Eluvial-alluvial gold from the gold-copper occurrence Borov Dol (R

ÑÏÈÑÀÍÈÅ ÍÀ ÁÚËÃÀÐÑÊÎÒÎ ÃÅÎËÎÃÈ×ÅÑÊÎ ÄÐÓÆÅÑÒÂÎ, ãîä. 68, êí. 1—3, 2007, ñ. 66—76
REVIEW OF THE BULGARIAN GEOLOGICAL SOCIETY, vol. 68, part 1—3, 2007, p. 66—76
Eluvial-alluvial gold from the gold-copper occurrence Borov Dol
(R. of Macedonia). Part I: Geochemistry of stream sediments
and their relation to the source rocks and ores
Veselin Kovachev1, Violeta Stefanova2, Rosen Nedialkov1, Veselin Mladenov1
1
Sofia University “St. Kliment Ohridski”, 1504 Sofia, Tsar Osvoboditel Blvd. 15;
E-mail: [email protected]
2 Faculty of Mining and Geology, 2000 Stip, Goce Delchev 89, R. of Macedonia;
E-mail: [email protected]
Â. Êîâà÷åâ, Â. Ñòåôàíîâà, Ð. Íåäÿëêîâ, Â. Ìëàäåíîâ. 2007. Åëóâèàëíî-àëóâèàëíî çëàòî îò çëàòíîìåäíîòî ðóäîïðîÿâëåíèå Áîðîâ äîë (Ð. Ìàêåäîíèÿ). ×àñò I. Ãåîõèìèÿ íà ïîòîêîâè ñåäèìåíòè è
âðúçêàòà èì ñ êîðåííèòå ñêàëè è ðóäè. – Ñï. Áúëã. ãåîë. ä-âî, 68, 1—3, 66—76.
Ðåçþìå. Îñíîâíàòà çàäà÷à íà íàñòîÿùàòà ðàáîòà å äà ñå èíòåðïðåòèðàò ïîëó÷åíèòå ðåçóëòàòè îò îáðàáîòêàòà íà àíàëèçèòå îò ïîòîêîâèòå ñåäèìåíòè ïî ïîðå÷èåòî íà Áîðîâ äîë ñ öåë óñòàíîâÿâàíå íà ãåîõèìè÷íî ñõîäñòâî ìåæäó ïîòîêîâèòå ñåäèìåíòè è ïîäõðàíâàùèòå ãè ñêàëè, êàêòî è äà ñå õàðàêòåðèçèðà ðàçïðåäåëåíèåòî íà
åëåìåíòèòå íà ïîòîêîâèòå ñåäèìåíòè ïî ïðîôèëà íà ïîòîêà. Çà ðåøàâàíå íà òàçè çàäà÷à å èçïîëçâàí êîìïëåêñ
îò ìåòîäè, âêëþ÷âàù îïðîáâàíå íà ñêàëè, ðóäè è ïîòîêîâè ñåäèìåíòè (äî 2 km îò ðóäíîòî òÿëî ïî ïîòîêà
Áîðîâ äîë), ïåòðîëîæêè, ïåòðîõèìè÷íè è ðóäàðñêè èçñëåäâàíèÿ, õèìè÷åñêè àíàëèçè íà ïîòîêîâèòå ñåäèìåíòè,
êëúñòåð è ôàêòîðåí àíàëèç. Óñòàíîâÿâà ñå ñõîäñòâî ìåæäó õèìè÷íèÿ ñúñòàâ íà ñêàëèòå è ïîòîêîâèòå ñåäèìåíòè îò áëèçêàòà îêîëíîñò (2 km ïî ïîòîêà) íà ðóäíîòî òÿëî Áîðîâ äîë. Âúç îñíîâà íà êëúñòåð àíàëèçà ñêàëîîáðàçóâàùèòå åëåìåíòè îò ïîòîêîâèòå ñåäèìåíòè îáîñîáÿâàò 4 åëåìåíòíè àñîöèàöèè: [(La-Ce)-(Th-S)]-(Zr-Hf)],
(Sr-Na)-K, [(Mg-Li)–(Mn-Cs)]–[(Ti-Fe)-Y] è (Ca-P), êîèòî äåôèíèðàò îïðåäåëåíè ìèíåðàëè èëè ìèíåðàëíè ãðóïè. Ðóäíèòå åëåìåíòè ôîðìèðàò 8 àñîöèàöèè: {[(Mn-Co)-As]Tl}-[(Hg-In)-Ag], {[(Ni-Cd)-Cr]-Zn}-[(Sb-Bi)-W], {[(VTi)-Ta]-Nb}-Sn , (U-Pb), (Ga-Ge), (Mo-Au), (Fe-S)-Re è (Ca-Cu) ïîäðåäåíè ïî ñèëà íà âðúçêàòà. Ïðîáèòå ïî ïðîôèëà íà ïîòîêà Áîðîâ äîë ïîêàçâàò ãîëÿìî ñõîäñòâî è ïðèíàäëåæàò êúì åäíà ãðóïà. Íåçàâèñèìî îò òîâà, òå ñå
ãðóïèðàò â äâà ïîäêëúñòåðà, ñúâïàäàùè ïðîñòðàíñòâåíî ñúñ ñòðúìíèÿ ó÷àñòúê íà çàñèëåí òðàíñïîðò è ñ
êóìóëàòèâíèÿ, ñðàâíèòåëíî ðàâíèíåí ó÷àñòúê íà ïðîôèëà ïðåäè âëèâàíåòî ìó â ðåêà Êðèâà Ëàêàâèöà. Ñúîáðàçíî ñâîåòî ïîâåäåíèå ïî ïðîôèëà îòäåëíèòå åëåìåíòè îôîðìÿò òðè ãðóïè: åëåìåíòè, êîèòî ñå íàòðóïâàò â
äîëíàòà ðàâíèííà ÷àñò íà ïðîôèëà; åëåìåíòè, èìàùè îòíîñèòåëíî âèñîêà êîíöåíòðàöèÿ â ðóäíîòî òÿëî è â
êóìóëàòèâíàòà ÷àñò íà ïðîôèëà; åëåìåíòè, ÷èåòî ðàçïðåäåëåíèå íå ñå õàðàêòåðèçèðà ñ îïðåäåëåíà òåíäåíöèÿ.
Êëþ÷îâè äóìè: çëàòî, ïîòîêîâè ñåäèìåíòè, åëåìåíòíè àñîöèàöèè, êëúñòåð àíàëèç, Áîðîâ äîë,
Ð. Ìàêåäîíèÿ.
Abstract. The basic purpose of this work is to interpret the obtained results from processing of analyses on stream
sediments along the Borov Dol River course aiming to establish geochemical resemblance between the stream sediments
and the source rocks, and also, to record the distribution of elements in the sediments along the stream profile. In order
to solve this problem a complex of methods is used including sampling of rocks, ores and stream sediments (up to 2 km
from the ore body along the Borov Dol stream), petrological, petrochemical and ore studies, chemical analyses on the
stream sediments, cluster and factor analysis. A similarity is established between the chemical composition of the rocks
and the stream sediments in close proximity (2 km along the stream) to the Borov Dol ore body. On the basis of cluster
analysis, the rock-forming elements in the stream sediments are grouped in 4 elemental associations: [(La-Ce)-(Th-S)](Zr-Hf)], (Sr-Na)-K, [(Mg-Li)–(Mn-Cs)]–[(Ti-Fe)-Y] and (Ca-P), which define particular minerals or mineral groups.
The ore elements comprise 8 associations: {[(Mn-Co)-As]Tl}-[(Hg-In)-Ag], {[(Ni-Cd)-Cr]-Zn}-[(Sb-Bi)-W], {[(V-Ti)-Ta]Nb}-Sn , (U-Pb), (Ga-Ge), (Mo-Au), (Fe-S)-Re and (Ca-Cu) arranged by linkage distance. The samples along the profile
of Borov Dol show great similarity and belong to one group. Irrespective of this, they are grouped in two subclusters
coinciding spatially with the steep sector of increased transport, and with the cumulative, relatively flat sector of the
profile before mouthing into the Kriva Lakavitsa River. In accordance with their behaviour along the profile the separate
elements comprise three groups: elements which accumulate in the lower flat part of the profile, elements having relatively high concentrations in the ore body and in the cumulative part of the profile, and elements whose distribution is not
characterized by a definite trend.
Key words: gold, stream sediments, geochemical associations, cluster analysis, Borov Dol, R. of Macedonia.
66
Introduction
The sampling of stream sediments in proximity to deposits of various metal mineral resources has become
one of the basic prospecting methods during the last
years. The gained experience allows to draw conclusions and to expand the sphere of its application.
Moreover, the interpretation of the obtained geochemical results from sampling of stream sediments might
be directed towards searching for geochemical relations with the rocks and ores which generate those
sediments. Interesting is also the opportunity to study
the degree of alteration during the exogenic processes
of the minerals in the stream sediments and particularly of native gold. The establishment of relation between the geochemical peculiarities of the stream sediments and the building minerals, as well as the correlation of the minerals from the primary ores and rocks
with those comprising the stream sediments, might give
important dependencies which could directly aid the
prospecting works and produce genetic conclusions.
For example, as a result it was established that during
exploration for Au in the Tertiary epithermal As-SbTl-Au deposit Alshar (R. of Macedonia) the study on
the stream sediments did not give good results because
the size of gold particles was below 5 µm and referred
to mountain streams (Kovachev et al., 2006). Dependencies were mentioned between the fineness of the
endogenic gold and the industrial-genetic type of deposits (Stefanova et al., 2006) which were later related
to the magmatic activity and the deep structure of the
crust in the territory of Bulgaria (Kovachev et al., 2007).
Endogenic gold in the gold-bearing deposits in
R. of Macedonia has been sporadically established
and data concerning its mineralogical and geochemical features are almost completely lacking in the
literature (Cifliganec et al., 1994; Bogoevski et al.,
1996; Serafimovski, Rakic, 1998; Stefanova, 2005).
On the other hand, it is not difficult to detect gold
aggregates in the slick of most copper and coppergold deposits in the country. The study on the mineralogy and geochemistry of the deluvial-alluvial gold
and the coexisting minerals, as well as the geochemical features of the stream sediments which contain
the gold, is the basic objective of the present work.
The solution of this task is a step toward a broader
investigation which is related with the opportunity
to define the type of the ore mineralization on the
basis of comparative analysis of the endogenic and
deluvial-alluvial gold.
Geological notes
The Borov Dol ore occurrence is located in the southern part of the Buchim—Damyan—Borov Dol ore region. The latter belongs to two geotectonic units:
Vardar zone and Serbo-Macedonian massif. The latter is defined by the porphyry-copper deposit Buchim,
the scarn-iron deposit Damyan and the Borov Dol
ore occurrence, the latter having unclarified position in terms of classification with Cu and Au being
the major elements (Stefanova et al., 2004a). Porphyry-copper mineralization type of Paleogene age has
been assumed. The geological framework prior to the
ore-forming processes comprises Precambrian metamorphic rocks (shales and gneisses), Paleozoic schists,
metagabbroids, diabases and carbonate rocks, Mesozoic ultrabasic rocks, granitoids and variegated sediments. The Paleogene period was an arena of
sedimentary and igneous activity in graben-like depressions resulting in the formation of conglomerates and limestones, which were later intersected and
covered by lavas and pyroclastics of andesitic composition. The magmatism started during the Late
Oligocene and ended towards the beginning of the
Neogene. The upper levels of the section are occupied by a sedimentary series including sandstones,
conglomerates and sands. The uneven relief of the
region predetermined the formation of proluvial-deluvial and alluvial sediments.
From the viewpoint of the assigned task, of special
interest is the geology in close proximity to the Borov
Dol ore body (Fig. 1), and particularly, the Borov Dol
River course. The latter and the nearby tributary of
Krundirov Dol are located within coarse porphyric
(after plagioclase and/or potassium feldspar) predominant latites, andesites and quartzlatites. These rocks
host ores in the upper sector of the river course and
are irregularly propilitized in the rest part down to the
mouthing into the Kriva Lakavitsa River. In the central part of the ore occurrence the latites are crosscut
by a younger isometric body of fresh ore-free andesites. The age of the coarse porphyric latites and andesites (K/Ar method) is 25—28 Ma, e. g. Oligocene (Petkovich, Ivanov, Stoianov, Serafimovski, personal communications) with single samples showing older age
– 42.3±4.0 Ma, e. g. Eocene (Tudjarov, 1993).
Material and methods
The present investigation was accomplished by applying field sampling, optical, geochemical, mineralogical and statistical methods.
Sampling methods. Two kinds of samples were collected from the area of the Borov Dol ore occurrence:
rock samples for petrological studies, and samples from
the stream sediments for geochemical and mineralogical studies. The former (2 samples) were collected
from the predominant rocks as sectors unaffected by
hydrothermal and exogenic alterations were selected
throughout the Borov Dol drainage area. The second
kind of samples (11 samples) was collected along the
Borov Dol river course at distance less than 2 km from
the ore body. The sample locations (coordinates by
GPS) are shown in Figure 1. Fine sediments were sampled that had been formed during the stage of running of high stream waters. Two samples from each
point were collected (total weight of 15 kg), which
were later separated by size in the laboratory. The fraction less than 0.17 mm was studied by means of ICPAES and MS, and the fraction less than 0.5 mm was
studied by means of BLEG analysis. The minimum
67
Fig. 1. Schematic geological map of the Borov Dol ore occurrence with sample locations (modified àfter Tudjarov, 1993 with
additions by autors)
Pleistocene: 1, alluvial sediments, 2, rivers terraces; Pliocene: 3, coarse pebble lacustrine sediments, 4, pebbly-sandy lacustrine
sediments; Oligocene-Miocene: 5, latites, 6, andesites and latites, 7, andesites, 8, pyroclastic tuffs, 9, volcanogenic-sedimentary
deposits; Eocene: 10, Paleogene flysch; 11, limestones, 12, and claystones, 13, claystones and sandstones, 14, sandstones and
conglomerates; Cretaceous: 15, volcanites; Paleozoic: 16, carbonate rocks, 17, metamorphosed ultrabasites, pyroxenites and
carbonate rocks, 18, chlorite-sericite schists; 19, geological boundary; 20, fault; 21, thrust; sample location for: 22, stream
sediments and 23, for rocks; 24, drainage area outlines
Ôèã. 1. Ñõåìàòè÷íà ãåîëîæêà êàðòà íà ðóäîïðîÿâëåíèå Áîðîâ äîë ñ ìåñòàòà íà îïðîáâàíå (ïî Tudjarov, 1993 ñ
äîïúëíåíèÿ íà àâòîðèòå)
ïëåéñòîöåí: 1 – àëóâèàëíè íàñëàãè, 2 – ðå÷íè òåðàñè; ïëèîöåí: 3 – ãðóáî ÷àêúëåñòè åçåðíè ñåäèìåíòè, 4 – ÷àêúëåñòî-ïåñúêëèâè åçåðíè ñåäèìåíòè; îëèãîöåí–ìèîöåí: 5 – ëàòèòè, 6 – àíäåçèòè è ëàòèòè, 7 – àíäåçèòè, 8 – âóëêàíñêè
òóôè, 9 – âóëêàíîãåííî-ñåäèìåíòíè íàñëàãè; åîöåí: 10 – ïàëåîãåíñêè ôëèø, 11 – âàðîâèöè, 12 – âàðîâèöè è ãëèíè,
13 – ãëèíè è ïÿñú÷íèöè, 14 – ïÿñú÷íèöè è êîíãëîìåðàòè; êðåäà: 15 – âóëêàíèòè; ïàëåîçîé: 16 – êàðáîíàòíè ñêàëè,
17 – ìåòàìîðôîçèðàíè óëòðàáàçèòè, ïèðîêñåíèòè è êàðáîíàòíè ñêàëè, 18 – õëîðèò-ñåðèöèòîâè øèñòè; 19 – ãåîëîæêà ãðàíèöà; 20 – ðàçëîì; 21 – íàâëàê; 22 – ìåñòîïîëîæåíèå íà ïðîáà îò ïîòîêîâè ñåäèìåíòè; 23 – ìåñòîïîëîæåíèå
íà ñêàëíà ïðîáà; 24 – êîíòóð íà âîäîñáîðíà ïëîù
68
amount of material for the first method was about
400 g, and for the second – 2.5 kg. A slick sample
was collected apart from each sample from stream
sediments, both location being close to each other. The
slick sample was rinsed in place until grey slick was
obtained. The separation of the gold aggregates and
the initial stage from the study of the coexisting minerals was performed by means of stereomicroscope.
Petrological studies. Optical petrographical descriptions were carried out in combination with wet
silicate analyses, major and trace element analyses
(atomic absorption spectrophotometry) and electron
microprobe analysis of minerals (apparatus JEOL
JSM 35CF).
Chemical analyses of the stream sediments. The
samples from stream sediments were analyzed for 49
elements by means of ICP-AES and MS in the ALS
Chemex Laboratory in Australia. Aiming at more
precise determination of Au, Ag and Cu, all samples
were additionally analyzed with BLEG analysis (with
cyanide leaching) in order to establish the possibility for extraction of gold by means of this technology.
The analyses were performed in the SGM Welshpool
Minerals Laboratory, Australia.
Methods of interpretation of the geochemical data.
Methods of basic statistical analysis and multivariate exploratory methods (cluster and factor analysis)
(Davis, 1973) were used for interpretation of the
geochemical data. This method classifies the variables (samples or chemical elements) by similarity.
The coefficient of Pearson was applied as distance
measure for performance of the cluster analysis. This
coefficient uses as starting index the coefficients of
correlation of the variables thus eliminating the influence of the size of the analyses (percent, ppm, etc.).
The coefficient is calculated on the basis of covariation of the elements from the excerpt, referred to their
variations. The variables are presented by values in
the interval from —1 to +1, as these tending toward 1 are expressed by strong negative dependence, those
tending towards +1 are expressed by strong positive
dependence, and those approaching 0 are assumed
as independent. In order to avoid the negative values, 1—r was used instead of r. The correlation of the
clusters was performed after the method of the
weighted pair-group average, which measures the
distances between the potential clusters on the basis
of their mean contents.
The factor analysis was realized with Varimax
normalized variables and by applying the method of
principal components. It was used as giving additional information about the interpretation of the
cluster analysis results.
Comparative analysis
of the geochemistry of rocks
and stream sediments
The stream sediments are composed of minerals
resulting from the destruction of rocks and ores which
build up the drainage area of the streams in close
proximity to the Borov Dol ore occurrence. This
requires a study on the major rock-forming and ore
minerals and the contained chemical elements in order
to compare them with data on the stream sediments.
The drainage area of Borov Dol and Krundirov
Dol is mainly built up of andesites and latites (as
well transitions between them), and subordinately of
basaltic andesites and pyroclastics with similar composition. The major rock-forming minerals were thoroughly studied by Stefanova et al. (2004b). They are
carriers of the following major oxides: plagioclases
(SiO2, Al2O3, CaO, Na2O; below 1% FeO, K2O, MnO,
MgO è TiO2), biotite (SiO2, TiO2, Al2O3, MgO, K2O,
FeO; below 1% MnO, CaO), hornblende (SiO2, Al2O3,
MgO, CaO, Na2O=K2O, FeO; below 1% TiO2, MnO),
pyroxene (SiO2, MgO, CaO, FeO; below 1% TiO2, MnO
and K2O), potash feldspars (SiO2, Al2O3, Na2O<K2O,
BaO, below 1% TiO2, FeO, MnO, CaO). These oxides
determine the stable geochemical associations, which
will be discussed further.
The ore body Borov Dol comprises many minerals as the commonest of them and the building elements are as follows: pyrite (Fe, S), chalcopyrite (Cu,
Fe, S), polydimite* (S, Fe, Cu, Ni>Co), bravoite* (Fe,
Ni, S), bornite* (Cu, Fe, S), native gold* (Au, Ag),
magnetite (Fe, O), pyrrothite (Fe, S), molibdenite (Mo,
S), coveline (Cu, S), chalcosine (Cu, S), galena (Pb,
S), sphalerite (Zn, S), hematite (Fe, O), rutile (Ti, O),
tenantite (Cu, As, S), tetraedrite (Cu, Sb, S), bismutinite (Bi, S) and polyanite (pyrolusite) (Mn, O). These
phases were studied initially by Tudjarov (1993), and
later, their list was complemented by the present authors (the ones marked with asterisk).
In the light of those data, a comparative analysis
of the geochemical similarities between the stream
sediments and the rocks could be made. Furthermore,
an interpretation of the elemental associations obtained from the cluster analysis is possible. In Table
1 are given the comparative geochemical data on
the predominant rocks and samples from stream sediments along the Borov Dol river course. A similarity
between those data is established. It is due to the small
variability and close composition of the rocks taking
part in the geological structure. The similarity is determined by the ratio of the mean values of the elements building up the rocks and those established in
the stream sediments. When this ratio is close to unity it means that there is no substantial change of the
concentration of the respective element in the stream
sediments relative to the rocks. The greater than unity is the value, the more depleted is the stream sediment in terms of the respective element. The studied
elements in the Borov Dol stream might be grouped
as follows: practically with unchanged concentration in the stream sediments (rock/stream sediment
ratio varying from 1.10 to 0.9) are the elements Al, Fe
and Rb. The tendency of Ti, K, Na and Co is to
weakly decrease in the stream sediments, and Ca
shows a reverse trend (rock/stream sediment ratio
varying from 1.50 to 0.5). Strongly reduced is the
content of Mg, Cr, Li and Zn in the stream sediments as the latter are enriched in Cu and Pb (rock/
69
70
0.12
9.57
2.03
0.59
1.59
0.09
Mn
Mg
Ca
Na
K
P
1439.00
116.00
66.00
Sr
Zn
Cu
-
-
-
-
As
Ba
Be
Bi
-
-
-
-
-
-
-
-
Ag
-
-
-
-
Au
Au BLEG
Ag BLEG
17.00
-
29.00
313.00
1035.00
46.00
3.00
13.00
22.00
26.00
2.65
3.15
4.15
1.44
0.12
1.55
1.99
9.19
0.43
27.11
BD6
<5.00
Pb
-
88.00
Rb
Cu BLEG
30.00
29.00
Co
Li
779.00
6.24
Fe
1054.00
7.71
Al
Ni
0.43
Cr
24.41
Ti
basaltic
andesite
(BD40)
Si
Elements
-
-
-
-
-
-
-
-
13.00
-
133.00
116.00
2584.00
62.00
5.00
5.00
14.00
36.00
3.21
3.69
3.68
1.07
0.08
1.97
2.36
8.67
0.38
27.37
BD9
latite
Element contents in rocks
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
1.98
2.81
2.81
1.51
3.26
1.21
3.53
8.52
0.41
26.30
mean
2.60
2.52
870.00
19.30
0.29
0.78
0.10
0.33
183.00
282.00
1155.00
168.00
933.00
68.60
5.70
20.10
68.50
114.00
0.13
1.56
2.02
1.50
1.03
0.05
4.11
9.15
0.32
-
BD1
0.94
2.60
840.00
18.90
0.43
0.89
0.12
0.21
89.60
571.00
2900.00
57.00
1130.00
56.30
4.70
19.6
38.0
37.0
0.24
1.76
2.28
2.39
0.93
0.04
3.40
8.49
0.29
-
BD2
1.28
2.23
1160.00
11.00
0.29
0.60
0.11
0.16
151.50
187.00
901.00
63.00
1090.00
74.8
3.50
8.90
18.5
36.0
0.15
1.97
1.99
1.52
0.83
0.02
4.41
8.84
0.29
-
BD3
1.00
2.36
1010.00
9.00
0.23
0.50
0.13
0.18
138.50
199.00
812.00
52.00
1200.00
66.20
3.40
6.70
19.5
33.0
0.15
1.99
2.30
1.60
0.77
0.02
3.49
8.94
0.29
-
BD4
1.09
2.45
1020.00
9.20
0.22
0.67
0.12
0.16
152.50
158.00
808.00
50.00
1280.00
68.40
3.50
6.50
18.60
30.00
0.14
2.13
2.46
1.60
0.76
0.02
3.50
9.03
0.29
-
BD5
0.82
2.40
910.00
7.60
0.14
0.41
0.05
0.07
117.00
125.00
571.00
39.00
1435.00
64.10
3.00
6.20
19.50
24.00
0.10
2.06
2.66
1.80
0.57
0.02
2.41
8.78
0.20
-
BD6
1.25
2.50
1550.00
8.60
0.20
0.48
0.11
0.24
157.00
108.00
833.00
44.00
1490.00
62.70
3.30
6.50
19.70
45.00
0.16
2.10
2.64
1.99
0.66
0.02
3.43
9.39
0.25
-
BD7
1.09
2.68
1000.00
9.20
0.19
0.47
0.09
0.12
135.50
332.00
1225.00
61.00
1315.00
67.00
3.20
11.00
27.60
36.00
0.13
2.01
2.46
1.69
0.74
0.03
3.29
9.16
0.26
-
BD8
Element contents in stream sediments
1.30
2.78
960.00
12.00
0.20
0.52
0.09
0.10
146.50
263.00
1340.00
63.00
1270.00
74.50
3.50
12.70
30.10
38.00
0.12
2.03
2.41
1.65
0.79
0.03
3.35
9.17
0.28
-
BD9
1.12
3.07
900.00
11.80
0.21
0.55
0.08
0.08
143.00
280.00
1635.00
100.00
1135.00
73.70
5.70
16.10
75.40
132.00
0.12
1.92
2.18
1.72
1.09
0.04
3.63
9.19
0.30
-
BD10
1.18
2.91
1110.00
13.60
0.16
0.60
0.10
0.47
153.50
271.00
1795.00
106.00
1320.00
69.90
4.50
14.10
48.90
75.00
0.14
2.15
2.52
1.85
0.88
0.03
3.69
9.48
0.30
-
BD11
Òàáëèöà 1
Cúäúðæàíèå íà ñêàëîîáðàçóâàùè (â òåãë.%) è ðóäíè åëåìåíòè (â ppm) â ñêàëè è ïîòîêîâè ñåäèìåíòè îò ðóäîïðîÿâëåíèå Áîðîâ äîë, Ð. Ìàêåäîíèÿ
Table 1
Contents of rock-forming (in wt.%) and ore elements (in ppm) in rocks and stream sediments from the Borov Dol ore occurrence, R. of Macedonia
1.24
2.59
1030.00
11.84
0.23
0.59
0.10
0.19
142.60
252.36
1270.50
73.20
1236.20
67.90
4.00
11.70
35.00
54.60
0.14
1.97
2.36
1.76
0.82
0.03
3.52
9.06
0.28
-
Mean
-
-
-
-
-
-
-
-
0.08
-
0.06
2.48
1.36
0.96
3.08
1.37
10.38
5.13
14.17
1.43
1.19
0.86
3.97
40.44
1.00
0.94
1.48
-
Ratio
rock/stream
sediment
(coeff.
exogenic
concentration)
71
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Sb
Se
Sn
Ta
Te
Th
Tl
U
V
W
Y
Zr
Hg
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
La
-
-
-
In
-
-
S (%wt)
-
Hf
Re
-
Ge
-
-
-
-
Ga
-
-
Cs
-
-
Mo
-
BD6
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
BD9
latite
Element contents in rocks
Nb
-
Ce
basaltic
andesite
(BD40)
Cd
Elements
Òàáëèöà 1
(ïðîäúëæåíèå)
Table 1
(continued)
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
mean
0.12
23.00
19.60
4.70
140.00
7.20
1.12
22.30
0.05
0.80
3.00
4.00
20.00
0.27
0.01
11.00
37.70
52.70
0.11
0.90
0.22
22.10
5.80
104.00
0.32
BD1
0.26
21.00
24.20
2.70
128.00
4.70
1.09
17.70
0.06
0.83
2.70
5.00
6.84
0.23
0.01
11.40
25.90
45.90
0.16
0.80
0.17
19.80
4.45
97.40
0.15
BD2
0.04
27.90
20.60
3.30
143.00
5.70
0.98
28.10
0.06
0.83
2.60
6.00
6.92
0.43
0.02
10.40
35.50
63.50
0.09
1.00
0.24
21.70
3.76
119.00
0.08
BD3
0.03
26.80
19.50
3.40
127.00
6.50
0.91
24.30
0.10
0.81
2.80
5.00
5.59
0.30
0.01
10.60
30.80
60.80
0.10
1.00
0.18
20.70
2.92
116.50
0.07
BD4
0.03
27.10
18.50
3.60
129.00
6.60
1.00
23.50
0.07
0.83
2.80
6.00
6.10
0.30
0.01
11.00
32.50
56.30
0.10
1.00
0.16
21.30
2.95
108.00
0.07
BD5
0.02
21.90
13.50
2.40
83.00
5.20
0.91
17.90
0.10
0.59
2.00
4.00
5.46
0.20
0.01
7.70
23.20
35.80
0.08
0.80
0.13
18.90
2.41
72.60
0.06
BD6
0.04
25.90
18.30
3.30
117.00
6.30
0.90
24.40
0.10
0.68
2.40
5.00
4.94
0.30
0.02
9.00
31.70
63.30
0.09
1.00
0.15
20.30
2.62
118.00
0.06
BD7
0.02
23.50
18.90
3.00
119.00
6.40
0.95
21.50
0.06
0.75
2.30
4.00
4.58
0.28
0.01
10.20
27.60
48.50
0.10
0.90
0.22
20.90
2.87
97.80
0.11
BD8
Element contents in stream sediments
0.03
24.20
20.20
3.10
122.00
6.80
1.00
22.20
0.06
0.75
2.50
4.00
5.42
0.27
0.01
10.90
29.20
51.10
0.09
0.90
0.23
21.70
3.04
102.00
0.10
BD9
0.03
26.80
22.10
3.20
133.00
6.70
1.02
23.00
0.05
0.82
2.70
4.00
5.24
0.25
0.01
11.80
25.90
53.40
0.10
1.00
0.22
21.90
4.20
107.50
0.28
BD10
0.03
26.80
21.40
3.50
133.00
6.50
1.02
22.20
0.06
0.80
2.60
5.00
5.64
0.27
0.02
11.60
38.00
53.80
0.09
0.90
0.20
21.10
3.86
106.00
0.27
BD11
0.06
24.99
19.71
3.29
124.91
6.24
0.99
22.46
0.07
0.77
2.58
4.73
6.98
0.28
0.01
10.51
30.73
53.19
0.10
0.93
0.19
20.95
3.53
104.44
0.14
Mean
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Ratio
rock/stream
sediment
(coeff.
exogenic
concentration)
stream sediment ratio reaching up to 10 and 0.1).
The greatest change is recorded in the concentration in the stream sediments of Mn and P, as both
elements are strongly depleted. The geochemical behaviour of the listed elements is due to two major
processes: their transformation into soluble form
during the chemical weathering and differentiation
of the bearing minerals by specific gravity in the
stream. For instance, it could be presumed that in
conditions of acid milieu, resulting from weathering
of the sulphides and acidification of waters in proximity to the ore body by H2SO4, Mn and P have passed
into the solution and have been carried away by the
stream, and part of the Cu and Pb have accumulated in the placer in mineral form due to their high
specific gravity.
When correlating the obtained data on the contents of Au, Ag and Cu by means of ICP-AES, MS
and BLEG analysis it is established that the latter
method gives systematically depleted values for the
contents of the enumerated elements (Table 1). Perhaps this results from the size of the mineral grains
(bearing these elements) considering that during the
BLEG analysis coarser fraction (below 0.5 mm) was
analyzed. This means that the bearing minerals of
the three elements have relatively fine sizes (<0.17 mm),
and enrich the fraction used for the ICP analysis.
Two elemental combinations are distinguished when
studying the geochemical characteristics of the
stream sediments. This is related with the fact that
these sediments are composed of two types of exogenically disintegrated minerals: rock-forming and
ore ones. As one mineral is principally composed of
two or more elements, it is expected that the spatial
associations separated by means of the cluster analysis should reflect the closeness of the elements forming definite mineral/minerals. This means that on
the basis of the obtained by the cluster analysis elemental associations it could be judged of the minerals which occur in the stream sediments. This interpretation might be very complicated in case the
same elements occur in the composition of various
minerals. Then mineralogical studies on the stream
sediments are required.
Preliminary division of the element totality in three
groups was made for the realization of the cluster
analysis. The reason is the fact that the catchment
area of the Borov Dol stream is composed of two
contrasting by chemical composition bodies: Tertiary volcanites and ore body. The first group comprises such elements that are typical for the basic rockforming minerals. These are Be, K, Mg, Na, P, Th, Zr,
Y, Hf, Al, Rb, Ba, Li, Cs, Ce, Sr, La. The elements
which are typical mostly for the ore body are Au, Ag,
Cu, As, Bi, Cd, Co, Cr, Ga, Ge, In, Mo, Nb, Ni, Pb,
Re, Sb, Se, Sn, Ta, Te, Tl, U, V, W, Zn, Hg, and Ca,
Fe, Mn, S, Ti are common for both groups as far as
they take part in the structure of the ore body and
the rocks. The last group of elements is incorporated
respectively in the two elemental populations in the
realization of the cluster analysis.
The obtained groups of elements (elemental associations) for both totalities of elements are shown in
Figure 2. The cluster arrangement is in accordance
with the linkage distance between the separate elements, as this closeness is best pronounced for the
first clusters (Table 2).
The elements typical for the rock-forming minerals are arranged in four elemental associations, respectively for hornblende and zircone, feldspars, bio-
a
b
Analysis of the elemental associations
Fig. 2. Groups in the totality of rock-forming elements (a) and in the totality of ore elements (b)
The discontinuous horizontal line shows the level of significance for the links at hypothesis probability of 95%
Ôèã. 2. Ãðóïè â ñúâêóïíîñòòà íà ñêàëîîáðàçóâàùèòå åëåìåíòè (a) è â ñúâêóïíîñòòà íà ðóäíèòå åëåìåíòè (b)
Ïðåêúñíàòàòà õîðèçîíòàëíà ëèíèÿ ïîêàçâà íèâîòî íà çíà÷èìîñò íà âðúçêèòå ïðè âåðîÿòíîñò íà õèïîòåçàòà 95%
72
10 Ñïèñàíèå íà Áúëãàðñêîòî ãåîëîãè÷åñêî äðóæåñòâî, êí. 1—3, 2007
73
(Fe-S)-Re
(Ca-Cu)
VІІІ
-
-
5.
(Mo-Au)
VІ
-
6.
-
-
(+): Au, Mo, Re.
(+): Ge
-
(+): Nb, Sn, Ta, Ti, V.
(+): Cd, Cr, Ni, Zn.
(-): Se.
VІІ
║{[(V-Ti)-Ta]-Nb}-Sn║
ІІІ
(+): Bi, Sb, W
3.
(+): Ag, Cu, As, In, Hg.
(+): Al, Be.
(+): Ca, P.
(-): Rb.
(+): Cs, Li, Mg, Mn, Ti.
(-): K, Na, Sr.
(+): Ce, Fe, Hf, La, S, Th, Zr.
element associations
Factor analysis
2.
4.
{[(Ni-Cd)-Cr]-Zn}-[(Sb-Bi)-W]
ІІ
1.
4.
(Ga-Ge)
{[(Mn-Co)-As]Tl}-[(Hg-In)-Ag]
І
V
-
-
3.
(U-Pb)
(Ca-P)
ІV
1.
2.
factors
IV
[(Mg-Li)–(Mn-Cs)]–[(Ti-Fe)-Y]
(Sr-Na)-K
ІІ
ІІІ
[(La-Ce)-(Th-S)]-(Zr-Hf)]
element associations
І
clusters
Cluster analysis
(+) – positive correlation link; (-) – negative correlation link
(+) – ïîëîæèòåëíà êîðåëàöèîííà âðúçêà; (-) – îòðèöàòåëíà êîðåëàöèîííà âðúçêà
Ore elements
Rock-forming elements
Groups of elements
Se, Te.
Ba, Rb, Be,
Al.
Elements
outside
clusters
Ca, Co, Fe, Ga,
Mn, Pb, S, Te,
Tl, U.
Ba, Y.
Elements
outside factor
groups
minerals of the vaterite
type (?)
pyrite, pyrrhotite,
marcasite
molibdenite, gold
expected gallium and
germanium phases (?)
(?)
magnetite and nonestablished tantalonyobates (?)
polydimite, bravoite.
(?)
(?)
apatite
biotite
feldspars
hornblende, zircone (for Zr
and Hf)
Element-bearing minerals
Òàáëèöà 2
Åëåìåíòíè êëúñòåðè íà ñêàëîîáðàçóâàùè è ðóäíè åëåìåíòè â ïîòîêîâè ñåäèìåíòè îò îêîëíîñòèòå íà çëàòíî-ìåäíî ðóäîïðîÿâëåíèå Áîðîâ äîë, Ð. Ìàêåäîíèÿ
Table 2
Element clusters of rock-forming and ore elements in stream sediments from the vicinity of the Borov Dol gold-copper ore occurrence, R. of Macedonia
tite and apatite (Table 2). The petrographic observations of Stefanova et al. (2004) confirmed that these
were some of the most characteristic minerals for the
andesite-latite vlocanites. The factor analysis confirms
the respective elemental associations by describing in
details the negative correlation links of the separate
elements. Independent elements which remain outside any association of rock-forming elements are Ba,
Rb, Be and Al. An explanation for the particular behaviour of Al could be its presence as major element
in many of the rock-forming minerals.
The ore elements are grouped in 8 associations as
part of them belong to minerals that are established
in the Borov Dol ore occurrence (Table 2). The elements Se and Te remain outside the clusters as they
display low concentrations and low variability in the
different samples (respectively standard deviation
0.79 and 0.02). The factor analysis defines a broader
group of free elements às: low standard deviation is
recorded for the elements Ca (Std. Dev. 0.26), Fe (Std.
Dev. 0.5), Ga (Std. Dev. 0.96), S (Std. Dev. 0.06), Tl
(Std. Dev. 0.07) and U (Std. Dev. 0.74), and another
part of them including Co (Std. Dev. 5.26), Mn (Std.
Dev. 118.21), Pb (Std. Dev. 23.84) occur in several
minerals of different composition.
Discussion
The grouping of samples along the Borov Dol stream
profile shows that they have close similarity. This is
easy to explain because the catchment area of the
Borov Dol stream and its tributary Krundirov Dol is
built up of the same rocks as both streams intersect
the ore body (Fig. 1). Evidence for this is that the
weakest correlation between the samples has linking
distance 0.14 (Fig. 3).
Considering this fact the samples from the stream
sediments are differentiated in two groups. The samples located in the middle part of the profile (BD 3
to BD 6) show relatively greater closeness. This part
of the profile is beyond the ore body being characterized by active transport of the stream sediments
due to a steeper slope (Fig. 4à). The second cluster
comprises two kinds of samples. Samples from the
first one were collected from the ore body (BD 1 and
BD 2), and the second cluster reflects the cumulative processes in the lower, less inclined part of the
profile (BD 8 to BD 11), where heavy ore minerals
plus some rock-forming phases were deposited.
The nature of the Borov Dol stream profile is characterized by three sectors (Fig. 4à). The first one has
relatively small inclination and comprises the ore
body and its proximity. The second one is steeper
and has greater opportunity for increased transport
of the placer material. The third one has also cumulative features and marks the location where the Borov
Dol stream mouths into the Kriva Lakavitsa stream.
This configuration predetermines the depositional
conditions along the Borov Dol stream profile. The
concentration of elements along the profile is different. Three groups of elements are distinguished (Fig.
4b). The first one (a typical element is Co) is characterized by relatively high contents in the range of the
Fig. 3. Linkage distance between samples along the Borov Dol stream profile
Ôèã. 3. Áëèçîñò ìåæäó ïðîáèòå ïî ïðîôèëà íà ïîòîêà Áîðîâ äîë
74
Fig. 4. Profile of the Borov Dol stream (à) and concentration distribution of elements-indicators Co, Zr and
Ni along the profile (b) with the location of both clusters
from Fig. 3
Ôèã. 4. Ïðîôèë íà ïîòîêà Áîðîâ äîë (à) è ðàçïðåäåëåíèå íà êîíöåíòðàöèÿòà íà èíäèêàòèâíèòå åëåìíòè
Co, Zr è Ni ïî ïðîôèëà (b) ñ ðàçïîëîæåíèå íà äâàòà
êëúñòåðà îò ôèã. 3
ore body. These elements decrease in concentration
within the steep interval and increase in the cumulative interval, but without reaching the concentrations in the ore body. Very similar is the behaviour of
the elements Ag, Cu, As, Cd, In, Mn, Sb, Ti, Tl, W,
Zn, Cs and Li.
The distribution along the profile of the second
group of elements differs from the previous one by
the fact that their concentrations in the cumulative
zone are higher relative to the ones in the ore body. A
typical element of this group is Ni (Fig. 4b), as heavy
elements which tend to accumulate in placers (Au,
Cr, Nb,) fall in this group, plus the elements Be, K
and Mg. The latter are related with rock-forming
minerals accumulated in the flat part of the valley at
the point of mouthing.
The elements from the third group are more variable and show no distinct trend of accumulation
along the profile. A typical representative of this group
is Zr (Fig. 4b), and the rest elements are Mo, Ca, Al,
Bi, Ga, Ge, Pb, Re, S, Se, Sn, Ta, U, V, Y, Hg, Ce, Fe,
Hf, La, P, Th, Te, Ba, Na, Rb and Sr. Their behaviour
is related either with the low concentration (>1 ppm)
for part of them (Table 1), or with the fact that they
occur in several minerals with different behaviour
during placer formation.
The described features of the element distribution along the Borov Dol stream profile elucidate
the mineral behaviour during the process of placer
formation and transport of material. They might be
used also as clues for the slick sampling with the
aim to search for respective minerals that indicate
the ore type. For example, the Au behaviour shows
that its mineral aggregates could be established in
the slick along the whole profile, and thus might
characterize its mineralogical features in order to
predict the ore type.
The profile distribution of Ba does not reveal any
trend of accumulation in its lower part, and hence, it
might be concluded that it is not in the form of barite
but rather occurs in the crystal lattice of the potassic
feldspars (Table 1). The occurrence of Ni in the cumulative part of the profile and its participation in
the respective elemental association (Table 2) show
that it is represented in the primary ores as a discrete
mineral – polydimite, which was established during
the mineralogical studies (Table 2). The behaviour of
other elements could be interpreted in a similar manner, depending of the concrete purposes.
Conclusions
The following conclusions could be drawn as a result from the accomplished investigation on the
stream sediments and rocks in the area of the Borov
75
Dol ore occurrence, as well as from the geochemical
behaviour of those sediments along the profile of
Borov Dol river course down to the mouthing into
Kriva Lakavitsa River:
– a similarity is established between the chemical
composition of the stream sediments and the one of
the rocks in the drainage area. The chemistry of the
rocks building up the drainage area might be specified using data on the chemical composition of the
stream sediments;
– the elements in the stream sediments are differentiated in spatial associations which reflect their
mineralogy as well as their behaviour during the
stream transport;
– the elements in the stream sediments are divided in three groups on the basis of their distribution
along the stream profile. The first one is represented
by elements which are typical for the upper part of
the profile (Co, Ag, Cu, As, Cd, In, Mn, Sb, Ti, Tl, W,
Zn, Cs and Li). The second group (Ni, Au, Cr, Nb)
comprises elements which have higher concentrations in the lower, relatively flat part of the profile
(heavy phases that are stable in exogenic conditions).
The third group is represented by elements for whose
distribution no particular trends could be determined. Most of the studied elements belong to this
group.
Acknowledgments: The current investigation was
accomplished in the framework of Project 1403, financed by the “National Scientific Research Fund”
at the Ministry of Education and Science, and was
financially sustained by the company Balkan Mineral and Mining Ltd.
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(Ïîñòúïèëà íà 17.11.2006 ã., ïðèåòà çà ïå÷àò íà 07.06.2007 ã.)