lesson 12: sedimentary iron deposits

Question 1

at least how many percent of iron are SIDs?

Answer 1

> 15%

Question 2

range of iron for SIDs during the mostly distribution periods?

Answer 2

24-40%

Question 3

explain the obvious distinction between iron rocks and iron stones

Answer 3

iron stones are the more modern occurrences that are nodular in texture, iron stones are the ones formed during the precambrian that are laminated or banded

Question 4

describe iron rocks

Answer 4

—precambrian
— >15% iron
—laminated
—thin bedded
—commonly cherty (not necessarily tho)

Question 5

periods of distribution for SIDs

Answer 5

—precambrian
—phanerozoic
—paleozoic
—jurassic
—cretaceous

Question 6

describe iron stones

Answer 6

— >15% Fe
—non laminated
—non cherty
—lower silica
—typically oolitic

Question 7

peak distribution of iron rocks

Answer 7

precambrian to devonian
—mid archean
—early proterozoic
—late proterozoic

Question 8

describe the spatial distribution or iron rocks

Answer 8

—mostly continental (old rocks)
—cratons formerly covered by the sea (cherty and sed) but then got uplifted after some time

Question 9

describe the mineralogy of SIDs

Answer 9

the rocks are commonly grouped based on their mineralogy
—oxides (hematitic, magnetitic)
—silicates (minnesotaite)
—carbonates (siderite)
—sulfates (pyrite)

Question 10

describe the structures of SIDs

Answer 10

—microbands (mm)
—mesobands (cm)
—chert matrix
—granule iron formation

Question 11

separation of iron bands by cherty material (sandwiched between them)

Answer 11

chert matrix

Question 12

non banded iron formation structures

Answer 12

granule iron formation

Question 13

structures that only apply to iron rocks

Answer 13

—microbands
—mesobands
—chert matrix

Question 14

what are the three associated facies for iron rocks

Answer 14

—Algoma type
—Superior type
—Raritan type

Question 15

facies that are thinly bedded, near volcanoes, volcanic related (pyroclastics), near MORs, explosive occurrences, lack oolitic, granular

Answer 15

Algoma type

Question 16

facies with no volcanic associations

Answer 16

Superior type

Question 17

superior type facies occur with?

Answer 17

quartzite, black carbonaceous shales, conglomerate, dolomite, cherts, breccia, argillites

Question 18

facies related to glacial deposits

Answer 18

raritan type

Question 19

iron stone facies

Answer 19

—sandy and shelly
—ferric oxide

Question 20

facies that are shallow marine sediments with abundant pellets of glauconite (green if not oxidized)

Answer 20

sandy and shelly iron stone facie

Question 21

facie that include chamosite (iron chlorite), oolite, and can include hematite and geothite

Answer 21

ferric oxide

Question 22

minerals that are associated with something being weathered

Answer 22

ferric oxides (esp geothite)
usually if fresh thered be magnetite, biotite, pyrite. but then if weathered, magnetite and biotite actually turns into geothite

Question 23

structures commonly found in iron stones (8)

Answer 23

—commonly interbedded with carbonates
—cross beds
—scour and fill
—rip-up clasts
—burrows
—shallow marine
—deltaic
—pelagic sediments

Question 24

nonferrous associations of iron stones

Answer 24

detrital quartz, calcite, dolomite, authigenic phospherite, authigenic chert

Question 25

aside from iron rocks and stones, what else?

Answer 25

—iron-rich shales —bog iron ores —iron rich laterites —manganese crusts and nodules —metalliferous sediments —heavy mineral placers

Question 26

the period associations of pyritic black shales

Answer 26

precambrian, phanerozoic

Question 27

SIDs that occurs as nodules, laminations and fossil replacements

Answer 27

pyritic black shales

Question 28

2 types of iron rich shales

Answer 28

—pyritic black shales —siderite black shale

Question 29

were transported as sediments or ions to small freshwater lakes of high altitude. usually hard, oolitic, pisolitic, concretionary forms to early soft types

Answer 29

bog-iron ores

Question 30

whats limonite

Answer 30

fine grained iron deposit dominated by geothite

Question 31

metallic encrustations that are widely distributed in oceans

Answer 31

manganese crusts and nodules

Question 32

what are manganese nodules associated with

Answer 32

red shales, cherts, pelagic limestones (and they also maybe rich in Cu, Co, Ni, Cr, V

Question 33

SIDs that occur in spreading ridges, black smokers, and are believed to be precipitated of dissolved metals in fluids and also be formed from weathered ocean rocks (pillow basalts)

Answer 33

metalliferous sediments

Question 34

SIDs common in beach and alluvial deposit

Answer 34

heavy mineral placers

Question 35

example of areas where heavy mineral placers could be found

Answer 35

beach, alluvial deposits, lakes, deltas, beds, rivers

Question 36

problems to account for when modeling deposition models

Answer 36

—sources of iron —transport of iron to the depositional basin —episodic precipitation of the iron within the basin

Question 37

3 sources of iron

Answer 37

—terrestrial (transported ions near rivers, physical) —mid-oceanic volcanism (magma chamber or mantle to the surface like iron in basalt —weathering of Fe-rich rocks (mantle sourced rocks) ((water can transport the ions themselves))

Question 38

explain iron transport in the ocean

Answer 38

ferrous (+2) iron that come from hydrothermal systems and dissolved from ocean-floor rocks was concentrated in anoxic layers to oxic layers above. that becomes easier to transport til to more distant places na madeposit sila again in anoxic areas that make them bedded. the movement of dissolved iron from deep water to shallower depths (continental shelves) due to upwelling or could be because of lateral spread as plume from mid oceanic ridges (same concept as black smokers, basta far)

Question 39

explain depositional basins and depositional processes

Answer 39

—interaction of upper anoxic bottom layer and aerobic upper layer results to the oxidation of Fe2+ to Fe3+ —microbial metabolism (microorganisms ingested whatever they could and ended up pooping out the same thing)

Question 40

explain chert layers and banding for SIDs

Answer 40

during the precambrian, silica content was higher could be due to silica secreting organisms (and could have been acidic so iron could survive)