Sulfide & related minerals

form nearly 600 minerals, few are abundant

have great economic value

Metals essential for industrial society extracted from sulfide include copper, zinc, lead, antimony, molybdenum, cobalt, nickel, silver

sulfur are law δ- than O, have about 10-20% ionic character (covalent or metallic)

There is no agreed on classification scheme

General Formula

MpXr

M: metal or semimetal
Such as: Fe, Zn, Cu, pb, Sb, or As

X: atoms
Such as: S, As, S + As, or Te

Sulfosalts

metal + semi-metal + sulfur

classified based on chemical notions that have long since been abandoned

SULFIDE PARAGENESIS

Hydrothermal Deposits: sulfide & related minerals characteristic of hydrothermal vein & replacement deposits, deposited from hot aqueous solutions in void spaces or by replacement of rock

Essential features of hydrothermal system:
1. Water
2. Heat
3. Source for metals precipitated by water
4. Migration pathways
5. Precipitation site

Water: may be meteoric, magmatic, metamorphic, or connate

Heat: by igneous intrusion, & burial

Source for metals precipitated by water: sulfur derived from crystallizing magma or leached out of rock by water

Migration pathways: Fluids flow via rock along fault, fracture, & normal pore space

Precipitation site: Minerals precipitate by filling spaces along faults, fractures, & in other voids, or by replacing minerals in rock

Supergene Processes

primary or hypogene mineralization produced in hydrothermal system extensively altered if exposed to nearsurface environment

metals found in sulfides form oxides, hydroxides, carbonates, & sulfates

Because reactions produce oxygen-bearing minerals at expense of sulfides, near zone is referred to as oxidized zone & result are called supergene or secondary minerals

Because pyrite are common sulfide, oxidized zones of most sulfide deposits colored yellow & red: iron oxides & hydroxide derived from it

These minerals insoluble & accumulate near surface to form encrusting mass “gossans”

Pyrite in deeper portions of super genealteration zone serve as host to extensive precipitation of copper sulfides in supergene enrichment process

sulfide-enriched or reduced zone: zone of concentrated mineralization at water table surface

Supergene processes cause extensive alteration of country rock hosting sulfide deposits

Excess acid produced by oxidation of sulfides neutralized by reaction with silicate & form clay

A typical reaction involves hydrolysis of K-feldspar (KAlSi₃O₈) to form kaolinite:
2KAlSi₃O₈ + 2H⁺ + H₂O
→ Al₂Si₂O₅(OH)₄ + 4SiO₂ + 2K⁺

Pyrrhotite Vs Pyrite

In Pyrrhotite principal variation in iron content 2Fe³⁺ + Φ –> 3Fe²⁺ (> 20% Φ)

Pyrrhotite has more bronze color, & softer

Pyrrhotite weakly magnetic

The End