Majalah Geologi Indonesia, Vol. 27 No. 1 April 2012: 1-11
1Naskah diterima: 03 Januari 2011, revisi terakhir: 12 Maret 2012Corresponding Author: [email protected]
Characteristics and the Occurrence of “Garnierite” from the Soroako Nickeliferous Laterite Deposits, Sulawesi, Indonesia
Karakteristik dan Keterdapatan Garnierit pada Endapan Laterit Nikel Soroako, Sulawesi
Sufriadin1, Arifudin Idrus2, I Wayan Warmada2, Irzal Nur1,Shigeki Ueno3, and Akira Imai3,4
1Mining Engineering Study Program, Hasanuddin University, Jln. Perintis Kemerdekaan Km. 10 Tamalanrea, Makasar 90245, Indonesia
2Department of Geological Engineering, Gadjah Mada University, Yogyakarta 55283 Indonesia
3Department of Earth Resources Engineering, Kyushu University, Fukuoka, Japan4Department of Earth Science and Technology, Akita University, Akita 010-8512, Japan
ABSTRACTAn investigation of Ni-Mg hydrous silicate ores called “garnierites” from the Soroako nickeliferous laterite deposits has been conducted by means of optical microscopy, X-ray diffractometry (XRD), and
-
sepiolite-falcondoite series. Nickel content of the garnierite samples studied by means of XRF methods
Keywords: garnierite, peridotite, kerolite, sepiolite, nickeliferous laterite
SARISuatu penelitian bijih Ni-Mg hidrous silikat yang dikenal dengan “garnierit” pada endapan nikel laterit Soroako telah dilakukan dengan menggunakan metode mikroskopi optis, XRD, dan XRF dengan tujuan untuk menguraikan keterdapatan, komposisi mineralogi, dan kimia garnierit. Percontoh garnierit diambil baik dari blok barat maupun Blok Petea. Blok Barat terutama disusun oleh batuan peridotit tak terserpentinisasi, sedangkan Blok Timur yang diwakili oleh daerah Petea ditutupi oleh protolit dengan tingkat serpentinisasi sedang sampai tinggi. Penelitian lapangan dan analisis mikroskopi menunjukkan bahwa garnierit pada blok barat terdapat dalam tiga bentuk yaitu: lapisan tipis pada bidang rekahan dan patahan, sebagai bahan pengisi rekahan atau urat, dan sebagai matriks pada peridotit konglomeratan. Sementara pada Blok Petea, garnierit hanya dijumpai dalam bentuk urat. Hasil analisis XRD menunjukkan bahwa komposisi mineral garnierit Soroako terdiri atas seri kerolit-pimellit, seri talk-wilemsit, Ni-serpentin, dan seri sepiolit-falkondoit. Kadar nikel pada percontoh garnierit yang ditentukan dengan metode XRF memperlihatkan nilai antara 1,8 - 19,2%. Variasi ini mungkin disebabkan oleh keterdapatan mineral gang terutama kuarsa/silika dan sedikit oksida besi.
Kata kunci: garnierit, peridotit, kerolit, sepiolit, laterit nikel
Majalah Geologi Indonesia, Vol. 27 No. 1 April 2012: 1-11
2
INTRODUCTION
Nickel laterite deposits contribute to
et al., 2011). In-donesia is one of the four largest nickel
deposits are mostly located in the eastern
Gag, and Waigeo Islands. These Nickel-
-
tropical condition. Nickel laterite ores are
et al et al.,
Ni-bearing materials.
Garnierite is a collective term for Ni-Mg hydrous silicate minerals that is commonly used by mine geologists. It is characterized
content (Proenza et al., 2008). Garnierite is eventually not a mineral approved by
Names (CNMMN), but it occurs as intimate -
ing minerals: serpentine, talc, sepiolite,
(1973) suggested that many garnierites are
(serpentine-like phase) and 2 : 1 layer sili-
7 Å and 10 Å respectively. Recent studies
reported by Wells et al. (2009) and Tauler et al. (2009).
The objectives of this paper are to describe the mode of occurrence of garnierites, to analyze their mineralogical and chemical composition of some garnierite samples col-lected from the Soroako nickeliferous laterite
protolith as host for garnierite mineralization.
GEOLOGICAL SETTINGS
The rock assemblages occupied Soroako
(ii) tectonite rocks, (iii) Mezosoic sedimen-
and (iv) Tertiary sediments (Simandjuntak et al., 1991) (Figure 1).
-
(Kadarusman et al
(Monier et al., 1995). It covers an area of ap-2
the north (Surono and Sukarna, 2001).
In Soroako and Petea areas that have been
PT. Vale Indonesia), the rocks commonly -
bronze-colour crystals. With the increas-ing degree of serpentinization, the colour of the rock generally gets darker (Ahmad,
-
Characteristics and the Occurrence of “Garnierite” from the Soroako Nickeliferous Laterite Deposits, Sulawesi, Indonesia (Sufriadin et al.)
3
-
in thin veinlets or along the edges of relic olivine crystals, or distributed as dissemi-
susceptibility of the rock and the degree of serpentinization are correlated.
-tensive deformation on the basis of crystal
-larly major thrust faults in the peripheral
the surrounding sediments.
SAMPLES AND METHODS
Fourteen garnierite samples have been col-
They comprise eight samples gathered from
using optical microscopy, X-ray diffractom-
spectroscopy.
light mode by means of Nikon Eclipse LV -
a Rigaku RINT 2000 X-ray diffractometer
o
o and counting time 4o/minute. Whole rock chemical analy-
a Rigaku RIX 3100 X-ray fluorescence
conducted at Laboratory of Economic Geol-ogy, Department of Earth Resources Engi-neering, Kyushu University, Japan.
et al., 1991).
Legend
Surfical Deposits
Larona Formation
Tomata Formation
Matano Formation
Ultramafic Complex
Wasuponda Melange
Masiku Formation
Town and village
Fault and lineament
Sample location
121 05’ E
o
121 05’ E
o
2 25’ S
o
2 25’ S
o
2 35’ S
o
2 35’ S
o
2 45’ S
o
2 45’ S
o
121 15’ E
o
121 15’ E
o
121 25’ E
o
121 25’ E
o
121 35’ E
o
121 35’ E
o
121 45’ E
o
121 45’ E
o
0 0
12 km
Wowondula
Tawuti Lake
Wasuponda
Malili
Matano Lake
Mahalona Lake
Soroako
Petea
Nuha
Lohia
0
200
Km
Majalah Geologi Indonesia, Vol. 27 No. 1 April 2012: 1-11
4
RESULTS AND DISCUSSION
The Occurrence and Microscopic Features
crosscutting relationship, their occurrences may be distinguished into three types: (i)
materials or veins, and (iii) matrices on peri-dotitic conglomerate (Figure 2). Garnierites
medium green colour and they appear as thin -
nierite also formed as en echelon vein arrays
and soft materials (Figure 2c). They can be
are also common to be found at Ni laterite mines. In the case of fault planes that formed at saprolite zones closed to bedrocks, they
crack opening (crack seal mechanism). In -
block. Garnierite is also found as cements/matrices in fault gouges or as garnierite matrices in peridotitic conglomerate (Figure
previously formed the brecciation zone. The presence of garnierite clasts indicate tectonic remobilization of the veins.
Figure 2. Field appearances of garnierite ores in Soroako. a. garnierite occurs as slickensided fault coating on
10 cm
10 cm
20 cm
20 cm
d
a
b
c
Characteristics and the Occurrence of “Garnierite” from the Soroako Nickeliferous Laterite Deposits, Sulawesi, Indonesia (Sufriadin et al.)
5
Results of microscopic analysis indicate -
alternating light and dark bands (Figure 3a).
crystals of magnetite have been found to be
(Figure 3b). Vuggy quartz or silica veins are
crosscut or parallel to the colloform banding
materials are common features observed microscopically developed on the garnierite
Mineralogy
Result of XRD analysis reveals that garnier-
-
series of talc like-phases have been identi-
-
-
0.2 mm
0.4 mm
0.2 mm
0.2 mm
Magnetite
Fibrous
Ni -Srp
Silica
Fibrous Ni
sepiolite
Ker-srp
mixture
void
A
B
C
D
0.4 mm
0.2 mm
0.2 mm
0.2 mm
b
a
c
d
Majalah Geologi Indonesia, Vol. 27 No. 1 April 2012: 1-11
6
at 7.10Å and 7.33Å, possibly chrysotile
analyzed samples indicate the presence of
-
strongest lines around 12 Å observed from
of sepiolite-falcondoite series.
Whole Rock Chemistry
Chemical compositions of garnierite sam-ples determined by XRF are presented in
2
2 is dependent on mineral-ogical composition particularly the presence of quartz or amorphous silica. In addition, the differences in layer silicates of minerals containing in garnierites may also contribute
2 concentrations.
-
2+
2+ (Faye, 1974). Ratio of
limit that can be used to provide the termi-nology of garnierite solid – solution series.
more than 0.5, then the better match for the
could be assigned to pimellite, a solid solu-
talc. Nickel concentrations of all samples are
presence of tiny magnetite crystals likely can contribute to increase the iron concen-tration in analyzed samples.
The concentration of Al2 3 in both Soroako
Table 1. Mineralogical Composition of Soroako Garnierite Samples analyzed by XRD Method
Minerals/phases
Sample CodeGarnierite from Soroako West Block Garnierite from Petea Block
KO1 SU2 WW3 WW-4 KO4 IN1 KR1 AN4 SG4 PG1 PG3 PG4 AS6 PB5
Kerolite-pimellite - ++ +++ ++ +++ - ++ - + - - +++ - ++
Talc- ++ - - - - +++ - - - - - ++ - +++
Ni-serpentine + + ++ ++ ++ + +++ + +++ +++ +++ - +++ -Smectite - - - - - ++ - +++ - - - - - -Quartz - +++ - +++ ++ ++ - - + + + + + -
++ - ++ - - - - + - - - - - -- - - - + - + - + - - - - +
Characteristics and the Occurrence of “Garnierite” from the Soroako Nickeliferous Laterite Deposits, Sulawesi, Indonesia (Sufriadin et al.)
7
anomalous Al2 3
-
sample AN-4 contains predominantly Ni-
high Al2 3related to the presence of “brindleyite”, a nickel-rich aluminous serpentine (Maksi-
AN-4, the high concentration of Al2 3 could be derived from decomposition of Al-rich smectite (beidellite) and partly originated from serpentine.
2 2 2
Water content of garnierite is highly vari-
-dent on mineral proportions in the samples. The presence of anhydrous phases such as
Table 2 Whole Rock Chemistry of Garnierite Samples from Soroako determined by XRF.
Composition(wt %)
Sample IDUnserpentinized Peridotite
(West Block)Serpentinized Peridotite
(Petea Block)KO-1 SU-2 WW-3 WW-4 KO-4 IN-1 KR-1 AN-4 SG4 PG-1 PG-3 AS-6 PG-4 PB-5
2 44.95 50.08 48.39 48.48 50.07 49.19
2 0.01 0.01 0.01
Al2 3 23.28 0.10 0.20 0.42 0.49 0.11 11.21 0.04 0.05 0.10 0.87 0.11 0.24
1.80 1.45 3.70 2.98 9.27 1.87 3.93 0.42 0.28 0.40 0.15 0.28
0.03 0.02 0.07 0.05 0.14 0.02 0.20 0.01 0.01 0.07 0.11
22.15 19.84 28.70 15.82 35.79 20.81 20.81 8.87 31.94
4.33 0.02 0.09 0.01 0.43 0.02 0.01 0.02 0.02 0.03
Na2 0.13 0.02
K2 0.02 0.02 0.03 0.01 0.01 0.01 0.01 0.01 0.01 0.01
P2 5 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01
H2 8.94 10.71 13.28 7.74 10.38 9.09 23.40 24.57 11.80 10.59
Total oxides 96.86 91.08 89.63 97.23 80.15 91.85 89.41 87.64 97.99 94.62 95.10 84.93 84.43 95.67
Zn 0.05 0.14 0.17 0.03 0.41 0.12 0.17 0.25 0.02 0.01 0.07 0.08 0.49 0.05
Cr 0.04 0.03 0.11 0.08 0.30 0.05 0.05 0.25 0.01 0.01 0.17
Ni 2.96 8.73 10.10 2.66 19.11 7.90 10.19 12.01 1.75 5.25 4.75 14.85 14.68 4.10
Co (ppm) 24 78 59 157 28 87 20 191 5 7 44 104
2 4.10 3.29 3.54 3.53 2.41 8.28 7.75 Ni/ 0.18 0.31 0.12 0.58 0.30 0.43 0.05 0.20 0.19 0.11
Majalah Geologi Indonesia, Vol. 27 No. 1 April 2012: 1-11
8
of talc and serpentine is different. Pure talc 2 -
2high moisture content of samples PG1 (23.4
sepiolite (Weaver and Pollard (1973).
Precipitation of Garnierite
Soroako nickeliferous laterite deposits are
and the principal Ni-bearing phases are hydrated silicates occurring in the form of veins, fracture coating, and clasts or matri-ces components of the breccias. They are
of unserpentinized peridotites.
-
could be originated from dissolution of the early-formed vein type and other Ni-bearing phases.
-cated by XRD patterns suggests that garni-erites have been precipitated from colloidal
et al., 1977).
Variations of mineralogy observed in the garnierite samples may indicate the episodic changes in chemistry of solution particularly activities of Si, Mg, and lesser Al (Golightly, 1981). The presence of discrete magnetite
et al., 1995). Precipitation of garnierite is possible
-ter interaction (Taylor and Eggleton, 2001). The occurrence of quartz replacement may
-tion or from a retarded drainage in a more acid environment (Golightly, 1981). During the dry season, silica concentrations are very high (Harder, 1977). The pH of solution is
humid substance, therefore the precipitation of silica is possible.
-
are mainly composed of sepiolites. Their occurrences are rare and generally hosted
-tite. Sepiolite-falcondoite has been found
rather than quartz, indicating more alkaline
Neoformation of sepiolite is most favored
alkaline (pH: ~8.0 to ~9.5), high (Mg+Si)/P 2 (Galan and Pozo,
that sepiolite can be formed directly from dissolution of serpentine in the presence of
8Mg3Si2 5 4 + H4 4 Mg8Si12 30 2)4.8H2
serpentine sepiolite
Fibrous aggregates of sepiolite morphology and banded veins of kerolite-pimellite are typical of crack seal crystallization. This is considered the evidence of episodic crack
-sure (Wiltschko and Morse, 2001). Pressure
minerals dissolve as result of the pressure
Characteristics and the Occurrence of “Garnierite” from the Soroako Nickeliferous Laterite Deposits, Sulawesi, Indonesia (Sufriadin et al.)
9
under pressure are more susceptible to dis-solve than unstressed minerals (Cluzel and Vigier, 2008). Transport of material from dissolution site to precipitation site may take
Jessel, 1997).
In general, the scarcity of garnierites occur-
differences in physico-chemical properties
products. Peridotite bedrocks at Soroaoko
are characterized by medium- to coarse-
thereby released the Ni ion into solution.
condition becomes slightly alkaline.
typically consist of the highly serpentinized
This properties may preclude precipitation of garnierite veins because Ni2+ -ing solution is readily adsorbed onto crystal surfaces or substitutes for Mg2+ in octahedral sites of serpentine structures.
CONCLUSIONS
Garnierite at Soroako occur as thin layer or -
ing materials or veins, and as matrices in peridotitic conglomerate.
Talc-like phases (kerolite-pimelite and talc-
nepouite series), and sepiolite-falcondoite
series are the main Ni-bearing minerals -
ence of quartz or amorphous silica in the
contribution to the high silica-magnesia ratio of mined ores in particularly of the
Nickel concentrations of all analyzed sam-
presence of gangue minerals as impurities
Precipitations of garnierite are not only controlled by environmental conditions
factors such as lithology (serpentinization degree of protolith) and structures (fracture intensities and tectonic reactivation) may also be responsible for the rates and intensi-ties of garnierite formation.
ACKNOWLEDGEMENTS
permission to collect samples. Special thanks are addressed to Prof. Koichiro Watanabe at the De-partment of Earth Resources Engineering, Kyushu University for providing access in using laboratory facilities. Thanks are also due to Dr. Ade Kadarus-
Short Terms Research Scholarship at Kyushu Uni-versity, Japan.
REFERENCES
Unpublished Training Manual, 118p.
collected in Petea, Mahalona, and Konde areas, Unpublished Internal Memo.
and related minerals from solution. Clays and Clay Minerals
Majalah Geologi Indonesia, Vol. 27 No. 1 April 2012: 1-11
10
-ised dissolution-precipitation creep. MineralogicalMagazine
AGSOJournal of Australian Gology & Geophysics, 17 (4), p.81- 88.
garnierites - I: Structures, chemical compositions and color characteristics. Clays and Clay Minerals,21, p.27-40.
nature of kerolite, its relation to talc and stevensite.Mineralogical Magazine, 41, p.443-452.
-
and faulted regolith. Resources Geology, 58 (2),
Robinson, T.E., and Devenport, W.G., 2011. Extrac-tive metallurgy of nickel, cobalt, and platinum-group metals. Elsevier, Amsterdam.
Elias, M., 2002. Nickel laterite deposits a geological -
versity of Tasmania. Centre for Ore Deposit Research Special Publication, 4, p.205-220.
Ni2+ in ganierite: A discussion. Canadian Mineralo-gist, 12, p.389-393.
Economic Geology 100th
Anniversary Volume
Galan, E. and Pozo, M., 2011. Palygorskite and sepiolite deposits in continental environments. Description, Genetic Patterns and Sedimentary Set-tings. In: Galan, E. and Siregar, A. (Eds.), Develop-ment in Palygorskite - Sepiolite Research, Elsevier, p.125-174.
Golightly, J.P., 1981, Nickeliferous laterite depos-its. Economic Geology, 75th Anniversary Volume,
Harder, H., 1977. Clay mineral formation under Clay Minerals, 12,
p.281-288.
Kadarusman, A. Miyashita, S. Maruyama, S. Par-
geochemistry and paleogeographic reconstruction of Tectonophys-
ics, 392, p.55-83.
nickel-rich aluminous serpentine mineral analogous to berthierine. American Mineralogist
Monnier, C., Girardieau, J., Maury, R.C., and Cotton,
Geology 23, p.851-854.
AustralasianInstitute of Mining and Metallurgy Publication Se-ries,
-
G., 2008. Garnierite mineralization from Falcondo Ni-laterite deposits (Dominican Republic). Macla, 9.
-Peta Geologi Lembar Malili,
Sulawesi. Pusat Penelitian dan Pengembangan Ge-
occurrence and characterization of Ni-serpentines Clay Minerals, 30,
p.211-224.
Surono and Sukarna, D.
In:Hartono, U. (Eds.), dan Kalimantan, Publikasi Khusus, 28, Pusat Pene-
Taylor, G. and Eggleton, R.A., 2001. Regolith geol-ogy and geomorphology
Wiltschko, D.V. and Morse, J.W., 2001. Crystalliza-tion pressure versus “crack seal” as the mechanism for banded veins. Geology, 29, p.79-82.
Weaver, C.E. and Pollard, L.D., 1973. The chemistry of clay minerals. Elsevier Sc. Publ. Amsterdam.
Characteristics and the Occurrence of “Garnierite” from the Soroako Nickeliferous Laterite Deposits, Sulawesi, Indonesia (Sufriadin et al.)
11
Wells, M.A., Ramanaidou, E.R. Verral, M., and Tes-sarolo, C., 2009. Mineralogy and crystal chemistry of “garnierites” in the Goro lateritic nickel deposit,
European Journal of Mineralogy,
hosted vein sepiolite occurrences in the Ankara ophiolite melange, central Anatolia, Turkey. Claysand Clay Minerals, 52, p.227-239.