5. ENDAPAN MAGMATIK.pdf

8/9/2019 5. ENDAPAN MAGMATIK.pdf

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END P N M GM TIK

Sutarto

Laboratorium Petrologi dan Bahan Tambang

Departemen Geologi Universitas Pembangunan Nasional “Veteran” Yogyakarta



TERMINOLOGITERMINOLOGI

MineralMineral--mineralmineral bijihbijih sepertiseperti magnetitmagnetit,, ilmenitilmenit,, kromitkromit terbentuk terbentuk padapadafasefase awalawal diferensiasidiferensiasi magma,magma, bersamaanbersamaan dengandengan pembentukanpembentukanmineral olivine,mineral olivine, piroksenpiroksen, Ca, Ca--PlagioklasPlagioklas..

SemuaSemua mineralmineral bijihbijih yangyang terbentuk terbentuk padapada fasefase iniini disebutdisebut sebagaisebagai

endapanendapan magmatik magmatik



KLASIFIKASIKLASIFIKASI

,,pada kimberlitpada kimberlit

,,kromitkromit (Cr),(Cr), magnetitmagnetit (Fe), platinum (Pt)(Fe), platinum (Pt)

,, ,, Pegmatik Pegmatik : Fe,: Fe, SnSn, U, gems, U, gems



rr uu uu uu rr --mineralmineral asesoriasesori, yang, yang mempunyaimempunyai nilainilai ekonomiekonomi

--..tersebuttersebut terbentuk terbentuk karenakarena kristalisasikristalisasi yang normal,yang normal,

dandan tidak tidak terkonsentrasiterkonsentrasi membentuk membentuk lapisanlapisan secarasecaraterpisahterpisah daridari mineralmineral--mineralmineral silikatsilikat pembentuk pembentuk batuanbatuan,, akanakan tetapitetapi tersebartersebar ((diseminasidiseminasi).).



on oon o yang pa ng popu aryang pa ng popu ar a a aa a adiseminasidiseminasi intanintan padapada batuanbatuan kimberlitkimberlitanan ampro eampro e,, ser aser a e erapae erapa a uana uan

alkalinalkalin lainlain menghasilkanmenghasilkan apatitapatit, niobium,, niobium,uran um,uran um, anan unsureunsure anaana ang aang a rarerareearths) earths) ..



MORFOLOGI KIMBERLIT

Based

on

studies

of

numerous

kimberlite

,

kimberlites

into

3

distinct

units

based

on

their morphology and petrology. These

units are:

1)

Crater

Facies

Kimberlite

2)

Diatreme

Facies

Kimberlite

3)

Hypabyssal

Facies

Kimberlite





GENESA KIMBERLIT



(Awang Satyana, 2008)









GRAVITATIONALGRAVITATIONAL

SETTLINGSETTLING

rr r vr v ,, ruru uuyangyang sangatsangat pentingpenting didalamdidalam prosesproses diferensiasidiferensiasi

--..yangyang terbentuk terbentuk awalawal,, padapada temperature yangtemperature yang

tinggitinggi,, karenakarena gravitasigravitasi akanakan mengendapmengendap didi bagianbagiandasardasar dapurdapur magma,magma, membentuk membentuk lapisanlapisan kumulatkumulat..KromitKromit (Cr),(Cr), magnetitmagnetit (Fe), platinum (Pt),(Fe), platinum (Pt),

merupa anmerupa an m neram nera --m nera yangm nera yang ser ngser ngterkonsentrasiterkonsentrasi membentuk membentuk kumulatkumulat,, dandan











(Huang et al, 2004)







Stratiform Podiform

Size: Very large >>>1 mT Very small, patchy < 1 mT. .

Production:53.7% 46.3%

Age Precambrian BIC is 1950 ma Varies, mostly Paleozoic or youngerSetting: Stable craton Orogenic belts, ophiolites in marginal basinsExamples: Bushveld--29 individual seams Guleman-Soridag District, TurkeyGreat Dyke - 15 cm ore PhilippinesStillwater (subeconomic-40% Cr2O3) UralsBird River Sill, Manitoba (sub) Bay of Islands, Nfld. (sub)

Muscox, NWT (sub)

to pyroxenite-gabbro-anorthosite-ore occurs in lower part of strati- -if gabbro present in peridotite,form deposit, but not at bottom. ore occurs at contact with um Alteration: Generally none Serpentinized

ruc ures: umu a e-we - orme crys a s oun e an e onga e gra ns;Sedimentary structures common pull-apart structures•graded bedding Structurally emplaced•scour and fill•la ered

(Huang et al, 2004)

•gradational boundaries







LIQUIDLIQUID

IMMISCIBILITY IMMISCIBILITY

PadaPada prosesproses fraksionasifraksionasi, magma, magma dapatdapat mengalamimengalami ,, ,,

besibesi,, tembagatembaga, sulfur,, sulfur, membentuk membentuk magmamagma bijihbijih,,

men ebabkanmen ebabkan membentuk membentuk dro lets andro lets an memisahmemisahdaridari magmamagma silikatsilikat padapada kantongkantong magma.magma.



--

NiNi didi Archean Archean greenstone belts,greenstone belts, bijihbijih

ProterozoikumProterozoikum..



Figure 7:Typical magmatic Ni-Cu sulphide

sulphides, Thompson, (B)matrix-textured sulphides, Lynn, ,

Lynn Lake, (D) sulphide breccia,

Lynn Lake. Pyrrhotite = mediumgray, pentlandite = light gray,chalcopyrite = yellow. Silicate

=

Photographs courtesy of L.J.Hulbert



Figure 1:World map (after Chorlton, 2003) showing magmatic Ni-Cu-PGE sulphide deposits having resources and/or production

greater than 100 000 tonnes of ore.











PEGMATITPEGMATIT

PadaPada fasefase akhirakhir magmatismemagmatisme,, sebelumsebelum fasefase,,

magmamagma padapada umumnyaumumnya mengalamimengalami peningkatanpeningkatan

kandun ankandun an asas dandan uaua air. Ma maair. Ma ma sisasisa ananbanyak banyak mengandungmengandung gas,gas, mencarimencari jalam jalam keluarkeluar,,memotongmemotong bagianbagian tepitepi kantongkantong magma yangmagma yang telahtelah

mementuk mementuk batuanbatuan bekubeku,, membentuk membentuk retasretas--retasretasyangyang dikenaldikenal sebagaisebagai batuanbatuan pegmatitepegmatite









How large can minerals grow?

many people to pegmatites, for thefirst time, are the abundance ofminerals that are found in them.There have been about 550

different minerals found inpegmatites. Pegmatite minerals are

minerals in other rocks. Forexample, the minerals in granites

are typically on the order of a fewmi imeters across w ereas simi arminerals in pegmatites may beseveral centimeters or metersacross. The ur le tourmaline on

the right, "The Rocket", illustrateshow large some minerals can grow.The largest known crystal in apegma e, a spo umene romSouth Dakota, measured almost 13

meters (42 feet) long.



Some of the world’s best-known gem material is

obtained from pegmatite deposits. Varieties of beryl (aquamarine, golden, morganite),spodumene (kunzite, hiddenite) and tourmaline

- , ,garnet and topaz are all valued precious stones

originating from pegmatites.



5. ENDAPAN MAGMATIK.pdf

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