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PRECAMBRIAN MANGANESE DEPOSITS: GEOLOGICAL SETTING,
METALLOGENESIS AND PALEOENVIRONMENTAL
IMPLICATIONS
NIC BEUKES AND JENS GUTZMER*
Paleoproterozoic Mineralization Research GroupDepartment of GeologyUniversity of Johannesburg
8 Department of Mineralogy, TU Bergakademie Freiberg, Freiberg, Germany.
UNESP, Brazil, 2011
PRECAMBRIAN MANGANESE DEPOSITS: GEOLOGICAL SETTING,
METALLOGENESIS AND PALEOENVIRONMENTAL
IMPLICATIONS
OUTLINE
PART 1; DISTRIBUTION, CLASSIFICATION, RESERVES, TEMPORAL VARIATIONS, CHEMICAL AND BIOGEOCHEMICAL CONTROLS ON DEPOSITION
PART 2: DEPOSITS PREDATING GOE
PART 3: DEPOSITS IMMEDIATELY POSTDATING GOE
PART4: MESOPROTEROZOIC DEPOSITS
PART 5; NEOPROTEROZOIC DEPOSITS AND CONCLUSION
Manganese Deposits 3
Geographic Distribution of important deposits
KMF
PMF
Urucum
Azul
Serra do Navio
Imini
Molango
Nsuta
Tambao
KisengeMoanda
Goa
IOGSausar
Chiatura
NikopolMangyshlak
Groote Eylandt
Sinian
Woodie Woodie
4
MINERALOGICAL CLASSIFICATION
• Mn-carbonate ± Mn-oxide
Kutnahorite Ca(Mn2+, Mg)(CO3)2 Rhodochrosite
(Mn,Ca)CO3
Mn-calcite (Ca, Mn)CO3
• Mn-oxide ± carbonate
Braunite Mn2+Mn3+6SiO12
Hausmannite Mn2+Mn3+2O4
Bixbyite
HematiteFe2O3
• Supergene altered Mn4+ oxyhydroxide
Todorokite (Na, Ca)Mg2+Mn2+lMn4+
6-lO12 * xH2O
Manganomelane (K, Na, Ba)Mn4+8O16 * xH2O
Pyrolusite Mn4+O2
5
Genetic subdivision of important Mn deposits
1. BIF-associated deposits
• Kalahari Manganese Field
• Rooinekke
• Urucum, Otjosondu, Malyi Khingan
2. Shallow marine oolitic/oncolitic deposits
• Nikopol, Bol’se Tokmak, Chiatura, Mangyshlak
• Groote Eylandt
• Bronkhorstfontein (Tolwe, South Africa)
3. Black shale-hosted deposits
• Azul
• Moanda, Nsuta, Tambao, Serro do Navio, Kisenge
• Goa, Sausar, IOG, Sinian, Woodie-Woodie
• Molango, Cambrian in China (Taojiang etc.)
4. Karst-associated deposits
• Imini
• Postmasburg manganese field, Woodie Woodie
Manganese Deposits 6
Geographic Distribution of important deposits
R-KMF
PMF
Urucum
Azul
Serra do Navio
Imini
Molango
Nsuta
Tambao
KisengeMoanda
Goa
IOGSausar
Chiatura
NikopolMangyshlak
Groote Eylandt
Sinian
Malyi Khingan
Otjosondu
Woodie Woodie
Manganese Deposits 7
Temporal Distribution
Total mineral resource: ca. 5 Gt
Manganese Deposits 8
Global Mn ore production
Total production: ~ 12 Mt
Manganese Deposits 9
South Africa’s manganese wealth (resources)
The KMF:
• ~ 4billion tons of mineable resource
• ~ 80% of world’s resource
Manganese Deposits 10
SA manganese mining in global context
Concentration of Mn in Precambrian vs Phanerozoic
Manganese Deposits 11
Manganese Deposits 12
Mn in sediments - a tale of three oxidation states
Mobile
Immobile
Immobile
Inorganic Precipitation of Mn-oxides
Manganese Deposits 13
Microbial Catalization of Mn-oxide Precipitation
Manganese Deposits 14
Microbial catalization process
• Bacteria first enzymatically oxidize Mn2+ to Mn3+
• 2Mn2+ + 0,5O2 + 2H+ = 2Mn3+ + H2O
• This Mn3+ remains bound to manganese oxidizing enzyme
• The same enzyme then catalyzes the oxidation of bound Mn3+ to MnO2 via reaction
• 2Mn3+ +0,5O2 + 3H2O = 2MnO2 + 6H+
• These reactions not only accelerates transformation of Mn3+ to Mn4+ but also ensures that more Mn3+ is converted to MnO2 than the only about 50% in case of disproportionation of hausmannite
Manganese Deposits 15
Manganese Respiration
Manganese and Timing of Oxygenic Photosynthesis
GOE
Anoxygenic vs Oxygenic Photosynthesis
• Anoxygenic
CO2 + 2H2S CH2O + 2S +H2O
• Oxygenic
CO2 + 2H2O CH2O + O2
Sunlight
Sunlight
When did the latter develop?
Unlike iron no anaerobic oxidation of Mn known:Mn oxidation implies presence of free oxygen
Microbial Catalization of Mn-oxide Precipitation
Manganese Deposits 21
Mn oxidation requires free oxygen: Oxygen = oxygenic photosynthesis
Manganese Deposits 22
Precambrian Mn Deposits
Temporal Litho- and Chemofacies Distribution
Manganese Deposits 23
GOE