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Elemental Mass Balance of the Hydrothermal Alteration Associated
with the Baturappe Epithermal Silver-Base Metal Prospect,
South Sulawesi, Indonesia
Irzal Nur1,*, Arifudin Idrus2, Subagyo Pramumijoyo2, Agung Harijoko2,
Koichiro Watanabe3, Akira Imai4, Sufriadin1, Asri Jaya HS1, Ulva Ria Irfan1
1
2
Department of Geological Engineering, Hasanuddin University, Makassar 90245, Indonesia
Department of Geological Engineering, Gadjah Mada University, Yogyakarta 55281, Indonesia
3
Department of Earth Resources Engineering, Kyushu University, Fukuoka 819-0395, Japan
4
Department of Earth Science and Technology, Akita University, Akita 010-8502, Japan
*
Corresponding author: [email protected]
Abstract
The Baturappe prospect situated in southernmost part of Sulawesi island, Indonesia, is a
hydrothermal mineralization district which is characterized by occurrences of epithermal
silver-base metal mineralizations. The mineralizations hosted in basaltic-andesitic
volcanic rocks of the late Middle-Miocene Baturappe Volcanics. This paper discusses a
recent study of relationships between alteration mineralogy and whole-rock
geochemistry, which focused on elemental mass balance calculation, of the hydrothermal
alteration zones within the prospect. Hydrothermal alteration is zoned around the
mineralizations from proximal quartz-carbonate and illite-quartz (argillic) to vein-related
propylitic (epidote-chlorite-calcite) to distal-district propylitic (chlorite) alteration. Mass
balance calculation indicates that in the vein-related propylitic altered zone there is a little
decrease in bulk composition of the altered rock with respect to the least-altered rock. In
contrast, the quartz-carbonate altered rocks show an increasing in bulk composition with
respect to the least-altered rocks. The gains and losses of the major oxides and trace
elements in the both alteration zones are generally consistent either with the hydrothermal
alteration mineral assemblages of each alteration zone, indications of the hydrothermal
alteration processes such as destruction of primary minerals and absorption of certain
elements in altered minerals, and the behaviours of early metal-bearing sulphides.
Keywords: Baturappe epithermal silver-base metal prospect, Indonesia, hydrothermal
alteration, mass balance.
Abstrak
Prospek Baturappe yang terletak di ujung selatan Pulau Sulawesi, Indonesia, adalah
sebuah distrik mineralisasi hidrotermal yang dicirikan dengan kehadiran mineralisasi
perak-logam dasar epitermal. Mineralisasi ini terbentuk pada batuan volkanik basaltikandesitik anggota Formasi Volkanik Baturappe yang berumur akhir Miosen Tengah.
Makalah ini membahas hasil studi terkini tentang hubungan antara mineralogi alterasi
dan komposisi geokimia batuan, yang difokuskan pada kalkulasi kesetimbangan massa,
pada zona-zona alterasi hidrotermal prospek Baturappe. Alterasi hidrotermal pada
prospek Baturappe terzonasi di sekitar mineralisasi dari proksimal ke distal: zona
kuarsa-karbonat dan illit-kuarsa (argilik), zona propilitik yang berhubungan genetik
dengan urat termineralisasi (epidot-klorit-kasit), dan zona propilitik berskala distrik
1
(klorit). Hasil evaluasi kalkulasi kesetimbangan massa menunjukkan bahwa pada zona
propilitik yang berhubungan genetik dengan urat termineralisasi terjadi sedikit
penurunan komposisi kimia total pada batuan yang teralterasi dibandingkan dengan
batuan ekuivalen tak-teralterasinya. Sebaliknya, batuan yang teralterasi kuarsa-karbonat
mengalami peningkatan komposisi kimia total dibandingkan dengan batuan ekuivalen
tak-teralterasinya. Peningkatan dan penurunan konsentrasi oksida-oksida mayor dan
unsur-unsur jejak pada kedua zona alterasi tersebut secara umum konsisten, baik
terhadap himpunan mineral alterasi hidrotermal yang terbentuk, indikasi-indikasi proses
alterasi hidrotermal seperti destruksi mineral-mineral primer dan absorpsi unsur-unsur
tertentu pada mineral-mineral teralterasi, maupun perilaku geokimia sulfida-sulfida
logam pra-alterasi.
Kata kunci: Baturappe epithermal silver-base metal prospect, Indonesia, hydrothermal
alteration, mass balance.
Introduction
The Baturappe prospect is situated in Baturappe Village, Gowa Regency, South
Sulawesi Province, Indonesia. It lies in the southwesternmost part of Sulawesi Island,
about 50 km southeast of Makassar, the capital city of South Sulawesi Province. The
prospect is characterized by occurences of epithermal silver-base metal mineralizations
which are hosted in basaltic-andesitic volcanic rocks of the late Middle-Miocene
Baturappe Volcanics (Nur et al., 2009). The most significant mineralization in the
prospect, the Bincanai vein, contains an average grade of: Pb 17.51 %, Zn 0.35 %, Cu
0.66 %, Ag 713 g/t, and Bi 308 g/t (Nur et al., 2010, 2011a,b).
Earlier works on the prospect and its vicinity included the regional geology around
the area (Sukamto and Supriatna, 1982); studies of volcanism and geodynamic evolution
of south Sulawesi, as well as petrology, geochemistry, and dating of the volcanics
(Yuwono et al., 1985, 1988; Leterrier et al., 1990; Priadi et al., 1994; Polvé et al., 1997.);
preliminary investigations of base metal mineralizations in the prospect and vicinity
(Sutisna, 1990; Sukmana et al., 2002; Zulkifli et al., 2002); and occurences and
distribution of significant hydrothermal ore mineralizations in the Western Sulawesi Arc
in related to its tectonic setting and metallogenesis (Idrus et al., 2011).
The works are generally based on regional scale studies and preliminary
investigations, no detailed study has been conducted on genetic aspects of the prospect. A
detailed investigation of some genetic aspects including alteration geochemistry and
elemental mass balance is needed to improve understanding of the prospect. This paper
discusses a recent study of relationships between alteration mineralogy and whole-rock
geochemistry, which focused on elemental mass balance calculation, of the hydrothermal
alteration zones within the Baturappe epithermal silver-base metal prospect. Mass balance
calculation following the example of Grant (1986) were used to quantify the effects of
hydrothermal alteration on the host rock. The present study allows better understanding of
the behaviour (enrichment or depletion) of the elements during hydrothermal alteration
processes.
Geology and Mineralization Zones
Regionally, the Baturappe area is situated in the southwestern part of the regional
geologic map of the Ujung Pandang, Benteng and Sinjai quadrangles, Sulawesi (Sukamto
2
and Supriatna, 1982). A detailed surface geological mapping has then conducted in an
area of 1000 ha to study the geological background of the mineralization in the prospect.
The older rock unit broadly distributed in the study area is lava of dominantly basalt and
less andesite, mostly porphyritic, with general orientations of N(80-85)oE/(18-20)oSE at
the centre and east of the study area, and N120oE/65oSW at the west. Locally, blocks of
volcanic breccia also exposed in the lava. Based on its lithological characteristics, this
unit is interpreted as a member of lava, Tpbl (Sukamto and Supriatna, 1982) which
according to K-Ar dating indicates age of 12.38 to 12.81 Ma or late Middle-Miocene
(Yuwono et al., 1985; Priadi et al., 1994). The basaltic-andesitic lava which distributed
from Bincanai and Ritapayung area at the west, through Bangkowa to the east, and Taloto
at the south portions of the study area, is identified as the host rock of the epithermal
mineralizations in the prospect. At the north, the lava was intruded by a gabbroic-dioritic
stock; and followed by a group of basaltic-andesitic dykes. At least 50 units of dykes with
a thickness range of 8 cm to 2.5 m are cropped-out in the study area, distributed radially
centered to the stock, forming a radial swarm of dyke. K-Ar dating on two samples of
basalt indicate ages of 7.5 Ma and 6.99 Ma, and 7.36 Ma on gabbro (Sukamto and
Supriatna, 1982). The basaltic-andesitic stock and dykes are interpreted as the
mineralization-bearing rocks in the study area, which is indicated by the occurences of
disseminated ore (i.e., pyrite, chalcopyrite, sphalerite, galena, covellite, magnetite,
hematite) recognized in the field and microscopic observations. Due to the orientation of
the dykes that are consistent to the trends of the fractures, it is interpreted that the
emplacement and distribution of the dykes brought mineralization is highly controlled by
geological structures (Nur et al., 2009; Figure 1).
More than 20 units of quartz veins along with disseminated sulphide and sulphide
stringer are distributed around the periphery of the stock in the study area, hosted in the
lava and dyke units. Among these, eight significant mineralizations are distributed in four
zones: Bincanai-, Baturappe-, Bangkowa- and Ritapayung zone. The mineralizations
namely: Bincanai vein, Baturappe vein-1, Baturappe vein-2, Bungolo vein,
Paranglambere vein (all clustered in the Baturappe zone); Bangkowa vein and Bangkowa
stringer (in the Bangkowa zone); and Ritapayung dissemination (in the Ritapayung zone).
The Bincanai vein and Baturappe veins are distributed and clustered along the main fault
in the study area, the NW-SE trend Bincanai-Baturappe normal fault; whereas the
Bangkowa- vein and stringer are hosted in NW-SE dykes. Distribution of the
mineralizations and orientation of the veins are shown in Figure 1.
The veins display the typical primary texture of epithermal veins: crustiform banding
texture; from symmetric-, multiphase- to simple crustiform of quartz ± carbonate –
sulphide (dominated by galena). In general, sulphide assemblages identified in the
mineralizations indicate a range of intermediate- to high sulphidation epithermal
assemblages. The sulphides include: galena, sphalerite, chalcopyrite, pyrite, tennantite,
tetrahedrite, bornite, enargite, freieslebenite, and polybasite. Very fine-grained silver and
bismuth minerals which occupy fractures of the early-stage minerals, were also identified
by SEM-EDX analysis; the minerals include bismuthinite, cupropolybasite, jalpaite,
angelaite, cuprobismutite, sorbyite, and launayite. Supergene minerals such as covellite,
chalcocite, iodargyrite, anglesite, cerrusite, as well as manganese coronadite and
chalcophanite were also identified. Bulk-ore chemical composition determined by XRF
analysis indicates a highest grade of: Pb 17.51%, Zn 0.35%, Cu 0.66%, Ag 713 g/t, Bi
3
308 g/t for the veins, and Pb 0.11%, Zn 0.15%, Cu 5.83%, Ag 140 g/t, Bi 60 g/t for the
dissemination (Nur et al., 2010, 2011a,b).
1
2
7
4
5
3
6
8
Figure 1. Geological map of the study area and distribution of significant
mineralizations in the prospect: (1) Bincanai vein, (2) Ritapayung dissemination,
(3) Baturappe vein-1, (4) Baturappe vein-2, (5) Bungolo vein, (6) Paranglambere vein,
(7) Bangkowa vein, (8) Bangkowa stringer.
Hydrothermal Alteration Zoning and Mineralogy
As an introduction to discuss the relationships between the alteration mineralogy and
whole-rock geochemistry, i.e., the elemental mass balance, this section briefly reviews
the hydrothermal alteration zoning and mineralogy of the Baturappe prospect that have
been previously reported on the earlier publications of the authors (Nur et al., 2011c,d).
Zonation of hydrothermal alteration in the study area is divided on the basis of the
dominant mineral assemblages and its spatial distribution relative to the mineralizations,
from distal to proximal include: chlorite, epidote-chlorite-calcite, and illite-quartz and
quartz-carbonate zones (Figure 2). The chlorite zone is a distal-district propylitic
alteration which is characterized by a low intensity of alteration and developed on the
4
periphery of the hydrothermal system in study area. The epidote-chlorite-calcite zone is a
vein-related propylitic alteration which is characterized by a higher intensity of alteration
and developed proximal to the structural-controlled veins in the prospect. The illite-quartz
(argillic) zone is characterized by clay mineral assemblages which distributed proximal to
the related-veins at Baturappe- and Bangkowa area, and interpreted as the centre of
hydrothermal activities responsible for the mineralization. The narrow and elongated
distribution of the zone (Figure 2) indicates that the distribution is controlled by
geological structure. The quartz-carbonate zone also distributed proximal to the relatedmineralization (the Bincanai vein and the Ritapayung dissemination), and also interpreted
as the centre of the hydrothermal activities that responsible for the mineralizations. The
narrow and elongated distribution of the quartz-carbonate zone around the Bincanai vein
indicates that the distribution is controlled by geological structure, i.e., the BincanaiBaturappe fault (Figure 2). On the other hand, at Ritapayung, regarding the lithological
host of the alteration-mineralization (volcanic breccia), the quartz-carbonate zone in this
area is controlled by permeability of the host rock (Nur et al., 2011c,d). The mineral
assemblages in each alteration zone is summarized in Table 1.
Figure 2. Hydrothermal alteration map of the Baturappe prospect.
5
Table 1. Mineral assemblage in each hydrothermal alteration zone
Hydrothermal
mineral
Chlorite
zone
Epidote-chlorite-calcite
zone
Illite-quartz
zone
Quartz-carbonate
zone
BC
BR
BK
BR
BK
BC
RP
1 to 10
7
 0.5
<7
< 0.5
<1
< 200
Chlorite
Epidote
Calcite
Quartz
Sericite
Albite
Biotite
Illite
Smectite
i/s
c/s
Kaolinite
Halloysite
Dolomite
Siderite
Pyrite
Magnetite
Hematite
Distance to
mineralization
(m)
District
scale
- Abbreviations: i/s: mixed layer illite/smectite, c/s: mixed layer chlorite/smectite; BC: Bincanai,
BR: Baturappe, BK: Bangkowa, RP: Ritapayung.
- Line weight indicates relative abundance.
Analytical Methods
In this study, the whole-rock geochemical analysis was performed by X-ray
fluorescence spectrometry (XRF) and inductively coupled – mass spectrometry (ICP-MS)
methods. The XRF analysis was conducted to measure the major oxides of altered and
less-altered rock samples, whereas the ICP-MS analysis was conducted to measure the
trace element composition of the altered and less-altered rock samples.
6
Sample preparation for the XRF analysis was performed at the Laboratory of
Economic Geology, Department of Earth Resources Engineering, Kyushu University.
The samples were firstly crushed and grinded, then pulverized by agate mortar, and then
milled by a CMT TI-100 model of vibrating sample mill machine, and finally were
pelletized using a Rigaku pressing machine to form pressed powder discs that ready to be
analyzed. Before the analysis conducted, one gram of each milled samples were separated
to measure their LOI (H2O) concentration. The analysis was then performed using an
XRF instrument of Rigaku ZSX Primus II, which calibrated by the fundamental
parameter (FP) sensibility calibration method using 15 standards of the Geological
Survey of Japan (JB-1a, JB-2, JB-3, JGb-2, JH-1, JA-1, JA-2, JA-3, JG-1a, JG-2, JG-3,
JSy-1, JCh-1, JSd-2, JSd-3, JLs-1 and JMn-1) and 17 synthesized standard compounds
(JA-3S, JB2-30Fe, JB2-40Fe, JB2-50Fe, JA3-20Fe, JA3-35Fe, 6elts-2, 6elts-3, AuAg-1,
AuAg-2, AuAg-3, Na-rich, Ag5-BiPb, Ag9-BiPb and Ag17-BiPb). Technical
specification of the analysis is, X-ray tube: Rh, voltage: 50 kV and current: 50 mA,
detection limit (for the major oxides): 0.01%. Peak overlapping was examined, and
overlap correction coefficients were used in the quantitative calculation in the FP
sensibility calibration. The analysis was conducted at the Research Institute for
Environment Sustainability (RIES) Laboratory, Kyushu University.
For the ICP-MS analysis, the rest of milled samples that have been previously
prepared and analyzed by the XRF method (for the major element composition) were sent
to a commercial laboratory: the Actlabs (Activation Laboratories Ltd.), Canada, to be
determined their trace- and rare earth element composition. Determination of 43 trace
elements was then conducted by ICP-MS method, with detection limit (in ppm) as
follows: Zn = 30; Cr and Ni = 20; Cu = 10; V, As and Pb = 5; Ba = 3; Sr and Mo = 2;
Co, Ga, Rb, Zr and Sn = 1; Ge, Y, Ag and W = 0.5; Nb and Sb = 0.2; In, Cs, Hf and Bi =
0.1; La, Ce, Nd, Tl and Th = 0.05; Pr, Sm, Gd, Tb, Dy, Ho, Er, Yb, Ta and U = 0.01; Eu,
Tm = 0.005; and Lu = 0.002 (analysis package code 4B2-research, Actlabs Service Guide
2010).
To evaluate quantitatively the chemical composition changes (major and trace
elements) of the host rocks of the mineralization due to hydrothermal alteration processes,
the method of mass and volume change calculation (mass balance) of Gresens (1967) and
its modification, the isocon diagram of Grant (1986) were applied. The Gresens’ formula
for the calculation is:
Xn = {[fv(gB/gA)CnB – CnA}100
where: Xn is mass gain or loss of an element between an unaltered rock (A) and its altered
equivalent (B); fv is volume change factor; g is density of the rock; and Cn is
concentration of an element.
The equation has then rearranged by Grant (1986) to calculate the concentration
changes of elements (∆C), as well as mass and volume changes (∆M and ∆V,
respectively) of rocks as a results of hydrothermal alteration. The formula of the
calculation is: ∆C = (MO/MA)*[(CA/CO)-1]; ∆M = [(MO/MA)-1]*100; and ∆V =
(MO/MA)*[(ρA/ρO)-1]*100; where: ∆C = concentration change of elements (major oxides
and trace elements) from altered rock to its unaltered equivalent (original rock), ∆M =
mass change in %, ∆V = volume change in %, MO = mass of original rock, MA = mass of
altered rock, CO = concentration of elements in original rock, CA = concentration of
elements in altered rock, ρO = specific gravity of original rock, and ρA = concentration of
elements in altered rock. Results of the calculation (elemental gains and losses) were
7
expressed in a graph where a line of iso-concentration (immobile elements) separates the
enriched elements from the depleted ones. This line is called isocon. Elements plot above
the reference isocon are enriched during alteration, whereas elements plot below are
depleted. The gradient of the isocon is defined by ratio of the mass of original (least
altered) rocks against the mass of altered rocks: MO/MA (Grant, 1986).
In this study, data processing and imaging of the mass balance calculation was
performed using the GEOISO software of J. Coelho (2005). Specific gravity of rock
samples was measured by the buoyancy method (Archimedes principle). Elements TiO2,
Zr and Y were used as immobile or inert elements (e.g., Mauk and Simpson, 2007) when
input the data to the software.
Result and Discussion
In this study, four samples around the Bincanai vein were selected to be evaluated.
The selection of the samples is because around the Bincanai vein a systematic sampling
was conducted from proximal to distal site of the vein. The samples include: WBC.2B,
WBC.2C and WBC.2D which were collected respectively 1 m, 2 m, and 3 m from the
vein. These samples represent altered rocks which according to their alteration mineral
assemblages (Table 1), the first two samples represent the quartz-carbonate zone and the
rest represents the epidote-chlorite-calcite zone or vein-related propylitic. For the leastaltered rock, sample BCFW.1 that was taken relatively far from the vein (10 m) is
selected. From the mineral assemblage identified by microscopic observation, this sample
is relatively weak altered compared to the other three samples. Chemically, the sample
also generally has a lower content of H2O, Cu, Zn and Pb relative to the other three
samples (Table 2). Thus, beside consider the relative distance from the mineralization, the
alteration mineral assemblage and chemical composition are also considered to select the
least altered and altered rocks in this evaluation.
Whole-rock chemical composition of the samples are listed in Table 2, and the
results of mass balance calculation, the isocon diagram of the three pairs of least-altered
and altered rocks (BCFW.1 vs WBC.2D, BCFW.1 vs WBC.2C, and BCFW.1 vs
WBC.2B) including their enrichment-depletion diagram of selected elements are
respectively shown in Figure 3, 4, 5. The gradient of isocons and results of mass and
volume change calculations are attached in each isocon diagram (Figure 3.A, 4.A, 5.A).
The propylitic altered rock (sample WBC.2D) indicates a little decrease in bulk
composition with respect to the least-altered rock. This is expressed by the slight negative
value of their mass and volume changes, -0.95% and -8.75%, respectively (Figure 3.A).
K2O and Rb are strongly enriched with enrichment factors of 0.52 and 0.60, respectively,
and Ba is slightly added with factor of 0.07 (Figure 3.B). The strong enrichment of K 2O
may related to the presence of illite and sericite; these secondary minerals are identified
in the samples of propylitic altered rock around the Bincanai vein. The addition of Rb and
Ba indicates that the elements are probably absorbed in altered plagioclase and sericite
(Idrus et al., 2009). MgO also moderately enriched with enrichment factor of 0.25 (Figure
3.A), which may related to the abundance of clinochlore in the sample (13.61 wt.% from
semi-quantitative XRD result, Nur et al., 2011c,d). CaO is slightly depleted (depletion
factor of 0.20). The depletion of CaO in propylitic alteration has been reported by Idrus et
al. (2009), which may indicates that replacement of the calcic plagioclase rims is more
intense than the formation of Ca-bearing hydrothermal minerals such as calcite and
8
epidote in the rocks. The depletions of Na2O, Sr and V reflect destruction of plagioclase
during the alteration. The strong gain of Cu and slight to moderate gain of Zn indicate a
high abundance of early copper- and zinc-bearing sulphides. Whereas the strong
depletions of Pb and Bi suggest that lead- and bismuth-bearing sulphides are still not well
developed in this alteration zone. Other elements such as MnO and Cs are enriched,
whereas Zr, In and Sn are depleted (Figure 3).
In contrast, the quartz-carbonate altered rocks (WBC.2C and WBC.2B) show an
increasing in bulk composition with respect to the least-altered rock. This is expressed by
the positive values of their mass and volume changes, +15.56% and +6.09% respectively
for sample WBC.2C, and +20.93% and +33.87% respectively for sample WBC.2D
(Figure 4 and 5). SiO2, CaO and FeO are enriched which explains the development of
quartz and carbonate calcite and siderite in this alteration zone. The enrichment of FeO
(0.11 in WBC.2C and 0.16 in WBC.2B) may also related to the occurrence of chamosite
in the alteration zone. K2O, Rb, Cr and Ba are moderately to strongly enriched with the
average enrichment factors for the two samples are 1.22, 2.99, 1.11 and 0.46, respectively
(Figure 4.B and 5.B). The strong enrichment of K2O may related to the presence of illite
and sericite in the samples (Table 1). The addition of Rb and Ba indicates that the
elements are probably absorbed in altered plagioclase and sericite (Idrus et al., 2009); this
may also explains the addition of Cr in the samples. MgO is slightly enriched in sample
WBC.2B, with enrichment factor of 0.29 (Figure 5.B), which may related to the presence
of clinochlore in the sample; result of semi-quantitative XRD indicates proporsion of
25.28 wt.% (Nur et al., 2011c,d). The depletions of Na2O and Sr reflect destruction of
plagioclase during the alteration. The moderate to strong gains of Zn, As, Ag and Pb are
respectively indicate a high abundance of early zinc-, arsenic-, silver- and lead-bearing
sulphides in this inner zone of alteration. Cu and Bi are depleted in sample WBC.2C, but
are then enriched in the more proximal sample, WBC.2B, which may explains that
copper- and bismuth-bearing sulphides are more developed in the more proximal zone (to
the vein). Other elements such as MnO, V, Ni, Y, Zr, Sb, Cs, Ce and U are enriched,
whereas In and Sn are depleted (Figure 4 and 5).
9
Table 2. Whole-rock geochemical data of the four samples
Sample code
Sample type
Alteration zone
BCFW.1
Andesite
Least-altered
WBC.2B
Andesite
Quartz-carbonate
WBC.2C
Andesite
Quartz-carbonate
WBC.2D
Basalt
Epidote-chlorite-calcite
(vein-related propylitic)
MnO
MgO
CaO
Na2O
K2 O
P 2 O5
H2 O
Total
49.14
1.04
15.28
9.50
0.20
6.54
8.07
3.15
2.45
0.40
3.66
99.43
44.67
0.86
13.28
9.13
0.36
6.97
8.53
1.85
4.20
0.37
9.47
99.69
47.33
0.90
13.63
9.13
0.25
6.08
7.33
2.46
5.01
0.39
7.23
99.74
48.51
1.05
15.35
9.35
0.26
8.26
7.18
2.21
3.77
0.37
3.00
99.31
Trace elements (ppm)
V
Cr
Co
Ni
Cu
Zn
Ga
Ge
As
Rb
Sr
Y
Zr
Nb
Mo
Ag
In
Sn
Sb
Cs
Ba
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Hf
Ta
W
Tl
Pb
Bi
Th
U
254
70
32
20
100
80
17
1.3
<5
57
729
22.2
104
5.5
<2
< 0.5
0.1
3
< 0.2
0.5
540
17.7
36.1
4.78
20.2
4.82
1.45
4.55
0.73
4.09
0.78
2.17
0.32
2.09
0.362
2.4
0.55
< 0.5
0.42
21
0.2
4.65
1.74
237
130
28
40
130
200
16
1
11
112
407
21
96
4.8
<2
0.6
< 0.1
2
33.4
4.7
592
16.7
34.9
4.64
19.4
4.86
1.45
4.43
0.69
3.88
0.73
2.06
0.302
1.99
0.319
2.2
0.5
< 0.5
0.51
29
0.2
4.84
2.16
229
120
26
30
50
160
15
1
<5
129
554
22
98
4.4
<2
< 0.5
< 0.1
2
4.7
3.3
748
17.8
37
4.89
20.5
5.07
1.46
4.75
0.73
4.13
0.79
2.23
0.326
2.05
0.311
2.2
0.46
< 0.5
0.55
42
0.1
5.22
2.27
246
70
32
20
190
90
16
1.3
<5
92
679
21.7
99
5
<2
< 0.5
< 0.1
2
< 0.2
1.4
583
17
35.5
4.64
19.5
4.77
1.47
4.52
0.72
4
0.76
2.15
0.322
2.05
0.318
2.3
0.45
< 0.5
0.4
13
0.1
4.52
1.71
Major elements (%)
SiO2
TiO2
Al2O3
FeO
10
30
Cu
(A)
K2O
Vein-related propylitic altered rock (WBC.2D)
SiO2
Zr
Ba
Sr
V
Tl
Rb
Zn
Ni
MnO
As
Ce
Hf La
Er
W Al2O3 Ga
Co
Yb
Tm Nd
P2O5
Y
Cr
Lu
Na2O
Sn
Pb
U
Cs
TiO2 Ge
Sb Mo CaO
Ho Sm
Th
Nb
DyPr Tb
Ag
In
Ta
H2O
MgO
Eu
FeO
Bi
Isocon gradient: 0.92
Mass change: -0.95%
Volume change: -8.75%
0
Concentration change (∆C)
0
1.0
30
Least-altered rock (BCFW.1)
(B)
BCFW.1 vs WBC.2D
0.5
0
-0.5
-1.0
SiO2 FeO MgO CaO Na2O K2O
V
Cr
Co
Cu
Zn
As
Rb
Sr
Y
Zr
Mo
Ag
Sn
Ba
Pb
Bi
Figure 3. A. Isocon diagram of sample BCFW.1 (least-altered rock) vs WBC.2D (veinrelated propylitic altered rock); major oxides in wt.% and elements in ppm.
B. Enrichment-depletion diagram of the sample pair.
11
30
Ce
(A)
SiO2
Zr
Ba
Quartz-carbonate altered rock (WBC.2C)
Zn
Rb
Cr
V
P2O5
Cs
Y
Tm
Lu
Na2O
As La
Hf
U
Er
MnO Yb W
Ga
Al2O3
Co
Pb
Ni
Sr
Nd
Sn
Cu
Eu
FeO
Mo CaO
Ge
MgO
K2O Th Tb Ho
TiO2
Gd
Nb
Tl Dy
In
Ta
H2O
Sb
Bi
Isocon gradient: 0.92
Mass change:+15.56%
Volume change: +6.09%
0
Concentration change (∆C)
0
2.0
30
Least-altered rock (BCFW.1)
(B)
BCFW.1 vs WBC.2C
1.5
1.0
0.5
0
-0.5
-1.0
SiO2 FeO MgO CaO Na2O K2O
V
Cr
Co
Cu
Zn
As
Rb
Sr
Y
Zr
Mo
Ag
Sn
Ba
Pb
Bi
Figure 4. A. Isocon diagram of sample BCFW.1 (least-altered rock) vs WBC.2C (quartzcarbonate altered rock); major oxides in wt.% and elements in ppm. B. Enrichmentdepletion diagram of the sample pair.
12
30
(A)
Ba
K2O
Pb
Zr
SiO2
Quartz-carbonate altered rock (WBC.2B)
Zn
Rb
V
Cu
Cr
P2O5
MnO
Y
Nd
Lu
Tm
Ni
Sb
U
W
Yb
Al2O3
Ce
Er
Co
La
Ga
Hf
Sr
Sn
Na2O
Bi
As
Eu
H2O
CaO
Cs
FeO
Mo
MgO
Th Ho
Gd
Ag
Nb TiO2
Dy
Tb
Tl Ta
In
Ge
Isocon gradient:1.11
Mass change:+20.93%
Volume change: +33.87%
0
Concentration change (∆C)
0
5.0
30
Least-altered rock (BCFW.1)
(B)
BCFW.1 vs WBC.2B
4.0
3.0
2.0
1.0
0
-1.0
SiO2 FeO MgO CaO Na2O K2O
V
Cr
Co
Cu
Zn
As
Rb
Sr
Y
Zr
Mo
Ag
Sn
Ba
Pb
Bi
Figure 5. A. Isocon diagram of sample BCFW.1 (least-altered rock) vs WBC.2B (quartzcarbonate altered rock); major oxides in wt.% and elements in ppm. B. Enrichmentdepletion diagram of the sample pair.
Conclusion
Mass balance calculation indicates that in the vein-related propylitic altered zone
there is a little decrease in bulk composition of the altered rock with respect to the leastaltered rock; the mass and volume changes is -0.95% and -8.75%, respectively. In
contrast, the quartz-carbonate altered rocks show an increasing in bulk composition with
respect to the least-altered rocks, which expressed by the positive values of their mass and
volume changes, +15.56% to +20.93% and +6.09% to +33.87%, respectively. The gains
and losses of the major oxides and trace elements in the both alteration zones are
generally consistent either with the hydrothermal alteration mineral assemblages of each
alteration zone, indications of the hydrothermal alteration processes such as destruction of
primary minerals and absorption of certain elements in altered minerals, and the
behaviours of early metal-bearing sulphides.
13
Acknowledgments
This paper is a section of the first author’s dissertation completed at the Graduate
Program of Geological Engineering, Faculty of Engineering, Gadjah Mada University,
Yogyakarta, Indonesia. The authors are very thankful to the management of PT. Sungai
Berlian Bhakti Mining for the permission to collect field data for the study. The authors
also wish to express honest gratitude to Dr. Ryohei Takahashi and Mr. Naohiro Goto,
respectively for the guidance and assistance in conducting XRF analysis at Kyushu
University. Sincere gratitude also directed to the Directorate of Higher Education,
Department of National Education, Indonesia for the grant of Hibah Disertasi Doktor
2010 that made possible for the authors to send samples to be analyzed by ICP-MS
method at the Actlabs, Canada. This study was made possible through the long-term
scholarship of the Fellowship Doctoral Degree Program, Hasanuddin University
Engineering Faculty Development Project under JBIC (Japan Bank International
Cooperation) Loan No.IP-541. The manuscript improvements from reviewers are
gratefully acknowledged.
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