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Classification of Ore Deposits Questions and Answers

1.

Match the metal associations in Column 1 to corresponding hosts in Column 2.

Column 1Column 2
P. Cu, Co, Zni. Tectonized dunite and harzburgite
Q. Mn, Co, Niii. MORB
R. Criii. I-Type granite in volcanic arc
S. Cu, Mo, Pbiv. Pelagic sediment

Exam Year(s)

IIT JAM - 2026,

Answer: A

The correct matching is P-ii; Q-iv; R-i; S-iii.

  • Cu, Co, Zn: Cyprus-type volcanogenic massive sulphides formed at spreading ridges in MORB (ii).
  • Mn, Co, Ni: ferromanganese nodules and crusts that grow slowly on the deep sea floor among pelagic sediment (iv).
  • Cr: podiform chromite in the tectonized dunite and harzburgite of ophiolite mantle sections (i).
  • Cu, Mo, Pb: porphyry copper-molybdenum deposits, with base-metal veins around them, related to I-type granitoids in volcanic arcs (iii).

Option B swaps the ridge and pelagic settings, and options C and D put chromium outside its ultramafic host.

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2.

Kuroko type Zn-Pb-Cu deposits are the examples of :

Exam Year(s)

MH SET - 2018, SET Exam - 2018,

Answer: A

Kuroko deposits are volcanic hosted massive sulphide deposits.

The Kuroko ('black ore') deposits of Miocene age in Japan are the type example of volcanogenic massive sulphide (VMS) deposits rich in zinc, lead and copper. They formed on or just below the sea floor from hydrothermal fluids associated with felsic submarine volcanism, and so are found within volcanic sequences.

Skarns form where intrusions meet carbonate rocks, magmatic concentration deposits (such as chromite or nickel sulphide) segregate within mafic and ultramafic magma, and pegmatite deposits crystallise from residual granitic melts. None of these describes the Kuroko type.

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3.

Skarn deposits are developed at the contact of :

Exam Year(s)

MH SET - 2018, SET Exam - 2018,

Answer: D

Skarns develop at the contact of felsic plutonic intrusives and carbonate rocks.

A skarn forms when hot, fluid-rich granitic or granodioritic magma intrudes limestone or dolomite. Silica, iron and aluminium carried by the fluids react with the carbonate to form calc-silicate minerals such as garnet, pyroxene and wollastonite, often with ores of tungsten, copper, iron, zinc or molybdenum.

Slates, sandstones and quartzites lack the reactive carbonate needed, so contacts with them produce hornfels or quartzite, not skarn, and gabbro is a mafic rather than a felsic intrusive.

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4.

Match the following :

List IList II
(a) Stock works(1) Mineralisation along the creasts of anticline
(b) Saddle reefs(2) Transverse and roughly parallel fraction filled with the ore
(c) Ladder veins(3) An interlacing network of small ore-bearing veinlets
(d) Gash veins(4) Small wedge-shaped fissures filled with the ore

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: C

The correct match is a-3, b-1, c-2, d-4.

  • A stockwork is an interlacing network of small ore-bearing veinlets cutting the host rock (a-3).
  • Saddle reefs are ore bodies formed along the crests of anticlines, where folding opens gaps between beds, as in the gold fields of Bendigo (b-1).
  • Ladder veins are short, roughly parallel transverse fractures filled with ore, arranged like the rungs of a ladder, typically across a dyke (c-2).
  • Gash veins are small wedge-shaped fissures filled with ore, often in limestone (d-4).

The other codes misplace the stockwork, the saddle reef or both.

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5.

Porphyry copper deposits are associated with :

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: B

Porphyry copper deposits are associated with subduction zones.

They form above subducting plates, where hydrous calc-alkaline magmas of intermediate to felsic composition rise into the crust of a continental or island arc. Hydrothermal fluids released from these porphyritic intrusions deposit copper (with molybdenum and gold) in disseminated grains and stockworks. The Andes of Chile and Peru, the classic porphyry copper belt, lie above the subducting Nazca plate.

Mid-ocean ridges and back-arc basins are typical settings for volcanogenic massive sulphides, and continental rifts host deposits such as sediment-hosted copper, not porphyry systems.

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6.

Diamond in kimberlite and corundum in nepheline syenite are the good examples of :

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: B

Diamond in kimberlite and corundum in nepheline syenite are examples of dissemination deposits.

In the classification of magmatic ore deposits, early magmatic deposits are divided into dissemination, segregation and injection types. In dissemination deposits the valuable mineral crystallised early and lies scattered through the rock in place, without being concentrated, which is exactly how diamonds occur in kimberlite and corundum in nepheline syenite.

Segregation deposits are early crystals concentrated by settling, such as layered chromite. Injection deposits are concentrations squeezed into other rocks, and pegmatitic deposits form from residual fluid-rich melts.

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7.

PGE are mostly associated with :

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: B

Platinum group elements are mostly associated with ultramafic rocks.

The PGE (platinum, palladium, rhodium, ruthenium, iridium, osmium) are siderophile and chalcophile, so they partition into early sulphide liquids and chromite that separate from very magnesian magmas. The great deposits lie in ultramafic and mafic-ultramafic layered intrusions, such as the Merensky Reef and UG2 chromitite of the Bushveld complex and the Stillwater complex, and in ultramafic-hosted nickel sulphide ores such as Norilsk.

Felsic and intermediate rocks contain only traces of PGE, and while mafic rocks host some PGE ores, the strongest association is with the ultramafic members.

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8.

Cyprus type Cu-Zn deposits are found in :

Exam Year(s)

MH SET - 2020, MH SET - 2025, SET Exam - 2020, SET Exam - 2025,

Answer: C

Cyprus-type Cu-Zn deposits are found at mid oceanic ridges.

These are volcanogenic massive sulphide deposits named after those in the Troodos ophiolite of Cyprus. They form on the sea floor at spreading ridges, where sea water circulates through hot basaltic oceanic crust, leaches metals and vents them as black smokers that deposit copper-zinc sulphides. They are now found in ophiolites, slices of oceanic crust thrust onto land.

Island arcs host Kuroko-type deposits, richer in lead and zinc; passive margins host sediment-hosted lead-zinc deposits; and continental rifts host deposits such as red-bed copper.

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9.

Match the following :

List IList II
(1) Dissemination(i) Chromite deposit of Keonjhar (Odisha)
(2) Segregation(ii) Titaniferous magnetite deposit of Adivondaek region of New York
(3) Residual liquid segregation(iii) Diamond deposit of Panna
(4) Residual liquid injection(iv) Titaniferous magnetite bands of Bushveld Complex

Exam Year(s)

MH SET - 2020, MH SET - 2024, SET Exam - 2020, SET Exam - 2024,

Answer: A

The correct match is 1-iii, 2-i, 3-iv, 4-ii.

This follows Bateman's classification of early and late magmatic deposits:

  • Dissemination: diamonds scattered through kimberlite, as at Panna (iii).
  • Segregation: early crystallised chromite settling into layers, as in the chromite of Keonjhar, Odisha (i).
  • Residual liquid segregation: iron-titanium-rich residual magma forming titaniferous magnetite bands in the Bushveld Complex (iv).
  • Residual liquid injection: such residual liquid injected into the surrounding rock, as in the titaniferous magnetite of the Adirondack region, New York (ii).

The other codes swap the two titaniferous magnetite examples or move the diamonds.

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10.

Placers formed upon hill slopes or along the foot hills from minerals released from a nearby source rock are called :

Exam Year(s)

MH SET - 2023, SET Exam - 2023,

Answer: B

These are Eluvial placers.

Eluvial placers form close to the source rock: weathering releases heavy, resistant minerals such as gold, cassiterite or ilmenite, and lighter material is removed by rain-wash and creep, concentrating the heavy grains on the slopes or at the foot of the hill below the outcrop.

Alluvial placers are concentrated by running water in stream channels farther away, beach placers by waves on the shore, and aeolian placers by wind removing lighter grains in deserts.

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