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odiform Chromite - Mineral Deposit Profiles, B.C. Geological Survey

ODIFORM CHROMITE 

M03by Chris Ash

BC Geological Survey  

sh, Chris (1996): Podiform Chromite, in Selected British Columbia Mineral Deposit Profiles, Volume 2 -

etallic Deposits, Lefebure, D.V. and Hõy, T, Editors, British Columbia Ministry of Employment and

vestment, Open File 1996-13, pages 109-112.

IDENTIFICATION

YNONYMS: Alpine type; ophiolite hosted chromite.

OMMODITIES (BYPRODUCTS ): Chromite (may contain platinum group elements

s, Ir and Ru).

XAMPLES (British Columbia (MINFILE #) - Canada/International ): Castle

ountain Nickel (082ESE091) and Scottie Creek (092INW001); Guleman ore field

Turkey); Kalimash - Kukes-Tropoje district, Bulquize and Todo Manco - Bater-

Martanesh district (Mirdita ophiolite, Albania); Tiébaghi ophiolite and Massif du Sud

New Caledonia), Acoje and Masinloc-Coto (Zambales range/ophiolite, Luzon,

hillipines); Batamshinsk, Stepninsk, Tagashaisai and Main SE ore fields (Kempirsai

assif, Southern Urals, Russia); Xeraivado and Skoumtsa mines (Vourinos ophiolite,

reece); Semail ophiolite (Oman); Luobusa, Donqiao, Sartohay, Yushi, Solun, Wudu

nd Hegenshan deposits (China) all > 1.5 Mt .

GEOLOGICAL CHARACTERISTICS 

APSULE DESCRIPTION: Deposits of massive chromitite occur as pods, lenses or

yers within ophiolitic ultramafic rocks.

ECTONIC SETTING: Obducted fragments of oceanic, lower crustal and upper

antle ultramafic rocks within accreted oceanic terranes.

EPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Formed as a primary

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odiform Chromite - Mineral Deposit Profiles, B.C. Geological Survey

agmatic differentiate during early olivine and chrome-spinel crystal fractionation of

asaltic liquid at an oceanic spreading centre; (1) as massive to disseminated pods

nd lenses of chrome-spinel surrounded by a dunite envelope within depleted mantle

arzburgite; or (2) as massive to disseminated cumulate layers in dunite at the base of

e crustal plutonic section.

GE OF MINERALIZATION: Mesozoic and younger.

OST/ASSOCIATED ROCK TYPES: Variably serpentinized peridotite; residual

antle harzburgite; cumulate dunite.

EPOSIT FORM: Podiform, tabular lenses, irregular masses, cumulate layers. Pods

nd lenses typically occur in clusters of variable size.

EXTURE/STRUCTURE: Massive to disseminated, nodular (syn. leopard, grape,

ean or shot ore), chromite net, occluded silicate, orbicular.

RE MINERALOGY: Chromite.

ANGUE MINERALOGY (Principal and subordinate ): Variably serpentinized olivine

nd orthopyroxene, magnetite, iddingsite.

WEATHERING: Black, no noticeable affects resulting from surface oxidation.

RE CONTROLS: Proximity to the crust-mantle transition zone. Restricted to dunite

odies in tectonized harzburgite below this transition, or lower dunitic portions of

tramafic cumulate section above it.

ENETIC MODEL: Early fractional crystallization of chromite from a basaltic liquid

ther (1) just below the crust-mantle transition (syn. petrological MOHO) in small

agma pockets or possibly conduits within the residual mantle harzburgite; or (2)

mmediately above the crust-mantle transition as cumulate layers within dunite at the

ase of the axial magma chamber. Pods and lenses in harzburgite obtain their

agonistic shape as a result subsolidus to hypersolidus ductile deformation due to

antle convection.

OMMENTS: Ophiolites of suprasubduction zone affinity with harzburgite mantle

ections appear to be the only ophiolite type to host economic deposits of podiform

hromite. A lack of any sizable chromite occurrence in British Columbia may reflect

e fact that most ophiolitic complexes in the province are of mid- ocean ridge affinity.

ccurrences of podiform chromite are found in ophiolitic ultramafic rocks in the Slide

ountain, Cache Creek and Bridge River terranes. Most of these known occurrences

ave been reviewed by Hancock (1990).

EXPLORATION GUIDES 

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odiform Chromite - Mineral Deposit Profiles, B.C. Geological Survey

EOCHEMICAL SIGNATURE: Cr 

EOPHYSICAL SIGNATURE: Gravity anomaly.

THER EXPLORATION GUIDES: Found in rocks formed near or within the ophiolitic

rust- mantle transition zone.

ECONOMIC FACTORS 

YPICAL GRADE AND TONNAGE: Grades range from 20 to 60% Cr2O3 and are a

nction of the texture of the chromite; i.e. amount of chromite relative to gangue

erpentinite. Tonnages are variable, ranging from several thousand tonnes to several

illion tonnes.

CONOMIC LIMITATIONS: The complex structure and irregular distribution make

xploration and development difficult.

ND USES: Chromium has a wide range of uses in the iron and steel industry which

ccounts for over 75% of its use. Chromite is also used in making refractory bricks for

rnace linings.

MPORTANCE: An important source of metallurgical-type chromite ores (45-60%

r2O3: Cr/Fe = 2.8-4.3). Podiform chromite is the only source of refractory-type ore

min. 25% Al2O3: min. 60% Cr2O3 + Al2O3: max. 15% FeO). Historically podiform-

pe ore fields account for 57% of all chromite produced.

REFERENCES 

lbers, J. P. (1986): Descriptive Model of Podiform Chromite; in Mineral Deposit

odels, Cox, D.P. and Singer, D.A., Editors, U.S. Geological Survey , Bulletin 1693,

age 34.

hristiansen, F.G. (1986): Structural Classification of Ophiolitic Chromite Deposits; in

etallogeny of Basic and Ultrabasic Rocks, Gallagher, M.J., Ixer, R.A., Neary, C.R.

nd Pichard, H.M., Editors; The Institution of Mining and Metallurgy , pages 279-289.

uke, J.M. (1983): Ore Deposit Models 7. Magmatic Segregation Deposits of

hromite; Geoscience Canada, Volume 10, Number 1, pages 15-24.

ancock, K.D. (1990): Ultramafic Associated Chrome and Nickel Occurrences in

ritish Columbia; B.C. Ministry of Energy, Mines and Petroleum Resources, Open File

990- 27, 62 pages.

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odiform Chromite - Mineral Deposit Profiles, B.C. Geological Survey

oberts, S. (1988): Ophiolitic Chromitite Formation: A Marginal Basin Phenomenon?;

conomic Geology , Volume 83, pages 1034-1036.

inger, D.A., Page, N.J. and Lipin, B.R. (1986): Grade and Tonnage Model of Major

odiform Chromite; in Mineral Deposit Models, Cox, D.P. and Singer, D.A., Editors, U.

. Geological Survey , Bulletin 1693, pages 38-44.

inger, D.A. and Page, N.J. (1986): Grade and Tonnage Model of Minor Podiformhromite; in Mineral Deposit Models, Cox, D.P. and Singer, D.A., Editors, U.S.

eological Survey , Bulletin 1693, pages 34-38.

towe, C.W. (1987): Evolution of Chromium Ore Fields; Van Nostrund Reinhold Co.,

ew York, 340 pages.

hayer, T.P. (1964): Principal Features and Origin of Podiform Chromite Deposits,

nd Some Observations on the Guleman-Soridag District, Turkey; Economic Geology ,

olume 59, pages 1497- 1524.

March 27, 1996

M03] [M04] [M05] [M06] [M07] [M08] [Published Profile Index]

Deposit Profiles]

ast Updated September 12, 2007

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