min 2030 final exam: Part 1 - Lecture 5 - Elements Sulphides Oxides Hydroxides

Native Elements (& Alloys)

Minerals composed of a single element uncombined with other

elements

•Metallic elements

•Semi-metallic elements

•Non-metallic elements

•Multiple metallic elements occurring as an alloy

most common native metals

gold, silver, copper

rare native metals

mercury, platinum

extremely rare native metals

lead, iron, zinc (very reactive)

How do you tell apart gold, silver, and copper from sulphide minerals? •E.g., pyrite, galena, stibnite, chalcopyrite, etc.

malleability, also colour, density etc

gold deposits

• epithermal, orogenic, placer deposits

• sometimes forms an alloy with silver

placer deposits

• Native gold eroded from rock and re-deposited in

sedimentary environment.

• High density leads to its concentration by fluvial

processes or beach wave action.

silver

• (bound in sulphides) commonly produced as a by product in mining

• occurs in:

  • lithogene deposits

  • magmatic hydrothermal vein deposits

  • five element vein deposits

lithogene deposits

Leaching, transport, and deposition of metals from sedimentary rocks in rift settings. Can include enrichment in Pb-Zn, Cu, or Co-Ni-U

Five-element veins

Hydrothermal vein deposits enriched in Ag-Co-Ni-Bi-As

copper

will typically be

encountered in:

•Hydrothermal deposits in brecciated

basalts (continental rift)

• oxide and enriched zones of supergene Cu deposits

platinum group deposits

• generally occurs as an alloy with Fe

• can be found in placers

native arsenic

•Typically massive or botryoidal

•Tin-white but tarnished to dark

grey or black (oxidized to

arsenolite)

•Metallic to sub-metallic if

crystalline and fresh surface

•Usually dull luster

•Brittle

•Poisonous

native sulphur

• Common in volcanic fumaroles

• You may see this in some

mineral deposits

• Bright yellow, smells like

sulphur when burned or

powdered

• transparent

• encountered in some sulphide ore deposits

semi, non-metallic elements

• carbon polymorphs

• graphite

• diamond

sulphides and sulphosalts

• important ore minerals of Pb, Zn, Ag, etc

• most frequently occurring: pyrite, pyrrhotite, chalcopyrite, sphalerite, galena

• oxidize and breakdown easily in near surface environments

  • cause of acid mine drainage (pollution)

• abundant in variety of mineral deposit types, where metals are enriched in hydrothermal fluids

stibnite

• Sulphide

• Sb₂S₃

• Silvery

• Soft (Moh’s 2)

• Flexible but not elastic

• Perfect cleavage in one

direction may be apparent

in massive stibnite

• Typical habit is as radiating,

acicular, or long prismatic

crystals

low-T hydrothermal deposits

• shallow

• feed hot springs

• As-Sb sulphide deposits

• Hg-sulphide deposits

As-Sb sulphide deposits

-Realgar: AsS–red –light sensitive

•Orpiment: As2S3–orange-yellow

•Stibnite: Sb2S3

•Pyrite, chalcopyrite, arsenopyrite, etc.

Hg sulphide deposits

-Cinnabar: HgS, deep red

•Native mercury: Hg, liquid

•Pyrite, marcasite,

sometimes stibnite

Mississippi valley type (MVT) deposits

• hosted in sedimentary carbonates

• typical gangue minerals: carbonates and accessory sulphates

Volcanogenic Massive Sulphide (VMS) deposits

• form on or below the seafloor due to volcanic and hydrothermal activity

• sulphur comes from seawater near the mid ocean ridge

• pyrite, chalcopyrite, sphalerite, galena, barite, quartz

bornite

•Cu₅FeS₄

•Copper-red to bronze brown on

fresh surfaces

•Moh’s~3

•Oxidizes fairly rapidly to have blue

or purple iridescent coating

• Informally called “peacock ore”

•Orthorhombic

•Usually massive, anhedral

copper porphyry deposits

•Hydrothermal deposits

formed from fluids

originating from a

magmatic intrusion

•Accompanied by

characteristic metasomatic

alteration

• very low grades compared to other sulphide deposits

supergene mineralization

•Leaching and re-deposition of

metals by meteoric water

circulation in the near-surface

•Higher Cu grades

•Oxide zone: Cu carbonates,

oxides, hydrated silicates

•Enrichment zone: Cu sulphides

supergene enriched zone minerals

• chalcocite

  • dark grey black, metallic, tabular

• covellite

  • deep blue iridescent, submetallic, basal cleavage

• bornite

  • blue to purple iridescent, metallic, massive

gossan

rust coloured oxide and hydroxide minerals that cap an ore deposit

weathering of Cu bearing sulphides…

may produce thin crusts of malachite or azurite

oxides

mostly have a high degree of symmetry

• widely distributed as accessory minerals

• do not contain other anionic groups- except ice

ice

• most common oxide on earths surface

• h₂O

• hexagonal

• 1.5 mohs

cuprite

• Cu₂O

• isometric-octohedral

• dark red-brownish red

• submetallic

• transparent- opaque

• mohs 3.5-4

• associated with native Cu

oxides- X₂O

ice and cuprite

oxides- XO

periclase and zincite

oxides- XY₂O₄

• spinel group: spinel series, chromite series, magnetite series

• chrysoberyl

oxides- spinel

• MgAl₂O₄

• common in Fe-poor, Mg rich environments

• dolomitic marble

• carbonate hosted serpentines

• usually black, greyish purple

  • purple/blue= low Fe

  • green-black=more Fe

• generally octahedral

• streak: white

• hardness: 7.5-8

oxides- hercynite

• black

• similar physical properties to spinel

oxides- chromite series

• chromite- FeCr₂O₄

• magnesiochromite- MgCr₂O4

• chromite is more common

• important ore of chromium

• octahedral crystals (but appears massive)

• mohs 5.5-6

• metallic to submetallic

• black, brown streak

oxides- magnetite

• spinel group

• Fe₃O₄

• magnetic

• octahedral

• metallic

• mohs 5.5-6.6

• black, black streak

• opaque in thin section (unlike spinel series)

spinel group

• spinel series

• chromite series

• magnetite series

oxides- chromite

• FeCr₂O₄

• forms in magma and settles by gravity (dense, sinks to the bottom)

oxides- chrysoberyl

• uncommon beryllium mineral

• BeAl₂O₄

• orthorhombic

• important gemstone

Oxides- X₂O₃

• hematite

• corundum

• ilmenite

oxides- hematite

• Fe₂O₃

• trigonal

• hardness 5-6

• massive, platy, or botryoidal

• red-brown streak

Banded iron formations

• Archean chemical sedimentary

rocks

• Alternating layers of iron oxides

(magnetite + hematite) and chert

(silica)

• Thought to have formed in sea

water from the combination of

dissolved Fe with oxygen

produced by cyanobacteria

oxides- corundum

• Al₂O₃

• trigonal

• hardness 9

• hexagonal crystals, tabular to prismatic

• transparent in thin section

• high RI

• commonly brown, black, white, bluish, yellowish

  • sapphire- blue, yellow, orange

  • ruby- red

• found in Al-bearing, Si-poor rocks

  • marble, Al-rich gneiss, nepheline syenites

oxides- ilmenite

• FeTiO₃

• trigonal

• mohs 5-6

• black, black streak

• metallic

• similar to hematite but different streak

• important Ti ore mineral

oxides- Rutile

• TiO₂

• very common accessory mineral

• mined for Ti

• reddish-brown, black, yellow

• reddish brown in thin section

• tetragonal

• white streak

• submetallilc

• twinning common

oxides- cassiterite

• SnO₂

• ore of tin

• adamantine/submetallic

• reddish brown to black

• tetragonal

• twinned along same law as rutile

• transparent in thin section

• uncommonly botryoidal- wood tin

• uncommon but present in some hydrothermal vein deposits and placer deposits

oxides- uraninite

• UO₂

• massive or cubic/octahedral

• pitchblend- massive, granular or botryoidal

• isometric

• opaque, black

• brownish black to grey streak

• radioactive

oxides- XO₂

• rutile

• cassiterite

• uraninite

hydroxides

• commonly produced by weathering or hydration of other minerals

• commonly occur as fine-grained aggregates, intermixed with other minerals

hydroxides- brucite

• Mg(OH)₂

• trigonal with basal cleavage

• hardness 2.5

• pearly/waxy

• typically found in marble as alteration of high T MgO mineral

• associated with serpentine in metamorphosed carbonate platforms

hydroxides- goethite

• FeO(OH)

• orthorhombic

• massive or botryoidal

• dark brown- black

• yellowish brown streak

hydroxides- limonite

• General term for rust

coloured mixtures of Fe

hydroxide (goethite or its

polymorph, lepidocrocite)

and other low-T alteration

minerals

• Common in weathered

near-surface rocks (outcrops), can be porous

hydroxides- bauxite

• General term for mixture of Al-hydroxide minerals

• Low-T surface alteration in tropical settings: Extensive weathering and leaching of most elements leaving enriched Al

• Gibbsite Al(OH)₃

• Boehmite and Diaspore, AlO(OH)

mn oxides and hydroxides

• not commonly encountered as distinct crystals

• typically as crusts or dendrites

manganese nodules

• sea floor, Mn oxides/hydroxides precipitating directly from seawater and sedimentary pore fluids