Conversations with the Earth

Monday, September 4, 2017

Regional Aspects of Economic Geology (North America-South America-Africa-Australia)

NORTH AMERICA

Major geological unit:
a. North American (Canadian) Shield (Precambrian)
b. Appalachian orogeny (paleozoic)
  - Mineralization in Paleozoic orogens (Pb/Zn)
c. North american cordillera (Mesozoic-cenozoic)
d. North American platform
a. North American (Canadian) Shield (Precambrian)
- Consolidation of Archean nuclei (2,7-2,5 Ga)
- Late Archean to early Proterozoic basic and ultrabasic (2,6 Ga)
- Hudsonian/ Penokean orogeny (1,9-1,75 Ga)
- Paleoproterozoic sediments (e.g. Huronian supergroup)
- Sudbury impact (1,85 Ga)
- Anorogenic orogeny (1,6-1,2 Ga)
- Greenvillian orogeny (1 Ga) 

A. Consolidation of Archean Nuclei Deposit:
- stratiform massive Zn-Cu sulphides (VMS)
--> ore types: massive, laminated, breccia, stringer-type
ex. Abitibi belt : Kidd Creek deposit (hydrothermal black smoker) Kidd Creek is source of indium
- Orogenic gold ex. Ontario (Porcupine district, Hemlo)
- Archean BIF (syn-genetic)
ex. Homestake type (commonly located along the contacts of ultrabasic-basic volcanic rock to sediments)
ex. Algoma type (keypoints: associated with submarine volcanic rock, siderite-hematite BIF, less-extensive than superior type)
- BIF-superior type --> up to 200 m (chemical carbonate sediments)
=iron ranges related with Dulluth gabbro (Cuyuna, stromatolitic), Biwabik Iron Formation
=textures in Superior BIF
==Cherty (oxide facies, shallow water, thick bedded, granular, massive)
==Slaty (carbonate-silicate facies, deep water, thin bedded, non-granular, laminated)
- Ni,Cu (sulphides) --> in komatiite rocks within greenstone belts
- Rare-element pegmatites Sudbury district: Ni up to 50% world production

B. Mineralization in paleoproterozoic (1,9 Hudson orogeny- Churchill province-Transhudson orogen) -massive polymetallic
-uranium/Ag in Great Bear Lake

 C. Sudbury complex (1.85 Ga)
- meteorite impact, almost near to the mantle, resulted in the lake of magma
= stratigraphy from top to the bottom:
a. Post-impact sedimentary rock (top)
b. Suevite (Onaping sediment)
c. Impact-melt layer (granophyre - quartz gabbro - norite)
d. Brecciated crater floor (bottom)
== differentiation of layered complex
== formation of Ni-Cu-PGE mineralization in sublayer and offset dikes

D. Mineralization in Middle Proterozoic clastic sedimentary basin: U, Cu, Ni
= native Cu
= sedimentary U
= thick clastic sediments, basalts and native Cu (Ni-Cu-Co Thompson,Voisey's, Duluth Complex)

E. Anorogenic magmatic province (1.5 - 1.4 Ga)
=Titanium deposits (rutile, ilmenite) in anorthosites

Appalachian-Ouchita orogen, Innuit-Ellesmere Orogen (Arctic), Antler orogen (Rocky mountains)
=Pb/Zn, baryte (VMS, SEDEX)
ex. Brunsswick no.12
=Iron ores
=Asbestos (ophiolites from ultramafic rocks around Quebec, biggest in the world)
=Rare element (Li) pegmatites


b. Mineralization in the forelands of Paleozoic orogens: 

Pb-Zn (MVT)
=forebulge, basinal brines
=major exploration target: forebulge unconformities, syncollisional faults and strike slip zones
==metal-bearing fluids migrate towards the marginal zones of the orogenic foreland due to hydrostatic and thermal gradients, compaction of fine-grained basin sediments and squeezing-out of basinal brines (by tectonic pressure)
==uptake of hydrocarbons and metal precipitation along permeability, boundaries, mainly in carbonates
==ore minerals: galena, sphalerite (Ag-poor),fluorite,barite,pyrite,marcasite,chalcopyrite,siegenite, bravoite. Carbonate occur as a "pod" for sulphide
==hydrocarbons and coal
==uranium (roll-front and colorado type)

c. Mineralization in the North American Cordillera

- part of the global circum-Pacific belt (Cu,Mo,Au,Ag)
==Deposits in the Lower Precambrian (>2500 Ma) 
ex. Stillwater complex (Montana),
==Deposits in the Middle and Upper Proterozoic (1500-600 Ma)
ex. SEDEX
-PGE, chromite, layered ultramafic-mafic intrusion (44 km strike length), 2.7 Ga
==Deposits in the Paleozoic (Cambrian to Carboniferous)
ex. Red Dog (Alaska)
==Deposits in the Mesozoic
ex. Stratiform VMS in volcanic rocks, porphyry copper deposits, Juneau
ex. Orogenic: Juneau, Klondike
==Upper Paleogene to recent
ex. Bingham (Utah), Climax (Colorado), epithermal vein-type Au-Ag ores

Deposit
==Disseminated Cu/Mo-porphyry (by products: Au,Ag,Pb,Zn,Mn,Fe,Mo)
==Epithermal Au-Ag
==Carlin deposit (polycyclic)
==Massive and banded VHMS (Cu-Pb-Zn) (ex: Red Dog, Selwyn)

AFRICA

3,5-3,0 Ga : greenstone belts : Nickel sulphide
  • Granite (Sn) 
  • Sediments 
  • Nickel in komatiite (most important) in Australia 
  • Zn-Cu in VMS (Barbara Mt, south Africa) + Sb+Au 
  • Banded-iron-formation
----------- break (granite intrusion) do not have much economic importances (Sn, Ta, Li) 
ex. Wodgina in Australia
3,0-2,5 Ga : greenstone belts
  • Witwatersrand gold (paleoplacer) Au
-----------Limpopo events associated with great dyke
  • LIC (chromium) PGE, REE, Sn-Ta
2,5-2,0 Ga : shelf sediments
  • Banded-iron-formation (most important), Mn
-----------big orogeny event in west aftrica (ebunean/ebundian) collision granite Sn-Ta
  • Bushveld LIC 
  • Vredefort impact (Transvaal)
2,0-1,0 Ga : anorogenic event (boring event) = Proterozoic
  • Kibaran belt 
  • SEDEX in Ghammsberg Zn-Pb-(Cu)
1,0 Ga       : big event granite Sn-Ta-W
----------- erosion causes mollase
1,0-0,5 Ga : Congo copper belt
  • Clastic: sediment-hosted kupferschiefer type (Cu,Co,U)
  • Carbonate: tsumeb type (Cu,Zn,Pb,As,Ag,…)
  • Carbonate: MVT (Pb-Zn)


0,5 Ga          : Pan African orogeny (major granites Ta-Nb-Sn)

1. Deposits of the African Precambrian platform and orogenies1.1 Deposits of the Guinean metallogenic province
- Fe ores (BIF; Archaean to Upper Proterozoic)
- Mn: Nsuta (Ghana) - upper Birimian gondites; 50-55% MnO2
- Cu: Guelv Moghrein (Mauretania)
- Au: in qz veins: Obuasi, Bibiabi, Prestra, Bondaie, Konongo, Nangodi (Ghana)- Birimian bearing conglomerates
- Diamonds: Ghana and Ivory coast. In Guinea: Mesozoic kimberlites. In Liberia: placers
1.2. Deposits of the Sahara-Cameroon metallogenic province
- Bou Azzer Co-(Ni-As-Au): ore shoots 40m thick in dolomitized serpentinite, amphibolite, chlorite schist
- Jos plateau, Nigeria Sb, Nb, W in younger granites

AUSTRALIA

Archean Yilgarn-Pilbara Craton
1.1. Kambalda Ni subprovince (komatiites)
1.2 Norseman-Wiluna goldbelt
1.3 Volcanogenic Cu-Pb-Zn-Ag
1.4 Archean Fe-ores(Algoma BIF)
1.5 Pegmatites(Ta, Sn, Li)
Wodgina (Pilbara)
- pegmatite
Greenbushes (Yilgarn)
- spodumene pegmatite (LCT) 2,5 Ga
- world largest hard rock lithium mine

Proterozoic Arunta Gawler Province2.1. Hamersley Range BIF
Hammersley BIF
- Mt Tom Price
mineralogy: Mt, Hm, mpHm
2.2. BangemallPb-Cu-Ba(Abra)
2.3. Kimberley Fe-Ni, diamonds
2.4. PineCreek Au-U, basemetal
2.5. Central Australia. TennantCreek Au-Cu-Bi
2.6. Mount Isa basemetal(SMS)
Mt Isa (1,54-1,45 Ga)
- Zn-Pb-Ag-(Cu)
- syngenetic base metal accumulation in the basin

2.7. McArthur basin base metal(SMS)
2.8. BrokenHill base metal(SMS)
- Zn-Pb, New South Wales
2.9. Gawler Range-Stuart Shelf: BIF, IOCG
Olympic Dam-IOCG
- Hm-qz breccia
- Hm-granite-breccia
- Volcanic rock diatreme
Keypoints:
o   1. Olympic dam granite
o   2. Extensional fault, volcaniclastic sediments preserved in fault basin
o   3. Breccia complexes emplaced along faults
2.10. Adelaide base metal
2.11. Georgetown, Yambo, CoAu-Cu

3. Paleozoic Tasman metallogenic province3.1. Delamere subprovince
= Mount read volcanic
= Au-Cu-Pb-Zn-Ag
= syngenetic
3.2. Lachlan subprovince
= Bendigo, gold-quartz saddle veins (orogenic Au)
= In addition to Au-Sn+Cu-W-Sb-U-Th-mineralization
= Saddle reefs
3.3. New England-Queensland subprovince

ex. Ridgeway PCD, Cadia District

4. Secondary deposits
5. Older Alpine province
6. Australasian Alpine province

-Related to Mesozoic-Cenozoic subduction along the eastern margin of the Australasiatic plate.
-Older and younger Alpine provinces
-Deposit: Au-Cu porphyry, Ni-laterites and lateritic Ni/Co ores



South America

Brazil 

Sketch after Vanecek 1994 (modified from the lecture note given by Frank Melcher-regional economic geology)


- Fe (3), Nb (1), Ta (3), Bauxite (4)
- Asbestos (3), graphite (3), kaolin (6), talc (4), vermicculite (3)

BIF in Brazil (2,8-1,6 Ga)
grade: primary Fe: 30-50%
a. Priasov type
ex. Sierra de Imataca
mineralogy: original magnetite ores upgraded to secondary "crustal ores"
b. Algoma type 
ex. Minas Gerais, Raposos
keypoints: Itabirite-Archean granitic gneisses and migmatites (metamorphosed at 2,75 Ga), phyllite
lithology: quartzite-phyllite-itabitite-dolomite
mineralogy: hematite rich, oxide
c. Superior type
ex. Serra dos Carajas, Para
mineralogy: hem-mag-martite-goethite
d. Uncertain genesis
ex. Urucum/ Mato Grosso

Bauxite
producer: Brazil, Venezuela, Guyana, Suriname
-HR: silicate rock with high-Al and low-Fe, SiO2 removal produces Al2O3 ranging from 28-60%
-formation condition:
humid to dry and warm climate
plateau
open anticlinal

Lowland type-bauxite: developed on kaolin-rich young sediments
Plateau type-bauxite: weathering of Precambrian rocks

Fe-Ti-V-Cr
associated with metabasite rocks in greenstone belts and LIC
mineralogy: scheelite, cassiterite
locality: Northern Brazil, Pitinga (1,8 Ga) with Sn, Nb, Ta, REE, Zr, Y

Gold
Serra Pelada
IOCG Carajas
host: granite, gabbronorite, metavolcanics, BIF, gabbro (age 2,8-1,6 Ga)

Pegmatite
commodity: gemstone, quartz, rare metal, elbaite (multicolor gemstones), beryl
related to Brasiliano orogeny (600-500 Ma, same event as Pan African orogeny)
Amethyst: basalt lavas, degassing lava at 1150 degree, filling the crack (epigenetic)

Argentina

Producer: Li (4), B (4), diatomite (3)
low- to intermediate- sulfidation Cu-Pb-Zn-Ag-Au-In
mineralogy: sphalerite with elevated In
- mainly mesozoic-cenozoic deposits (part of Circum Pacific megaprovince, subduction Nazca plate with South America plate)
Chile
Producer: Mo (3), As (2), Cu (1), Li (1), B (4)
IOCG: Archean to tertiary
setting:
- within magmatic arc (Jurassic to Lower Cretaceous)
- related to intrusions of gabbro-granodiorite
- primitif mantle signature, tholeiitic-calc-alkaline
- extensional tectonic and formation of orogen-parallel fault system
- east of the arc: volcanosedimentary rock in back-arc setting
- alteration: pervasive feldspar destructive
- forms of IOCG: Veins in magmatic rocks(gabbro, diorite), hydrothermal breccia, mantos, skarn, composite deposits in volcano sedimentary settings

Cordilleran Mineral Province
porphyry Cu-Au

Manto deposit
stratabound, associated with andesites

Colombia
Platina di Pinto (platinum) from 17th

Bolivia
Producer: W (4), Sb (4), Sn (4)
Peru
Producer: Mo (4), Cu (3), Pb (4), Zn (3), Sn (3)

> 30% world porphyry-Cu
shape: elongated, ovoid, mineralized zones

Pb/Zn deposits
- vein system in shallow and peripheral parts of PCD systems
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