Forum Group Discussion: An Overview of Ore Minerals

Untitled-11Figure 1. Head of  Fieldtrip and Research Division opening the discussion

Ore deposits are rocks that contain one or more metallic minerals. It would have economic value when it is mined, which calls as ore minerals (only metallic minerals which can be extracted. If it is not, it cannot be said as ore minerals). A deposit called as an ore deposit based on its economic value, if production and market price is being fluctuated, it can be said so, if not it can be said as an ore deposit. Extracting process that produces metallic element and gangue can produce tailing.
  • Economic trap factors:
    1. Form of its trap
    2. Large and volume of reserve
    3. Content
    4. Geographical location
    5. Production cost

Most of ores come from ore minerals, which was deposited by hydrothermal solution. Hydrothermal solution comes from magmatic water, which released water during magma transmigration and magma cooling. Beside magmatic water, hydrothermal solution can be produced by meteoric water or sea water that circulated inside earth crust.

  • Geological enriched factors:
    1. Mineralization
    2. Weathering
    3. Metamorphism

Forming of minerals can be divided into 2 ways, those are:

  • Internal:
    1. Magma crystallization: ore minerals precipitation as major or minor component of igneous rocks
    2. Magma segregation: separation as a result of crystallization fractionation and connected processes during magma   differentiation
    3. Liquation: unmixed of magma. Releasing of sulphides, sulphides-oxides, or melt of magma oxides, which accumulated beneath silicates.
    4. Hydrothermal: deposited from magmatic water through magma body surface, metamorphic rocks, etc.
    5. Lateral secretion: ore material diffusion or gangue of origin rocks through fault or joint.
    6. Metasomatism : pyrometasomatism (skarn) which produced by replacing process of origin carbonate rocks.
  • External:
    1. Secondary enriched (supergene): releasing of valuable elements from top of mineral deposit then precipitated again in the deeper part of the deposit, and resulting higher concentration.
    2. Volcanic exhalation: exhalation of hydrothermal solution on earth surface, mostly in marine environment.
    3. Mechanical accumulation: concentrating ((heavy mineral)) into placer deposit.
    4. Sedimentary precipitation: precipitation of certain elements in certain sedimentary environment, whether with intervention by certain organism or not.
Genesis model of ore mineral deposits
Figure 2. Genesis model of ore mineral deposits

Distribution of mineral groups:
Siliceous ores (Keiko): containing sulphides, mainly chalcopyrite, disseminated inside silicified rocks.
2. Yellow ores (Oko): mainly pyrite, fewer chalcopyrite and quartz.
3. Black ores (Kuroko): strong mixing of Fe-rich sphalerite galena, barite, and small amount of pyrite and chalcopyrite; wurtzite, enargite, tetrahedrite,  marcasite, and also other minerals that found in small amount.
4. Vein and large amount of gypsum (sekkoko), connected by each other but in different bodies
5. Stringer zones, rich of chalcopyrite inside beneath ore pipes (ryukoko)
6. Ferruginous (tetsusekiei layer), bottom of layer is its place. 

Type of mineral deposit (Pohl, 2013)

  • Magmatic ore deposit
    1. Magmatic liquid deposits: Cr in ophiolite or layered intrusion with Pt, Fe/Ti, and Ni as its byproduct

    2. Pegmatite: Sn, Nb/Ta, Li, Be, etc
    3. Hydrothermal deposits:  Cyprus-type (VMS); skarn (W, Sn, Cu, etc), porphyry (Cu, Mo, Sn, etc); vein deposit (Sn, W, U); Au-Ag epithermal deposit; BIF (Algoma type)

  • Weathering product deposit
    1. Residual deposit: placer, bauxite, and Fe-Laterit
    2. Residual solution: Ni and Au Laterite deposit, enriched Mn, Fe, Cu, Ag

  • Sedimentary ore deposit
    1. Allochtone: alluvial and marine placer deposit (Au, Sn, Ti, REE)
    2. Autochthone: BIF (superior type), Mn nodule

  • Digenetic-hydrothermal deposit
    1. Kupferschiefer type: Cu, Pb, Zn
    2. Mississippi type (MVT): Pb-Zn-Ba-F on marine carbonates
    3. Deposit on salt dome: Pb-Zn-Ba-F
    4. Metamorphic-hydrothermal deposit
    5. Quartz vein on metamorphic (Au) or lode gold

Physically gold, pyrite, and chalcopyrite look alike based on their colors, though it still can be recognized by its density and gold fiber. Quartz, pyrite, arsenopyrite, and silver are associated with gold.