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Advanced Materials Research Vol. 828 (2014) pp 1-10
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doi:10.4028/www.scientific.net/AMR.828.1
MICROSCOPIC STUDIES OF GOLD DEPOSIT SOUTHERN ASHALY IN
EASTERN KAZAKHSTAN
Adilkhan Baibatsha1,a, Kulyash Dyussembayeva2,b, Aimkhan Kassenova3,c
1, 2, 3
Kazakh National Technical University named after K.I. Satpayev, Kazakhstan
a
[email protected]; [email protected]; [email protected]
Keywords: gold, sulfides, deposit, black shale strata.
Abstract. The gold-sulfide deposit Southern Ashaly is localized in carbonaceous terrigenous formation (black shale strata) of the middle carboniferous (Bukon suite, which is the ore-hosting for
super large deposit Bakyrchik). The Southern Ashaly is at the exploration stage and according to
preliminary estimates of the expected resources belongs to a large deposit in scale.
Ore gold mineralization of such level as Southern Ashaly in southwestern Kalba is found for
the first time and gives hope for the discovery of such objects in the Boko Vassilyevskoye ore field.
Ore-hosting at the field Southern Ashaly is carbonaceous terrigenous formation of the middle carboniferous, with no visible signs of volcanic formations. But, it was revealed, at microscopic research by us, paragenetic relation of the gold mineralization with small intrusions of plagiogranites
and zones of plagiogranite porphyry dykes and found volcano-sedimentary rocks (aleuritic tuffsandstone, tuff breccia) which have undergone hydrothermal-metasomatic changes. The veindisseminated gold-sulfide mineralization is associated with beresitizated plagiogranites and plagigranite-porphyries and hydrothermally altered tuff sandstones, tuff breccia and carbonaceous
shales. Southern Ashaly unlike Bakyrchik deposit which contains invisible gold in sulfides, all the
gold is concentrated in the pyrite mainly in the form of micro-sized (1-5 µm or less) in arsenopyrite
is noted rarely.
Introduction
Gold deposits in black shale stratas are characterized by significant resource potential for the
noble metals [1, 2]. In the CIS countries known by such large fields as Bakyrchik (Kazakhstan),
Sukhoi Log, Natalkinskoye, Nezhdaninskoye (Russia), Muruntau (Uzbekistan), Kumtor (Kyrgyzstan) (Fig. 1).
Figure 1. The scheme of the large gold deposits in the black shale strata in Asia (fragment) [3]
Deposits: 1 – Kokpatas, 2 – Muruntau, 3 – Kumtor 4 – Suzdalskoe, 5 – Bakyrchik, 6 – Southern
Ashaly, 7 – Sukhoi Log, 8 – Nezhdaninskoe
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Harnessing of Nonferrous Minerals, Metals and Wastes
Large deposits of Bakyrchik in Kazakhstan is still not executed, because of the difficulties of
its enrichment of ores (the presence of carbonaceous matter, arsenic as a harmful impurity, finding
the gold in pyrite and arsenopyrite in an invisible form).
Figure 2 shows a structural position, geological soning and gold mineralization of westernKalbinsky belt [3]. The Southern Ashaly is the part of Akzhal-Daubaisky ore region and is timed to
the Ashaly-Daubaisky ore field.
Figure 2. Structural position, geological soning and gold mineralization
of Western-Kalbinsky belt [3]
1 – ores of regions, 2 – ores of clusters (numbers in circles), 3 – industrial deposits, 4 – small deposits and ore occurrences, 5 – occurrences. The ores of clusters: 1 – Espinsky, 2 – Bakyrchiksky,
3 – Kazan-Chukursky, 4 – Sarytaussky, 5 – Zhanatassky, 6 – Sentshsky, 7 – Zhumbinsky, 8 – Kuludzhunnsky, 9 – Akzhal-Vasilevsky, 10 – Daubai-Ashalinsky, 11 – Baladzhalsky
The Southern Ashaly deposit is located in the south-western part of the Kalba range (East Kazakhstan region) in the south-eastern part of Ashaly-Daubaisky ore field. The total area of the ore
field is estimated at about 50 km2 and incorporates Daubaisky group of the fields and Ashalinsky.
There are about 20 ore occurences and small-scale gold deposits in the field.
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The host rocks for the ore bodies of the deposit are terrigenous formation of the middle carboniferous of the Bukon suite. The block rocks that holds the deposit is restricted from west and east by
faults northeastern direction, they are Baiburinsky and Dolinnoye faults. The distance between these
structures in the plan is about 1000-1200 m.
The main factors which control placement of the ore bodies on the deposit is lithologic- and
stratigraphic (ore bodies are confined to the upper shale assise of the Bukon suite, the most differentiated in composition of part of its geological record, represented fine-laminated carbonaceous
shales, siltstones and sandstones), and structural (localization of ore bodies is controlled by fault
zones that transect the lamination and schistosity at an acute or steeper angles).
Ore bodies in relation to lamination of the rocks are mostly take the obliquely cutting position
close to substratified. This includes, first of all, to the largest and most rich in content of gold ore
body № 3 and accompanying it ore bodies - 2, 4, 5, 6 and 7. Other leading the body number 1, tending to the shale assise, which is controlled by the cross-section of relative to lamination of the
crushing and crumpling zone, which has the north-western direction. The largest ore bodies (№ 1, 2
and 3) are presented by ribbon-like bodies which have steeply dipping and sub-lateral west-northwestern strike.
Gold-sulfide Southern Ashaly belongs to the deposits which are localized in the carbonaceous
terrigenous (black shale) stratas, confined to areas of infolded and post infolded tectonic deformation [4, 5].
Experimental (covering materials and methods)
In the Southern Ashaly the host rocks and ores composing the main ore bodies № 1 and 3 were
studied by microscopically. The results of microscopic study of thin rock section show that the gold
mineralization is associated with small intrusions of plagiogranites and zones of plagiogranite
porphyry dykes. It is located in the hydrothermal-metasomatic altered volcanic and sedimentary
rocks (aleuritic tuffsandstone, tuff breccia) and sericite-carbonaceous shales. There are carbonsericite, quartz-sericite, carbonate-quartz metasomatic associations in the deposit. Carbonaceous
formations are represented by the oxidized (carbonates) and reclaimed (disperse carbonaceous particles and anthraxolite) forms.
The main ore-forming minerals are pyrite and arsenopyrite, which form the an uneven fine disseminations in silicified, carbonatized and sericitized host rocks, and also encountered in thin quartz
and quartz-carbonate veinlets. It is noted the presence of subordinate amount of chalcopyrite,
chalcosine, tetrahedrite ore and carbonaceous matter and rutile. The amount of sulfides reach 5-8 %
in total. Pyrite is the main sulphide among them. In arsenopyrite gold is extremely rare. The particles of gold in pyrite have been viewed and pictures are taken on a microprobe JCXA-733 because
of their poor visibility in the light microscope (finely dispersed particles). There are two types of
gold mineralization: 1) is a richer in beresitizated plagiogranites and plagigranite-porphyries and 2)
in hydrothermally altered tuff sandstones, tuff breccia and carbonaceous shales.
The beresitizated plagiogranites and plagigranite-porphyries
Pyrite and arsenopyrite in them are presented in the form of individual rare disseminations, in
some plots to dense that visually observed among the host rock in the form as spots and nests which
have 1-1.5 cm in size. Such areas with fine inclusions of sulfides rich in gold. Pyrite is the main
gold-bearing mineral. The disseminated pyrite-arsenopyrite ore is cut differently oriented quartz,
rarely quartz-carbonate veinlets, from 0.5 mm to 1.5 cm in thickness.
Pyrite - there are four of generation. Early – syngenetic pyrite I is in the close association with
carbonaceous matter and is found in the second type of mineralization.
Pyrite II and arsenopyrite are in close intergrowths and form the pyrite-arsenopyrite aggregates
which have 0.25x0.5 mm in size. Pyrite II in these aggregates is in subordinate amount, representing a thin aggregative segregations in prevailing arsenopyrite intergrowths. As a rule, such a finely
aggregative segregations of pyrite II are located in the center of arsenopyrite intergrowths. Arsenopyrite is crystalline grained, shape of the grains is rhomboid. The finely aggregative segregations of
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pyrite II have 0.05х0.1-0.1х0.4 mm in size. Sometimes the finely aggregative pyrite II is recrystallized into crystalline grained, especially in the marginal parts.
Pyrite III is crystalline grained and is formed apparently through recrystallization of pyrite II. It
has a cubic and pentagonal dodecahedral habitus and occurs in the form of intergrowths with each
other and arsenopyrite. Gold is also related with pyrite III, but in lesser quantities. In pyrite III, arsenopyrite grains are found. Between grains of pyrite and arsenopyrite and pyrite-arsenopyrite aggregates the dense disseminations of leucoxene are observed.
Arsenopyrite prevails and is represented as prisms forming a rhombus in the cross section. It is
in close intergrowths with finely aggregative pyrite II and replaces it. lamellar elongated forms of
its absent. Single crystals are rare, basically it is intergrowths of two or more grains. Arsenopyrite
has dimensions of 0.06-0.1 mm, rarely larger than 0.35 mm. Sometimes arsenopyrite-pyrite aggregates together with pyrite are arranged in the form of chains.
Hydrothermally altered tuff sandstones, tuff breccia and carbonaceous shales
This is usually dark rock in color with rare of pyrite, which is intersected differently oriented
quartz and quartz-carbonate veinlets, from 0.35 mm to 1 cm in thickness. Arsenopyrite is present in
sharply subordinate amount. Small segregations of carbonaceous matter along fractures en mass of
the rock are observed.
Pyrite I – early syngenetic generation of the globular pyrite I, together with carbonaceous matter more frequent here. Together they form usually along cracks rare disseminations of their grains
1-20 µm in size, sometimes subtle rash. Globules of pyrite, 5-30 µm in size are found in carbonaceous matter. In the larger pyrite globules we can see framboidal internal structure. Pyrite globules
and carbonaceous matter are also found in the grains of dolomite. Globules, though rarely scattered,
but meet everywhere en mass of the rock. It is noted recrystallization globular pyrite into crystalline
grained cubic form.
Pyrite II is the thin aggregative in intergrowths with arsenopyrite. It is confined to silicified areas and quartz-carbonate veinlets. The size of thin aggregative pyrite II – 0.1-0.5x0.6 mm. Pyrite III
is found rarely.
Pyrite IV is aggregative in the form of the veinlets with small inclusions of chalcopyrite and
pyrrhotite (5x10 µm) and rare fine grains of arsenopyrite. Pyrite is also found as individual disseminations and is in the form of the intergrowths, chains, sometimes with arsenopyrite. The form of
pyrite grains is cubic. The size of grains 0.1-0.2 mm, rare more than 0.6 mm. Aggregates of pyrite
intergrowths up to 1.7 mm. Pyrite IV meets in hydrothermal-altereted volcano-sedimentary rocks
and carbonaceous shales, intersecting of thin quartz and quartz-carbonate veinlets, which in the
form of net. Pyrite IV is in quartz and quartz-carbonate thin veinlets. Pyrite aggregates have 0.5x2
mm in size.
Arsenopyrite is in sharply subordinate amount. It basically intergrowths of arsenopyrite of
prismatic shape with thin aggregative pyrite II. Pyrite-arsenopyrite aggregates reach 0.25x0.4 mm
to 0.8 mm rarely. Usually in the the larger arsenopyrite secretions (0.2x0.5 mm), are enclosed the
individual thin aggregative pyrite II (0.1x0.2 mm).
Gold – there are three paragenetic associations: 1) gold-pyrite associated with the thin aggregative pyrite II; 2) gold-pyrite-arsenopyrite near simultaneous with the gold-pyrite (gold is rare in the
arsenopyrite and in recrystallized pyrite III); 3) gold-pyrite-chalcopyrite (gold is in the veinlets pyrite IV in association with chalcopyrite, rare with arsenopyrite).
1) gold-pyrite association related to the thin aggregative pyrite II
Gold in thin aggregative pyrite II is generally in the form of point, barely any visible in the
light microscope inclusions 1-2 µm in size [6]. In different places of thin aggregative pyrite II found
about 35 gold grains. Their size is from 1 µm or less and up to 6 µm. Often there are grains of gold
in pyrite along the border with arsenopyrite and even moving in arsenopyrite. Below are pictures of
gold, made by light microscopy and micro-probe in different modes – compo and back-scattered
electrons (Fig. 3, Fig. 4, Fig. 5, Fig. 6).
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Figure 3. The gold (Au) in the thin aggregative pyrite II (Py). Asp-arsenopyrite.
The photograph was taken under light microscope. Polished section 4/1
Figure 4. Enlarged fragment of Figure 3. The micro-sized grains of gold (white) in the thin aggregative pyrite II (black). Gray – arsenopyrite. The photograph was taken with a microprobe in the mode
of compo. Polished section 4/1
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Harnessing of Nonferrous Minerals, Metals and Wastes
Figure 5. The gold (Au) in the thin aggregative pyrite II (Py). Asp-arsenopyrite.
The photograph was taken under light microscope. Polished section 4/2
Figure 6. Enlarged fragment of Fig. 5. The micro-sized grains of gold (white)
in the thin aggregative pyrite II (black). Gray – arsenopyrite. The photograph was taken with a microprobe in the mode of compo. Polished section 4/2
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2) gold-pyrite-arsenopyrite near simultaneous with the gold-pyrite (gold is rare in the arsenopyrite and in recrystallized pyrite)
The rare point inclusions of gold (1 µm) were found in arsenopyrite, which develops from the
edge of pyrite II. Gold this association is found in individual grains of pyrite III and in intergrowths,
which contain fine grains of arsenopyrite (Fig. 7, Fig. 8). There is about 20 µm – sized of gold particles (1-6 µm).
Figure 7. The gold (Au) in the grain of pyrite III (Py) with inclusions of grains arsenopyrite.
Polished section 3
Figure 8. Enlarged fragment of Fig. 7. Gold (light gray) in the grain of pyrite III (dark). The photograph was taken with a microprobe in the secondary-scattered electrons. Polished section 3
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Harnessing of Nonferrous Minerals, Metals and Wastes
3) gold-pyrite-chalcopyrite (gold is in veinlets pyrite IV in association with chalcopyrite, arsenopyrite is rare)
The veinlets pyrite IV contains small inclusions of chalcopyrite (10 µm) and pyrrhotite (5-10
µm). Gold is in intergrowths with small inclusions of chalcopyrite (Fig. 9, Fig. 10). There are about
16 of gold particles (1-10x15 µm).
The form of gold particles in the described associations – in the form of points, drop-shaped,
oval, in some grains are observed prominent cubooctahedron faces and cube, the subtlest veinlets.
According to the composition is electrum and high fineness of gold.
Figure 9. Gold (Au) in intergrowths with chalcopyrite in a streaky pyrite IV (Py) from
quartz vein. Polished section 1/1
Figure 10. Enlarged fragment of Fig. 9. Gold (light) in the veinlets pyrite IV (dark). The photograph
was taken with a microprobe in the secondary-scattered electrons. Polished section 1/1
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Results and discussion
Significant role in the formation of gold mineralization played hydrothermal-metasomatic processes that took place in zones of dynamo-metamorphism among the black shale strata. Intensive
metamorphism of the host rocks is expressed in their boudinage, brecciation and crumpling. Plagioclases in plagiogranites and plagiogranite porphyries have curved polysynthetic twinning, which is
the result of cataclastic metamorphism. Some aggregates and grains of sulfides have clastic and corrosion borders.
The host rocks are beresitizated in different degrees, which is manifested in their silification,
carbonatization and sericitization and enrichment of vein-disseminated of the sulphide mineralization and the presence of usually leucoxenized titaniferous minerals (sphene, rutile). Sericitized acid
plagioclase – Oligoclase in plans giogranitah and plagiogranite porphyry
Acid plagioclase – oligoclase in plagiogranites and plagiogranite porphyries and clay mineral in
sandstones, tuff breccias and carbonaceous shales are sericitized. Often, aggregates and grains of
sulfides bordered by sericite and quartz-sericite aggregates. The concentration of sericite in zones of
of intensive sulfide enrichment is significant.
The plagiogranites and plagigranite-porphyries, volcanic and sedimentary and black shale rocks
intersected numerous of thin quartz and quartz – carbon-bearing veinlets. In quartz and carbonbearing-quartz veinlets is present as a separate scattering of the sulphide dissemination and their aggregates.
The presence of titanium-containing minerals in the clasts of plagiogranites and plagioranite
porphyries is explained complete pseudomorphic metasomatic replacement in their composition of
color components (hornblende and biotite). In the clast of porphyry plagiogranite marked relic skeletal formation of inclusions of non-ferrous components isometric form, completely substituted carbonate and rutile.
The disperse carbonaceous of particles and sometimes lenticular formations of anthraxolite,
marked both as a part of the host rocks and in the hydrothermal veinlets. In the rocks they usually
perform a curved of micro cracks that sometimes in pinch gain lenticular shape. The carbonaceous
formation are due to presence in the composition of hydrothermal-altered rocks by squeezing out
and additional supply of hydrothermal solutions of black shale strata.
Gold mineralization is associated with beresitizated plagiogranites and plagioclase-graniteporphyries and hydrothermally altered volcanic and sedimentary rocks and carbonaceous shales.
The main ore-forming minerals – pyrite and arsenopyrite are represented by several generations.
The thin aggregative pyrite II is the main concentrator of gold, wherein the gold is present as finedispersed particles (1-5 µm and less one µm).
Conclusion
The Southern Ashaly deposit has the features of similarity with such large deposits as Bakyrchik, Suzdalskoye and others and the first presented as a large deposit, found in the Southwestern
Kalba. For the ores of deposit is picked paragenetic relationship with small intrusions of plagiogranites and zones plagiogranite porphyry dykes, which take place on a super large Bakyrchik gold deposit. In addition, volcanic and sedimentary rocks, which are defined in the Southern Aschaly also
present in the terrigenous section of Bakyrchik and in the similar large Kokpatas deposit in Uzbekistan. In South Ashaly as distinguished from Bakyrchik deposit with invisible gold in sulfides, gold
is visible and in the form of µm particles concentrate in pyrite II (1-5 µm or less). The gold is found
as in the beresitizated plagiogranites and plagioclase-granite-porphyries as well as in hydrothermally altered volcanic and sedimentary rocks and carbonaceous shales.
Two-stage scheme allowed to get flotation tailings containing gold 0.17-0.19 g/t and flotation
concentrate containing 52.78 g/t gold, with the output of 7.1 %. The recovery of gold in resulting
concentrate amounted 92.73 %. In this part of the study required a more detailed checking of fragmentation size in the first and second flotation. The use of oxidizing roasting of sulphide ores 5 mm
in size, allows at 700°C for 2 hours completely remove carbon and oxidize the sulfides. The re-
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Harnessing of Nonferrous Minerals, Metals and Wastes
grinding of calcine of ore and sorption of cyanidation in the solution is extracted 75.84% of all the
gold. In this part of the experiments require more detailed checking entire complex of method.
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shale strata: the conditions of formation, signs of similarity, Almaty, 2011, 272 p.
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Microscopic Studies of Gold Deposit of Southern Ashaly in Eastern Kazakhstan
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