representative gold collection from weathering crusts. The great attention was paid to the Vjatka-Kama Depression (the Western Urals) in the eastern part of the.
Aggregation of Nanogold Particles in Environment B. M. Osovetsky1 Abstract Nanogold is wide-spread metal formation in environment. For instance, a great number of nanogold particles are appeared in the weathering crust due to chemical decomposition of mineral-concentrators (pyrite, arsenopyrite, pyrrotite, magnetite, etc.). Usually nanogold is represented by isolated particles dispersed in minerals and sedimentary rocks. But in definite conditions gold nanoparticles are capable to combine each other with origin of simple or complicated aggregates. The mechanisms of their aggregation are connected with geochemical situation in environment. The leading role play special chemical compounds as concentrators of gold nanoparticles. Among them the most prominent are mercury, iron, chlorine, silicate and organic substances. Besides, superfluous surface energy of metal nanoparticles and their chemical activity are essentially promoted to aggregation. There are two main ways of their concentration that are adsorption on the surface of minerals (first of all placer gold grains) and gradual consolidation of separate gold nanoparticles due to the process of natural amalgamation. The aggregation of gold nanoparticles is natural mechanism of their concentration in sedimentary rocks that may be reproduced in nanotechnologies. KEY WORDS: nanogold particles, weathering crust, electron microscopy, microprobe analysis, aggregation, natural amalgamation.
INTRODUCTION At the last time nanogold became the rather popular object of investigation. The presence of nanogold particles is really established in many geological objects especially with “invisible” gold. The real natural “factory” of nanogold is the weathering crust above gold-sulfide-quartz deposits where its primary sources are mineralconcentrators such as As-pyrite, arsenopyrite, pyrrotite, chalcopyrite, magnetite, etc. (Schweigart 1965; Cook and Chryssoulis 1990). Nanogold may origin in the weathering crust of laterite profile too where spherical gold nanoparticles were found (Mann 1984). Under conditions of weathering agents influence ferriferous sulfides are transformed into ferriferous hydroxides with getting free of nanogold particles (Zhmodik et al. 2012). For instance, very small oval nanoparticles of gold were found on the grains of pyrite, galena and arsenopyrite with application of atom-field microscope (Palenik et al. 2004). Gold nanoparticles up to 10 nm in a form of distorted hexagon were discovered in Karlin deposit (Reich et al. 2005). The great achievement of high resolution electron microscopy was the investigation of biogenic nanogold. Their origin was connected with bacterial activity and it is arranged in some deposits of gold (Lengke and Southam 2006). Nanogold migrates in environment as component of colloidal or ionic solutions. During movement it is absorbed by different minerals including placer gold (Mikhlin et al. 2006). The main reasons of this phenomenon are very high specific surface energy of metal nanoparticles and unsaturated electric ties of placer gold surface due to defects of crystal lattice. As a result sub-surface zone of many placer gold grains has got numerous very fine hollows. Really the investigation of placer gold surface under electron microscope of high resolution is discovered a lot of morphological micro- and nanodefects such as cracks, furrows, pores, etc. (Osovetsky 2012). It is proved in experiments that nanogold is capable to fall into sediment from mineralized underground waters migrating in the weathering crust. For instance, in such experiments flat gold nanoparticles up to 6 nm in thickness and about 200 nm in diameter were given off from solution (Hough et al. 2008). The precipitation of nanogold from colloidal and other solutions happens on the geochemical barriers due to influence of ferriferous, chlorine, silicate and organic substances. Thus, nanogold was discovered in salt and iron deposits, black schist rocks, etc. Nevertheless many peculiarities of nanogold particles behavior in environment are not investigated yet. Theoretical analysis gives the opportunity to assume that the most probable result of nanogold migration in colloidal or ionic solutions is the process of dissipating in sediments. In favour of this point of view testifies very high chemical activity of nanomatter established in the experiments. The investigation of weathering crust minerals under high resolution electron microscope shows that nanogold particles are intensively absorbed by clay particles, hydroxides, sulfides, etc. As a result the environment near the deposits with “invisible” gold is filled in nanogold particles. But they are dispersed in primary minerals (first of all sulfides), secondary mineral products, sediments and solutions. Are there any natural ways to concentrate them, for example to combine into the bigger grains accessible to extraction by modern technologies? The answer to this question has got a great meaning with theoretical and practical points of view. The article is devoted to this problem. 1
Perm State National Research University. Bukirev Street 15, 614990, Perm, Russia. E-mail: opal@[psu.ru
OBJECTS, MATERIALS AND METHODS The objects of investigation were gold deposits and orebodies in different Russian regions (the Urals, European part of Russia, Siberia, Kuzbass, Yakutia, Altai) and abroad (Kanada, Kazakhstan). Among them the Urals placers were presented by many objects (Andreevskaya, Eleninskaya, Nazarovskaya, Kazanskaya, Kolchinskaya, Mikhailovskaya, Chernoborskaya, Shakhmatovskaya, Chernorechenskaya, Kytlym placers, etc.). Many of these placers were directly connected with source rocks that gave the opportunity to choose very representative gold collection from weathering crusts. The great attention was paid to the Vjatka-Kama Depression (the Western Urals) in the eastern part of the East-European Platform where concentrations of nanogold were discovered in Jurassic rocks. From Siberian placers the objects in valleys of the Viluy river, the Kitat river, the Tutujas river, the Sololi river, the Bodaibo river were investigated. The metal from the placers of the Yukon Territory (Canada) was extracted during the field expeditions of Perm University’s researchers in Canada (2006, 2007) and was used for description too. In addition some source rock deposits and orebodies of gold were investigated in the Urals (Svetlinskoe, Tykotlov) and in Kazakhstan (Vaigul). Thus in the article the gold placers are mainly represented as the objects of investigation. Their geological age changes from Cenozoic to Jurassic. The great part of placers is connected with rocks of gold-sulfide-quartz formation. Among source rocks are predominated deposits of hydrothermal origin and partly of Karlin type (Svetlinskoe in the Urals). The grains of gold for investigation were chosen from concentrates of spiral separator that was applied in the process of sample enrichment by gravitation method. The gravitational enrichment was produced very carefully in order to extract small particles of gold (up to 30 µm). Sometimes panning method was applied too. Under laboratory conditions gold particles were collected with help of special concentration methods (separation in heavy liquid, chemical treatment, etc.). A great number of gold particles were used for electron microscopy investigation. For instance, a number of gold grains that was researched only from the Urals placers predominated 1000 particles. The main results were received on the scanning electron microscope with cool emission JSM 7500F (“JEOL”). These are represented by electronic photos with magnification from 1,000 to 300,000. As a result it is possible to distinguish the details on the gold surface up to 10 nm in size. The standard regimes of investigation were acceleration voltage of 15 kv, emission current of 10 µA, work distance – 8 mm. The microprobe analysis was carried out in the scanning electron microscope JSM 6390LV (“JEOL”) with ED-spectrometer INCA x-act (“Oxford Instruments”). The operation conditions were an acceleration voltage of 20 kv and a current of 10–12 µA, work distance – 9 mm. The collection of etalons (metals, oxides, silicates, etc.) was prepared by JEOL. The different particles of gold were chosen under binocular microscope: big (more than 1 mm) and very small (up to 50 micron or less), flat and bulky, homogeneous and complex structure. Under the electron microscope different nanoparticles of gold were diagnosed on the surface and inside of placer gold grains. All electronic photos and microprobe analyses were made by the author. RESULTS AND DISCUSSION First of all during scanning of placer gold surface a lot of isolated nanogold particles were observed under electron microscope of high resolution. This fact may be considered as the confirmation of their capacity to dissipate in environment. The usual places of their attachment to the surface are the slopes and walls of microcavities (Fig. 1). In some places of surface gold nanoparticles are placed not far from each other but in any case they don’t come into contact with each other. Principally another picture is presented by nanogold aggregates that were discovered on the surface of placer metal too. Such aggregates are composed by a lot of gold nanoparticles in very complex and variable combinations. They are also concentrated near different surface defects such as micro- and nanocracks, hollows, breaks, pores, etc. The morphological and other peculiarities of nanogold aggregates may be connected with the process of nanogold concentration. That is why they were investigated in details. The types of nanogold aggregates on the surface of placer gold Different types of nanogold aggregates are discovered on the surface of gold particles in placer deposits. They are distinguished on position, morphology, size, structure, chemical composition, etc. The aggregates of nanoparticles on the gold grains are mainly situated in deepened parts of their surface (in microfurrows, microcracks, microcavities, etc.) (Fig. 2). The nanogold aggregates may be subdivided into several types on their morphology. There are such varieties as isometric, pole-alike, chain-alike, honeycomb-alike, starry, cluster-alike, etc. By the way with help of microprobe analysis the difference of chemical composition of aggregates was later confirmed that gave the opportunity to appreciate the influence of some chemical substances on their morphology.
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Figure 1. Gold nanoparticles on the wall of microcavity
Figure 2. Typical nanogold aggregates in the hollows of the placer gold surface
The aggregates have got different density of nanoparticles arrangement. Sometimes only two or three particles may directly contact each other. The majority of aggregates are presented by rather dense accumulations. But there are examples where separate nanoparticles combined with help of some binding substance. The
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microprobe analysis of such aggregates doesn’t discover the presence of any specific component besides gold and sometimes silver. Probably the binding substance is presented by secondary (authigenic) gold masses without visible internal structure. The prominent peculiarity of aggregates is availability of several levels of nanoparticles combinations in their structure. The smallest combinations have got sizes not more than 10–20 nm and they are composed by small number of tiny nanoparticles. Next level of structure is originated by combinations of previous compounds and so on. For explanation of nature and genesis of nanogold aggregations on the surface of placer gold the great meaning have got the results of microprobe analysis. We haven’t the opportunity to determine a chemical composition of every nanogold particle because of its tiny size. But there is a chance to get an average element percentage of their groups that belong to one aggregate. Taking into opinion a diameter of electron-beam probe (about 1 µm) an average chemical composition was determined in aggregates of such size. On the whole microprobe analysis was applied for investigation of more than 200 aggregates. As a result three main chemical varieties were discovered among them: 1) pure gold and gold with silver or copper, 2) gold with mercury and 3) gold-silicate-ferriferous compounds. The first chemical group is presented by rather small nanoparticle aggregates. They have got typical morphological peculiarities: a round form of nanoparticles and the presence of several levels in their internal structure. Such aggregates are discovered in many placer deposits situated even far from source rocks. Below the results of some single chemical analyses are mainly adduced (Table 1). Table 1. Chemical Composition of Nanogold Aggregates on the Surface of Placer Metal (the Urals), mas. % Element 1 2 3 4 5 6 7 8 9 10 11 12 Au 98.98 96.85 93.52 92.80 87.25 88.07 82.89 54.89 49.33 87.97 94.73 88.38 Ag 0 0 5.84 4.06 12.65 11.52 11.20 42.74 50.36 2.50 0.15 0.38 Cu 0 2.94 0.19 0.54 0 0.13 0 1.19 0 0.65 0.47 0.64 Hg 0 0 0 0 0 0 0 0 0 5.37 1.66 8.14 Se 0 0 0 0 0 0.21 0.29 0.25 0 0 0 0.08 As 0 0 0 1.66 0 0.15 0.24 0 0 0 0.06 0 Sb 0 0 0 0 0 0 0 0.24 0 0 0 0.12 Ni 0 0 0 0 0 0 0 0 0 0 0 0.07 Co 0 0.21 0 0 0 0 0 0 0 0 0 0.07 Pd 0 0 0 0.47 0 0 0 0 0 0 0 0.19 Fe 0.37 0 0 0.48 0 0 2.06 0.19 0.23 0.45 0.43 0.30 Al 0 0 0 0 0 0.40 1.27 0.51 0 0.70 0.90 1.00 Cl 0 0 0 0 0 0 0 0 0 1.21 0 0 Sum 99.35 100 99.55 100.01 99.90 100.48 97.95 100.01 99.92 98.85 98.40 99.37 Notes: 1 – pure gold (Kolchinskaya placer), 2 – gold with copper (Nazarovskaya placer); gold with silver: 3 – VjatkaKama Depression, 4 – Tykotlov orebody, 5 – Nazarovskaya placer, 6 – Kazanskaya placer, 7 – Chernorechenskaya placer; 8, 9 – electrum (Tykotlov orebody); gold with mercury: 10 – Kytlym placer, 11 – Vjatka-Kama Depression, 12 – other the Urals placers (average from 4 analyses).
The second chemical group is usually presented by dense aggregates with binding matter between nanoparticles. The average mercury percentage changes in wide limits (Table 1, analyses 10–12). They may propose that mercury is concentrated in any parts of aggregate and especially in binding matter. Perhaps some quantities of mercury belong to amalgams. The third group has got very specific morphological peculiarities. Its aggregates have included a lot of scalesalike and fibrous components. The starry-alike forms are very often separated off in their structure (Fig. 3). The lithophile elements (usually Fe, Si, Al, O, rarely Mg, Mn, Ca, Ti, Na, K) are constantly presented in different correlations with gold. They may belong to clay minerals and iron hydroxides that are the usual components of weathering crust (Table 2). Silver is an ordinary element in composition of these aggregates and may be an indicator of low temperature of environment. The appearance of mercury and lead in some aggregates is often marked as well as chlorine. All facts indicate to very complex mineral composition of aggregates with amalgams and other intermetallic compounds. Globular gold In the process of sampling of the Urals objects (first of all weathering crusts) another unusual forms of gold were discovered. They had got round or irregular form of grains (instead of usual flat), porous and uneven surface, yellow-grey color, weak luster. The main their difference from placer gold was globular structure (Fig. 4). During investigation some of them have disintegrated into several fragments.
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The size of globular grains is rather alike (100–50 µm) but very seldom reaches 1 mm. So far as they were received during panning or enrichment of samples in spiral separator they may propose that a lot of analogous small grain were washed off.
Figure 3. Gold-silicate-ferriferous aggregates on the placer gold surface
Even under binocular microscope it was established that globular grains usually consist of round fragments (globules) less than 20 µm, sometimes up to 50 µm, but extended form. The internal structure of globular gold was found out under electron microscope using variable magnification. Low level of magnification (200–500) gives the opportunity to appreciate a common structure of grain, size of globules, their forms and so on. Under higher magnification (2,000–10,000) every globule is considered as a number of the smaller grains having analogue globular structure (Fig. 5). The last have got sizes up to 1–2 µm, but their folded particles are rather small and sometimes don’t exceed 100 nm. At last under the nanolevel magnification (more than 100,000) every globule of 1–2 µm has distinctly imagined as different accumulations of nanoparticles which sizes usually aren’t more than 10–50 nm (Fig. 6). The space between small globules is filled in separate nanoparticles as well as binding masses of authigenic gold (?). It is rather porous space with a lot of canals. Chemical composition of granular gold was determined by microprobe analysis too. An average composition of nanoparticles composing globules up to 1 µm was found out (Table 3). In every globular grain from 5 to 20 globules were chosen for determination. The whole number of analyses is 113. All analyses have shown the presence of mercury as the second (after gold) component. Average mercury percentage reaches almost 60% in separate globules. Such percentage corresponds to gold amalgam. In some objects this percentage doesn’t prevail 12.8%. Therefore there globules are composed by mercurious gold. Silver is rather typical element for granular gold too, its percentage reaches 10%. The separate group of granular grains is presented by intermetallic compounds containing Au, Hg and Pb. For instance, such grains with abnormal high percentage of Cu, Pd, Fe, Al, Sn are discovered in several grains of granular gold of Vjatka-Kama Depression. An indicator element in globular gold is chlorine, its percentage sometimes increases to almost 7%. Chlorine probably promotes to combining of nanogold particles into small globules. The presence of such elements as Cu, As, Si, Al, Fe in abnormally high quantities confirms the fact that granular gold has been growing simultaneously with development of the weathering processes. Another unusual for gold elements (Zn, Se, Cd, Pt) are being met too. They may be connected with specific minerals of weathering rocks and the products of their decomposition. Processes of nanogold aggregation All varieties of nanogold accumulations are the results of different aggregation processes. They may be reconstructed using the results of high resolution electron microscopy and microprobe analysis. The mechanism connected with the origin of aggregates on the surface of placer gold is realized due to simultaneous coordinated action of two main processes. Every of them are supported by definite properties of nanogold particles (very high superficial energy and chemical activity) and that of placer gold surface (abundance of defects and unsaturated electric ties near them). That is why nanogold aggregates for the first time are originated only in the parts of placer gold surface deformed by internal or external processes.
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Table 2. Ranges and Averages of Chemical Compositions of Silicate-Ferriferous Nanogold Aggregates on the Placer Metal, mas. % Element Au
1 2.63-78.58 45.77
2 27.97-69.22 49.78
3 15.88-68.37 41.56
4 45.39-80.15 68.88
Ag
0.58-23.93 8.34
2.43-19.42 9.21
0-4.06 1.12
0-1.40 0.50
Cu
0-1.25 0.41
0-1.43 0.53
0.73-2.64 1.42
1.38-5.64 2.94
Hg
0-9.87 0.98
0-8.46 1.56
0-3.29 1.66
3.00-5.26 4.49
As
0-0.38 0.05
0
0-0.16 0.06
0
Pt
0-1.57 0.12
0
0
0
Pb
0-6.08 1.22
0-11.06 1.58
0-6.91 0.99
0
Fe
2.18-44.01 11.99
4.51-15.35 9.37
11.67-40.70 25.00
4.32-21.22 8.50
Al
0.89-11.80 3.92
0.85-9.19 3.01
0.98-3.73 2.16
0.73-1.94 1.23
Si
0.88-11.83 3.55
0.97-6.03 2.28
1.10-5.16 2.68
1.32-2.16 1.79
O
6.33-36.16 23.32
16.65-29.22 22.01
15.65-26.82 22.93
5.13-23.22 10.46
Cl
0
0
0-0.72 0.16
0-0.72 0.26
Number of analyses 18 7 7 5 Notes: 1 – Yukon Territory placers, Kanada; 2 – Chernorechenskaya placer, the Northern Urals; 3 – Ekatherininskaya placer, the Northern Urals; 4 – Vjatka-Kama Depression.
In connection with this topic it is necessary to apply to one of the known problem of gold geology – that of the so called “new” gold. The last term was devoted by F. Freise (1931) for re-depositional metal in wastes of ancient exploitation of gold deposits where the unusual forms of gold were observed on the surface of placer grains. Analogous gold was afterwards discovered in other regions including the Russian placers (Nikolaeva 1958; Jablokova 1965; Petrovskaya 1973, etc.). The main peculiarities of “new” gold are morphological originality and variability. The most typical their forms are thin coats with porous structure on the surface of gold grains, bud-alike aggregates, and accumulations of fine crystals. Porous growths on the gold grains have got thickness up to 15 µm. Such forms are usually presented only in definite parts of surface. Sometimes “new” gold fills in space between round placer particles of gold with origin a kind of small “conglomerates”. The “new” gold is typical secondary form for deposits of weathering crust. The detailed investigations have shown that it includes not only golden substance but ferriferous hydroxides, tellurides of bismuth and iron, etc. (Novgorodova 2005). Sometimes the aggregates with participation of “new” gold contain quartz and other secondary minerals (Shadrina 2005). The data of electron microscopy give the opportunity to distinguish spherical gold particles of micron sizes at the structure of such aggregates (Kalinin et al. 2010). The results of our investigations (Osovetsky 2012, 2013) have shown that at least a part of “new” gold accumulations is connected with the mechanism of nanogold aggregation on the placer gold. If compare different grains of gold they may make a conclusion about long period of nanogold precipitation on the surface. It begins with filling in nano- and microcracks in lowering parts of surface. Then aggregates gradually growing up and sometimes make continuous films having several layers of nanoparticle aggregates.
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Figure 4. Morphological varieties of globular gold
The process of “new” gold origin with participation of nanogold particles can be subdivided into three stages: 1) sedimentation of individual nanoparticles on the placer gold surface (initial stage); 2) aggregation of gold nanoparticles under influence of specific mechanism (main stage); 3) growth of compact coats on placer gold (final stage). The initial stage. The beginning of “new” gold genesis is sedimentation of individual nanoparticles on the placer gold surface. There are a lot of proofs that their accumulation is accomplished near the edges of micro- and nanocavities, cracks, pores, etc. The size of primary gold nanoparticles observed on the gold surface under electron microscope is usually more than 50 nm. But there is an opinion that they are complex objects and consist of several more less particles that closely grow together. The main stage. The individual gold nanoparticles have been becoming the centers of nanogold attraction. This process may prolong for a long time and leads to origin of aggregations that include gold nanoparticles, binding gold masses, ferriferous hydroxides, clay minerals, chlorides, organic compounds, etc. The intensity of the process may be increased due to activity of such chemical agents as ferriferous, chloride, carboniferous compounds and mercury. In that case the complex aggregates are appeared on the metal surface. So far as ferriferous compounds are wide-spread components in the weathering crust of gold deposits they play a great role in origin of nanogold aggregates. The final stage. After filling in all negative forms of nano- and microrelief of placer gold surface the metal nanoparticles have been covering the adjacent parts. As a result one-layered films are appeared there. Then they are covered again by following layers of gold nanoparticles and their aggregates. The prominent role in origin of compact coats plays authigenic gold of colloidal nature. It promotes quick growth of nanogold films and their variable chemical composition. This metal executes the function of cement material in “new” gold films and coats filling in a space between nanogold particles and their aggregates. The process of nanogold collection on the placer gold surface doesn’t foresee its dense packing because of the local distribution of authigenic metal. The formed films and coats are composed by rather friable nanogold aggregates. There are numerous gaps in coats and parts of surface without gold nanoparticles. Near the margins of
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coats there are only separate islands of nanogold aggregates. Nanogold coats are sometimes crossed by nanocracks (Fig. 7).
Figure 5. The internal structure of globules in the composition of aggregates
The structure of “new” gold coverings is rather different. The main factors that influence on their structure are forms, sizes and chemical composition of nanoparticles, role of authigenic gold, speed of absorption processes, peculiarities of surface, etc. As it was shown before chemical composition of nanogold aggregates is rather changeable and variable. For instance, chlorine is found in many aggregates in combination with sodium and (or) potassium. This fact indicates in probable participation of chloride solutions in origin of “new” gold (Schoomen et al. 1992). As to origin of globular gold the previous mechanism isn’t effective. Specifically the mechanism of globular gold genesis is accomplished due to active participation of gold amalgams and nanoparticles of gold with mercury (Slowey 2010). Unlike the aggregates on the placer gold surface globular gold has originated their own grains dispersed in the products of weathering crust.
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Figure 6. Gold nanoparticles as the components of microglobules
This mechanism is realized as the process of globule growth due to unification of small nanoparticles. The reality of such mechanism is proved by the presence of a lot of size levels of globules composed by nanoparticles of mercury gold or amalgams. Some globules have got the most complex internal structure included authigenic masses of gold. The structure of globular gold fixed with help of high resolution electron microscopy let us to do the conclusion about their origin as a result of natural amalgamation mechanism. This process may prolong for a long time with temporary stops. At the initial stage of the process only very simple combinations of nanoparticles composed by mercury gold are originated. Their sizes may be not more than several nanometers. Next stages conclude in growth of previous combinations due to joining of new nanoparticles with origin of small globules. The last then are united into the bigger globules. CONCLUSION It is proved that after appearance as separate particles in environment nanogold origins complex aggregates due to their specific properties and favourable external factors (presence of such components as mercury, ferriferous, chlorine, organic compounds). This phenomenon they may regard as capacity of nanogold to concentration at definite geological objects, first of all in weathering crust on gold-sulfide-quartz deposits. The aggregation of nanogold particles on the surface of placer gold is one of the ways of “new” gold genesis. It is a very specific subject of investigation due to its complex structure, chemical composition and localization. The aggregation process has been developing only in weathering crust above gold-sulfide-quartz or analogues ores. There the processes of chemical dissolution of Fe-sulfides (pyrite, arsenopyrite, pyrrotite, etc.) result in getting free nanogold particles. After that nanogold particles are settling into micro- and nanocavities of placer gold surface. The origin of “new” gold films and coats is a result of definite combination of several factors such as gold surface properties, high surface energy of nanogold particles and presence of their rich source. This process with participation of gold nanoparticles embraces three successive stages. The initial stage consists in adsorption of individual nanogold particles in defect zones of placer gold surface. Next stage connects with aggregation processes that are sometimes stimulated by compounds of iron, mercury, silicon, carbon, chlorine and some other elements. During the final stage separate nanogold aggregates have combined into extended films and coats on the gold surface.
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Table 3. Ranges and Averages of Chemical Compositions in Globular Gold, mas. % Element
1
2
3
4
Au
32.74-68.68 54.69
64.83-93.52 77.53
42.26-66.43 60.02
51.20-89.34 76.45
Hg
25.12-58.25 38.91
0-21.56 15.24
1.84-12.80 5.41
4.68-29.53 11.40
Ag
1.03-10.25 4.02
2.15-10.72 5.32
1.28-4.78 3.17
0-6.48 3.01
Cu
0-4.30 1.18
0-1.75 0.53
0.40-6.35 2.28
0.99-26.30 3.79
Pb
0
0
17.91-43.63 25.84
0
As
0
0-0,19 0.02
0-0.47 0.18
0-0.28 0.07
Fe
0
0-0.10 0.03
0.75-5.19 1.68
0.26-7.29 2.25
Al
0
0.31-0.63 0.33
0.99-4.32 2.19
0.72-6.41 1.46
Si
0
0
0
0.78-3.18 1.61
Cl
0
0
0
0.37-6.84 1.06
Number of analyses 16 20 7 70 Notes: Late Mesozoic weathering crust, the Upper Kama basin: 1 – amalgams, 2 – mercurious gold, 3 – lead-gold-mercury alloys; 4 – mercurious gold (weathering crust of black schist, the Western Urals).
Figure 7. Coat of nanogold particles on the gold surface
Besides, globular gold is appeared in the weathering crust due to mechanism of natural amalgamation. Globular gold origin is a result of interaction of gold amalgams and gold nanoparticles with mercury. It has got multi-level structure and is composed by the globules of different size and chemical composition with obligatory participation of mercury. Globular gold grains are not connected with a surface of placer gold. They usually
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dispersed in weathering crusts but are sometimes concentrated near the zones of depth faults that are the canals of mercury migration. The results of gold investigation from weathering crusts have confirmed the effectiveness of high resolution electron microscopy methods. This level of researching is rather useful for finding of new forms of gold migration and concentration there. They may be presumably used in nanotechnologies. The necessary conditions for origin of nanogold aggregates and their duplicating may be realized in wastes of gold excavation or in special fabrics. ACKNOWLEDGEMENTS The author wants to acknowledge some persons who placed at his disposal grains of gold for description (AG Barannikov, JA Kisin, VA Naumov, AJ Konopatkin) and colleagues of Mineralogy and Petrography Department of Perm State University for participation in field expeditions and extraction of gold grains under laboratory conditions. REFERENCES Cook, N. J., & Chryssoulis, S. L. (1990). Concentrations of “invisible gold” in the common sulfides. Canadian Mineralogist, 28, 1–16. Freise, F. W. (1931). The transportation of gold by organic underground solutions. Economic Geology, 26, 412–431. Hough, R. M., Noble, R. R. P., Hitchen, G. J., Hart, R. D., Reddy, S. M., Saunders, M., Clode, P. L., Vaughan, D., Lowe, J., Gray, D. J., Anand, R. R., Butt, C. R. M., & Verrall, M. (2008). Naturally occurring gold nanoparticles and nanoplates. Geology, 36 (7), 571–574. Jablokova, S. V. (1965). Origin of “new” gold in some placers of the South Yakutia. Placer geology. Мoscow, Nauka, 152–155 (in Russian). Kalinin, J. A., Zhmodik, S. M., & Spiridonov, A. M. (2010). Spherical gold of laterite weathering crust // Placers and weathering crust deposits: modern problems of investigation and utilization. Novosibirsk: Geology and Mineralogy Institute, 290–294 (in Russian). Lengke, M., & Southam, G. (2006). Bioaccumulation of gold by sulfate-reducing bacteria cultured in the presence of gold(I)-thiosulfate complex. Geochimica et Cosmochimica Acta, 70, 3646–3661. Mann, A. W. (1984). Mobility of gold and silver in laterite weathering profiles: Some observations from Western Australia. Economic Geology, 79, 38–50. Mikhlin, Y., Romanchenko, A., & Asanov, J. (2006). Oxidation of arsenopyrite and deposition of gold on the oxidized surfaces: A scanning probe microscopy, tunneling spectroscopy, and XPS study. Geochimica et Cosmochimica Acta, 70, 4874–4888. Nikolaeva, L. A. (1958). “New” gold in placers of Lena Region. Works of TSNIGRI, 25 (2), Мoscow, 19–122 (in Russian). Novgorodova, M. I. (2005). Methacolloid gold. New data on minerals, 40. Мoscow, 106–114 (in Russian). Osovetsky, B. M. (2012). Nanosculpture of gold surface (p. 232). Perm: Perm State University Press (in Russian). Osovetsky, B. M. (2013). Natural nanogold (p. 176). Perm: Perm State University Press (in Russian). Palenik, C. S., Utsunomiya, S., Reich, M., Kesler, S. E., & Wang, L. (2004). “Invisible” gold revealed: Direct imaging of gold nanoparticles in a Carlin-type deposit. American Mineralogist, 83, 1359–1366. Petrovskaya, N. V. (1973). Native gold (p. 253). Moscow, Nauka (in Russian). Reich, M., Kesler, S. E., Utsunomiya, S., Palenik, C. S., Chryssoulis, S. L., & Ewing, R. C. (2005). Solubility of gold in arsenian pyrite. Geochimica et Cosmochimica Acta, 69 (11), 2781–2796. Schoomen, M. A. A., Fisher, N. S., & Wente, M. (1992). Gold sorption onto pyrite and goetite: a radiotracer study. Geochimica et Cosmochimica Acta, 56, 1801–1814. Schweigart, H. (1965). Solid solution of gold in sulfides. Economic Geology, 6 (7), 1540–1541. Shadrina, S. V. (2005). Free gold from hypergene zone of the Suzdal deposit, North Kazakhstan. Placers and weathered rock deposits: facts, problems, decisions. XIII Inter. symp. on geology of placers and weathered rock deposits. Russia, Perm, 313–315. Slowey, A. J. (2010). Rate of formation and dissolution of mercury sulfide nanoparticles: The dual role of natural organic matter. Geochimica et Cosmochimica Acta, 74, 4693–4708. Zhmodik, S. M., Kalinin, Y. A., Roslyakov, N. A., Mironov, A. G., Mikhlin, Y., Belyanin, D. K., Nemirovskaya, N. A., Spiridonov, A. M., Nesterenko, G. V., Airiyants, E. V., Moroz, T. N., Bul’bak, T. A. (2012). Nanoparticles of noble metals in the supergene zone. Geology of Ore Deposits, 54 (2), 141–154.
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