124
Part 3.
AURIFEROUS EPOCHS OF THE EARTH
Krutoyarskiy M.A. ( 2008 ) –
Independent Consultant Geologist, U.S.Geological Survey;
International Academy of Natural and Social Sciences ( IANSS ), Moscow, Russia.
INTRODUCTION
Native gold, in essence, is the first metal discovered by people. Gold is
known to mankind from the extreme antiquity. Since 4000 BC, products made
of gold, at first as ornaments and in religious practices, were widely spread
among the ancient peoples of Egypt, Phoenicia, Mesopotamia, Caucasus, China,
India, Central and South America. For the first time the gold coins came into
circulation near 1500 BC in Egypt, Babylonia, India, and in China.
Altogether between 4000 BC and 1984 C.E. about 93,731 tons of gold
were extracted (Bache,1987), and considering subsequent annual production of
gold of 1,000 – 2,550 tons, the total production of gold
in the World comes up to
close 154,724 tons at the end of 2004, and the reconnoitered reserves of gold is
approximately 49,000 tons. (Table 1) ( Mineral Summary, 2000; Minerals
Yearbook, 2004).
The most significant reserves of gold are owned such countries as the South
African Republic, USA, Australia, Canada, China and Russia. The World
extraction of gold reached 2,430 t in 2004. Among these 342 t are produced by
the South African Republic, then from Australia – 259 t, USA – 258 t, China –
215 t, Peru – 173 t, Russia –169 t, Canada – 129 t, Uzbekystan – 93 t,
Indonesia –93 t, Papuan –73 t, Ghana – 60 t, Brazil – 41 t, and from all other
countries – 525 t (Minerals Yearbook, 2004).
Table 1
World production of gold on the historical periods
Historical periods
Century
Time
Gold amount (t)
1
Slaveholding
Copper
4000 –2100 BC
920
2
“ “
Bronze
2100-1200 BC
2,645
3 “ “
Iron
1200 BC –500 CE
6,692
Total slaveholding:
4000 BC- 500 CE
10,257
4
Feudal
Early
500 –1000
934
5
“ “
Middle
1000-1492
1,378
6
“ “
Latest
1492-1789
10,000
Total feudal:
500 –1789
12,312
7
Capitalistic
Newest
1790-1977
80,380
8
“ “
Modern
1977-2004
51,615
Total capitalistic:
1790-2004
131,995
9
In total:
4000BC-2004
154,724
125
Gold presents in rocks in a scattered state (5.10
-7
%) ,
and also in river and
ocean waters (0,01-0,05 mg / t), in plants and animal cells. In nature there is
mainly native gold, which contain as impurities silver, copper, palladium,
bismuth. It is frequently found in chemical compounds with tellurium. Crystals
of gold are rare, mainly as octahedrons, occasionally as dodecahedrons and
cubes. Native gold appears in lamellar and scaly grains, threadlike and spongy
segregation, occasionally as dendrites. The size of gold grains varies: from
submicroscopic segregations up to large incorrect nuggets of gold, raging in
weight from many grams up to several tens kilogram. Chemical stability and
high densities of gold causes formation of significant placers of gold at
destruction of many bedrock deposits.
Industrial concentrations of gold are genetically connected with granites of
moderately acid composition, less often to alkaline, basic and ultra basic
magmatic rocks. Gold is primarily connected with plagiogranites and also with
pre-batholith small intrusion or post-batholith stocks and dykes of diorites and
granodiorites. Gold does not stay in magmatic hotbed, forming mobile complex
chemical compounds, which concentrate and are taken out mainly
postmagmatic, by fluids and hydrothermal solutions. Usually, they form various,
veins and metasomatic interspersed lodes deposits. Gold is partly connected
with early sulfides. The most part of gold drops out from postmagmatic
solutions after silica and sulfides of polymetals, closer in time to bulangerite,
freibergite, tellurides and selenides . Native gold is more often associated with
pyrite, arsenopyrite, faded ores, bulangerite, chalcopyrite, tellurides Bi, Pb, Ag,
less often with galena, sphalerite, stibnite, pyrrhotite, pyrargyrite, molybdenite,
producing with them joints or microscopic inclusions. In hypothermalic
hydrothermal deposits industrial value is obtained by tellurium connections of
gold, such as cavalerite AuTe
2
, sylvanite AuAgTe
4
, naguanite Au (Pb, Sb, Fe)
8
(S, Te)
11
and others.
1. GEOCHEMISTRY OF GOLD
*)
Gold’s chemical symbol is Au, it has an atomic number 79 and is
between platinum and mercury in Mendeleev’s periodic table of the elements.
Gold belongs to a group which consists of Cu, Ag and Au. The atomic weight
of Au is 196.967. The atom of gold contains 79 electrons and has a lattice of a
central facet cube with a parameter of 4.0701 A . The melting temperature of
gold is 1064
o
C and its boiling is 2860
o
С. The hardness of gold 2-3, its
density 19,5, Its specific weight ranges from 15,6 up to 18,3 depending on the
amount of impurity Ag, Cu, Te, Se, Bi, Pt, Ir, Pd. Only one stable isotope exists
in nature
197
Au. However, three short-lived unstable isotopes are known:
196
Au,
198
Au and
199
Au.
This metal ranges in color from golden-yellow to silver-white, it is very
much malleable and viscous. It can be cold-hammered or rolled into very thin
leaves which appear through the slate aeruginous color. The principal states
of gold are monovalent Au
+
(aurous) or trivalent Au
+++
(auric). These oxidation
states are found in the following complexes: [Au(CN)
2
]
-
[AuCl
2
]
-
, [AuS
2
O
3
]
-
,
[Au(OH)
4
]
-
, [AuCl
4
]
-
and [AuCl
3
OH]
-
.
_____________________________________________________
*
)
This subtitle have been written after J.J.Bache (1987).