Introduction to Ore-Forming Processes. Laurence Robb

occurring in the native form include copper, silver, gold, and platinum which are all characterized by cubic close packing of atoms, high densities, and are malleable and soft. The carbon atoms in diamond are linked in tetrahedral groups forming well cleaved, very hard, translucent crystals. Sulfur also occurs as rings of eight atoms and forms bipyramids or is amorphous.

      Metals

      1 Gold – Au

      2 Silver – Ag

      3 Platinum – Pt

      4 Palladium – Pd

      5 Copper – Cu

      Non‐metals

      1 Sulfur – S

      2 Diamond – C

      3 Graphite – C

      Halides

      The halide mineral group comprises compounds made up by ionic bonding. Minerals such as halite and sylvite are cubic, have simple chemical formulae, and are highly soluble in water. Halides sometimes form as ore minerals, such as chlorargyrite and atacamite.

      1 Halite – NaCl

      2 Sylvite – KCl

      3 Chlorargyrite – AgCl

      4 Fluorite – CaF2

      5 Atacamite – Cu2Cl(OH)3

      Sulfides and Sulfosalts

This is a large group of minerals in which bonding is both ionic and covalent in character. The sulfide group has the general formula A_MX_P, where X is typically S but can be As, Sb, Te, Bi, or Se, and A is one or more of the metals. The sulfosalts, which are less common than sulfides, have the general formula A_MB_NX_P, where A is usually Ag, Cu, or Pb, B is commonly As, Sb, or Bi, and X is S. The sulfide and sulfosalt minerals are generally opaque, dense, and have a metallic to sub‐metallic luster.

      Sulfides

      1 Chalcocite – Cu2S

      2 Bornite – Cu5FeS4

      3 Galena – PbS

      4 Sphalerite – ZnS

      5 Chalcopyrite – CuFeS2

      6 Pyrrhotite – Fe1–xS

      7 Pentlandite – (Fe,Ni)9S8

      8 Millerite – NiS

      9 Covellite – CuS

      10 Cinnabar – HgS

      11 Skutterudite – (Co,Ni)As3

      12 Sperrylite – PtAs2

      13 Braggite/cooperite – (Pt,Pd,Ni)S

      14 Moncheite – (Pt,Pd)(Te,Bi)2

      15 Laurite – RuS2

      16 Cobaltite – CoAsS

      17 Gersdorffite – NiAsS

      18 Loellingite – FeAs2

      19 Arsenopyrite – FeAsS

      20 Molybdenite – MoS2

      21 Realgar – AsS

      22 Orpiment – As2S3

      23 Stibnite – Sb2S3

      24 Bismuthinite – Bi2S3

      25 Argentite – Ag2S

      26 Calaverite – AuTe2

      27 Pyrite – FeS2

      Sulfosalts

      1 Tetrahedrite – (Cu,Ag)12Sb4S13

      2 Tennantite – (Cu,Ag)12As4S13

      3 Enargite – Cu3AsS4

      Oxides and Hydroxides

      This group of minerals is variable in its properties but is characterized by one or more metals in combination with oxygen or a hydroxyl group. The oxides and hydroxides typically exhibit ionic bonding. The oxide minerals can be hard, dense, and refractory in nature (magnetite, cassiterite) but can also be softer and less dense, forming as products of hydrothermal alteration and weathering (hematite, anatase, pyrolusite). Hydroxides, such as goethite and gibbsite, are typically the products of extreme weathering and alteration.

      Oxides

      1 Cuprite – Cu2O

      2 Hematite – Fe2O3

      3 Ilmenite – FeTiO3

      4 Hercynite – FeAl2O4

      5 Gahnite – ZnAl2O4

      6 Magnetite – Fe3O4

      7 Chromite – FeCr2O4

      8 Rutile – TiO2

      9 Anatase – TiO2

      10 Pyrolusite – MnO2

      11 Cassiterite – SnO2

      12 Uraninite – UO2

      13 Thorianite – ThO2

      14 Columbite‐tantalite – (Fe,Mn)(Nb,Ta)2O6

      Hydroxides (or Oxyhydroxides)

      1 Goethite – FeO(OH)

      2 Gibbsite – Al(OH)3

      3 Boehmite – AlO(OH)

      4 Manganite – MnO(OH)

      Oxysalts

      The carbonate group of minerals form when anionic carbonate groups are linked by intermediate cations such as Ca, Mg, and Fe. Hydroxyl bearing and hydrated carbonates can also form, usually as a result of weathering and alteration. The other oxysalts, such as the tungstates, sulfates, phosphates, and vanadates, are analogous to the carbonates, but are built around an anionic group in the form .

      Carbonates

      1 Calcite – CaCO3

      2 Dolomite – CaMg(CO3)2

      3 Ankerite – CaFe(CO3)2

      4 Siderite – FeCO3

      5 Rhodochrosite – MnCO3

      6 Smithsonite – ZnCO3

      7 Cerussite – PbCO3

      8 Azurite – Cu3(OH)2(CO3)2

      9 Malachite – Cu2(OH)2CO3

      Tungstates

      1 Scheelite – CaWO4

      2 Wolframite – (Fe,Mn)WO4

      Sulfates

      1 Baryte(s) – BaSO4

      2 Anhydrite – CaSO4

      3 Alunite – KAl3(OH)6(SO4)2

      4 Gypsum – CaSO4·2H2O

      5 Epsomite – MgSO4·7H2O

      Phosphates

      1 Xenotime – YPO4

      2 Monazite – (Ce,La,Th)PO4

      3 Apatite – Ca5(PO4)3(F,Cl,OH)

      Vanadates