Transcript Lecture 14 Native Elements and Sulfides mod 10

Lecture 14
Systematic Description of Minerals
1. Mineral Classifications
 Principally by dominant anion or anionic group
 Secondarily by internal mineral structure
Silicates
Native Element
Nesosilicates
Sulfides (S)
Sorosilicates
Sulfosalts (Sb2S3)
Cyclosilicates
Oxides (O)
Inosilicates
Hydroxides (OH)
Phyllosilicates
Halides (Cl, F, Br, I)
Tectosilicates
Carbonates (CO3)
Sulfates (SO4)
Phosphates (PO4)
Nitrates, Borates, Tungstates, Molybdates, Arsenates, Vanadates...
Minerals for term paper
electronics
Native Elements and Sulfides
are frequently the targets of mining companies
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 (“CCP”)
properties: soft, malleable, ductile, sectile, good heat and electrical
conductors
Melting points: low-Au, Ag, Cu
Au
Ag
Cu
Pt
Native Non-metals
Sulfur
Diamond
Graphite
Strong
Covalent
Bonds
C6 ring molecules
bonded by weak
van der Waals
forces; good
electrical
conductivity
S8 ring molecules
bonded by weak
van der Waals
forces
Synthetic (industrial) Diamonds
Native Element Occurrences
Gold – Hydrothermal fluids related to magmatism, especially late
fractionation; commonly occurs in veins of quartz and pyrite; may
form detrital grains to produce placer deposits; Rarely occurs alloyed
with other elements.
Silver – Hydrothermal ore deposits rich in sulfides, arsenides, and
bismuthides; 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.
Native Element Occurrences
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. Needs a subduction zone to
pressurize ocean floor carbon, the a rising plume to hit the right depth
in the subduction zone. That’s why they are rare.
Sulfur – Precipitates near volcanic vents from volcanic gasses and
secondarily by oxidation of sulfide minerals.
Sulfides and Sulfosalts
 Most common ore source of metals
 XmSn
 As (arsenic) 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 to Oxidizing,
Acidic to Basic
Environments
Eh-pH diagrams are used for
reactions that occur from
aqueous solutions at low
pressures. The voltage
across a galvanic cell and the
pH determine which mineral
precipitates in a laboratory
vessel containing all needed
elements. These atmospheric
pressure conditions model
the formation of many major
ores
Cu-H2O-O2-S-CO2 phase diagram
at 25°C and 1 atm pressure
High Temperature Low Pressure Sulfide formation at MORs
Cu-Fe Sulfide Minerals
Py
Cv
Po
Dg
Cp
Cc
Bn
Other Common Sulfide Minerals
Galena
Zn
 Galena PbS - dense, cubic cleavage
may contain substantial silver
Zn>>Fe
 Sphalerite (Zn,Fe)S – submetallic
black to resinous yellow, brown luster
Yellow streak
Zn>Fe
Pt
 Pentlandite (Fe,Ni)9S8 – yellowbronze; in magmatic ores
 Cinnabar HgS – vermilion-red color,
dense

Molybdenite MoS2 – silver metallic
sheets
Arsenosulfides, Arsenides and Sulfosalts
Cobaltite (Co,Fe)AsS – silver white metallic
Arsenopyrite FeAsS – silver white metallic
Realgar AsS
(red)
- Orpiment As2S3
(yellow)
Skutterudite (Co,Ni)As3 silver-gray cubes
Stibnite Sb2S3 silver-gray prisms
(Antimony sulfide)
Enargite Cu3AsS4 – striated metallic columns
and blades – a sulfosalt