Controls on Ore Deposition

Question 1

Controls on Ore Deposition

Answer 1

Chemical

Lithologic

Stratigraphic

Structural

Question 2

Chemical Controls

Answer 2

temp change

pressure change

reaction between solution and wallrocks

chem changes due to solution mixing

Question 3

Temperature Change (Cooling)

will

Answer 3

affect mineral solubilities

affect stabilities of aqueous metal bearing complex ions

influence io-pairing hydrolysis constants of ions

affect oxygen fugacity

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 H+ and H2O, increase Na+ and Ca+2

Answer 6

hydrolysis and hydration

Question 7

loss of volatiles disabling metal transport without change in temperature

Answer 7

Retrograde

Question 8

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

Answer 8

Dilution

Question 9

T & P drop will result in precipitation from aqueous solution

Answer 9

Solubility

Question 10

separation of one mineral from another in a natural solution

Answer 10

Exsolution

Question 11

certain microbes are agents of mineral precipitation

Answer 11

Bacterial Precipitation

Question 12

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

Answer 12

Replacement

Question 13

loss and gain of electrons to specific ions

Answer 13

Oxidation and Reduction (redox)

Question 14

certain substances cause precipitation from solution without themselves entering into solution

Answer 14

Catalytic Action

Question 15

taking up of one substance at the surface of another

kaolin absorbing copper to form chrysocolla

Answer 15

Adsorption

Question 16

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

Answer 16

Base Exhchange

Question 17

ratio of pore volume to the total volume of rock

Answer 17

Porosity

Question 18

necessary for passage of solution through host rock to depositional sites

Answer 18

Permeability

Question 19

High Permeable Rocks

Answer 19

Rhyolite/Quartzite/Limestone/Silicified Rocks

Question 20

Less Permeable Rocks

Answer 20

Shale/Schist/Basaltic Rocks/ Chloritized Rocks

Question 21

some constituents in rocks are more reactive

Answer 21

Composition

Question 22

thick accumulation of sediments in orogenic environments

Answer 22

Geosynclines

Question 23

regional loci of ore deposition

-deposits cluster within or about stocks or batholiths

Answer 23

Igneous Intrusions

Question 24

it is related to uplift, folding, faulting, and intrusion

Answer 24

geosynclines

Question 25

control location of syngenetic sedimentary deposits

Answer 25

Unconformitites

Question 26

are permeable pathways replacement or metasomatic deposits extend or deposit along it

Answer 26

Bedding

Question 27

serve as barriers for mineralizing solutions: Concentrate deposition in strata below or above

Answer 27

Impervious Layers (Covers and bases)

Question 28

most important loci of ore

Answer 28

Structural Control

Question 29

broader localization of ore belts/mineral districts

Answer 29

Regional

Question 30

immediate localization of ore

Answer 30

Detailed

Question 31

provide zones of porosity and permeability

Answer 31

structural control

Question 32

deposits can be located if fluid is lighter than magma

Answer 32

Structural highs - cupolas (cut of a stock dome)

Question 33

sulfide melt is heavier than silicate melt so located at bottom of intrusive

Answer 33

Structural Lows -lopoliths

Question 34

axes with increased fracturing provide channelways for pre-ore depostion

Answer 34

Folds

Question 35

control deposition of ore deposits can result from regional stresses

Answer 35

Fractures/Lineaments

Question 36

favorable for deposition increased permeability loci for interaction of different fluids

Answer 36

Structural Intersections

Question 37

controlling structure

Answer 37

Syngenetic

Question 38

a high velocity volcanic explosion vent

Answer 38

diatreme

Question 39

physical and chemical properties of host rocks exact properties are seldom evident operate along with structural features

Answer 39

lithologic control

Question 40

cut and displace ore bodies change attitude, width, and grades of ores

Answer 40

Epigenetic