Water-rock interactions To concentrate a material, water must: –Transport the ions –A ‘trap’ must cause precipitation in a spatially constrained manner Trace metals which do not go into igneous minerals easily get very concentrated in the last bit of melt Leaching can preferentially remove materials, enriching what is left or having the leachate precipitate something further away

Ore deposit environments Magmatic –Cumulate deposits – fractional crystallization processes can concentrate metals (Cr, Fe, Pt) –Pegmatites – late staged crystallization forms pegmatites and many residual elements are concentrated (Li, Ce, Be, Sn, and U) Hydrothermal –Magmatic fluid - directly associated with magma –Porphyries - Hot water heated by pluton –Skarn – hot water associated with contact metamorphisms –Exhalatives – hot water flowing to surface –Epigenetic – hot water not directly associated with pluton

Metal Sulfide Mineral Solubility Problem 1: Transport of Zn to ‘trap’: ZnS + 2 H O 2 = Zn 2+ + S 2- + H 2 O Need to determine the redox state the Zn 2+ would have been at equilibrium with… What other minerals are in the deposit that might indicate that?  define approximate f O2 and f S2- values and compute Zn 2+ conc.  Pretty low Zn 2+

Must be careful to consider what the conditions of water transporting the metals might have been  how can we figure that out?? What other things might be important in increasing the amount of metal a fluid could carry? More metal a fluid can hold the quicker a larger deposit can be formed…

How about the following: ZnS + 2 H O 2 + Cl - = ZnCl + + S 2- + H 2 O Compared to That is a BIG difference…

Geochemical Traps Similar to chemical sedimentary rocks – must leach material into fluid, transport and deposit ions as minerals… pH, redox, T changes and mixing of different fluids results in ore mineralization Cause metals to go from soluble to insoluble Sulfide (reduced form of S) strongly binds metals  many important metal ore minerals are sulfides!

Piquette Mine 1-5 nm particles of FeOOH and ZnS – biogenic precipitation Tami collecting samples

cells ZnS

Piquette Mine – SRB activity At low T, thermochemical SO 4 2- reduction is WAY TOO SLOW – microbes are needed! ‘Pure’ ZnS observed, buffering HS - concentration by ZnS precipitation

Fluid Flow and Mineral Precipitation monomineralic if: –flux Zn 2+ > HS - generation –i.e.  there is always enough Zn 2+ transported to where the HS - is generated, if sequential precipitation if: –Zn 2+ runs out then HS - builds until PbS precipitates z HS - generated by SRB in time t x Zn 2+ y Pb 2+ ZnS PbS ZnS

Model Application Use these techniques to better understand ore deposit formation and metal remediation schemes

Sequential Precipitation Experiments SRB cultured in a 125 ml septum flask containing equimolar Zn 2+ and Fe 2+ Flask first develops a white precipitate (ZnS) and only develops FeS precipitates after most of the Zn 2+ is consumed Upcoming work in my lab will investigate this process using microelectrodes  where observation of ZnS and FeS molecular clusters will be possible!

Hydrothermal Ore Deposits Thermal gradients induce convection of water – leaching, redox rxns, and cooling create economic mineralization

Sedimentary –Placer – weathering of primary mineralization and transport by streams (Gold, diamonds, other) –Banded Iron Formations – 90%+ of world’s iron tied up in these (more later…) –Evaporite deposits – minerals like gypsum, halite deposited this way –Laterites – leaching of rock leaves residual materials behind (Al, Ni, Fe) –Supergene – reworking of primary ore deposits remobilizes metals (often over short distances) Ore deposit environments

Placer uranium gold Stratiform phosphate Stratiform iron Residually enriched deposit Evaporites Exhalative base metal sulphides Unconfornity-associated uranium Stratabound clastic-hosted uranium, lead, copper Volcanic redbed copper Mississippi Valley-type lead-zinc Ultramafic-hosted asbestos Vein uranium Arsenide vein silver, uranium Lode Gold Ore Deposit Types I

Clastic metasediment-hosted vein silver-lead-zinc Vein Copper Vein-stockwork tin, tungsten Porphyry copper, gold, molybdenum, tungsten, tin, silver Skarn deposits Granitic pegmatites Kiruna/Olympic Dam-type iron, copper, uranium, gold, silver Peralkaline rock-associated rare metals Carbonatite-associated deposits Primary diamond deposits Mafic intrusion-hosted titanium-iron Magmatic nickel-copper-platinum group elements Mafic/ultramafic-hosted chromite Ore Deposit Types II