Native elements, sulfides, oxides, & hydroxides. JD Price

Transcription

1 Native elements, sulfides, oxides, & hydroxides JD Price

2 Native Elements Gold Au Silver Ag Diamond C Graphite C Sulfur S Images from mineral.galleries.com

3 Gold deposits

4 Cyanide Leaching NaCN combines with Au or Ag to form a liquid. Gold can be removed from the gangue. 4Au + 8NaCN + O 2 +2H 2 0 = 4Na[Au(CN) 2 ] +4NaOH This is employed at a number of scales.

5 Tetrahedral Sulfides Sphalerite ZnS Chalcopyrite CuFeS 2 Bornite Cu 5 FeS 4 Tetrahedrite Cu 12 Sb 4 S 13 Image from mineral.galleries.com Octahedral coordination Pyrrhotite Fe 1-x S 2 Galena PbS Niccolite NiAs Copyright James A. Burbank, Jr.

6 Tetrahedral Sulfides Image from Klein and Hurlbut, 1993

7 Other Sulfides Molybdenite MoS 2 Arsenopyrite FeAsS Marcasite FeS 2 Pyrite FeS 2 Stibnite Sb 2 S 3 Orpiment As 2 S 3 Realgar Cinnabar Covellite Chalcocite AsS HgS CuS Cu 2 S Image from mineral.galleries.com

8 Pyrite Marcasite Arsenopyrite Image from Klein and Hurlbut, 1993

9 Marcasite habit Image from Klein and Hurlbut, 1993

10 Covelite CuS Image from Klein and Hurlbut, 1993

11 Seafloor Hydrothermal Black Smoker Deposits Grow as fast as 30 centimeters per day. Begins with a ring of anhydrite around a jet of 350 C fluid, which exits the seafloor at velocities of between 1 and 5 meters per second WHOI

12 WHOI

13 MVT Migration of hydrothermal fluid and its interactions with limestone form large sulfide deposits

14 Tri-state (KS-OK-MO) 200 foot tall tailings (chat) piles from Zn-Pb mines. Ground water Cd 93 µg/l Pb 130 µg/l Time Zn 240,000 µg/l (Parkhurst, 1987). Mining concentrates, relocates, and makes accessible materials to the surface environment

15 Disseminated Sulfide Igneous rocks may host small amounts of sulfide minerals. At Bingham canyon, these are economic.

16 Oxides Oxides are typically either Tetrahedral Octahedral Mixed (Tetra- and Octahedral) Simple packing of O with cations in interstices - packing! These are clear representations of the ionic crystal structures we talked about in the first few weeks of the class.

17 Coordination in oxides Few significant Tetrahedral Oxides ZnO, BeO Octahedral oxides more common MgO, Al 2 O 3, Fe 2 O 3, FeTiO 3, TiO 2

18 Octahedral Oxides Corundum group Corundum Al 2 O 3 Hematite Fe 2 O 3 Ilmenite FeTiO 4 Rutile type Rutile TiO 2 Cassiterite SnO 2 Pyrolusite MnO 2 Image from mineral.galleries.com Periclase MgO Columbite (Fe,Mn)Nb 2 O 6 Tantalite (Fe,Mn)Ta 2 O 6 Perovskite CaTiO 3

19 Octahedral Oxides Corundum group

20 Mixed Coord. Oxides Spinel Group Spinel MgAl 2 O 4 Magnetite Fe 3 O 4 Chromite FeCr 2 O 4 Ulvospinel Fe 2 TiO 4 Image from mineral.galleries.com Franklinite ZnFe 2 O 4 Cuprite Cu 2 O

21 Mixed Oxides XY 2 O 4 X octahedral Y tetrahedral Chromite FeCr 2 O 4 Spinel MgAlAlO 4 Magnetite FeFe 2 O 4

22 TiO2 - FeO - Fe2O3

23 Oxygen and oxides Iron oxides differ because of the valency of the transition element, Fe. The result of oxidation 2 FeFe 2 O O 2 = 3 Fe 2 O 3 With increasing depth, there is less oxygen available. Fe becomes more reduced.

24 Yet another thermodynamic parameter f fugacity Chemical potential! (not really new)! = U+PV-TS (that s G) for an individual component f = exp!! = exp [! T,P -! ss ] Fugacity as a measure of how much the chemical potential of the component in the gas deviates from the chemical potential of the standard state due to changes in P and/or the mole fraction of the component. Just like a partial pressure (just not so ideal).

25 Oxygen and oxides MH - 2Fe 3 O 4 +O = 3Fe 2 O 3 WM - 3FeO + O = Fe 3 O 4 IW - Feº + O = FeO NNO - Niº + O = NiO

26 Now with fo 2 Maun and Osborne

27 Meet BIF (Banded Iron Formation) Rock is 2.5 billion years old (found world wide from Ga) Dark: Hematite (Fe 2 O 3 ) Red: Quartz (with iron) Yellow: Crocidolite (blue asbestosform) The accumulation of iron as seafloor sediments is thought to result from early photosynthesis on the ocean surface under N 2 CO 2 rich conditions. A lack of atmospheric O 2 permits Fe ions in surface seawater these bond with O 2 produced by photosynthesis.

28 Prolonged runs at high temperature produce a solid state reaction between MgO and Al 2 O 3, forming a layer of spinel This study Evaluated spinel growth rate as function of t, T, and P Constrained the thermodynamic stability of spinel at elevated P Constructed Al-Mg coupled diffusion model

29 EMPA traverses of spinel 1400 o C 4 GPa 89 hr 30 µm Boundary compositions Stoich. spinel 600 o C 3.2 GPa 16 hr 66 µm Al enriched 1978 o C 2.5 GPa 0.4 hr 115 µm

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31 Hydroxides Goethite FeO(OH) Bauxite Monhydrate Diaspore AlO(OH) Boehmite AlO(OH) Trihydrate Gibbsite Al(OH) 3 Image from mineral.galleries.com

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