Ore-Forming Processes and Ore Occurrences of the Eastern Greater Caucasus Georgian Segment

Abstract

In the Eastern Greater Caucasus Georgian segment Lower-Middle Jurassic shales and sandstones experienced crush, hydrothermal alteration and ore mineralization processes. At some hydrothermally altered areas mainly copper-pyrrhotitic and pyrite-polymetallic ores were formed. Already known ore occurrences were studied and, at the same time, new and interesting ore occurences were discovered in the hydrothermally altered zone in the r. Stori canyon (Bendena,Gelia, and enriched with Th zone) and pyrite-polymetallic ore mineralization at the village Lechuri. The latter should be of great interest, since it shows lots of similarities to Filizchay pyrite-polymetallic deposit by its geologic position and mineralogical-geological parameters, which makes necessary further detailed study of the area. It should be noted that at some areas, on the result of conducted research, for the first time the increased concentrations of Au (at Artana and Tebulo ore fields) were reported. At Tebulo ore field gold increased concentrations were defined as in massive polymetallic ores, so-in hydrothermally altered zones, which should be considered as one of the most important results of the research study. These ore occurrences are also characterized with the significant concentrations of Th, Bi, Co and Cd.

Full text

Ore-Forming Processes and Ore Occurrences of the
Eastern Greater Caucasus Georgian Segment
Nona Gagnidze
PhD student, Ilia State University, Department of Natural Sciences and Engineering. 3/5 Cholokashvili Ave., Tbilisi 0162,
Georgia. nonagagnidze@gmail.com
Avtandil Okrostsvaridze
Doctor of Geological Sciences, Ilia State University, Department of Natural Sciences and Engineering. 3/5 Cholokashvili
Ave., Tbilisi 0162, Georgia.
Abstract. In the Eastern Greater Caucasus Georgian
segment Lower-Middle Jurassic shales and sandstones
experienced crush, hydrothermal alteration and ore
mineralization processes. At some hydrothermally altered
areas mainly copper-pyrrhotitic and pyrite-polymetallic
ores were formed. Already known ore occurrences were
studied and, at the same time, new and interesting ore
occurences were discovered in the hydrothermally
altered zone in the r. Stori canyon (Bendena,Gelia, and
enriched with Th zone) and pyrite-polymetallic ore
mineralization at the village Lechuri. The latter should be
of great interest, since it shows lots of similarities to
Filizchay pyrite-polymetallic deposit by its geologic
position and mineralogical-geological parameters, which
makes necessary further detailed study of the area. It
should be noted that at some areas, on the result of
conducted research, for the first time the increased
concentrations of Au (at Artana and Tebulo ore fields)
were reported. At Tebulo ore field gold increased
concentrations were defined as in massive polymetallic
ores, so - in hydrothermally altered zones, which should
be considered as one of the most important results of the
research study. These ore occurrences are also
characterized with the significant concentrations of Th, Bi,
Co and Cd.
Keywords: Eastern Caucasus, Georgia, ore-forming,
ore occurences.
1 Introduction
More than 100 quartz-pyrite-pyrrhotite and copper-
polymetallic ore manifestations of different scale are
detected in the eastern Greater Caucasus Georgian
segment, which are represented by impregnations, lodes,
veins and massive sulphide bodies. Our research interest
to the above area is mainly caused by the fact that, in the
60-ies of the last century in the neighboring Azerbaijan
(southern slope of the Greater Caucasus) within the same
geological structure and sediments, were discovered
important stratiform pyrite-copper-polymetallic deposits:
Katsdag, Filizchay and Katekh (Novruzov and Agaev
2010). In addition, almost in the same years, on the
northern slope of the Greater Caucasus was opened
copper-polymetallic deposit Kizil-Dere in Dagestan,
Russian Federation (Bogush and Kurbanov 1999). After
almost thirty years gap in research of the above
segment, the authors conducted new geological
prospecting works, within the region. In particular, it
was carried out more detailed study of geological
construction, magmatic and post-magmatic hydrothermal
processes and ore occurrences. The results allowed the
researchers to make essential corrections in geological
structure of the region, and in metallogenic point of
view, significant news were uncovered.
2 Material and methods
During the geological field works over 200 petrographic
samples, and about 700 geochemical samples were
taken. Geochemical analysis on metal content in samples
were conducted at AcmeLab Vancouver laboratory at the
ICP-MS facility, by different methods, and also at the
laboratory of "CMG" Ltd (Georgia) by the atomic
absorption spectrometry method.
3 Geological settings
The Greater Caucasus represents a Phanerozoic
orogenic unit formed between the Euro-Asian south
continental margin and Arabian plate, and is stretched
on 1200 km among the Black and Caspian seas (fig.1).
The Greater Caucasus is the northernmost terrane of the
Caucasus orogen, which is accreted on the southern
margin of the Euro-Asian continent. It is currently a
folded-nappe formation, in which two major structural
stages are distinguished: a Pre-Mesosoic crystalline
basement and Meso-Cenozoic sedimentary and
volcanic-sedimentary cover (Gamkrelidze and
Shengelia 2005).
Figure 1. Tectonic zoning of the Caucasus and adjacent area
on the basis of the terrane analysis Adapted after I.
Gamkrelidze (1997).
Terranes: GC- Greater Caucasian, BT- Black Sea-Central
Transcaucasian, BS-Beiburt-Sevanian, IA-Iran-Afganian, AT –
Anatolian. EGCGS- Eastern Greater Caucasus Georgian
Segment.

The eastern Greater Caucasus Georgian segment, with
40-25 km width, can be traced for about 125 km east
from the rr. Iori-Alazani watershed till the r. Mazim-
Chay valley (Azerbaijan border) (fig.2). Its northern
border runs along the boundaries of Dagestan and
Chechnya, and to the south is separated from the r.
Alazani depression by the regional fault and covers
approximately 3900 km2area.
On the southern slope of the Greater Caucasus the
research area is outcropped by the Alazani River sources
and its left tributaries: rr. Makhvali, Stori, Didi Khevi,
Lopota, Chelti and others (Kakheti region), and on the
northern slope - the River Alazani of Tusheti and its
tributaries (Tusheti region) (fig.2). The sedimentary
Figure 2. Schematic map of main ore occurences in the
Georgian Segment of the Eastern Greater Caucasus and
neighbouring Azerbaijan
cover of both segments is approximately the same and is
mainly represented by intensively folded Lower-Middle
Jurassic schists, shales and sandstones (Topchishvili
1996), and subordinated dacite-andesite-basaltic layers
and tuffs (Akimidze 2010). In the Middle Jurassic this
sedimentary cover was intersected by numerous
magmatic bodies of different composition and thickness.
The whole complex of rocks has experienced intensive
crush, brecciation, hydrothermal alteration and ore
mineralization (Okrostsvaridze et al. 2011).
4 Ore-Forming Processes
The research conducted in the eastern Greater Caucasus
Georgian segment showed that ore mineralization
processes are related to activities of hydrotherms formed
in magmatic centers. As it is known hydrothermal
mineralizations represent a big class, which includes
economically so important deposits as porphyry,
epithermal, orogenic Au and others (Goldfarb et al.
2005; Ridley 2013).
Field observations showed that hydrothermal alterations
and ore mineralization processes occur only in Lower-
Middle Jurassic formations, and these processes don't
take place within the younger formations. This fact is
one of the important arguments indicating that ore
mineralization processes of the Greater Caucasus
Kakheti segment genetically are linked to Bathonian
granodioritic magmatic activity. Ore mineralization is
preceded by hydrothermal alteration of rocks, during
which chlorite+sericte, quartz+sericite+pyrite (phyllic),
quartz+sericite+chlorite+pyrite (propylitic), epidote+
chlorite+calcite+pyritic associations were formed.
Within the later crack systems of these rocks quartz-
pyrite-pyrrhotitic, quartz-chalcopyritic – and, at the end,
quartz-calcite-polymetallic associations have been
crystallized from hydrotherms (fig.3).
Figure 3. Silicified and ore mineralized Lower Jurassic
shale, r.Stori canyon. A- silicified, sericitized and carbonatized
shale; B- quartz vein, C-carbonate veins, D - quartz-pyrite-
pyrrhotite vein.
5 Ore Occurrences
The research of ore occurrences in the eastern Greater
Caucasus Georgian segment has a long history.
Nowadays over 100 copper-pyrrhotite and pyrite-
polymetallic ore occurrences of different scales are met
in the eastern Georgian segment of the Greater Caucasus,
which at the present erosion level form impregnations,
lodes, veinlets or massive ore bodies. We have studied
the known ore occurrences of Tebulo, Ilurta, Satskhvre
Khorkhi, Abano, Quachadala, Artana, Loduani, Chelti,
Shorokhevi and Areshi. Besides the above-noted, some
ore manifestations were observed and studied for the
first time, in particular, in the limits of the
hydrothermally altered zone of the r. Stori (Gelia,
Bendena and zone enriched with Th) and also at the
village Lechuri in the Stori river valley. Considering the
results of the study, Tebulo and Stori orefields and
Lechuri polymetallic ore occurrence are of particular
interest. Below is given brief characterization of some
ore manifestations.
5.1 Stori orefield
It represents complex of ore occurrences within the
altered zone of the Stori River canyon on the southern

slope of the Great Caucasus and is traced about 3.7 km.
Rocks, altered at the present erosion levels, are mainly
presented by quartz-sericite-pyrite and quartz-sericite-
chlorite-pyrite mineralizations, which undergo intense
pyritization. This fact indicates that hydrotherms were
rich in iron and sulfur. These rocks are easily
distinguished in the relief because of their distinctive
reddish, yellowish and grayish colours. We believe that
they are typical phyllitic and prophyllitic, which tend to
develop around the large porphyry deposits (Ridley
2013).
The Stori hydrothermal zone was sampled on gold
content along the motorway Phshaveli-Omalo. Over 200
samples were analyzed on ICP-MS device, by 1F15 and
3B methods but we have not got favorable results.
However, four zones of general Caucasian trend have
been allocated in the northern part with a thickness of
several of hundred meters, in which the gold
concentration ranges within 0.01-0.94 g/t. In particular,
in the first zone the metal concentration ranges in 0.01 -
0.66 g/t, in the second – 0.01-0.94 g/t, in the third – 0.01-
0.68 g/t, and in the fourth – 0.01-0.87 g/t.
Three ore occurrences – Gelia, Bendena and zone with
Th mineralization, were distinguished within the Stori
hydrothermal zone in the valleys. The thorium
occurrence is localized at the north part of the ore field
and high concentrations of thorium are associated with
quartz-plagioclase veins, where the content of this
element varies in the large range from 50 g/t to 3880 g/t.
It should be noted that in addition to thorium high
concentrations of bismuth are also marked in this
occurrences (55 g/t – 4800 g/t).
5.2 Artana orefield
In the Aratana ore field ten ore occurrences are known.
Among them the ore veins Samchedlo and Inglisuri are
studied best of all. Vein Samchedlo is situated in the left
rocky cornices of the r. Okhotistskali, 12 km north of the
village Artana. The thickness of ore vein amounts 2-2.5
m, and is traced along the strike at about 500-550m. The
central part of the vein is built up by massive
chalcopyrite-pyrrhotitic brecciated ore. 18 samples of
vein Samchedlo were analyzed and the following results
were obtained: copper concentration in massive ores
ranges between1.40-3.54%, iron – 19.6-61.4%, lead –
17-21 g/t, zinc – 173-610 g/t, cobalt – 118-1040 g/t,
cadmium 8-22 g/t, bismuth – 15-50 g/t, and silver– 2-4
g/t. In massive chalcopyrite-pyrrhotitic ores of the
manifestation increased content of gold was detected for
the first time (0.32-1.31 g/t).
Vein Inglisuri is located on the left rocky cornices of the
r. Okhotistskali, in 1.5 km distance from the outcrop of
the vein Samchedlo. It is situated in a tectonic crush
zone with general Caucasian strike (dip 50°, < 75°), with
capacity of 4.5–5.0 m. The zone is built up with
Pliensbachian brecciated, chloritized and silicified
shales, in the middle of which ore body of 1.4-1.8 m
thick is formed. It is represented by pyrrhotite-
chalcopyrite lences, lodes and veinlets (fig. 4), where
small amount of pyrite, galena and sphalerite is detected.
A tunnel by length of 38 m and 2 m diameter is made
through the ore body. It should be noted that the
cornices, in the south from the vein, experience intense
silicification and malachitization, where some small
tunnels were made by English miners in the past.
Our research data for the vein Inglisuri are as follows
(12 samples were analyzed on the same equipment and
by using the methods as for vein Samchedlo): copper
concentration in massive ores varies in the range 1.09-
5.14% , iron - 16.4- 61-4%, lead - 6 - 44 g/t, zinc - 140 -
8540 g/t, cobalt - 118 -1040 g/t, Cadmium 8 - 22 g/t,
bismuth 19 - 75 g/t, f arsenic 12 - 28 g/t, and silver - 2 -
4 g/t. In the selvage of the mineralization quartz-pyrite-
chalcopyrite veinlets gold increased content was
determined for the first time (3.09 g/t). It should be
noted that the increased gold content couldn’t be fixed
again by the method 1F15 and it was still fixed only by
method 3B.
Figure 4.Orebearing quartz-pyrrhotite-chalcopyrite veinlets
in selvage of vein " Inglisuri ".
5.3 Lechuri ore occurrence
South from the village Lechuri, approximately 1.5 km in
the valley of the Stori River left tributary, for the first
time was observed pyrite-polymetallic ore occurrence,
which forms about 2 m height rocky cornices in the
riverbed. Ore occurrence is covered by alluvial-delluvial
deposits that make impossible its tracing or thickness
detection. Metal concentration of Lechuri ore (16
samples) varies: Au – 0.02-0.08 g/t, Ag – 5-16 g/t, As –
40-292 g/t, Bi – 7-28 g/t, Cd – 9-26 g/t, Co– 7-21 g/t, Cu
– 300-1470 g/t, Pb > 10000 g/t, Zn > 10000 g/t.
5.4 Tebulo orefield
Tebulo orefield outcrops in Tusheti, on the eastern slope
of the Tebulo Mountain, at 2700-2900 m.a.s.l. and covers
about 22 km2area. In the western part of the ore field
oriented parallel to each other 8 mineralized ore bodies
are outcropped, which represent massive quartzites. 48
samples from this zone were analyzed and Au contents
were detected almost in all samples and the
concentrations vary in the range of 0.03 - 0.64 g/t. In the
eastern part of the ore-field, the shales undergo intense

hydrothermal alteration and is represented by quartz-
sericite-chlorite formations. On the right slope of the r.
Tebulo, copper-polymetallic mineralization massive
veins of 1.3-1.7 m thickness outcrop hypsometrically
250-300 m down the basis of the cornices. Defining the
exact number of the veins is impossible due to slide
rocks cover. Large ore boulders (1.-1.5 m3), torn from
these veins, are met in several places in the valley. Metal
concentration in this ore (14 samples) varies: Cu - 500-
725 g/t, Pb -1300-1430 g/t, Zn >10.000 g/t, Fe – 25.3-
30.9%, Cd – 452.3-745.4 g /t, Co – 82.8-146.7g /t, Bi –
72.3 -81.9 g/t, Mn – 56.-721 g/t, Ni – 21.7-18.4 g/t, and
As – 178.8-219.0 g/t. As for the silver and gold, their
increased concentrations were detected in all samples
and range within 8.19-10.57 g/t (Ag) and 0.029-0.141 g/t
(Au).
6 Conclusion
Thus, from the analysis of the conducted metallogenic
research could be concluded that numerous hydrothermal
ore occurrences localized in the Eastern Greater
Caucasus Georgian segment represent magmatic-
hydrothermal genetic formations, which were formed in
different thermodynamic conditions. There is no doubt
that Artana and other similar ore occurrences are small-
scaled manifestations for modern industrial demands. In
contrast, Stori and Tebulo orefields are large-scaled,
around which thick quartz-sericite-chlorite-pyritic and
albite-epidote-chlorite-pyritic zones characteristic for
porphyry deposits are developed. The both orefields,
besides traditional division (copper-pyrrhotite and pyrite-
polymetallic), could be belonged to iron oxide-gold-
nonferrous metal hydrothermal genetic type, because of
high concentration of iron oxide (> 10%) in both
mineralized areas (Ridley 2013). It should be noted that
iron content in mineralized zones of the region was
firstly determined by the authors. Iron mostly is
represented by oxides, which is very important in
practical point of view.
Lechuri ore occurrence, which was found by the authors,
is of great interest. The mineralization shows similarity
to Filizchay pyrite-polymetallic deposit by its geological
position and mineralogical-geochemical parameters. It is
necessary further detailed study of the ore manifestation.
Also it should be highlighted Tebulo ore field, where
gold content was determined as in massive polymetallic
ores, so in silicified zones.
In conclusion we note that it is necessary to undertake
more detailed metallogenic research in the eastern
Greater Caucasus Georgian segment in future, as there
are a lot of arguments that here too can be detected as
important fields as in neighbouring Azerbaijan and
Dagestan.
Acknowledgements
The authors wish to express gratitude to Shota Rustaveli
National Science Foundation for financial support of the
project (# GNSF / ST09-1071-5-150) through which the
research works were conducted in the Greater Caucasus
Kakheti region and to the Ilia State University for
funding fieldworks in Tusheti region. The authors wish
also to thank the leadership of "CMG" Ltd for
determining metal contents in Tusheti samples.
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