Lecture 17 (11/27/2006) Systematic Description of Minerals Part 1: Native Elements and Sulfides

Mineral Classifications  Principally by dominant anion or anionic group  Secondarily by internal mineral structure Native Element Sulfides (S) Sulfosalts (AsS) Oxides (O) Hydroxides (OH) Halides (Cl, F, Br, I) Carbonates (CO 3 ) Sulfates (SO 4 ) Phosphates (PO 4 ) Nitrates, Borates, Tungstates, Molybdates, Arsenates, Vanadates... Silicates Nesosilicates Nesosilicates Sorosilicates Sorosilicates Cyclosilicates Cyclosilicates Inosilicates Inosilicates Phyllosilicates Phyllosilicates Tectosilicates Tectosilicates

Native Elements  Metals – Gold, Silver, Copper, Platinum, Palladium, Osmium, Iridium, Iron, Fe-nickel  Semi-metals – Arsenic, Bismuth, Antimony  Non-metals – Sulfur, Diamond, Graphite

Native Metals  metallic bonding  dense, cubic close packing  properties: soft, malleable, ductile, sectile, good heat and electrical conductors  variable melting points: low-Au, Ag, Cu; high-PGEs Au AgCuPt

Native Non-metals SulfurDiamondGraphite S 8 ring molecules bonded by weak van der Waals forces C 6 ring molecules bonded by weak van der Waals forces; good electrical conductivity StrongCovalentBonds Synthetic (industrial) Diamonds

Native Element Occurrences Gold – Hydrothermal fluids related to magmatism; commonly occurs in veins quartz and pyrite; may form detrital grains to produce placer deposits; Rarely occurs alloyed with other elements. Silver – Hydrothermal ore deposits rich in sulfide, arsenides, and bismithides; also commonly associated native copper. Copper – Sulfide-poor hydrothermal ore deposits or secondary oxidation of Cu-sulfide minerals; most abundant occurrence is the native copper deposits of the Keweenawan Peninsula of Upper Michigan where it occurs in lava flows and interflow conglomerates. Platinum – Occurs as primary deposits in mafic intrusions and as secondary placer deposits. Diamond – Occurs in mantle-derived kimberlite pipes with other high temperature/high pressure minerals Sulfur – Precipitates near volcanic vents from volcanic gasses and secondarily by oxidation of sulfide minerals.

Sulfides and Sulfosalts  Most common ore source of metals  X m S n  As may substitute for S giving rise to sulfarsenides, and arsenides  X= Fe, Cu, Zn, Pb, Ni, Co, Hg, Mo  Magmatic and hydrothermal origin  Sulfosalts, As, Sb, and Bi take the place of metals (X)

Sulfide Stability Reducing, Acidic Environment Cu-H 2 O-O 2 -S-CO 2 phase diagram at 25°C and 1 atm pressure

Cu-Fe Sulfide Minerals Py Po Cp Bn Cc Dg Cv

Other Common Sulfide Minerals  Galena PbS - dense, cubic cleavage  Sphalerite (Zn,Fe)S – submetallic black to resinous yellow, brown luster  Pentlandite (Fe,Ni) 9 S 8 – yellow- bronze; w/ Cp and Po in magmatic ores  Cinnabar HgS – vermilion-red color, dense  Molybdenite MoS 2 – silver metallic sheets Pt Galena Zn>>Fe Zn>Fe Zn

Arsenosulfides, Arsenides and Sulfosalts Cobaltite (Co,Fe)AsS – silver white metallic Arsenopyrite FeAsS – silver white metallic Realgar AsS (red) - Orpiment As 2 S 3 (yellow) Stibnite Sb 2 S 3 silver-gray prisms Enargite Cu 3 AsS 4 – striated metallic columns and blades – a sulfosalt Skutterudite (Co,Ni)As 3 silver-gray cubes

Next Lecture 11/29/06 Systematic Description of Minerals Part 2: Oxides, Hydroxides Halides, Carbonates, Sulfates, and Phosphates Read: Klein Parts of Chaps. 9 & 10