Lec 4 - Controls On Ore Deposition

Question 1

4 controls on Ore Deposition

Answer 1

1. Chemical
2. Lithological
3. Stratgraphic
4. Structural

Question 2

Factors under chemical

Answer 2

• temperature change
• pressure change
• reaction between solution and wall rocks
• chemical changes due to solution mixing

Question 3

• It affects mineral solubilities,
• influences ion-pairing hydrolysis constants of ions such as Cl and HS
• affects oxyfen fugacit

Answer 3

Temperature change (cooling)

Question 4

Loss of volatiles disabling metal transport

Answer 4

Boiling

Question 5

Change in pressure regime from lithostatic to hydrostatic across an obstruction

Answer 5

Throttling

Question 6

Loss of volatiles without change in temperature but only in pressure

Answer 6

Retrograde Boiling

Question 7

• Addition of anions or cause of disolution

- disolution can cause precipitation by causing dissociation of some metal complexes and recombination

Answer 7

Solution mixing

Question 8

T and P drop will result in precipitation from aqueous solution

Answer 8

Solubility

Question 9

Separation of one mineral from another in a natural solution (unmixing)

Answer 9

Exsolution

Question 10

Certain microbes are agents of mineral precipitation

Answer 10

Bacterial precipitation

Question 11

Simultaneous capillary solution and deposition by which new minerals are substituted for earlier mineral or rocks

Answer 11

Replacement

Question 12

Loss and gaiin of electrons to specific ions

Answer 12

Oxidation and reduction

Question 13

In openspace without outright replacement

Answer 13

Direct Deposition

Question 14

Precipitation from solution without themselves entering into solution

Answer 14

Catalytic action

Question 15

Taking up of one substance at the surface of another

Answer 15

Adsorption

Question 16

Occurs between solids and liquids whereby cations are exchanged, producing changed characteristics of both

Answer 16

Base exchange

Question 17

Rate of pore volume to the total volume of rock

Answer 17

Porosity

Question 18

Necessary for passage of solutions through host rock to depositional sites
-main factor of localization in absence of fracture

Answer 18

Premeability

Question 19

Brittle rocks crackle readily

Answer 19

High permeability

Question 20

Ductile rocks do not crackle

Answer 20

Less permeable

Question 21

Thick accumulation of sediments in orogenic environments

Answer 21

Geosynclines

Question 22

Regional loci of ore deposition, deposition cluster within or about stocks or batholiths

Answer 22

Igneous Intrusions

Question 23

Weathered zones beneath unconformities are more porous, control location of syngenetic sedimentary deposits

Answer 23

Unconformities

Question 24

Permeable pathways, replacement or metasomatic deposits extend or deposit along these_____

Answer 24

Bedding

*cross bedding are more favorable

Question 25

Serves as barriers for mineralizing solutions; concentrate mineral deposition in strata below or above

Answer 25

Impervious Layer

Question 26

Supergene Sulfides deposits at

Answer 26

Above Impervious layers

Question 27

* The most important loci of ore * Provides zone of porosity and permeability * provides channelways for hydrothermal fluid to pass

Answer 27

Structural

Question 28

Broader localization of ore belts/mineral districts

Answer 28

Regiona

Question 29

Immediate localization of ore

Answer 29

Detailed

Question 30

Cupolas, deposits can be located if fluid is lighter than magma

Answer 30

Structural Highs

Question 31

Cut of a stock dome

Answer 31

Cupolas

Question 32

Lopoliths, sulfide melt is heavier than silicate melt so located at bottomof intrusives

Answer 32

Structural Lows

Question 33

Fold axes with increased fracturing provided channel ways for pre-ore deposition

Answer 33

Folds

Question 34

- Control deposition of ore deposits | - Can result from regional stresses

Answer 34

Fractures / Lineament

Question 35

When your ore deposits in a structural intersection

Answer 35

Ore shoot

Question 36

- favorable for deposition - increased permeability - loci for interaction of different fluids

Answer 36

Structural intersection

Question 37

Faults that occur before deposition if ore minerals, Controlling structure

Answer 37

Syngenetic Faults

Question 38

The deposition of ore minerals happened first before faulting, it cut and displaces ore bodies

Answer 38

Epigenetic Faults

Question 39

High veolocity explosion vent

Answer 39

Diatremes