PETROLOGICAL ORE ASSOCIATIONS

 

The earth's crust and mantle have passed through an evolutionary sequence of changes throughout geological time. These changes have influenced and are reflected in petrogenesis and the nature and extent of related mineralization. Definite associations of rocks with specific mineral deposits occur.  The association of tin mineralization with granites, restriction of Banded Iron Formations to sedimentary sequences and the association of nickel deposits with orthomagmatic rocks are all examples of ore deposits associated with particular rock types. Conversely, the absence of certain metallogenic entities with certain rock types may be attributed to an incompatible relationship between these.

This fact permits us to make certain generalizations regarding rock types and ore associations.  It must be considered that since ores are rocks, they are likely to be intimate parts of the geological/geochemical environment in which they occur. This is supported by the evidence obtained from the examination of a wide variety of ores and their associated rocks. It is confirmed that most ore deposits indeed appear to be related fundamentally to specific rock types.

Magmas are an important source of many ingredients of mineral deposits.  Indeed different kinds of magmas yield different kinds of mineral deposits.  Secondary processes like weathering, erosion, solution, and precipitation either inorganic or biochemical, may act upon many of these mineral deposits and their parent/host rocks to form yet other sets of ore-rock assemblages.

ORE MINERAL ASSEMBLAGES AND ROCK ASSOCIATIONS

  1. Ore mineral assemblages occurring with mafic/ultramafic rocks
    1. Chromiun ores in intrusives Eg Paleozoic to Tertiary "Serpentine Belts" all over the world.
    2. Iron-nickel-copper sulfide deposits
    3. Native copper and associated sulfides as orthomagmatic disseminations and vesicular fillings Eg Solomon Islands.
    4. Nickel and associated sulfides in volcanic sills Eg Kambalda, W Australia, Manitoba. iii) Precious metals viz. tellurides Eg Fiji.
    5. Nickel also occurs as Ni-rich olivine which may be concentrated to ore by later weathering
  2. Ore mineral assemblages occurring with intermediate rocks
    1. Iron-titanium oxide deposits with anorthositic-gabbroic rocks
    2. Copper-molybdenum sulfides associated with porphyritic intrusives
  3. Ore mineral assemblages occurring with silicic rocks
    1. Cassiterite deposits as disseminations in granites, contact metamorphic deposits and pegmatitic deposits.
    2. Cu-Pb-Zn-Ag veins
    3. Quartz-Ag-Bi-Co-Ni-As-U veins
    4. Quartz-Sn-W-Bi veins
    5. Quartz-Au veins
    6. As-Sb-Hg bearing basemetal veins
    7. Skarn deposits (containing magnetite, molybdenite, sphalerite, galena, chalcopyrite, wolframite, scheelite)
    8. Stibnite and stibnite-scheelite-gold veins.
    9. Basemetal sulfide veins with arsenopyrite and greater proportions of Pb & Zn as compared to Cu.
  4. Ore mineral assemblages occurring with sedimentary rocks
    1. Iron ores in sedimentary rocks Banded Iron Formations developed as volcanic chemical sediments as a result of sea-floor exhalative activity. Deposition of these took place in troughs (eugeosynclines) in inter-island regions of arcs.
    2. Manganese ores in sedimentary rocks
    3. Minor chemical sedimentation of manganese and iron with jasper.
    4. Gold-uranium ores in conglomerates of Witwatersrand-Bhind River- Jacobina Type in coarse conglomerates and grits of braided stream channels.
    5. Lead zinc deposits in carbonate rocks and other sediments
    6. Stratiform basemetal sulfide ores in sedimentary rocks
    7. Limestone-lead-zinc deposits often associated with oil bearing strata and evaporites, Eg Pine Point, Canada.
    8. Non-volcanic sedimentary manganese deposits (orthoquartzite-glauconite-clay association), Eg Nikopol, USSR, and Morocco.
    9. Ironstones of the Clinton, Lorraine and English type associated with near-shore, estuarine or lagoonal sedimentation.
    10. "Sandstone Type" Cu-U-V ores formed in coarse sediments of outwash fans, near-shore braided streams and deltas, Eg Colorado.
    11. Basemetal sulfide deposits of non-volcanic association occurring with evaporites, Eg Kupferschiefer Marl Slate of Europe and England and the Copperbelt of Zambia. viii) A very minor category of iron ores -- the bog or marsh iron ores such as those of the present northern hemisphere.
  5. Ore mineral assemblages occurring in volcanic rocks
    1. Cu-Fe-Zn assemblages in volcanic rocks
    2. Stratiforn Sulfide Deposits of marine and marine-volcanic affiliation. These include chemical sedimentation and sulfide pyroclastic concentrations interbedded with some lavas. All these are essentially sea floor volcanic accumulations. A few of these are associated with basaltic and more mafic lavas Eg Cyprus and Japan, whereas a vast majority are associated with andesitic and dacitic rocks. Eg Base metals of Ontario, Mount Isa and McArthur River (Precambrian); Bathurst, New Brunswick and E. Australia (Paleozoic) and Japan (Tertiary).
    3. Mineral deposits associated with flood basalts, for example the copper bearing lavas of the Keweenaw  Peninsula, Lake Superior; copper bearing lavas of the Deccan traps around Bhawani Mandi, Rajasthan.

MAJOR ORE TYPES OF INDIA, THEIR ROCK ASSOCIATIONS AND TECTONIC SETTING 

 

ORE DEPOSIT AND ASSOCIATED ROCKS 

TECTONIC SETTING

LOCALITY

GEOLOGICAL AGE

1.

RELATED TO BASIC/ULTRABASIC IGNEOUS INTRUSIVES. 

1.1

Stratiform deposits in layered complexes

Cratons

Kondepalle

Sitampundi

Hassan

Early Proterozoic

Early Proterozoin

Archaean

2.

MASSIVE SULFIDE DEPOSITS IN VOLCANIC ASSOCIATION 

2.1

Cupreferous deposits associated with mafic volcanics

Rift-ridges/island arcs/craton-margin dislocations.

Kalyadi (S. India)

Ingaldahl

Singhbhum

Archaean

Archaean-E. Proterozoic

Early-Late Proterozoic

3.

ORES IN SEDIMENTS  

3.1

Sediment hosted sulfide deposits

Ensialic Rift Basins

Khetri

Mid-Late Proterozoic

3.2

Lead-zinc ores in clastic sediments

Ensialic Rift Basins/Epicontinental Basins

Agucha

Rajpura-Dariba

Archaean

Mid-Late Proterozoic

3.3

Lead-zinc ores in carbonate rocks (Bulk Mississippi Valley type)

Ensialic Rift Basins/Epicontinental Basins

Zawar

Early Proterozoic

3.4

3.4.1

Iron Ores

 Banded Iron Formations

Greenstone Belts/Epicontinental Basins

Bababudan-Sandur

Bihar Orissa

Archaean-E. Proterozoic

Late Archaean

3.5

Manganese Ores

Ensialic Basins/epicontinental seas/eugeosynclines

Bihar-Orissa

Madhya Pradesh-Maharashtra

Late Archaean

Mid- Late Proterozoic

4.

ORE DEPOSITS ASSOCIATED WITH ACID-INTERMEDIATE PLUTONIC/HYPABYSSAL ROCKS 

4.1

Porphyry-type copper deposits

Orogenic belts/subduction zones

Malanjkhand

Early-Middle Proterozoic

4.2 Tin-tungsten deposits Orogenic belts with ensialic magmatism Chhendapathar(?) Late Proterozoic

5.

VEIN DEPOSITS IN METAMORPHOSED ROCKS 

5.1

Gold-quartz veins

Greenstone belts and Phanerozoic orogens

Kolar

Hutti

Archaean

Archaean

5.2

Uranium veins in shear zones

Regional shear zones

Singhbhum

Middle-Late Proterozoic

6.

LATERITIC DEPOSITS 

6.1

Bauxite deposits

Continental platforms

Bihar-Madhya Pradesh

Phanerozoic

6.2

Lateritic Ni-deposits

Non-specific

Sukinda

Phanerozoic

 

Notes & Handouts

The Himalayas

Kumaon Himalayas

Askot Basemetals

University

   


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