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Fadlin, ST, Meng Teknik Geologi

SEKOLAH TINGGI TEKNOLOGI NASIONAL

ENDAPAN RESIDUAL (KIMIAWI)

ENDAPAN SEDIMENTER (MEKANIK)

MATA-KULIAH BGI (Bahan Galian Industri)

(2 SKS)

If DNA is the building block of life,

then industrial minerals and rocks

are literally the building blocks of

our way of life

ENDAPAN RESIDUAL (KIMIAWI ATAU LATERIT)

DEFINISI

● = Endapan/material yang terbentuk oleh proses kimiawi, biasanya oleh pelarutan atau pencucian (leaching) (Whitten & Brooks, 1988)

● = Endapan yang terbentuk oleh proses pelapukan dan dekomposisi kimiawi terhadap batuan induknya (Jensen & Bateman, 1986)

● Syarat terbentuknya:

– Terdapat batuan/lode sumber unsur/mineral valuable

– Iklim yang favorable tejadinya dominan pelapukan kimia

– Relief rendah/landai

– Kestabilan kerak yang lama

– Time

Residual processes

● Chemical weathering leads to mineral concentration through the removal of soluble materials and the concentration of a less soluble residue.

● A common example of a deposit formed through residual concentration is bauxite.

● Pelapukan kimia ada 2 tahap:

– Tahap alkaline: K, Na, Ca akan hilang (removed) dan menyisakan material yang kaya akan Fe, Si, dan Al

– Tahap acid: Alumunium hidroksida dan besi akan berpindah (migrate) pada tingkat/daerah terbatas

● Contoh endapan residual

– Alumunium (bauksit)

– Endapan Nikel laterit:

● Batuan ultrabasa (peridotit: olivin, Mg-silikat, Fe-silikat)

● Berasosiasi dengan mineral garnierit, krisopras

● Zone limonit dan saprofil, dibatasi oleh m.a.t

– Endapan besi (hematit-limonit)

– Mangan (manganit)

Blue_Kyanite

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1. Bauksit (endapan bauksit laterit)

● Bauksit bauxite: Les Baux (Prancis)

● Bauksit soil/batuan yang utamanya tersusun oleh mineral-mineral hidroksida alumunium (hasil pelapukan kimiawi batuan „silicate aluminium‟ yang sedikit mengandung Fe dan kuarsa.

● Batuan asal:

Endapan bauksit dapat berasal dari berbagai jenis batuan yang kaya akan mineral pembawa aluminium (Al-bearing minerals):

– syenit nefelin (Arkansas, USA)

– batugamping (Jamaika),

– batu lempung, serpih (Gove, Australia),

– batupasir kaolinitik (Brazil, Weipa-Australia) dan

– granit (Los Pijiguaos, Venezuela).

Bauxite occurrences

– The source of the world‟s aluminum.

– Concentrated in the tropics because that is where lateritic weathering occurs.

– Found in present-day temperate conditions, such as France, China, Hungary, and Arkansas, where the climate was tropical when the bauxites formed.

– Not found in glacial regions.

● Glaciers scrape off the soft surface materials.

– Bijih bauksit (ekonomis ditambang), bila:

● Al2O3 > 45%

● Fe2O3<20%

● SiO2<5%

– Mineralogi:

● Mineral bijih :

– Gibbsit (Al2O3.3H2O)

– Boehmit (Al2O3.H2O)

– Diaspor (Al2O3.H2O)

● Gangue:

– Oksida (Fe2O3)

– Kuarsa (SiO2)

– Titanium (TiO3)

– Air (water)

● KLASIFIKASI ENDAPAN BAUKSIT

– Endapan Karstik 14% produksi

– Endapan Lateritik 85% produksi

– Endapan Allochthonous 1% produksi

Endapan bauksit lateritik (residual)

Pelapukan kimia

● Desilisikasi

● Pengkayaan Alumina dalam soil

Alumina: Oksida alumina murni (Al2O3)

Al = 52,9%

O = 47,1%

Bentuk endapan bauksit residual

● Blanket: dekat permukaan horisontal

● Inter-stratified bedding

● Lensis

● Pocket deposits atau irregular masses

● Endapan klastik „transported deposits‟

Ages of residual bauxites

● More than 90 percent of all known bauxite deposits formed during the last 60 million years,

● All of the very large bauxite deposits formed less than 25 million years ago.

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Gambar 13 Distribusi vertikal (vol.%) dari mineral gibbsite (gbs), nordstrandite (nsd), kaolinit (kaol), kuarsa (qtz), goethit (gt), hematit (hem) dan anatase (ant) pada endapan bijih bauksit Pijiguaos, Venezuela (Meyer et al., 2002). Kuantifikasi fase dilakukan dengan analisis Rietveld.

Zona Top Soil

● Merupakan lapisan material overburden dengan ketebalan yang bervariasi dari 1 – 2 meter namun pada umumnya kurang dari 1 meter, banyak mengandung unsur-unsur pengotor seperti akar akar tumbuhan.

Zona Limonit

● Secara kimiawi zona limonit umumnya ditentukan atas kelimpahan unsur – unsur yang tidak mudah larut (residual) seperti Al, Fe, Cr, Ti, Mn dan Co. Akan tetapi unsur yang paling sering dipakai adalah Fe karena biasanya berasosiasi dengan mineral utama yang dijumpai pada zona limonit seperti goetit, mangan oksida (asbolit) dan oksida besi limonit dan hematit. Sedangkan dari hasil deskripsi lapangan zona limonit dicirikan oleh kenampakan fisik berupa warna coklat kemerah – merahan sampai coklat tua, ukuran butir lempung – lanau, dijumpai mineral seperti magnetit, limonit, dan goethit.

KIMIA MINERAL

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Bauksit (endapan bauksit laterit) Laterite bauxite at West Borneo

Andesite-Rhyolitic Source Rock

Laterite bauxite at West Borneo

Granit Source rock

Sample bauksit laterit

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Laterite Exsploration Alat dan Bahan

Peralatan dan perlengkapan lapangan yang

digunakan selama pekerjaan penelitian di lapangan:

● Peta Geologi (skala 1:100.000)

● Peta Topografi/RBI (skala 1:25.000)

● Palu geologi batuan beku

● Kompas geologi Kamera Digital

● Loupe (kaca pembesar 10 – 30 x)

● GPS (Global Positioning System)

● Peralatan menulis

● Peralatan sampling (Kantong/plastik sampel, pita

sampel, tali rafia, dll)

Tahapan dan metode penelitian untuk

prospeksi terbagi atas 3 (tiga) pekerjaan utama

antara lain :

1. Desk study (literatur)

2. Pekerjaan lapangan :

● Pemetaan Geologi

● Pemeteaan laterite

● Sampling

3. Analisa laboratorium.

Prospection/Pre-Exploration

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● Sebelum dilakukan analisa geokimia batuan

(XRF) di laboratorium, sampel bauksit laterit

terlebih dahulu di lakukan preparasi berupa

pencucian sampel. kemudian pengeringan

dengan menggunakan matahari maupun

microwave oven

● Kemudian sampel di packing.

Wacthing this....!!, do you know him??

Lazy Geos...:D

Sampel Packing

Geokimia Batuan dengan XRF (X-Ray Fluorescence)

● Sampel bauksit yang telah dilakukan preparasi terlebih dahulu kemudian di kirim ke laboratorium dilakukan analisa geokimia menggunakan metode XRF (X-Ray Fluorescence)

● sampel bauksit masing-masing 1-2 kg, mewakili blok prospek dan tipe batuan asal endapan bauksit

● Hasil (geochemistry analysis) akan dipakai untuk menjelaskan proses-proses yang sudah terjadi dan untuk dijadikan data dalam meginterpretasikan karakteristik suatu endapan mineral tersebut.

No.

Kode

Sampel Al2O3 Fe2O3 Fe SiO2 TiO2

1 BX-01/3-4M 30.75 14.26 9.97 17.29 1.26

2 BX-01/4-5M 32.61 14.77 10.33 17.10 1.53

3 BX-02/0-1M 40.70 4.04 2.83 13.72 0.43

4 BX-02/1-2M 30.75 3.74 2.61 13.29 0.39

5 BX-02/2-3M 38.61 2.55 1.79 17.10 0.21

6 BX-03/0-1M 40.70 4.22 2.95 12.72 0.64

7 BX-03/1-2M 30.75 4.42 3.09 18.29 0.63

8 BX-03/2-3M 35.61 4.86 3.40 17.10 0.63

9 BX-03/3-4M 40.70 4.20 2.94 17.72 0.59

10 BX-04/3-4M 30.75 18.29 12.79 18.29 2.16

11 BX-04/5-6M 42.61 17.10 11.96 11.10 1.99

12 BX-05/5-6M 40.70 17.72 12.39 10.72 2.04

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How about the Detil Exploration...??

I Dont Do Miracles, I Just Teach Geology So, Keep fight to be a GOOD GEOLOGIST

Thanks for you

Attention

See you later..

2. Endapan nikel laterit

Endapan bijih nikel sekunder (laterit), dikarakterisasi oleh silika nikel (nickeliferous silicates) seperti garnierit ((Ni,Mg)6(OH)8Si4O10) yang mengandung Ni dengan variasi 4-36 %.

Terbentuk oleh proses pelapukan dan pengkayaan kimiawi terhadap batuan ultramafik, seperti peridotit, harzburgit dan lherzolit yang mengalami proses serpentinisasi.

Zona pelapukan kimiawi yang kaya akan bijih nikel berada pada zona saprolit

Contoh: endapan nikel laterit di Soroako, Sulawesi.

Istilah “Laterite” berasal dari bahasa latin “later” yang berarti “brick” dalam bahasa Inggris (batu bata). Dewasa ini, istilah Laterit ditujukan untuk menyebut lapisan tanah yang kaya akan oksida besi (Fe2O3), Nikel, Crom, dan almunium, yang terbentuk akibat pengaruh pelapukan kimia dan pengaruh kondisi air tanah

Proses pembentukan

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Endapan Ni laterit

Profil endapan bijih nikel laterit, (a) endapan Exmibal, Guatemala, dan (b) endapan nikel Soroako (Edwards dan Atkinson, 1986). Bijih nikel kaya terjadi pada zona saprolit.

Perbedaan penurunan muka airtanah akan menyebabkan perbedaan pola ketebalan profil endapan laterit, perbedaan tsb disebabkan (Dariyanto,1999) : • struktur batuan asal, • morfologi yang mempengaruhi intensitas “leaching”, • intensitas curah hujan, • iklim dan waktu.

Freeze & Cherry, 1979, op cit Darijanto, 1999

Ketebalan Limonit dipengaruhi oleh faktor morfologi berkaitan dengan pergerakan air tanah

• Di daerah punggungan lapisan limonit lebih tipis drp daerah lembah atau cekungan

• Hal tsb karena pola aliran air tanah di punggungan cenderung divergen, dibandingkan di lembah yang relatif konvergen

• Pola divergen cenderung punya kecepatan penurunan air yang lamban dibanding yang bersifat konvergen

• Kecepatan penurunan muka air berpengaruh pada intensitas arah pergerakan-lateral air tanah

• Makin intensif pergerakan-lateral air tanah, proses “leaching” makin intensif.

• Makin intensif proses “leaching”, memungkinkan proses pembentukan limonit yang makin tebal

Variasi ketebalan laterit pada variasi topografi

● Bila topografi tidak memungkinkan migrasi (topografi rata/flat), unsur yang tercuci (Si, Mg, Ni, Co) terutama (Si, Mg) akan membentuk lapisan kaya lempung “nontrolite”.

● Bila leaching efektif, hasilnya akan membentuk garnierit (Ni>>) yang terakumulasi pada zona-zona rekahan.

● Mineral mengandung Nikel dalam laterit :

Limonit (< 2% Ni)

Nontrolite (<5% Ni, berkembang di Australia)

Saprolit (<10% Ni)

Garnierit (10-20% Ni)

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GARNIERITE

Nikel tidak hanya berasosiasi dengan garnierit, tapi Ni juga dapat mensubstitusi Fe dan Mg pada mineral silika, khususnya olivin.

KIMIA MINERAL

Limonit

Bedrock

Saprolit

Pulau Sebuku (Prayudha , 2006)

Limonit

Bedrock

Saprolit

ENDAPAN SEDIMENTER (MEKANIK ATAU PLACER)

Placer deposit

● A mineral with a high specific gravity will become concentrated by flowing water.

● Deposits of minerals having high specific gravities are placers.

● Most placers are found in stream gravels that are geologically young.

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Placer deposit

● The most important minerals concentrated in placers are gold, platinum, cassiterite (SnO2), and diamond.

● More than half of the gold recovered throughout all of human history has come from placers.

Placer deposit

● The South African fossil placers are a series of gold-bearing conglomerates (next Figure).

– They were laid down 2.7 billion years ago as gravels in the shallow marginal waters of a marine basin.

– Associated with the gold are grains of pyrite and uranium minerals.

– Nothing like the deposits in the Witwatersrand basin has been discovered anywhere else.

● Mining the Witwatersrand basin has reached a depth of 3600 m (11,800 ft).

● The deposits are running out of ore. South African fossil placers (gold-bearing conglomerates)

● Konsentrasi mekanik: Pemisahan gaya berat secara alamiah terhadap mineral-mineral berat dari mineral ringan oleh pergerakan air atau udara dimana mineral - mineral berat terkonsentrasikan membentuk endapan.

● Syarat pembentukan:

– Berat jenis tinggi (3,5 – 19,4)

– Tahan terhadap pelapukan kimia dan mekanis

– Mempunyai daya tahan (durabillity, malleability)

– Kekerasan (toughness, hardness) tinggi (2,5 – 10)

– Tidak mudah larut

● Jenis endapan placer (komoditi):

Emas - Timah - Platinum - Magnetit - Kromit - Ilmenit - Rutil - Gemstone -Zirkon - Monasit

● Sumber material endapan:

– Endapan lode komersial

– Lode non komersial

– Mineral bijih terhambur: platinum

– Rock-forming minerals: butiran magnetit, ilmenit, monasit, zirkon

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● Prinsip pembentukan:

– Tahap pembentukan

1. Pelapukan mineral-mineral stabil dari matriksnya

2. Konsentrasi

– Mineral stabil dipisahkan dari matriknya, dicuci oleh air ke arah downslope

– BJ>> akan mengendap lebih dulu

– Terkonsentrasi

● Laju pengendapan dipengaruhi oleh:

– Kecepatan pergerakan fluida

– Perbedaan BJ (di air >> di udara)

– Ukuran

– Bentuk partikel

Placer Deposits

● Placer deposit : formed by the mechanical concentration of resistant minerals, which are released by weathering from source rocks

● Main Commodities:

Tin, Gold, Platinum, Niobium, Tantalum, Titanium, Zircon, Diamond

● Paleo-placers:

The lithified equivalents of placer deposit

● Economic deposits are limited geographical distribution

– (Archean – Proterozoic)

– Uranium, Canada

– Gold & Uranium, South Africa

– Tin – bearing paleo-placer: Nigeria, Brazil, Malaysia

Klasifikasi Endapan Placer

Kastalov (1971):

Two types of alluvial placer:

● Autochthonous = nearby primary source/paleo-placer (not have been fluvially transported)

~ elluvial, colluvial deposits

● Allochthonous = have been fluvially transported

~ fluvial placer deposit

Youngsen & Craw (1999):

● Primitive placer

● Trunk placer

MacDonald (1983):

Based on geological environment

Klasifikasi Endapan Placer (Mac Donald, 1983)

• Continental placer

– Elluvial placer

– Colluvial placer

– Alluvial placer Fluvial

– Desert Placer

– Glacial placer

• Transitional placer

Endapan pada pantai (transisi laut dan darat)

Agen: Arus & Angin

• Marine placer

- Mulanya endapan transisional

- Transisi tergenang

- Endapan placer marine

General Characteristics

1. Distribution in space & time

● Have a wide geographical distribution, some of them as „a giant placer‟

– Otage fluvial gold deposit, New Zealand = 148 to Au – Bakwanga eluvial diamond deposit, Zaire – Titanium – bearing beach sand, eastern Australia

● The bulk of the world`s placer deposit is of Tertiary & Quarternary age.

– Alphine orogeny; Post Mesozoic ● Primary deposits – outcropping – weathering –

detrital gold – Sea level change during Quarternary

2. Size and Grade

– Average grade: lower than from hard rock mining

– Eluvial/Colluvial are smaller & lower grade than the fluvial deposit

– Beach deposit are much larger than in continental deposits

General Characteristics 3. Mineralogy

● Placer minerals: – Very high specific gravities – Usually highly hardness – Physically durable – Chemically inert

Fluvial beach deposit are liberated from their gangue mineral

4. Tectonic Setting

● Transitional Environment – Major influenced by:

● Source material ● Fluctuation of sea level in Quarternary ● Mechanical concentration by wave & current

activity ● Continental encvironment

– Large fluvial gold placer restricted to region of tectonic instability e.g.: Otago Au placer

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● Eluvial – Coluvial

– Overlie or very near source rock

– No reworking of resistant mineral

– Grade is normally lower than other

– Enrichment is partly caused by the removal of soluble minerals by groundwater & partly by transport of the lighter mineral by running water & wind action

● Fluvial

– Relatively far from source rocks

– Any reworking of resistate minerals

– Gold & cassiterite main are mineral

– Size larger & grade higher

– Important environment: river terraces & valley fill

– Requirements for formation:

● Appropriate source rock ● Climate ● Morfology ● Distance from sources

Beach Sand Deposits

Genesis

Natural sorting of the surf, which is concentrated heavy minerals at the high-water mark and removes the lighter fraction

Transport sediment by wind

Climate change in Plio-Pleistosen, during which changes of sea level have resulted in several periodes of marine transgression and regression, which have reworked an extensive zone of clastic sediments

e.g. Eneabba rutile – zircon – ilmenit sand deposit – Western Australia

Diamondiferous beach sands of the south – weatern coast of Africa.

Marine Placers

Genesis

Occurs on the continental shelf ±5 km of the coast

Formed by the submergence of heavy mineral accumulation, which originally concentrated in a continental or litoral environments

Offshore current activity redistribution the heavy minerals

Ore minerals: mainly cassiterite (Thailand, Malaysia & Indonesia)

Also : Gold, diamond, titaniferous magnetite, chromite, ilmenite, monazite, rutile, zircon and wolframite

Marine placers in Indonesia

Tin = Tin islands, Sumatera (Bangka, Belitung, etc).

Paleo placer Deposit

Distribution in space & time

Space: Canada, South Africa, Ghana, Brazil

Ore mainly: Gold & Uranium

Time: Proterozoic - Archaean

Size & grade deposits

Witwatersrand Gold placer deposits

Production: > 35.000 ton & grade 10 g/t Au

Reserves: 50.000 tonnes

Blind-Elliot Lake: 300 x 106 ton U

Grade: 0.1% U3O8 & 0.05% ThO2

Jacobina – Brazil: 7.1 – 12.7 g/t Au

Mineralogy -- Host rock

South Africa, Brazil, Ghana: Native Gold

Blind –Elliot lake: Uraninite, Brannerite – Qzt, Py

Host-rock: Conglomerate (>90% Clasts)

Tectonic Setting

Intra Continental setting

Thick succession of dominantly shallow water

Terrigenous sediment

Basement : metamorphed continental rock

Physical properties

Provenances

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I Dont Do Miracles, I Just Teach Geology So, Keep fight to be a GOOD GEOLOGIST

Thanks for you

Attention

See you later..