter-sheet atoms. It also differs fundamentally from the structuresof synthetic phases Ag3TlTe2 and Ag18Tl4Te11, both of which have an analogous stoichiometry. In contrast to the pyramidal TeAu3 group of honeaite and krennerite, Ag does not form the corresponding TeAg3 group in itstellurides.

Gold–(silver) telluride minerals constitute a major part of the gold endowment at a number of important deposits across the globe. A brief overview of the chemistry and structure of the main gold and silver telluride minerals is presented, focusing on the relationships between calaverite, krennerite, and sylvanite, which have overlapping compositions. These three minerals are replaced by gold–silver alloys when subjected to the actions of hydrothermal fluids under mild hydrothermal conditions (≤220 °C). An overview of the product textures, reaction mechanisms, and kinetics of the oxidative leaching of tellurium from gold–(silver) tellurides is presented. For calaverite and krennerite, the replacement reactions are relatively simple interface-coupled dissolution-reprecipitation reactions. In these reactions, the telluride minerals dissolve at the reaction interface and gold immediately precipitates and grows as gold filaments; the tellurium is oxidized to Te(IV) and is lost to the bulk solution. The replacement of sylvanite is more complex and involves two competing pathways leading to either a gold spongy alloy or a mixture of calaverite, hessite, and petzite. This work highlights the substantial progress that has been made in recent years towards understanding the mineralization processes of natural gold–(silver) telluride minerals and mustard gold under hydrothermal conditions. The results of these studies have potential implications for the industrial treatment of gold-bearing telluride minerals.

Chemical composition and mode of occurrences of (Au, Ag)Te2 minerals such as calaverite (AuTe2), sylvanite (AuAgTe4) and krennerite ((Au, Ag)Te2) in epithermal gold telluride ores from Suzaki, Kawazu and Teine are examined. In the ores from Suzaki, (Au, Ag)Te2 minerals occur in microbands of tellurides and fine quartz. The minerals in telluride bands change from krennerite, via calaverite-native tellurium, to sylvanite, in the order of crystallization. A sample from Kawazu contains sylvanite and native tellurium with stutzite, hessite and tetradymite in the coarser gray quartz part. The Teine sample also contains sylvanite and native tellurium with barite and quartz. The peak patterns of XRD of calaverite, krennerite and sylvanite from Suzaki are almost identical to that of JCPDS 43–1472, JCPDS 8–20 and JCPDS 9–477, respectively. The Te, Au, Cu, and Ag contents of calaverite from Suzaki range from 56.4 to 57.9 wt.%, from 41.6 to 42.6 wt.%, from 0.28 to 0.45 wt.% and from 0.14 to 0.31 wt.%, respectively, corresponding to the formula Au0.97Ag0.01Cu0.02Te2. The Te, Au, Ag, and Cu contents of krennerite from Suzaki range from 59.6 to 61.4 wt.%, from 31.3 to 33.6 wt.%, from 4.91 to 6.13 wt.% and from 0.66 to 0.80 wt.%, respectively, corresponding to the formula Au0.71Ag0.22Cu0.05Te2 with Au and Ag ranging from 0.68 to 0.74 and from 0.20 to 0.25, respectively. The Te, Au, Ag, and Cu contents of sylvanite from Suzaki range from 61.5 to 63.4 wt.%, from 24.1 to 27.4 wt.%, from 10.0 to 12.5 wt.% and from 0.00 to 0.12 wt.%, respectively. The Te, Au, Ag, and Cu contents of sylvanite from Kawazu range from 62.7 to 63.3 wt.%, from 23.5 to 24.1 wt.%, from 12.0 to 12.5 wt.% and from 0.09 to 0.16 wt.%, respectively. The Te, Au, Ag, Cu and Fe contents of sylvanite from Teine range from 61.8 to 63.5 wt.%, from 23.6 to 24.7 wt.%, from 11.9 to 13.3 wt.%, from 0.01 to 1.65 wt.% and from 0.00 to 0.02 wt.%, respectively. The average formulae of sylvanite from Suzaki, Kawazu, and Teine are expressed as Au1.06Ag0.94Cu0.02Te4, Au1.00Ag0.95Cu0.02Te4 and Au1.01Ag0.95Cu0.06Te4, respectively. Judging from the mineral assemblages of these ores and other localities, Au–Te mineralization in the Japanese Islands can be divided into four types: native gold–calaverite at Date and Agawa, krennerite(−native tellurium) at Osore-zan and Mutsu, sylvanite–native tellurium–hessite at Teine, Kawazu, Kobetsuzawa, and Kato, and polyminerallic assemblages at Suzaki and Kushikino. The pH–Eh diagram of aqueous tellurium species and tellurium minerals at 250°C indicates that (Au, Ag)Te2 minerals in epithermal gold telluride mineralization would have been formed under middle to low Eh and acidic (to intermediate) pH conditions. It is possible that dilute tellurium-containing fluid would scavenge dilute gold.

The Sandaowanzi gold-telluride deposit, with a total reserve of ≥ 25 t of Au and an average grade of 15 g/t, is located in the Great Hinggan Range Metallogenic Belt in NE China. This deposit is the first reported case of a dominantly Au (±Ag)-telluride deposit in this area and it reveals highly economic bonanza Au- and Ag-telluride ores. Ore bodies principally occur in quartz veins and stockworks and minor in disseminations hosted by trachyandesites and andesitic breccias. Four paragenetic stages of mineralization are identified, demonstrating an early deposition of sulfides and subsequent precipitation of tellurides, which are mainly composed by petzite, sylvanite and to a lesser extent, hessite, calaverite, altaite, unnamed telluride (Au1.8Ag0.2Te), krennerite, empressite, stutzite and coloradoite. Abundant telluride assemblages identified from Sandaowanzi ores are mostly attributed to breakdown of early tellurium-bearing phases (i.e., γ- and χ-phases) during cooling. The deposition of substantial Au-Ag-Te minerals are constructed under physicochemical conditions of T = 240 to 280 °C, pH = 4.39 to 5.64, logfO2 =–44.8 to –41.8, logfTe2 =–9.75 to –9.43, logαAu+(aq)/αAg+(aq) = −6.87 to –6.56, and gold is mostly scavenged from a HTe−-dominant ore-forming fluid. The unusually high Te concentrations in the Sandaowanzi epithermal system are likely attributed to alkaline to calc-alkaline magmatic degassing.

Recent experiments have shown that microporous gold can be obtained via the oxidative dealloying of Au(Ag)-tellurides such as calaverite (AuTe2), krennerite (Au3AgTe8), and sylvanite [(Au,Ag)2Te4] under mild hydrothermal conditions. The same Au textures have been found in natural gold-telluride ores from the Late Miocene epithermal Aginskoe Au-Ag-Te deposit in Kamchatka, Russia. This confirms that natural microporous gold can form via the replacement of telluride minerals. This replacement may take place under hydrothermal conditions, e.g., during the late stage of the ore-depositing event, explaining the wide distribution of “mustard gold” in some deposits. At Aginskoe, the oxidation of Au-tellurides appears to have resulted only in local redistribution of Au and Te, because the associated oxidation of chalcopyrite scavenged the excess Te, inhibiting the crystallization of secondary Te minerals more than a few micrometers in size. Such cryptic mobility may explain the lack of reported secondary Te minerals in many Te-bearing deposits.

Natural variability of stable Te isotope compositions in terrestrial settings, including hydrothermal ore deposits, and the geochemical conditions that control their compositions are poorly understood. Previously published Te isotope data on tellurides, sulfides, and native tellurium are limited in number and derived from samples that were geologically unconstrained with regards to their location within an ore deposit. Here, we have obtained a range of values of δ130/125Te of −0.47 ± 0.13 to 0.66 ± 0.13‰ (n = 13), relative to an in-house, gravimetrically prepared Te standard of 99.9999% Te metal, for located samples of sylvanite ((AuAg)2Te4), krennerite ((Au,Ag)Te2), and native tellurium from the alkaline igneous rock-related Emperor gold telluride deposit, Fiji. Based on similarities in the geologic setting of the alkaline-igneous rock related gold-silver telluride deposits in Colorado (Cripple Creek, Boulder County, and La Plata) with Emperor, and the narrow range of δ130/125Te values for tellurides and native tellurium from Emperor and previously published, unlocated samples from Colorado deposits (Cripple Creek, δ130/125Te = −0.53 to 0.44‰, n = 13; Boulder County, δ130/125Te = −0.25 to 0.16‰, n = 7; La Plata, δ130/125Te = −0.78 to 0.0.17‰, n = 11), it is likely that the main factor controlling the range of isotope values in these epithermal systems is the Te isotope composition of the genetically-related alkaline igneous source rocks. In comparison, previously published unlocated samples of tellurides from the giant orogenic Golden Mile Au deposit, Kalgoorlie, Australia, show an isotopic range of δ130/125Te = −1.00 to 0.51‰ (n = 6) and appear to have been more affected by the metamorphic nature of the ore fluids and/or the higher degree of water-rock interaction during hydrothermal fluid transport. It is speculated that the zonation from isotopically heavy to light Te isotopic compositions with distance from the likely causative intrusion within the Emperor deposit is primarily controlled by Rayleigh fractionation of isotopes within the ore fluid.

The measurement of stable isotopes in ore- and ore-related minerals can provide insight into the geochemistry and formation of metal-bearing ore systems. Currently, there are few high-precision studies of the natural variability of stable tellurium isotopes, most of which are focused on meteorites and sulfides and are related to cosmogenesis; there are no modern studies on the variability of tellurium isotopes within native tellurium and tellurides from ore-forming systems. Tellurium is an element of interest due to its common association with gold in geologic systems, as well as its rarity in the Earth's crust and increasing industrial demand for applications such as photovoltaics. This study presents a method by which tellurium can be sampled from Au–Ag tellurides and native tellurium, isolated by ion exchange chromatography, and analyzed for isotopic composition by multi collector-inductively coupled plasma-mass spectrometry (MC-ICP-MS). Using a micromill, a sufficient mass of telluride or native Te sample can be extracted from coexisting ore and gangue minerals from ∼100 μm wide by ∼50 μm deep drilled holes. Acid digestion of micromilled samples and subsequent ion exchange chromatography isolated Te from matrix metals. The chromatography procedure has Te yields of 96% and produces no net fractionation of Te isotopes. MC-ICP-MS analyses were performed using two techniques, both of which employed the doping of samples using Cd to correct for instrumental mass bias. The first method was the introduction of 100 ppb Te-bearing solutions (with 100 ppb Cd) using a desolvating nebulizer (Aridus II). The second method involved solution nebulization of 2 ppm solutions of Te (with 1 ppm Cd) into the plasma of the MC-ICP-MS. Although the wet and dry methods produce statistically identical delta values, precision is increased using the wet method. The average uncertainty (two standard deviations of the mean) using the Aridus II is ±0.20‰ for 130/125Te (dry method), whereas that for the wet method is ±0.08‰. Repeated analyses of the Te standard over a period of ∼15 months by solution nebulization yielded an external precision of ±0.10‰ for 130/125Te. Natural, hypogene tellurides (calaverite, hessite, krennerite, and sylvanite) and native tellurium samples (n = 32) have a range of 1.64‰ in the isotope composition 130/125Te, demonstrating resolvable, disparate isotope ratios between samples from different areas and between samples from the same locality (e.g., Cripple Creek, Colorado). Fractionation of Te isotopes was caused by mass-dependent geological processes.

Calaverite, krennerite, and sylvanite are Au-Ag-tellurides with close compositions and related crystal structures. Previous experimental studies show that both calaverite and sylvanite transform to porous “mustard” gold under hydrothermal conditions; however the transformation of sylvanite follows a complex reaction path with several intermediary products, contrasting with the simple replacement of calaverite by gold. Here we report results of an experimental study of the transformation of krennerite, a phase with Ag contents intermediate between those of calaverite and sylvanite. Krennerite was replaced by Au-Ag alloy under all experimental conditions explored (160 to 220 °C; pHT ∼ 3 and 9; varying availability of oxygen). No reaction was observed at the same temperature under dry conditions. The replacement was pseudomorphic and the resulting Au-Ag alloy was porous, consisting of worm-like aggregates with diameters ranging from 200 nm to 1 µm. The replacement of krennerite proceeds via an interface coupled dissolution-(re)precipitation (ICDR) reaction mechanism. Tellurium is lost to the bulk solution as Te(IV) complexes, and may precipitate away from the dissolution site. In contrast, Au-Ag alloy precipitates locally near the krennerite dissolution site. Overall, the hydrothermal alteration of krennerite is very similar to that of calaverite, but differs from the alteration of sylvanite, for which multi-step reaction paths led to complex products and textures under similar conditions. These striking differences are driven by the competition between solid-state reactions and ICDR reaction in sylvanite. This reflects the fact that a metastable, Ag-rich calaverite nucleates on sylvanite during the early steps of its dissolution, as a result of the close relationship between the structures of these two minerals and the enrichment in Au, Ag, and Te in solution at the reaction front. In contrast, for calaverite and krennerite, no such phase precipitates, and both minerals are transformed in a pseudomorphic manner into Au-Ag alloy.

The Sandaowanzi epithermal gold deposit (0.5 Moz or ca. 14 tons), located at the northern edge of the Great Xing'an range, NE China, is unique in that nearly all the gold (> 95%) is contained in gold tellurides mostly in bonanza grade ore shoots (the highest grade being up to 20,000 g/t). The bonanza ores are hosted in the central parts of large-scale (> 3 m wide, 200 m long) quartz veins which crosscut Early Cretaceous andesitic trachyte and trachytic andesite, and are, in turn, crosscut by diabase dykes of similar age. There are two ore types: low-grade disseminated ores and high-grade vein ores. In the former, very fine grains of Ag-rich tellurides (mainly hessite and petzite) coexist with sulfides (pyrite, sphalerite, galena and chalcopyrite), occurring as disseminated grains or sometimes as grain aggregates. In the high-grade vein ores, coarse-grained Au–(Ag)–tellurides (calaverite, sylvanite, krennerite, and petzite) form a major part of quartz–telluride veins. Chalcopyrite forms separate monomineralic veins emplaced within the quartz–telluride veins. Spectacular textures among coarse-grained (up to 3 cm in diameter) tellurides, and micron-scale bamboo shoot-like grains are observed. Two- and three-phase telluride symplectites are common in the vein ores. Fluid inclusion studies suggest that the mineralizing fluids are a mixture of magmatic and meteoric fluids, that homogenized in the temperature range of 260–280 °C. Sulfur isotope compositions of pyrite and chalcopyrite (δ34S − 1.64 to 1.91‰) support the origin of fluids from a deep source. It is suggested that faulting, temperature changes and variation in fS2 and fTe2 were major factors contributing to the two main types of mineralization and the differences between them. Early rapid cooling and subsequent slow cooling of the later fluids along fault and fracture zones were instrumental in formation of the two superposed ore types. Open-space filling and crack-sealing along fractures predominates over replacement during telluride mineralization. The Sandaowanzi deposit is a unique bonanza-grade accumulation of gold tellurides genetically related to subalkaline magmatism, which was genetically associated with Early Cretaceous regional extension.

Mineralogic studies of major ore minerals and fluid inclusion analysis in gangue quartz were carried out for the for the two largest veins, the Aginskoe and Surprise, in the Late Miocene Aginskoe Au–Ag–Te deposit in central Kamchatka, Russia. The veins consist of quartz–adularia–calcite gangue, which are hosted by Late Miocene andesitic and basaltic rocks of the Alnei Formation. The major ore minerals in these veins are native gold, altaite, petzite, hessite, calaverite, sphalerite, and chalcopyrite. Minor and trace minerals are pyrite, galena, and acanthine. Primary gold occurs as free grains, inclusions in sulfides, and constituent in tellurides. Secondary gold is present in form of native mustard gold that usually occur in Fe-hydroxides and accumulates on the decomposed primary Au-bearing tellurides such as calaverite, krennerite, and sylvanite. K–Ar dating on vein adularia yielded age of mineralization 7.1–6.9 Ma. Mineralization of the deposit is divided into barren massive quartz (stage I), Au–Ag–Te mineralization occurring in quartz-adularia-clays banded ore (Stage II), intensive brecciation (Stage III), post-ore coarse amethyst (Stage IV), carbonate (Stage V), and supergene stages (Stage VI). In the supergene stage various secondary minerals, including rare bilibinskite, bogdanovite, bessmertnovite metallic alloys, secondary gold, and various oxides, formed under intensely oxidized conditions. Despite heavy oxidation of the ores in the deposit, Te and S fugacities are estimated as Stage II tellurides precipitated at the log f Te2 values −9 and at log fS2 −13 based on the chemical compositions of hypogene tellurides and sphalerite. Homogenization temperature of fluid inclusions in quartz broadly ranges from 200 to 300°C. Ore texture, fluid inclusions, gangue, and vein mineral assemblages indicate that the Aginskoe deposit is a low-sulfidation (quartz–adularia–sericite) vein system.

The crystal structure of a natural krennerite (Au 3 AgTe 8 ) from Cripple Creek, Colorado, USA has been refined in space group Pma 2 using 3,151 observed unique (acentric) reflections. The final R value for observed reflections was 0.022. Unit cell parameters are a 16.590(3) A, b 8.867(2) A, c 4.4886(8) A, V 660.29(13) A 3 , and Z = 2. The precision of the atom position parameters is improved by up to a factor of ten over previous studies. The three Au–Ag sites in the structure are ordered, with Ag = 43% occupancy at the Au1 (2 a ) position (point symmetry 2) and 59% at the Au2 (2 c ) position (point symmetry m ); the Au3 (4 d ) position (point symmetry 1) is 100% Au. The observed ordering in the structure appears to be due to avoidance of Ag–Te–Ag bonding. Ordering of Au and Ag in the structure may thus limit the composition range to being between those of calaverite and sylvanite. Detailed petrographic study of the sample in thin section, accompanied by electron microprobe data, demonstrates the paragenesis of the ore that provided the crystal for refinement. The petrographic study provides evidence for sylvanite exsolution from krennerite in natural systems, consistent with the narrow compositional range inferred from the crystallographic study.

The Sandaowanzi gold telluride deposit is a new discovery with dominance in gold tellurides in Northeastern China. The deposit is hosted in quartz veins intruding sub-alkaline volcanic rocks. There are two types of gold telluride ores in the Sandaowanzi ore deposit, i.e. the vein ores and the disseminated ores. Calaverite, krennerite, sylvanite, petzite, empressite, hessite and stuetzite are the dominant Au–Ag bearing minerals either in vein ores or in disseminated ores. Minor amount of other tellurides, e.g. coloradoite altaite and sulfides, e.g. pyrite, sphalerite, galena, chalcopyrite and chalcocite mostly occur in the disseminated ores. The gold-bearing quartz veins crosscut volcanic host rocks, which are dated at 135.3–124.7 Ma by LA-ICP-MS U–Pb zircon method. The latter unconformably overly a monzogranite dated as 181.6 Ma. Diabase dikes, dated at 116.6 Ma, intrude the gold-bearing quartz veins. The age data thereby bracket the timing of gold mineralization between 125.3 and 116.6 Ma. These geochronologic data are consistent with field relations. Regional comparison reveals that the widespread volcanism in the Great Xing’an range is a product of the subduction of the Izanagi plate beneath the Eurasian plate. Gold telluride mineralization was contemporaneous with regional extension and magmatism as the subducting Izanagi plate rolled back.

Gold telluride ores, treated commercially in various regions in the world, most notably Kalgoorlie, Western Australia; Vatukoula, Fiji; Cripple Creek, Colorado, and Kirkland Lake, Ontario, exhibit slow leaching kinetics. There are many telluride mineral species and the most common gold bearing varieties include calaverite, krennerite, sylvanite and petzite. This chapter presents information on the composition and properties of gold telluride, the assay method, the processing methods and the latest developments. Roasting followed by cyanidation proved to be the preferred method to extract gold from telluride ores. Ultrafine milling of a flotation concentrate followed by cyanidation replaced roasting because of environmental issues. The first application of this approach, at KCGM (Kalgoorlie Consolidated Gold Mines), presented significant challenges in terms of high consumption of cyanide and losses of gold in leach residues. These issues were overcome by conducting cyanidation with a high concentration of lime and the addition of lead nitrate. The mechanisms involved in the dissolution of calaverite were identified by determination of the reaction products at the surface of leached grains.

The Panormos Bay Au-Ag-Te vein system, Tinos Island, Greece, which is hosted in Mesozoic marbles, comprises 30 subparallel, steeply dipping quartz veins that extend for at least 500 m. In places, gold telluride mineralization occurs in hydraulic breccias and alteration halos, which are the products of CO 2 effervescence of the ore fluid and wall-rock interaction, respectively. Seventy ore and gangue minerals have been identified. Zones of chlorite, talc, and muscovite-albite-tourmaline alteration, up to 50 cm wide, are associated with precious metal-bearing milky and clear quartz veins. The Au-Ag-Te mineralization is developed in stage V of eight hydrothermal stages. Stage V consists of three substages (early, middle, and late) that are characterized by Ag-, Cu-, and Au-bearing tellurides, respectively. Hessite, sylvanite, altaite, native tellurium, stutzite, cuprian cervelleite, and an unnamed Cu-bearing precious metal sulfotelluride [(Ag,Au,Cu) 9 Te 2 S 3 ] characterize the early substage, whereas melonite, rickardite, vulcanite, weissite, and native tellurium are present in the middle substage. The late substage contains rickardite, kostovite, krennerite, petzite, and calaverite. Unexploited Au-Ag-Te mineralization at Panormos Bay is though to be genetically related to a fluorine- and boron-bearing per-aluminous leucogranite (Tinos leucogranite). A combination of fluid inclusion microthermometry and sylvanite geothermometry suggests that the hydrothermal mineralization was deposited under hydrostatic pressures at a minimum depth of 1 km from moderate-temperature (155°–320°C), low- to moderate-salinity (0.2–13.2 wt % NaCl equiv), effervescing, CO 2 -bearing fluids that contained appreciable amounts of CaCl 2 and MgCl 2 . Calculated isotope compositions of δ 18 O = −3.3 to +5.1 per mil and δD of −73 to −62 per mil for waters in equilibrium with muscovite, quartz, and talc are consistent with the ore fluids being derived from the Tinos leucogranite (δ 18 O = +4.2‰ and δD = −71‰) and their subsequent mixing with a more dilute, low-temperature Miocenic meteoric hydrothermal fluid. Calculated δ 13 C fluid (−2.0 to −0.3‰) and δ 34 S H 2 S (−10.5 to +0.8‰) compositions of the ore fluids indicate an igneous source of carbon and sulfur, which were highly exchanged with a metasedimentary source. Physicochemical conditions of the ore fluids were T = 300° to 200°C, pH = 4.6 to 6.5, f S 2 = 10 −10.9 to 10 −15 , f O 2 = 10 −31.5 to 10 −41 , f Te 2 = 10 −7.7 to 10 −10.7 , f CO 2 = 10 −0.2 to 10 −0.8 , and f H 2 S = 10 −1.7 to 10 −1.8 .

Mina Capillitas is an epithermal-type deposit located in Catamarca province of NW Argentina. Six separate stages of mineralization were identified in this complex Cu-Au-S-As-Sb-Pb-Zn association; the native elements (Au and Te) and Te minerals are concentrated in the fourth stage. Gold occurs as small grains with an average fineness of 920, hosted mainly by quartz and coexists with hübnerite and Bi minerals. Tellurium occurs locally in grains up to 10 μm in diameter, and is associated with the Te-bearing minerals of Au, Ag, Bi, Cu, and Ni. These Te minerals include krennerite, calaverite, sylvanite, petzite, hessite, stützite, goldfieldite, melonite, tetradymite, and possibly volynskite. The grains are generally arranged in larger polycrystalline aggregates. These minerals occur in quartz, generally accompanied by hübnerite, pyrite, chalcopyrite, and Bi- and Sn-bearing minerals. The mineralizing fluids cooled gradually with the typical temperatures ranges characteristic of epithermal systems. Based on the preponderance of the different gangue minerals, we suggest that the pH of the environment became progressively more basic after the third stage of mineralization. This mineral assemblage together with the fluid inclusion homogenization temperature data indicate that the log f S2 values declined as the fluids deposited the Te-bearing minerals. The absence of tellurium phases in the first three stages suggests that either the source of the tellurium had not yet been tapped or that the log f Te2 lay below -10 to -17, the minimum activity for the Te phases present in stage IV to form. Fil: Marquez Zavalia, Maria Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina Fil: Craig, James R.. University Of Waterloo; Canadá

¶The epithermal, low sulfidation Emperor gold telluride deposit in Fiji, hosted by Late Miocene-Early Pliocene shoshonitic rocks, is spatially related to a low-grade porphyry Cu system on the western flank of the Tavua Caldera. Gold is largely in the form of “invisible” gold in arsenian pyrite but 10 to 50% of gold is in the form of precious metal tellurides. Gold mineralization occurs in steeply dipping dikes and faults, flat-dipping structures (

Gold is found in three different forms in the Emperor gold deposit: as "invisible" or submicrometer-size inclusions of gold in arsenian pyrite, as visible native gold and/or electrum, and as tellurides (calaverite, krennerite, sylvanite, and petzite). Similarly, Te occurs as invisible tellurium or submicrometer-size inclusions of tellurium in arsenian pyrite, as visible native tellurium, and as tellurides. Scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and secondary ion mass spectroscopy (SIMS) show that pyrite from Emperor is among the most Au- (up to 11,057 ppm Au), Te- (up to 5,796 ppm Te), and As-rich (up to 16.60 wt % As) yet reported from any mineral deposit type. Arsenian pyrite manifests itself as uniformly distributed grains, as As-rich rims on preexisting grains, or as As-rich cores. The estimated proportion of Au as invisible gold at Emperor ranges from 47 to 92 percent, with the remainder of Au occurring predominantly as gold-bearing tellurides. Native gold constitutes

The gold balance in an ore deposit where the ore is treated by cyanide is the sum of the ‘visible gold’ that is amenable to cyanidation and ‘visible gold’ and the ‘invisible gold’, which are not amenable to cyanidation. Petrographic analyses, electron and ion microprobe as well as scanning electron microscope studies of ore from the Golden Sunlight deposit, Montana, suggest that periods of relatively poor gold recoveries are primarily due to the presence of inclusions

We have measured the amounts of radiogenic 128 Xe and 130 Xe in two, old telluride minerals-krennerite (AuTe 2 ) from Western Australia and altaite (PbTe) from Quebec. We calculated values of (4.2±0.8) × 10 −4 and (4.4±0.8) × 10 −4 for the ratio of the total ββ-decay half-lives, 130 T 1 2 / 128 T 1 2 , from the amounts of radiogenic 130 Xe and 128 Xe in the krennerite and the altaite, respectively. These values are in good agreement with the ratio of half-lives calculated by the quasi-particle random phase approximation for 2 v ββ-decay.

Gold telluride ores, treated commercially in various regions in the world, most notably Kalgoorlie, Western Australia; Vatukoula, Fiji; Cripple Creek, Colorado, and Kirkland Lake, Ontario, exhibit slow leaching kinetics. There are many telluride mineral species and the most common gold bearing varieties include calaverite, krennerite, sylvanite and petzite. This chapter presents information on the composition and properties of gold telluride, the assay method, the processing methods and the latest developments. Roasting followed by cyanidation proved to be the preferred method to extract gold from telluride ores. Ultrafine milling of a flotation concentrate followed by cyanidation replaced roasting because of environmental issues. The first application of this approach, at KCGM (Kalgoorlie Consolidated Gold Mines), presented significant challenges in terms of high consumption of cyanide and losses of gold in leach residues. These issues were overcome by conducting cyanidation with a high concentration of lime and the addition of lead nitrate. The mechanisms involved in the dissolution of calaverite were identified by determination of the reaction products at the surface of leached grains.

The structure of krennerite (Au0.8Ag0.2Te2) as determined using X-ray diffraction, is confirmed by means of electron diffraction and high resolution electron microscopy. The structure can be considered as a twin interface modulated long period superstructure of calaverite. The images suggest that gold and silver are ordered, silver being preferentially located along the twin interface. Planar defects associated with variable width of the twin lamellae are discussed in detail and a structural model can be deduced from the high resolution observations.

Some minerals of the Au-Ag-Te system, krennerite, petzite and hessite, have been reported from the Date mine, southwestern Hokkaido by Watanabe and Yamaguchi (1942a, b) and Ishibashi (1960). We have re-examined the (Au, Ag) Te2 type minerals from the mine by the X-ray powder diffraction and EPMA methods. As the results, calaverite was newly recognized but krennerite, reported bythem, was not found in this sample. And, cassiterite and pyrite associated with calaverite were confirmed by the X-ray powder diffraction, EPMA methods and optical observations. This mineral paragenesis is very rare (e. g., Kelly and Goddart, 1969). Based on the experimental results (Nakata et al., 1980) and the mode of occurrence (Watanabe and Yamaguchi, 1942a, b), on the other hand, calaverite is considered to have been formed under alkaline conditions with the variations of the formation temperature.

Experimental investigations of subsolidus phase relations in the ternary system gold-silver-tellurium are discussed in the light of their significance for interpretation of the mineralogy and conditions of formation of telluride deposits, particularly those of Kalgoorlie, Western Australia, and Vatukoula, Fiji. Calaverite is the most abundant telluride mineral at Kalgoorlie; krennerite, indicated by the experimental results to be the low-temperature, low-pressure polymorph of AuTe 2 , is subordinate, suggesting somewhat higher temperatures and pressures than those obtaining during formation of the Vatukoula deposits, in which krennerite is relatively abundant but calaverite has not been reported.

This mineral was found upon several specimens of argentite from Chañarcillo which were acquired for the British Museum in 1886.The specimens consist of argentite in large drusy octahedra implanted on quartz or calcite, and associated with proustite and a little asbestos.The proustite is mostly in the form of small brilliant prisms with sealenohedral terminations {201̅}, capped by the rhombohedron {110}, which are grouped upon the argentite. But dispersed on the argentite, together with these crystals of proustite, are a number of fine glittering scales, which present at first sight precisely the appearance of the pyrrhosiderite or göthite of Siegen, having the same bronzy red colour, and a lustre resembling that of earthy haematite when seen on the matrix, that is to say partly by reflected and partly by transmitted light. Under the microscope the scales are easily distinguished from göthite ; they are without striations, remain dark when rotated between crossed nicols, and appear of a nearly blood-red colour by transmitted light ; whereas scales of göthito are striated in one direction, and exhibit marked differences of absorption when rotated above the polariser.

Some interest attaches to crystals of krennerite, since this mineral has apparently the same composition as calaverite, the crystalline development of which presents such peculiar features. After completing the study of crystals of the latter substance, the author naturally turned his attention to krennerite to ascertain whether any similar peculiarities were noticeable, but nothing abnormal could be detected.Good crystals of krennerite are rare. The Mineral Collection of the British Museum has however a specimen from Nagyág, on which are dotted numerous small crystals possessing a large number of brilliant faces. This specimen was examined by Prof. H. A. Miers rather more than twelve years ago, and the measurements of one good crystal are recorded in this Magazine.

By X-ray and microscopic techniques, equilibrium relations were determined in the presence of vapor at 290 degrees , 335 degrees , and 355 degrees C, and changes in assemblages studied from about 50 degrees to 800 degrees C. A new ternary eutectic at about 304 degrees C has the approximate composition 50 percent Au, 15 percent Ag, 35 percent Te (wt. percent). Krennerite, a single mineral entity with the approximate formula Au 4 AgTe 10 , is stable up to its incongruent melting at about 382 degrees C. Sylvanite melts incongruently at about 354 degrees C. Hessite and petzite each have three polymorphs.

The compounds (Au,Ag)Te2 exhibit remarkable modulated structures of different types, depending on the exact ratio of the concentrations of gold and silver. Calaverite (AuTe2) has a deformation modulated structure, which in the case of non-stoichiometric Sylvanite (Au1+x Ag1−x Te4) is moreover coupled with a long period anti-phase boundary superstructure. Finally in Krennerite (Au0.8 Ag0.2 Te2) the structure is modulated by poly-synthetic twinning. In all cases the modulation planes are approximately along the (101) planes of calaverite. The modulation periods are also approximately of the same magnitude in the different cases.

Structural investigations of several minerals belonging to the calaverite group with composition Au1–xAgxTe2 (x = 0.00, 0.02, 0.05, 0.09, 0.19, and 0.33) indicate that Ag is randomly distributed on the Au sites. This suppresses the valence fluctuation of Au and, therefore, the structure modulations. The results are compared with the previously published incommensurately modulated structure of calaverite, Au0.9Ag0.1Te2, which is characterized by valence fluctuations of Au reinforced by an ordered distribution of Ag. The (3+1)-dimensional calaverite structure type is able to reproduce both (3+1)D and 3D related structures with the general formula AB2 (A = Au, Ag, Cu, Nb, Ta; B = Te). Keywords: Calaverite, modulated structure, valence fluctuations, krennerite

Tellurium is the only element which forms a variety of minerals with gold as principal component (e.g. calaverite AuTe2, krennerite (AuAg)Te2, petzite Ag3AuTe2 and sylvanite AgAuTe4). These minerals have been known for a long time and are of economic value in many deposits such as Cripple Creek (Colorado), Emperor (Fiji), and Sacarimb (Romania), and “orogenic” gold deposits, including the giant Golden Mile deposit (Western Australia). However, knowledge the formation of these minerals is still incomplete.

MONTBRAYITE, a rare mineral of idealized formula Au2Te3, is closely related to a group of gold-silver ditellurides comprising calaverite, (Au,Ag)Te2, krennerite, (Au,Ag)Te2 and sylvanite, AuAgTe4. The structure of the three ditellurides consists of rows of atoms along which gold and silver atoms are separated by pairs of tellurium atoms. It can also be described as a derivation, by a small distortion, of a simple cubic arrangement with an atom of gold, silver or tellurium at each lattice point3. The similarities between montbrayite and the ditellurides have been used to postulate a model of its structure.