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GLE 2024 (Day 3) > ORE DEP (ORE-BEARING FLUIDS) > Flashcards

ORE DEP (ORE-BEARING FLUIDS) Flashcards

1
Q

Factors affecting ore fluid movement

A

1 Precepts of Geohydrology
2 Permeability
3 Porosity
4. Density
5. Viscosity
6. Presence of Fractures
7. pressure Gradients
8. Time
9. Rules of Igneous Petrology

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2
Q

Important modes of movements for Ore formation from Magmatic fluids

A

1 Filter Pressing
2 Late Liquid Gravitative Accumulation
3. Magmatic Injection

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3
Q

A partly melted magma, when exposed to external stress, can be squeezed away the melt fraction from the crystalline mush like a toothpaste

A

Filter Pressing

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4
Q

Sinking of high density globules due to immiscibility and density variation within and from parent fluid after some differentiation

A

Late Liquid Gravitative Accumulation

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5
Q

Deposts which are products of 6

A

Podiform Chromites

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6
Q

Residual liquid is squeezed into the surroindung country rocks

A

Magmatic Injection

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7
Q

Deposit formed from Magmatic Injectin

A

Magmatic Injection deposits

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8
Q

Deposit example of 8

A

Manetite-Apatite Dike

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9
Q

What causes magma to move up

A

1Expansion of Gases and decrease in Sp.G
2Tectonic stresses squeezing the magma or fraction of magma into the overlying or adjacent rock
3 Movement through stoping

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10
Q

The process by which country rock is broken up and removed by the upward movement of magma

A

Stoping

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11
Q

Ratio of pore volume and total volume of rocks

A

Porosity

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12
Q

Measure of the interconnectedness of pores which gives a rock the capacity to transmit a fluid through it across a pressure gradient

A

Permeability

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13
Q

Permeability which is intrinsic to the rock

A

Primary

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14
Q

Permeability which is superimposed on the rocks

A

Secondary

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15
Q

This forms when contact metamorphism and ore emplacement occur sequentially in a limestone section around a coolint pluton

A

Skarn

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16
Q

What are the processes which may increase permeability in rocks

A

Exposure to Heat
Movement or pressure of fluids
Tectonic processes

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17
Q

These are very important in epigenetic deposit which are emplaced during a tectonic activity

A

Structural Cntrol

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18
Q

A type of structural control formed due to phreatomagmaytic phreatic and hydrothermal process

A

Breccia

19
Q

At shallow depths, which type of permeability is more significant to ore transport and deposition

A

Secondary

20
Q

Type of shallow deposit

A

Epithermal Au

21
Q

Why do permeability and porosity decrease with depth?

A

Because Lithostatic Pressure increases with depth

22
Q

Deep fluid flow depends on what type or permeability

A

Primary

23
Q

Until how much depth is secondary permeability significant

A

<3kms

24
Q

The spontaneous movement of molecular or ionic particels down concentration gradients that cause one substance to become uniformly intermingle with another

Major mechanism of mass transport in deep environment of restriceted mechanical fluid flow

A

Diffusion

25
Q

Sample deposit where diffusion plays part

A

Orogenic Au Deposits

26
Q

Factors which affetcs ore deposition
ORE DEPOSITION CONTROLS

A

1) Physical effects - Gravity settling, Settling due to agitation
2) Cooling of Temp
3) Pressure Changes
?Retrograde Boiling (due to depressuring)
?Throttling (Depressurization w/ heat loss or adiabatic decompression)
4) Chemical Changes
?Reaction of ore fluid w/ wall rocks
?Mixing of Different ore fluids

27
Q

Deposition of Magmatic Segregation Deposits

A

?Direct effects of igneous melt differentiation
?Magmatic Sedimentation - settling and accumulation of crystallizing mienrals in high-T mafic Magmas (Bushveld Cr-Pt, Magn-Ilme)
?Direct crystallization of magma chamber walls or floors (Stillwater PGE)
?Separation of mgamatic liquids and their solidifcations
?Consolidation of an igneous rock w/ an entrained accessory economic mineral
?Crstallization of melt

28
Q

Depostional textures of hydrothermal fluid deposits varies with

A

?Nature of fluids
?Physical and chemical character of the host rock
?Mode of emplacement

29
Q

What are the data which can be extracted from depositional texture of hydrothermal fluid deposits?

A

1) Temporal relationship of sucessive miernal assemblages in a rock
2) Overall environment of formation
3) Manner of deposition

30
Q

Types of Deposition of HFs

A

1) Exsolution
2) Replacement
3) In-Filling
(ManyOre deposits shows Evidences of both replacement and open-space filling)

31
Q

Compositional or Structual adjustments as the fluids cool down
Particularly formation of two separate solid phase from a high-temp solid solution

A

Exsolution or inversion

32
Q

Exsolution pairs imply that 2 minerals are in

A

Isomorphic Solid Solution at higher temp

33
Q

Differentiate Exsolution from replacement as seen in the samples

A

Exsolution shows depletion at the junction of intersecting lamellae while Replcement shows greater concentrations at intersections

34
Q

Exsolution Pairs

A

?Pyrrho-Pentl
?Chalcopy-Bornite
?Spha-Chalcopy
?Magnet-Ilmen

35
Q

Inversion Pairs

A

?Argentite-Acanthite (173 deg C)
?Enargite-Luzonite (275-300 degC)

36
Q

Exsolution Textures

A

?Lamellar
?Emulsoidal
?Myrmekitic

37
Q

The process of simultaneous capillary solution and deposition by which a new mineral of partly or wholly differing chemical compostion may grow in the body of an old minral aggregates (diffusion)

A

Replacement (Metasomatism)

38
Q

Rules of Replacement

A

1) Sulfides (Arsenides,Sulfosalts) + Tellurides - any Gangue, Rock and Ore Minerals

2) Gangue - Only Gangue and Rock Minerals, rarely Oxides

3) Oxides - Only Gangue and Rock rarely sulfide and tellurides

39
Q

Criterial for replcement textures

A

?Pseudomorph - replacement mineral or mineral aggregates retaining the EXTERNAL Form of the origg mineral or mineral aggregates

?Widening of a fracture filling to an irregular mass where a fracture crosses a chemically reactive mineral grain or rock

?Islands (Isolated) unreplace host minerals or wall rock
?Concave surfaces into the host (Cusp and Caries)

40
Q

Most common feature in Shallow zones (<3Kms below) where Brittle Rocks yield breaking rather than plastic flow

A

Open Space Filling

41
Q

Examples of Open Spaces which can be filled

A

1) Veins
2) Factures fills
3) Vugs or Open Cavities
4) Breccias

42
Q

The distribution in time or the sequene of mienrals or element depositon which can be determined using Ore Textures

A

Paragenesis

43
Q

any regular patten in the distribution of mienrals or elements in space

A

Zoning (Take note a bit dfferent to zoning in minerals)

GLE 2024 (Day 3) (48 decks)

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