sedimentary iron deposits

Question 1

how many percent iron should a rock have to be considered a sedimentary iron deposit?

Answer 1

> 15% Fe

Question 2

sedimentary iron deposit was mostly distributed during _________% Fe

Answer 2

24-40%

Question 3

differentiate iron rocks and iron stones

Answer 3

iron rocks: laminated, thin bedded, cherty

iron stones: non-laminated, non-cherty, lower silica, oolitic

Question 4

iron stones peak distribution:

Answer 4

1. paleozoic
2. mesozoic - cretaceous and jurrasic

Question 5

iron rocks peak distribution

Answer 5

Precambrian (primarily) to Devonian

-mid archean
- early proterozoic
- late proterozoic

Question 6

three principal classes of iron-rich sed rx

Answer 6

1. Detrital chemical iron-rich sediments
   - cherty iron formation
   - minette-type ironstone (aluminous iron formation)
2. Iron-rich shales
   -pyritic black shales
   -siderite black shales
3. Miscellaneous iron-rich deposits
   - bog-iron ores
   - nickel laterite
   - manganese nodules and oceanic iron crust
   - metalliferous sediments
   - placer deposits

Question 7

aluminous iron formation

Answer 7

minette-type ironstone

Question 8

minerals associated with iron-rich sed rx:

Answer 8

oxides
silicates
carbonates
sulfides

Question 9

separation of iron bands by chert material

Answer 9

chert matrix

Question 10

non-banded iron formation

Answer 10

granule iron-formation

Question 11

structural characteristics of iron rocks/formations

Answer 11

microbands
mesobands
chert matrix
granule iron-formation

Question 12

associated facies of iron formation and describe each

Answer 12

1. Algoma Type
2. Superior Type
3. Raritan Type

Question 13

depositional environments of ironstones

Answer 13

shallow marine
deltaic
pelagic

Question 14

shallow marine sediments with abundant pellets of glauconite

Answer 14

sandy and shelly

Question 15

iron chlorite (chamosite), oolitic, can include hematite and goethite

Answer 15

ferric oxide

Question 16

non ferrous association in iron stones

Answer 16

detrital qtz, authigenic phosphorite, authigenic chert, calcite, dolomite

Question 17

pyritic black shale is associated with what formations?

Answer 17

precambrian and phanerozoic

Question 18

pyrictic black shales occur as?

Answer 18

nodules, laminations, fossil replacements

Question 19

small freshwater lakes with high altitude

Answer 19

bogs

Question 20

hard, oolitic, pisolitic, and concretionary forms to soft earthy type

Answer 20

Bog-Iron Ores

Question 21

are surficial, weathered rinds formed on ultramafic rocks

Answer 21

nickel laterite

Question 22

nickel laterite account for how many percent of global nickel supply?

Answer 22

60%

Question 23

differentiate limonite and saprolite

Answer 23

limonite - low magnesium, high iron, includes hematite and goethite

saprolite - high magnesium, low iron

Question 24

metallic encrustations widely distributed in oceans

Answer 24

manganese crusts and nodules

Question 25

manganese crust and nodules are associated with:

Answer 25

red shales, cherts, pelagic limestones

Question 26

metals enriched in manganese nodules and crust

Answer 26

Cu, Co, Ni, Cr, V

Question 27

occurs particularly near spreading ridges, black smokers

Answer 27

metalliferous sediments

Question 28

believed to be precipitates of dissolved metals in fluids

Answer 28

metalliferous sediments

Question 29

mechanical concentrations of heavy metallic sediments

Answer 29

iron-rich placer deposits

Question 30

explain difference between ferrous and ferric

Answer 30

ferrous Fe2+ : soluble, transported as ions, reducing conditions

ferric Fe3+ : insoluble, transported as solids, oxidizing conditions

Question 31

examples of iron minerals precipitated in reducing conditions

Answer 31

siderite (FeCO3), magnetite (Fe3O4), pyrite (FeS2)

Question 32

examples of iron minerals precipitated under oxidizing conditions:

Answer 32

hematite (Fe2CO3), goethite (FeO2H)

Question 33

primary minerals for iron ore

Answer 33

Goethite, hematite and magnetite

Question 34

problems to account for modelling of iron-rich deposits

Answer 34

1. sources of iron
2. transport or iron to depositional basins
3. episodic precipitation within the basin

Question 35

explain how Fe3+ can be transported and precipitated if it is insoluble?

Answer 35

During precambrian, there is low level of oxidation therefore, Fe3+ are reduced to Fe2+ and are transported as ions from streams into marine basins. In the basins, oxidizing conditions prevail in upper aerobic environment, thereby, oxidizing Fe2+ to Fe3+, then precipitates.

Question 36

sources of iron:

Answer 36

1. terrestrial
2. mid-oceanic ridges
3. weathering of Fe-rich rocks (mantle sourced rocks)

Question 37

explain how iron deposits are transported into the ocean

Answer 37

Iron are deposited in marine basins with stratified water column composed of an anoxic bottom layer and an aerobic upper layer. Ferrous deposits derived from hydrothermal systems and melting of ocean floor-rocks was concentrated in lower anoxic layer, and was subsequently uplifted through upwelling or spread as a plume from MOR

Question 38

explain the depositional processes of iron deposits

Answer 38

it comes from interaction of aerobic upper layer and anoxic bottom layer as well as microbial metabolism

Question 39

explain the reason for the abundance of chert in banded iron-formations

Answer 39

silica content of the ocean during precambrian is higher than the modern ocean

silica secreting organisms