Mineralogy Of Gold Research Articles

Mineralogy of Gold, Tellurides and Sulfides from Lianzigou Gold Deposits in the Xiaoqinling Region, Central China: Implications for Ore-Forming Conditions and Processes

The Lianzigou deposit, which has an Au–Te paragenetic association, is hosted in plagioclase gneiss of the Qincanggou Formation in the Taihua Group in the Xiaoqinling region, central China. This quartz vein-type Au deposit comprises native Au and a variety of tellurides. The latter include calaverite (AuTe2), krennerite (Au3AgTe8), petzite (Au3AgTe2), hessite (Ag2Te), melonite (NiTe2), and altaite (PbTe). Four stages have been recognized in this deposit: stage I consists of K-feldspar and quartz; stage II is of milky quartz veins accompanied by coarse-grained disseminated and lumps of pyrite with weak Au mineralization; stage III is composed mainly of Au, tellurides, and sulfides; and stage IV is characterized by abundant carbonate and quartz. Based on mineral assemblage and thermodynamic data, we estimated the physicochemical conditions of the main metallogenic stages. Based on thermodynamic modelling, the physicochemical conditions of Au–Ag–Te mineral associations were estimated. The Au–Ag–Te minerals from stage III formed mainly under conditions of logƒO2 = −43.15 to −33.31, logƒH2S = ~−9.29, pH < 7, logfTe2 = −10.6 to −9.8 and logαAu+/αAg+ = −7.2 to −6.5. In contrast, the physicochemical conditions of stage II were higher, specifically pH (8.3–8.5) and logƒO2 (−34.90−31.96). In the ore-forming fluids of the Lianzigou deposit, the dominant Au species was Au(HS)2− while the dominant Te species were HTe−(aq) and Te22−(aq). Moreover, the Au–Ag–Te metal associations in the Lianzigou Au deposit were derived from mantle materials related to lithospheric thinning of the eastern North China craton in the Early Cretaceous under an extensional tectonic system.

Pavel Ivanovich Kutyukhin (1899–1962) and former kutyukhinite (now kumtyubeite)

Pavel Ivanovich Kutyukhin, a prominent specialist in geology and mineralogy of gold, rare metal and tungsten deposits of the Urals. For about 15 years he headed the departments of exploration and geology of ore deposits of the Geological Exploration Faculty at the Sverdlovsk Mining Institute. In honor of Pavel Ivanovich, a new mineral was named – kutyukhinite, calcium fluorosilicate, which was discovered by B. V. Chesnokov in the burnt dumps of the Chelyabinsk coal basin. The International Mineralogical Association did not approve it as a new mineral species, and recently a natural analogue, kumtyubeite, was found in the North Caucasus.

Tolstykhite, Au3S4Te6, a new mineral from Maletoyvayam deposit, Kamchatka peninsula, Russia

AbstractTolstykhite, ideally Au3S4Te6, is a new mineral from the Gaching ore occurrence of the Maletoyvayam deposit, Kamchatka peninsula, Russia. It occurs as individual anhedral grains up to 0.05 mm or as intergrowths with native Se, native Te and tripuhyite. Other associated minerals include calaverite, fischesserite, Cu–Te-rich ‘fahlores' [stibiogoldfieldite, ‘arsenogoldfieldite', tennantite-(Cu), tetrahedrite-(Zn)], galena, gold, maletoyvayamite, minerals of famatinite–luzonite series, pyrite, baryte, ilmenite, magnetite, quartz and V-bearing rutile. Tolstykhite is bluish-grey, opaque with metallic lustre and grey streak. It is brittle and has an uneven fracture. Cleavage is good on {010} and {001}. Dcalc = 7.347 g/cm3. In reflected light, tolstykhite is grey with a bluish shade. No bireflectance, pleochroism and internal reflections are observed. In crossed polars, it is weakly anisotropic with bluish to brownish rotation tints. The reflectance values for wavelengths recommended by the Commission on Ore Mineralogy of the International Mineralogical Association are (Rmin/Rmax, %): 32.6/34.3 (470 nm), 32.4/34.1 (546 nm), 32.6/34.5 (589 nm) and 33.0/35.0 (650 nm). The Raman spectrum of tolstykhite contains the main bands at 297, 203, 181, 151 and 127 cm–1. The empirical formula calculated on the basis of 13 atoms per formula unit is (Au2.98Ag0.01)Σ2.99(S3.59Se0.41)Σ4.00Te6.01. Tolstykhite is triclinic, space group P$\bar{1}$, a = 8.977(5), b = 9.023(2), c = 9.342(6) Å, α = 94.03(3), β = 110.03(3), γ = 104.27(4)°, V = 679.0(3) Å3 and Z = 2. The strongest lines of the powder X-ray diffraction (XRD) pattern [d, Å (I, %) (hkl)] are: 8.59 (18) (010); 2.90 (100) (0$\bar{1}$3); 2.23 (13) (13$\bar{3}$); 1.89 (21) (13$\bar{4}$). Tolstykhite is the S-analogue of maletoyvayamite, Au3Se4Te6. The structural identity between them is confirmed by powder XRD and Raman spectroscopy. The mineral honours Russian mineralogist Dr. Nadezhda Dmitrievna Tolstykh for her contributions to the mineralogy of gold and platinum-group elements and the study of ore deposits.

Characterization of Gold Mineralization in the Northern Cariboo Gold District, British Columbia, Canada, Through Integration of Compositional Studies of Lode and Detrital Gold with Historical Placer Production: A Template for Evaluation of Orogenic Gold Districts

There is a strong association between regions containing orogenic gold mineralization and exploitation of placer gold, although, in many cases, the nature of the source mineralization for these placer deposits remains unclear. This study describes a novel approach to evaluating the economic potential of in situ orogenic gold mineralization through characterization of both lode and placer gold mineralogy, followed by synthesis of this information with records of both mineral occurrences and historical placer mining. The northern Cariboo Gold District in east-central British Columbia, Canada, was chosen as a location for the study because of the gold endowment of the area (1.2 million ounces [Moz] of lode gold and between 0.5 and 3 Moz. of placer gold) and the information available from both placer and lode gold mining. Compositional analysis of 533 gold grains from 21 lode localities and 1,914 gold grains from 30 placer localities from throughout the Cariboo Gold District has identified four main compositional types in terms of their alloy compositions and associated suite of mineral inclusions revealed in polished section. A distinctive low (4–7%)-Ag gold that exhibits a strong Bi association in the mineral inclusion suite is geographically limited to the Wells area, where it is recorded in both lode mineralization and its placer expression. Regionally pervasive mineralization yields gold of binary Au-Ag alloy and a simple inclusion suite of sulfides and sulfarsenides. Gold in most large placers in trunk drainages was derived from multiple (mostly small) occurrences of this type. The nature of compositional variation between gold grains liberated from hypogene ore has informed the history of episodic mineralization and suggests multiple stages of gold emplacement at some localities, while others are dominated by gold deposited in a single stage. The new information from gold grain analysis has been considered in the context of other information. Classification of a placer as either allocthonous or autocthonous both informs interpretation of compositional characteristics of the detrital gold grains and provides information on distance to the hypogene source. Mineral inclusion assemblages observed in sample populations of placer gold grains have been correlated with reports of hypogene vein mineralogy described in mineral occurrence records to clarify the geographical extent of specific mineralization types. The compositional range of alloys of different gold types has been compared to historical records of gold production and gold fineness (Au-Ag ratio) to reconstruct the size and distribution of hypogene sources prior to erosion. Synthesis of gold compositional studies with other publicly accessible data sets provides a new generic approach capable of evaluating the most attractive targets for future exploration and highlighting compositional signatures of placer gold which relate to undiscovered in situ sources.

Old landscapes, pre-weathered materials, and pedogenesis in tropical Africa: How can the time factor of soil formation be assessed in these regions?

The present paper is an overview of tropical West Africa soils with the aim to compile soil characteristics and identify research gaps in respect to rates of soil forming processes. Compilation of morphological, mineralogical and chemical data on soil development has distinguished several types of soils. The major soils identified and described include ferrallitic soils, ferruginous tropical soils, vertisols, semi-arid tropical soils, and hydromorphic soils. Their formation and their evolution depend on climate and paleoclimate actions, parent materials, vegetation, and geomorphology. Most of these soils have been mapped using FAO, CPS classification, and Worldwide Reference Base (WRB).Some aspects of the pedogenesis process are also discussed. Three new methods of investigation used by researchers: Potassium–argon, gold mineralogy, and cosmogenic beryllium-10 allow dating chemical and weathering processes and also led to a quantification of geochemical and mechanical processes in this area. The modern climate has an impact on soils. All these types of soils are experiencing secondary pedogenic processes such as rejuvenation, and especially reworking to some extent by water or wind erosion, giving rise to younger soils. Rapid disturbance through reworking leads to induration and armouring.Soil dating data in this area are very scarce. Some approaches (e.g. mass balance, relative chronology, chronostratigraphic, archaeological, luminescence, paleobiological, radiocarbon, OSL, and termite activity) have been implemented to assess the time factors of soil formation. Finally, this work highlights some gaps about soil research, particularly the need to define soil parameters which can be related to soil age.

Influence of gold mineralogy on its flotation recovery in a porphyry copper–gold ore

The present study investigates the implications of gold mineralogy on its flotation recovery, in a typical porphyry copper–gold ore (1.7g/t Au feed grade). Also, flotation strategies to optimise gold recovery and grade without compromising copper recovery and grade were examined. The approach used in this study involves a combination of different mineralogical techniques such as quantitative X-ray diffraction (QXRD) and scanning electron microscopy (QEMSCAN). Based on the mineralogical information obtained, different collector regimes involving sodium iso-butyl xanthate (SIBX), N-butoxycarbonyl-n butyl thionocarbamate (XD5002), mercaptobenzothiazole (MBT) and dithiophosphate (DTP) at different grind sizes (p80, i.e. a nominal product size of 80wt% passing (a) 70µm and (b) 38µm screen) were tested to examine the flotation behaviour of gold in relation to copper recovery. Chalcopyrite and covellite are the principal copper mineral phases in the ore, with pyrite as the main sulphide gangue mineral. Quartz, Fe oxide and carbonates were identified as the main non-sulfide gangue minerals. The identified gold particles occurred as either liberated particles (∼10–22µm) or fine inclusions (∼1–3µm) in pyrite, biotite and sphalerite. Two-stage flotation (copper and pyrite rougher stages) at a p80 of 70µm indicated that high gold (95.2%) and copper (97.4%) recovery can be achieved, but the levels of pyrite in the concentrate are also very high (49.1%). At finer grind (p80=38µm) and without pyrite flotation stage, gold recovery decreased from 95.2% to 73%, but at an improved grade (5.3g/t) compared to 3.5g/t in the baseline. This approach improved gold grade significantly due to a drastic reduction in pyrite recovery. The flotation study indicates that the collector regime, SIBX/XD5002 (at 38µm feed size) gives the maximum gold recovery and grade while rejecting significant pyrite without compromising copper recovery and grade. Further studies are warranted to identify means of recovering Au from the copper flotation tail.

Modern mineralogy of gold: overview and new data

We suppose that it should be useful for archaeologists to have an overview on gold mineralogy, because 1) in ancient times, part of the golden objects were made directly from natural golden nuggets; 2) most of the Au in ores exists as its own minerals. The major part of the Au in the planets and meteorites of our Solar system is found in high temperature solid solutions: metallic Fe-Ni and monosulfides Fe-Ni and Fe-Cu. Au leaves them under fluid or some other reworking. As a result, Au minerals are formed. They are mainly developed in hydrothermal deposits of the upper part of Earth’s continental crust. Au is the noblest chemical element. Thus, the most part of Au in deposits appears as native gold: Au-Ag, Au-Ag-Hg, Au-Cu, Au-Pd, and Au-Pt system minerals. The most important feature of native gold is its fineness, i.e. the Au content in the mineral species, expressed in ‰. Chalcogenides of Au – sulfides and selenides, and, similar to them, tellurides, plumbotellurides, antimonides, bismuthides – are not so widespread. Data on the 44 Au mineral species known today are provided in this overview. The first quantitative estimations of natural native gold nano-dimensional crystallites of several mesothermal deposits are enclosed.

Use of ferricyanide for gold and silver cyanidation

Low gold and silver leaching kinetics has been commonly observed in traditional gold-silver cyanidation process, especially in heap leaching and in situ leaching operations. The different mineralogy of gold and silver in the ores is suspected to be the main reason, e.g., the occurrence of low solubility acanthite (Ag 2S) typically results in low overall silver extraction. Due to the low solubility of oxygen in cyanide solution, the reactivity and availability of oxidant is believed to be the critical limitation for gold and silver dissolution. The use of ferricyanide as the auxiliary oxidant for gold and silver cyanidation has been examined. The rotating disc test results prove the assistant effect of ferricyanide on increasing the dissolution rate of gold and silver. The potential use of ferricyanide in gold/silver cyanidation process is proposed based on the leaching results of actual ores.

The novel application of ferricyanide as an oxidant in the cyanidation of gold and silver

Low gold and silver extractions have often been observed in the traditional gold–silver cyanidation process. The reactivity and availability of oxidant is a potential limitation for gold and silver dissolution in cyanide solution, especially in heap leaching operations. The oxidant reactivity seems to have more of an effect on silver extraction due to the different mineralogy of gold and silver in the ores. For example, the occurrence of silver sulfides such as acanthite (Ag 2S) typically results in low overall silver extraction which may be due to slow kinetics of oxygen reduction on the acanthite mineral. The leaching of metallic gold and silver sulfide in the novel ferricyanide–cyanide leaching medium was investigated. The potential application of ferricyanide as a supplemental oxidant in gold–silver cyanidation process was proposed and the possible reagent regeneration methods were discussed.

Leaching of silver sulfide with ferricyanide–cyanide solution

Significantly lower silver extraction than gold has been commonly observed in traditional gold-silver cyanidation process, especially in heap leaching operations. The different mineralogy of gold and silver in the ores is suspected to be the main reason, e.g., the occurrence of low solubility acanthite (Ag 2S) typically results in low overall silver extraction. Leaching of silver sulfide with ferricyanide–cyanide has been investigated with the purpose of increasing the silver extraction. Ferricyanide proved to be an effective oxidant to dissolve silver sulfide in cyanide solution. The main reaction involved under the experimental leaching conditions was determined, indicating the formation of thiocyanate as the sulphur reaction product. The dissolution rate of Ag 2S in ferricyanide–cyanide leaching system (0.5 g/L Fe as ferricyanide) in a rotating disc experiment gives the value of 21 μmol m − 2 s − 1 (0.78 μm/h), much higher than that in aerated cyanide solution (13 μmol m − 2 s − 1 , or 0.38 μm/h). The effect of pH, temperature, ferricyanide and cyanide concentration, and rotating speed on the dissolution rate of Ag 2S were examined. A diffusion-controlled process was confirmed with an activation energy of 6.7 kJ/mol. Study on the leaching kinetics of several mixed sulfide minerals in ferricyanide–cyanide solution shows that the presence of non-silver sulfide minerals may decrease silver extraction from silver sulfide to different extents. A significant decrease in silver extraction is observed in the presence of chalcopyrite (CuFeS 2) and pyrrhotite (Fe 7S 8). It is believed that chalcopyrite and pyrrhotite consume ferricyanide, making it unavailable for silver sulfide leaching.

Gold-bearing arsenopyrite and pyrite in refractory ores: analytical refinements and new understanding of gold mineralogy

Abstract A multidisciplinary approach has been used to study Au occurrences within pyrite and arsenopyrite in four refractory Au ores from Colombia, France (Le Châtelet and Villeranges) and Portugal (Neves Norte). The Au was characterized by optical and scanning electron microscopy and analysed using electron and ion microprobes to determine Au distribution, with particular attention to spectral interferences in electron and ion microprobes, background measurements in electron probes, and quantitative analysis using external standardization in ion probes. The ionic emission rate is proven to be dependent on the Au status; combined Au has a greater ion emission than metallic Au. Invisible Au occurrences are closely linked to As distribution. Gold bonding in arsenopyrite, examined by transmission electron microscopy, is shown to be dispersed within the FeAsS crystal structure. Typical growth patterns and As-Au diffusion zoning in pyrite and arsenopyrite may account for the very irregular distribution of Au in these minerals.

An overview of the advantages and disadvantages of the determination of gold mineralogy by automated mineralogy

The gold mining industry is experiencing boom times with the gold price pushing towards record levels and interest in new projects picking up. It is, however, becoming increasingly important to fully understand the intricacies of each project as more complex ores are encountered and lower grade ores are processed. This overview aims to highlight the advantages and disadvantages of using automated mineralogical and associated techniques in gaining a greater understanding of gold ore behaviour. Recent developments in techniques, such as QEMSCAN and MLA, have made them more applicable to the analysis of traditionally difficult gold-bearing ores and more accessible to the industry. These techniques are continuously challenged by the need of the industry to gain representative results, but a good understanding of their limitations can allow complementary techniques to be employed, validating the results and providing a comprehensive picture of how the mineralogy of an ore can affect its metallurgy. The nature of the complementary techniques will be examined in relation to their association and use with automated mineralogical methods.

The process mineralogy of gold: The classification of ore types

The principal gold minerals that affect the processing of gold ores are native gold, electrum, Au-Ag tellurides, aurostibite, maldonite, and auricupride. In addition, submicroscopic (solid solution) gold, principally in arsenopyrite and pyrite, is also important. The main causes of refractory gold ores are submicroscopic gold, the Au-Ag tellurides, and very fine-grained gold (<10 µm) locked in sulfides. Other types of problem gold ores include copper-gold ores and preg-robbing carbonaceous ores.

Gold the Noble Mineral.: ExtraLapis English No. 5, R.B. Cook, E.R. Coogan, G. Neumeier and G.A. Staebler, editors. Lapis International LLC, P.O. Box 263, East Hampton, Connecticut, U.S.A., 2003, 112 p. US$24 (plus $2 for shipping to non-US addresses), soft cover (ISBN 3 921 656 23 0).

According to a summary statement on this issue’s back cover “Beginning with the basics of gold mineralogy and enrichment, our expert team of authors traces the history of gold and man from the Egyptians to the modern-day, technoprospectors. Along the way, they describe localities, share stories

R. Herrington, C. Stanley and R. Symes Gold. London (Natural History Museum), 1999, 64 pp. Price £7.95. ISBN 0-565-09141-7.

This latest slim book in this popular series (previous titles include ‘Crystals’, ‘Gemstones’, ‘Meteorites’, and ‘Volcanoes’) presents an attractive combination of colour photographs, maps and diagrams, with a clear, concise yet authoritative text. The mineralogy of gold is summarized, with a list of its alloys, tellurides, selenides and sulphides. The authors then embark on descriptions of how and where gold is found, enlivened by a colourful cross-section through the Earth’s crust, though the reader is warned that no single part …

Process design for gold ores: A diagnostic approach

Much careful work and thought are needed from the time an ore is discovered until a marketable product is produced. Most often, incomplete or imprecise information on the deposit must be used to decide to continue or not with the development and implementation of a project. This paper presents a diagnostic methodology to deal with gold projects at the preliminary stages. We have developed “IntelliGold”—an expert system for gold process design. A knowledge base on gold mineralogy and processing is used to provide the user with feasibility information on a given gold ore. Decision-makers can have a preliminary, yet reliable view of the mineral processing project, based on lab results supported by mineralogical characteristics, operational issues and economic analysis.

Industrial experiences in the evaluation of various flotation reagent schemes for the recovery of gold

This paper is a summary of the author’s industrial experiences on the selection and optimization of flotation reagent schemes for the recovery of gold species. The trends given are a composite of data and experiences gained on 24 different gold ores from around the globe. The primary emphasis is on the benefits of matching the associated gold mineralogy to a reagent scheme most appropriate for that mineralogy. Two general categories are discussed: the flotation of free or native gold species and the flotation of gold associated with a variety of sulfide minerals. Important plant operating factors influencing each of these two categories are presented with supporting examples. Carefully matching reagent chemistry and appropriate operating conditions to any given gold-bearing ore will not only lower the total reagent cost but, more importantly, can lead to measurable increases in gold recovery.

Gold mineralogy and extraction

Several examples are examined in which Mossbauer spectroscopic analysis of gold mineral samples, treated concentrates and extracted species has provided information not obtainable by competing techniques. Descriptions are given of current work on bacterial oxidation of pyritic ores and on the adsorbed species from gold extracted from cyanide and chloride solutions onto activated carbon and polyurethane foams. The potential benefits for the gold mining industry from Mossbauer studies and some limitations on the use of the technique are also discussed.

Mineralogy of gold in the Elshitsa massive sulphide deposit, Sredna Gora zone, Bulgaria

The Elshitsa volcanic hosted massive sulphide deposit occurs in the central part of the Srena Gora metallogenic zone in Bulgaria. The gold-bearing massive sulphide mineralization is considered to be the product of an island arc volcano-plutonic process and hydrothermal activity that took place during the Late Cretaceous. In addition to the major gold-hosted opaque minerals such as pyrite, chalcopyrite, sphalerite and galena there are minor phases of tennantite, goldfieldite, Se-bearing aikinite, native silver and bornite in the massive sulphide lenses and stringer zones. Most of the sulphide minerals are Se-bearing. All of the six mineral assemblages that were deposited during the pyrite and copper-pyrite stages of mineralization are gold-bearing. The gold tenor as a rule is less than 1 g/t. Native gold and electrum occur as blebs or intergranular particles in the sulphide minerals. Gold in the early massive pyrite is of submicroscopic type ( 100 μm) in the late gold-sulphide assemblages. The electrum fineness in 41 individually studied grains varies between 780 and 992‰ with a mean of 895‰. Native silver was found in association with bornite. Cu, Te, Sb and Bi are the most common trace-elements in gold and electrum. The Cu-Zn-Pb association is most important as a Au-Ag-carrier. A model for gold behaviour during sulphide deformation is proposed involving coarsening of gold grain size from the earlier to the later sulphide mineral assemblages.

Supergene gold mineralogy at Ashanti, Ghana: Implications for the supergene behaviour of gold

AbstractAt the Ashanti concession, Ghana, gold-bearing quartz veins and disseminated sulphide lodes occur in narrow (1-3 m) shear zones with altered argillites and metatholeiite host rocks. The mineralisation is concealed by up to 10 m of kaolinite-mica forest ochrosol soils, beneath which is a saprolitic zone of leached rock extending down 60-70 m to the hypogene ore zone. In the unweathered hypogene orebody, gold occurs as free grains in quartz, as sub-microscopic inclusions in the disseminated arsenopyrite, as gold tellurides and as aurostibite. The gold is released from the hypogene orebody by physical dissaggregation and chemical dissolution, the latter involving hydroxyl, thiosulphate, cyanide, and fulvate complexing. Dissolution and reprecipitation of the gold appears to have taken place largely in situ with little evidence of supergene enrichment. Consequently, the gold mineralogy of the soils is complex with residual and secondary gold grains exhibiting widely different textural and compositional characteristics. Residually enriched grains display pitted, rounded surfaces and have silver-depleted rims, while supergene gold grains are compositionally homogenous and have unpitted surfaces. The supergene grains display platelet, dendritic, irregular and octahedral habit. A fine grained spongy form of gold has also been observed from weathered telluride-bearing quartz veins. Much of the secondary gold is intergrown with iron oxides and hydroxides. The gold mineralogy of the Ashanti soils appears to be controlled by physico-chemical processes active during the lateritic pedogenesis producing residual and supergene enrichment of gold.