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2. What is manganese (Mn) and what is it used for? What mineral forms does it occur in? How has the amount of Mn changed through time? How has the chemistry of Mn ores changed through time? isotopes major elements trace elements rare-earth elements Outline: What Will We See? Molango What do these changes tell us about the history of the Earth? 2

3. Mn deposits come in 6 flavors, increasing in diversity with time >2400 Ma Archean style 2400 – 1700 Paleoproterozoic style 1700 – 900 No deposits 900 – 550 Neoproterozoic style 550 – 150 Paleozoic-Jurassic style < 150 Post-Jurassic style Each reflects changes in ocean- atmosphere chemistry or the radiation of new life forms What Will We Learn? Giant stromatolites Chocolate-brown dolomites 3

4. What is Manganese? Element 25, manganese was isolated by Johan Gottlieb Gahn, a Swedish chemist, in 1774 by heating the mineral pyrolusite (MnO 2 ) in the presence of charcoal. Nearly 90% of all of the Mn produced each year is used in the production of steel to make it easier to form and to increase its strength and resistance to impact. Manganese is also used to give glass an amethyst color and is responsible for the color of amethyst gemstones. First, it is not magnesium ! 4

5. The fortunes of Mn follow that of Fe 5

6. How Does it Behave? Mn is nearly identical to Fe in its geochemist ry. ManganeseIronMn/Fe Formula wt54.9455.85 Oxidation states @ 1 atm, 398K4+, 3+, 2+3+, 2+ Coordination number w O66 Ionic radius, Å0.830.78 Crustal abundance, ppm95056 000 0.017 Concentration in seawater, µg/L0.0720.25 0.288 in Black Sea surface water0.560.29 1.93 in Black Sea deep water3334.14 80.4 Because of its much lower crustal abundance, it is submerged by Fe except in special environments 6

7. How Does it Behave? Mn is nearly identical to Fe in its geochemistry. ManganeseIronMn/Fe Formula wt54.9455.85 Oxidation states @ 1 atm, 398K4+, 3+, 2+3+, 2+ Coordination number w O66 Ionic radius, Å0.830.78 Crustal abundance, ppm95056 000 0.017 Concentration in seawater, µg/L0.0720.25 0.288 in Black Sea surface water0.560.29 1.93 in Black Sea deep water3334.14 80.4 Because of its much lower crustal abundance, it is submerged by Fe except in special environments Dissolves 7 Unless S 2- present Sulfidic

8. How Does it Behave? Mn is nearly identical to Fe in its geochemistry. ManganeseIronMn/Fe Formula wt54.9455.85 Oxidation states @ 1 atm, 398K4+, 3+, 2+3+, 2+ Coordination number w O66 Ionic radius, Å0.830.78 Crustal abundance, ppm95056 000 0.017 Concentration in seawater, µg/L0.0720.25 0.288 in Black Sea surface water0.560.29 1.93 in Black Sea deep water3334.14 80.4 Because of its much lower crustal abundance, it is submerged by Fe except in special environments Precipitates 8

9. Eh-pH Behavior: Oxides Manganese in Solution Oxides and hydroxides only: manganese should be mobile under reducing conditions but will precipitate as the oxidation state of the solution r ises Manganese in solution Manganese in solids

10. 10 Eh-pH Behavior: + Carbonate Adding carbonate reduces size of the area of solubility

11. 11 Eh-pH Behavior: + Sulfide Upwards flux Fe immobilized in deep water

12. Where Does It Come From Today? Most Mn is ultimately volcanic, but is hosted by sediments because it is carried so much farther than Fe 90 %10 % 2+ Mn 4+ oxides FeS 2 2+ O2O2 Fe 3+ oxides 12

13. Why Is Mn Carried So Much Farther? Fe follows relatively simple homogeneous kinetics (note strong pH dependence) -d[Fe 2+ ]/dt = k[Fe 2+ ][O 2 ][OH - ] 2 Mn reaction is heterogeneous, requiring a solid catalyst -d[Mn 2+ ]/dt = k 0 [Mn 2+ ] + k 1 [Mn 2+ ][MnO 2 ][O 2 ][OH] 2 Mn is oxidized (hence precipitated) much more slowly than Fe 13

14. How Is It Precipitated? Mn bacteria, production wells GMA Fe bacteria, production wells GMA Most Mn is precipitated bacterially; Fe can be, but most is abiotic 14

15. What are its Common Mineral Forms? The dominant Mn mineral, percentage of land-based deposits Rhodochrosite MnCO 3 32.0 Braunite (Mn 2 O 3 ) 3 (Mn,Fe)SiO 3 24.3 Cryptomelane KMn 8 O 16 8.7 Manganite MnOOH 7.8 Pyrolusite MnO 2 4.9 Hausmannite Mn 3 O 4 2.9 Psilomelane MnO 2 3.9 amorphous oxides 1.9 Kutnahorite CaMn(CO 3 ) 2 1.9 Mn-calcite (Mn,Ca)CO 3 1.9 Todorokite (Mn,Ca,Mg)Mn 3 O 7 _H 2 O 1.9 Others (oxides) 7.8 Mn 2+ 4*Mn 2+ + 3*Mn 4+ Mn nodules 15

16. A Conflict Between Fact and Theory Rhodochrosite and braunite, both of which are Mn 2+ minerals, make up over half of the Mn phases in land-based ore deposits. But we just said Mn is transported as Mn 2+ and deposited as Mn 4+ How then is the Mn in land-based deposits transported and precipitated? 16

17. Primary Mn Deposits Molango – Jurassic, Mexico Most Mn ore is black, dominated by low-oxidation state minerals 17

18. Primary Fe Deposits Hamersley IF – Paleoproterozoic, Australia Most Fe ore is red, dominated by high-oxidation state minerals 18

19. Time as a Controlling Variable: Mn Deposit Tonnage Through Time Fan Delian 19

20. How Are Deposits Distributed by Age? Testable Hypothesis 1 Observation: Fe ores show a concentration in the Paleoproterozoic related to the advent of atmospheric oxygen and a much smaller concentration in the Neoproterozoic related to glaciations. Hypothesis: Mn should follow the same pattern. 20

21. How Are Deposits Distributed by Age? Two Major Episodes of Iron Deposition Peak 1 - Paleoproterozoic Peak 2 - Neoproterozoic Peak 3 - Oligocene IF No IF IF 21

22. Six Major Episodes of Mn Deposition III V VI IVIII 22

23. Archean Mn Deposition IIIV VIIVIII 23

24. Archean Mn Deposits Relatively small – 3.7 million tonnes avg, Fe-rich – 14 % Fe 2 O 3 Often produced by artisanal mining (Equivalent Fe ores = Algoma type) 24

25. Paleoproterozoic Mn Deposition IIIV VIIVIII 25

26. Paleoproterozoic Mn Deposits Very large – 99 mt, low-Fe – 8.1 %; Dominated by Mamatwan, which has 55 % of world’s reserves (Equivalent Fe ores = Lake Superior type) Mamatwan – Paleoproterozoic, South Africa 26

27. Mesoproterozoic Mn Deposition IIIV VIIVIII 27

28. Mesoproterozoic Mn Deposits Small – 3.9 mt, high-Fe – 11 %; Mostly volcanic except Wafangzi (No Fe ores from this period) 28

29. Neoproterozoic Mn Deposition IIIV VIIVIII 29

30. Neoproterozoic Mn Deposits Widespread but small – 12.1 mt, low-Fe – 5.7 %; Dominated by Urucum –Mutun with 6.3 % of world reserves (Equivalent Fe ores = Rapitan type) Tanganshan – Neoproterozoic, China 30

31. Paleozoic Mn Deposition IIIV VIIVIII 31

32. Cambrian-Jurassic Mn Deposits Small – 7.8 mt, high-Fe – 12 %, high P – 0.8 %; Larger deposits are Karadzhal, 3.8 % of world reserves, and Molango, 1.3 % (Equivalent Fe ores = Clinton oolitic type) Taojiang – Ordovician, China 32

33. Post-Jurassic Mn Deposition IIIV VIIVIII 33

34. Post-Jurassic Mn Deposits Large – 20.4 mt, low-Fe – 4.4 %; Dominated by Oligocene deposits around the Black Sea with 16.2 % of world reserves (No significant Fe ores of this age) 34

35. How Are Deposits Distributed by Age? Conclusion – Fe and Mn ores show some commonalities of distribution, but Mn is (1) more evenly distributed in time (2) less evenly distributed in space, being concentrated in a few giant deposits in each time period 35

36. Mn Deposit Chemistry Through Time Andrey Becker 36

37. Mn Deposit Chemistry: Isotopes Testable Hypothesis – None. This question was first addressed by Pat Okita for Molango as part of the exploration of the deposit 37

38. Mn Deposit Chemistry: Isotopes in Space Implication : Rhodochrosite incorporates significant organic-derived C. 38 Observation : Mn grade is closely associated with 13 C depleted carbon

39. Mn Deposit Chemistry: Isotopes in Space New hypothesis : Mn carbonate forms during early diagenesis by reaction of Mn oxide with organic carbon Test : Redox buffering at Mn4+/Mn2+ couples should prevent pyrite formation at the sediment-water interface S isotopes at Molango indicate late-stage FeS 2 formation 39

40. Mn Deposit Chemistry: Isotopes in Time Observation : The spread of C isotopic values increases with time Working hypothesis : there is an increase in diversity of environments with time 40

41. Mn Deposit Chemistry: Major Elements Testable Hypotheses? Nothing in the literature – lets see what the rocks themselves have to say 41

42. Mn Deposit Chemistry: Major Elements - Fe 42

43. Mn Deposit Chemistry: Major Elements - Fe I high Fe V low Fe IV lower Fe II lower Fe III high Fe VI very low Fe 43

44. Mn Deposit Chemistry: Major Elements - Fe 44 Observation : The Mn/Fe ratio in volcanic deposits increases dramatically at ~ the J-K boundary Working hypothesis : ???????

45. Mn Deposit Chemistry: Major Elements - Si 45

46. Mn Deposit Chemistry: Major Elements - Si I V IV II III VI Diatoms 46

47. Mn Deposit Chemistry: Major Elements - P 47

48. Mn Deposit Chemistry: Major Elements - P I V IV II III VI Phosphatized hard parts (Cloudina) 48

49. Mn Deposit Genesis: Calvert’s Upwelling Model Early Cambrian phosphogenesis episode/ radiation of shelly faunas – both related to increased diversity of environments and water chemistries Mn 2+ Mn 4+ O2O2 49

50. A Conflict Between Fact and Theory Most Mn ores are not associated with high P Most are associated with light C isotopes, which the OMZ model does not explain How then is this Mn transported and precipitated? 50

51. Mn Deposit Chemistry: Trace Elements -- Ba 51

52. Mn Deposit Chemistry: Trace Elements -- Ba I V IV II III VI Observation: Ba is high in all but Mesoproterozoic deposits; spread increases in 2 cycles, highest in post-Jurassic 52

53. Force & Cannon’s Euxinic Basin Model of Mn Mineralization Mn is soluble in anoxic-sulfidic bottom water; precipitates as oxide at oxic/anoxic interface light δ 13 C 53

54. Euxinic Basin Model of Ba Incorporation Ba is also soluble in anoxic-sulfidic bottom water; precipitates as sulfate at oxic/anoxic interface when seawater has SO 4 Ba ++ BaSO 4 SO 4 = 54

55. Mn Deposit Chemistry: Conflict Resolution Euxinic basin deposits are more numerous than OMZ deposits; all giant deposits are in euxinic category 55

56. Mn Deposit Chemistry: New Hypothesis I V IV II III VI No euxinic basins Ba in manganese deposits and Mo in black shales indicate monotonous Mesoproterozoic with no euxinic basins 56

57. Mn Deposit Chemistry: Trace Elements –V D i v e r s i t y i n c r e a s e s Mesoprotoerozoic gap V is typical of other trace elements – Cu, Mo, Pb, Zn – in showing a trend to a widening spread of values with time 57

58. Mn Deposit Chemistry: What Have We Learned So Far? Fe, Si, P, V show a trend to a widening spread of values with time 58 This pattern suggest a widening spread of environments with time, likely coupled with increased diversity of organisms But we haven’t learned anything about the oxidation state of the atmosphere and ocean

59. Mn Deposit Chemistry: REE REE in chemical sediments are often invoked as indicators of oxidation state: Ce 3+  Ce 4+ Deviation = Ce/Ce* Eu 3+  Eu 2+ Deviation = Eu/Eu* 59

60. Mn Deposit Chemistry: REE - Ce Ce 3+  Ce 4+ catalyzed by Mn oxides, produces insoluble Ce and a positive Ce anomaly on Mn nodules; residual seawater has a negative Ce/Ce* Hypothesis = no oxygen in bottom water in Precambrian Test = no negative Ce/Ce* in seawater  no Mn nodules in deep sea 60

61. Ce Systematics Today Under oxic conditions, Ce is oxidized and scavenged on surface of Mn nodules in deep sea Ce/Ce* = 1.65 Ce/Ce* = 1.03 Ce Ce/Ce* = 0.17 61

62. Mn Deposit Chemistry: REE – Ce Diversity in Mn ores increases to both higher and lower oxidation state Low O 2 oceans – no deep-sea Mn nodules 62

63. Mn Deposit Chemistry: REE - Eu Eu 3+  Eu 2+ (only at high T) produces vent fluids with positive Eu anomalies, but Fe oxides remove all REE close to vents Hypothesis = No oxygen in bottom water of restricted basin w. vents Test = no vent-derived Fe oxides  no REE scavenging  positive Eu/Eu* in local seawater or in global seawater for global anoxia 63

64. Eu Systematics Today Under oxic conditions, REE are scavenged at the vent by Fe oxides; seawater Eu/Eu* reflects continental sources Eu/Eu* = 7 - 11 Eu/Eu* = 0.61 Eu 64

65. Fe Deposit Chemistry: REE – Eu Low O 2 oceans; vent- signature Eu in BIF O 2 in surface water; REE vent-signature lost in Fe deposits 65 diversification

66. Mn Deposit Chemistry: REE – Eu Greater variety of Mn environments with time 66

67. Barrie Bolton What Do We Learn About Earth History? 67

68. What Have We Learned about the History of Mn? I pre –2400 Ma. No O 2 in atm. No oxidative weathering on continents; anoxic but non-sulfidic bottom waters owing to absence of SO 4 Small, Fe-rich manganese deposits, perhaps in localized higher oxidation state environments II 2400 – 1700 Ma. Low O 2 in atm. Anoxic deep water, intermittently sulfidic, but low SO 4 surface water Giant Kalahari Mn deposit, great era of Banded Iron Formations III 1700-900 Ma. Low O 2 in atm. Minor Mo-enriched black shales; euxinic basins absent? Virtual disappearance of sediment-hosted Mn IV 900-550 Ma. Increased O 2 in atm. Reappearance of euxinic basins Large number of glacial-associated Mn deposits V VI 550 – 0 Ma. High O 2. Continental break-up; radiation of metazoans, shelly faunas Abrupt increase in Ba, P, and V in sed- hosted Mn ores 150-0 Ma. High O 2. Continental break-up; radiation of diatoms Abrupt increase in Si, Cu, Mo, Pb, V, Zn in volc-hosted Mn ores 68

69. Ore deposits are a sensitive repository of Earth history What Have We Learned in the Broader Sense? Geology is a science with an interplay between hypothesis- driven and exploration- driven inquiry The diversity of life, of sedimentary environments, and of their ore deposit products increases through time 69

70. Mn Deposit Workers Liu Tie-bing 70

71. Mn Deposit Workers Eric May 71

72. Mn Deposit Workers Pat Okita Jessamine 72

73. Mn Deposit Workers Enjoy the adventure 73