Introduction to Mineralogy Dr Introduction to Mineralogy Dr. Tark Hamilton Chapter 15: Lecture 33-c Systematic Mineralogy Chemistry of Sulfides Camosun College GEOS 250

Mineral Chemical Classification Families based on chemical types: Silicate, Sulfide, Element Groups: Similar structures e.g rhombohedral carbonates, orthorhombic pyroxenes Series: Common structure & related cation substitutions e.g. Augite-Hedenbergite Pyroxenes, Pyrope-Almandite-Spessartite Garnet Species: A single mineral with 1 structure, definite composition Calcite, Gold Varieties: Unusual colours, chemical substitutions, analyses Chromian (Cr+3) diopside, Ferrian (Fe+3) annite, Manganoan (Mn+2) Calcite, Quartz (var. Adventurine, Amethyst, Citrine etc.)

Crystal Structure of Native Elements Weak Metallic Bonding: Closest pack array of metal ~cations + Conduction band electrons shared as a uniform crystal field Few Common Lattice Types: 4 points-FCC-12 cn, HCP, 2 points BCC-8 cn 12-fold coordination: || {111} plane, 3-fold axis

Sulfides: Wurtzite vs Enargite Cu3AsS4 fig_15_09 Striated pseudohexagonal 5 mm mm2 Orthorhombic prisms on quartz, Furtei Mine Sardinia Italy, Photo Antonio Gamboni, Mindat.

Juan de Fuca Ridge Black Smokers – VMS Chimneys – Vent Communities

Chalcocite: Cu2S Monoclinic 2/m below 105°C, Hexagonal above Chalcocite: Cu2S Monoclinic 2/m below 105°C, Hexagonal above. Shining lead grey tarnishing to black. Sectile poor (110) Cleavage. Abundant ore mineral in Porphyry Copper Deposits. Assiciated with blue to black Digenite Cu9S5 and black to dark grey Djurleite Cu31S16. Massive rarely well formed crystals. With blue tarnished Bornite, Cu Creek Mine Mamainse Point, Algoma Ontario, Photo M. Wilson, Mindat. fig_15_18

Cross Section of a Cu Sulfide Bearing Ore Deposit & Weathering Environments fig_box15_03a Mal, Azu carbonate hydroxides, Cuprite + Tenorite Oxides, Chrysocolla phosphate

Cu Minerals: Stability and Solubility for oxidation state versus acidity in aqueous solutions CuSO4-5H2O Cu2CO3(OH)2 Cu+2 CuO2-2 CuS Cu2S Cu0

As per Klein and Dutrow fig_box15_03b

Galena Crystal Forms: a) Cube (100) & b,c) Cube + Octahedron (100) + (111) fig_15_19

Hydrothermal + Skarn + Igneous Iron deficient, Magnetic, Mono-sulfides Pyrrhotite Crystal Monoclinic 2/m Prismatic (pseudohexagonal or pseudo cubic) Fe1-xS Hydrothermal + Skarn + Igneous Iron deficient, Magnetic, Mono-sulfides Setting: Massive Sulfide deposits, Skarns, Porphyries Association: Pentlandite, Magnetite, Chalcopyrite fig_15_23

A Phase Diagram for Fe-Sulfide Minerals fig_15_24

Pentlandite (Fe,Ni)9S8 4/m32/m hexoctahedral contains up to 40% Co for Ni, Occurs as exsolution lamellae in Pentlandite. Notable Octahedral Parting & non-magnetic character distinguish this from yellowish bronze Pyrrhotite. Common ore mineral Sudbury Ontario in Norites (Enstatite Gabbros). Sample 5.4 cm tall: Pyrrhotite (grey) > Chalcopyrite (gold-brassy) > Pentlandite. fig_15_26

Realgar 2/m Prismatic AsS – Earthy Encrustations Supergene Sulfarsenide mineral, Arid settings fig_15_27

Orpiment 2/m prismatic As2S3 Foliated habit and perfect (010) Cleavage distinguish from Sulfur fig_15_28

Stibnite Sb2S3 2/m2/m2/m Prismatic pseudotetragonal, striated across prism faces splendent silver Fuses easily in a candle flame, low melting point, black streak fig_15_29

Structure of Stibnite Projected along (001), The c axis zig-zags within the hatched regions. fig_15_31

Tetrahedrite 43m: Cu12Sb4S13 solid solution Tennantite Cu12As4S13 Tetrahedral Crystal Forms: o(111), n(121) (011) not shown but makes 3 faces on the corners Pb + Hg substitute for Cu, Freibergite contains up to 18% Ag for Cu and is an ore of Ag fig_15_39

Isothermal Slice of the Phase Diagram for Sulfur-Copper-Iron Mineral Stability Fields & Tie Lines for Co-existing Phases fig_box15_04

table_15_01