How to identify Polymetallic Sulfide Ore in Carbonate

To correctly identify Polymetallic Sulfide Ore in Carbonate (Galena (PbS), Pyrite (FeS2), Enargite (Cu3AsS4) in a carbonate matrix), check each of these features in order. Many rocks and minerals look alike, so cross-reference multiple properties before deciding.

Step-by-step identification

1. 1

   Color

   Overall color and any zoning or banding

   Galena: Silvery-gray. Pyrite: Brassy-yellow. Enargite: Grayish-black to brownish-black, often with a purplish tarnish. Carbonate matrix: White, gray, buff, or light brown.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Galena: Bright metallic. Pyrite: Metallic. Enargite: Metallic to sub-metallic. Carbonate matrix: Vitreous to dull.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Crystalline, massive, granular, or disseminated. Sulfides can form euhedral crystals, anhedral grains, or massive aggregates within the carbonate matrix.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Galena: Cubic, cubo-octahedral, massive. Pyrite: Cubic, pyritohedral, octahedral, massive, radiating. Enargite: Orthorhombic, prismatic, tabular, massive. Carbonate: Rhombohedral, scalenohedral, granular.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Galena: Perfect cubic cleavage (three directions at 90°). Pyrite: None (conchoidal to uneven fracture). Enargite: Perfect prismatic cleavage (one direction), distinct pinacoidal (one direction). Carbonate: Perfect rhombohedral cleavage (three directions not at 90°).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, replacement deposits, skarns, and disseminated deposits within carbonate sedimentary rocks, often associated with fault zones, intrusive bodies, or volcanic activity.

Key Facts

Hardness

Galena: 2.5-2.75 (Mohs). Pyrite: 6-6.5. Enargite: 3. Carbonate (Calcite): 3. Carbonate (Dolomite): 3.5-4.

Specific Gravity

Galena: 7.4-7.6. Pyrite: 4.95-5.10. Enargite: 4.4-4.5. Carbonate (Calcite): 2.71. Carbonate (Dolomite): 2.85.

Crystal System

Galena: Isometric. Pyrite: Isometric. Enargite: Orthorhombic. Carbonate (Calcite/Dolomite): Trigonal.

Color

As described above, variable depending on the mineral.

Luster

As described above, metallic for sulfides, vitreous to dull for carbonate.

Transparency

Galena: Opaque. Pyrite: Opaque. Enargite: Opaque. Carbonate: Transparent to translucent.

Fracture

Galena: Subconchoidal to uneven. Pyrite: Conchoidal to uneven. Enargite: Uneven. Carbonate: Conchoidal to uneven.

Cleavage

Galena: Perfect cubic. Pyrite: None. Enargite: Perfect prismatic, distinct pinacoidal. Carbonate: Perfect rhombohedral.

Composition

Galena: Lead sulfide (PbS). Pyrite: Iron disulfide (FeS2). Enargite: Copper arsenic sulfosalt (Cu3AsS4). Carbonate: Calcium carbonate (CaCO3) for calcite, Calcium magnesium carbonate (CaMg(CO3)2) for dolomite.

Physical characteristics

• Crystal Habit: Galena: Cubic, octahedral, massive. Pyrite: Cubic, pyritohedral, massive. Enargite: Prismatic, tabular, massive. Carbonate: Rhombohedral, scalenohedral, granular, massive.
• Cleavage Type: Galena: Perfect {001} cubic. Pyrite: None. Enargite: Perfect {110} prismatic, distinct {001} pinacoidal. Carbonate: Perfect {1011} rhombohedral.
• Fracture Type: Galena: Subconchoidal to uneven. Pyrite: Conchoidal to uneven. Enargite: Uneven. Carbonate: Conchoidal to uneven.
• Tenacity: Galena: Brittle. Pyrite: Brittle. Enargite: Brittle. Carbonate: Brittle.
• Luster Type: Galena: Metallic. Pyrite: Metallic. Enargite: Metallic to sub-metallic. Carbonate: Vitreous to dull.

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