Laurence Robb - Introduction to Ore-Forming Processes

Both metals and non‐metals exist in nature in the native form, where essentially only one element exists in the structure. Metals 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.

1 Gold – Au

2 Silver – Ag

3 Platinum – Pt

4 Palladium – Pd

5 Copper – Cu

1 Sulfur – S

2 Diamond – C

3 Graphite – C

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

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.

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

1 Tetrahedrite – (Cu,Ag)12Sb4S13

2 Tennantite – (Cu,Ag)12As4S13

3 Enargite – Cu3AsS4

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.

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

1 Goethite – FeO(OH)

2 Gibbsite – Al(OH)3

3 Boehmite – AlO(OH)

4 Manganite – MnO(OH)

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 .

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

1 Scheelite – CaWO4

2 Wolframite – (Fe,Mn)WO4

1 Baryte(s) – BaSO4

2 Anhydrite – CaSO4

3 Alunite – KAl3(OH)6(SO4)2

4 Gypsum – CaSO4·2H2O

5 Epsomite – MgSO4·7H2O

1 Xenotime – YPO4

2 Monazite – (Ce,La,Th)PO4

3 Apatite – Ca5(PO4)3(F,Cl,OH)

1 Carnotite – K2(UO2)(VO4)2·3H2O

The bulk of the Earth's crust and mantle is made up of silicate minerals that can be subdivided into several mineral series based on the structure and coordination of the tetrahedral anionic group. Silicate minerals are generally hard, refractory, and translucent. Most of them cannot be regarded as ore minerals in that they do not represent the extractable part of an ore body, and the list provided below shows only some of the silicates more commonly associated with mineral occurrences as gangue or alteration products. Some silicate minerals, such as zircon and spodumene, are ore minerals and represent important sources of metals such as zirconium and lithium, respectively. Others, such as kaolinite, are mined for their intrinsic properties (i.e. as a clay for the ceramics industry).

1 Quartz – SiO2

2 Orthoclase – (K,Na)AlSi3O8

3 Albite – (Na,Ca)AlSi3O8

4 Scapolite – (Na,Ca)4(Al,Si)4O8)3 (Cl, CO3)

5 Zeolite (analcime) – NaAlSi2O6·H2O

1 Zircon – Zr(SiO4)

2 Garnet (almandine) – Fe3Al2(SiO4)3

3 Garnet (grossular) – Ca3Al2(SiO4)3

4 Sillimanite – Al2SiO5

5 Topaz – Al2SiO4(F,OH)2

6 Chloritoid – (Fe,Mg,Mn)2(Al,Fe)Al3O2(SiO4)2(OH)4

1 Beryl – Be3Al2Si6O18

2 Tourmaline – (Na,Ca)(Mg,Fe,Mn,Al)3(Al,Mg,Fe)6Si6O18(BO3)3(OH,F)4

1 Lawsonite – CaAl2Si2O7(OH)2·H2O

2 Epidote – Ca2(Al,Fe)3Si3O12(OH)

1 Kaolinite – Al4Si4O10(OH)8

2 Montmorillonite – (Na,Ca)0.3(Al,Mg)2Si4O10(OH)2·nH2O

3 Illite – KAl2(Si,Al)4O10(H2O)(OH)2

4 Pyrophyllite – Al2Si4O10(OH)2

5 Talc – Mg3Si4O10(OH)2

6 Muscovite – KAl2(AlSi3O10)(OH)2

7 Biotite – K(Fe,Mg)3(Al,Fe)Si3O10(OH,F)2

8 Lepidolite – K(Li,Al)3(Si,Al)4O10(OH,F)2

9 Chlorite – (Fe,Mg,Al)5–6(Si,Al)4O10(OH)8

1 Tremolite‐actinolite – Ca2(Fe,Mg)5Si8O22(OH)2

2 Spodumene – LiAlSi2O6

3 Wollastonite – CaSiO3