lesson 12: sedimentary iron deposits Flashcards
at least how many percent of iron are SIDs?
> 15%
range of iron for SIDs during the mostly distribution periods?
24-40%
explain the obvious distinction between iron rocks and iron stones
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
describe iron rocks
—precambrian
— >15% iron
—laminated
—thin bedded
—commonly cherty (not necessarily tho)
periods of distribution for SIDs
—precambrian
—phanerozoic
—paleozoic
—jurassic
—cretaceous
describe iron stones
— >15% Fe
—non laminated
—non cherty
—lower silica
—typically oolitic
peak distribution of iron rocks
precambrian to devonian
—mid archean
—early proterozoic
—late proterozoic
describe the spatial distribution or iron rocks
—mostly continental (old rocks)
—cratons formerly covered by the sea (cherty and sed) but then got uplifted after some time
describe the mineralogy of SIDs
the rocks are commonly grouped based on their mineralogy
—oxides (hematitic, magnetitic)
—silicates (minnesotaite)
—carbonates (siderite)
—sulfates (pyrite)
describe the structures of SIDs
—microbands (mm)
—mesobands (cm)
—chert matrix
—granule iron formation
separation of iron bands by cherty material (sandwiched between them)
chert matrix
non banded iron formation structures
granule iron formation
structures that only apply to iron rocks
—microbands
—mesobands
—chert matrix
what are the three associated facies for iron rocks
—Algoma type
—Superior type
—Raritan type
facies that are thinly bedded, near volcanoes, volcanic related (pyroclastics), near MORs, explosive occurrences, lack oolitic, granular
Algoma type
facies with no volcanic associations
Superior type
superior type facies occur with?
quartzite, black carbonaceous shales, conglomerate, dolomite, cherts, breccia, argillites
facies related to glacial deposits
raritan type
iron stone facies
—sandy and shelly
—ferric oxide
facies that are shallow marine sediments with abundant pellets of glauconite (green if not oxidized)
sandy and shelly iron stone facie
facie that include chamosite (iron chlorite), oolite, and can include hematite and geothite
ferric oxide
minerals that are associated with something being weathered
ferric oxides (esp geothite)
usually if fresh thered be magnetite, biotite, pyrite. but then if weathered, magnetite and biotite actually turns into geothite
structures commonly found in iron stones (8)
—commonly interbedded with carbonates
—cross beds
—scour and fill
—rip-up clasts
—burrows
—shallow marine
—deltaic
—pelagic sediments
nonferrous associations of iron stones
detrital quartz, calcite, dolomite, authigenic phospherite, authigenic chert
aside from iron rocks and stones, what else?
—iron-rich shales
—bog iron ores
—iron rich laterites
—manganese crusts and nodules
—metalliferous sediments
—heavy mineral placers
the period associations of pyritic black shales
precambrian, phanerozoic
SIDs that occurs as nodules, laminations and fossil replacements
pyritic black shales
2 types of iron rich shales
—pyritic black shales
—siderite black shale
were transported as sediments or ions to small freshwater lakes of high altitude. usually hard, oolitic, pisolitic, concretionary forms to early soft types
bog-iron ores
whats limonite
fine grained iron deposit dominated by geothite
metallic encrustations that are widely distributed in oceans
manganese crusts and nodules
what are manganese nodules associated with
red shales, cherts, pelagic limestones
(and they also maybe rich in Cu, Co, Ni, Cr, V
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)
metalliferous sediments
SIDs common in beach and alluvial deposit
heavy mineral placers
example of areas where heavy mineral placers could be found
beach, alluvial deposits, lakes, deltas, beds, rivers
problems to account for when modeling deposition models
—sources of iron
—transport of iron to the depositional basin
—episodic precipitation of the iron within the basin
3 sources of iron
—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))
explain iron transport in the ocean
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)
explain depositional basins and depositional processes
—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)
explain chert layers and banding for SIDs
during the precambrian, silica content was higher could be due to silica secreting organisms (and could have been acidic so iron could survive)
