Ultra Ma Fic

7/27/2019 Ultra Ma Fic

http://slidepdf.com/reader/full/ultra-ma-fic 1/25

Ultramafic rocks and their

geological environment

Geology of Sulawesi

Ade Kadarusman PhD

Senior Geologist Specialist

Exploration and Mine Development Department

PT INCO Tbk, Sorowako, South Sulawesi



COMPOSITION OF

THE UPPER MANTLE

• The upper mantle is aperidotitic metamorphiccomplex dominated byolivine with increasinglylesser amount of

orthopyroxene,clinopyroxene and analuminous phase(plagioclase, spinel or garnet depending on

pressure). Eclogite andpyroxenite are omnipresent.



Ultramafic Rock the presence of essentially mafic

minerals without considering the silica content

Ultramafic rocks

classification

Rock classification for peridotites and pyroxenitesClassification according to Aluminuous phase content :

-plagioclase peridotite, spinel peridotite or garnet peridotite



Three principle sources of upper mantle

rock exposed in the Earth’s surface

• Orogenic peridotite massifspackages of ultramafic rocks (m to km in scale) that were

tectonically emplaced onto continental crust or island arc during

continental collision

- Layered intrusion (Mostly Pre-Cambrian Environment)- Alpine type of Peridotites

• Oceanic peridotite

uplifted onto continental margin or island arc in ophiolite sequences

• Peridotitic xenolithscm to m scale samples carried in rapidly erupted host volcanics

such as alkali basalts and kimberlites



The upper mantle beneath pre-Cambrian cratonperidotite as mantle xenoliths

Menzies &

Chazot, 1995

• Peridotitic rocks were sampled by kimberlite-like rock fromdepth of 40 km minimum as mantle xenoliths

Th tl k i ti t l lli i



The upper mantle rock in continental collisions

-Orogenic Peridotite-Deep subducted crustal rocks (to depth of at least 40 km) in continental

collision zone can uplift peridotitic rocks to the surface



The Origin of Ophiolites

SSZ SSZOPMOR



Origin of Ophiolites (oceanic crust on the land):• Mid Oceanic Ridge (MOR)

• Supra Subduction Zone (SSZ)

• Oceanic Plateau / Seamounts (OP)

Worldwide Database showed that SSZ ophiolite is

common for:

-Ultramafic hosted chromite deposit

-Chromite and nickel sulphides hosted PGM-Volcanic Massive Sulphides Deposit

i iti tl



primitive mantle =

basalt/gabbro + peridotite



Key for laterites development : ultramafic rock on

the surface and equatorial locations



Ultramafic rocks

of oceanic origin

emplacement

onto continental

margins or

island arcs :

- Obduction

- Accretion

Obduction

Accretion



Ultramafic rocks

(Upper Mantle Origin)

Expose on the Earth’s Surface

(oceanic or orogenic peridotite)

Laterite Development Sulphides Mineralization

Equatorial Location Magmatism

Nickel LateriteNickel Sulphides



Geology of Sulawesi

See the animation



Eastern Indonesia :The World’s largest of ultramafic rock outcrops,



East Sulawesi Potential :the Batui

Thrust Development



Lakes area and Matano fault



Coastal Area and Mekongga Block



Conclusions

• Unique geology and tectonic of EasternIndonesia exposed large distribution of

ultramafic rocks on the land

• Exposing ultramafic rocks in the surface,means potential economic values not only

for Nickel laterite, but also for Nickel

sulphides, diamond, rare metal/PGE



SSZ



Supra Subduction

Ultra Ma Fic

Documents

Transcript of Ultra Ma Fic