EARTH 471 - Mineral Deposits

Chris Yakymchuk

Estimated reading time: 1 minutes

Table of contents

From baidu:

矿床(mineral deposit)是指在地壳中由地质作用形成的,其所含有用矿物资源的数量和质量,在一定的经济技术条件下能被开采利用的综合地质体。一个矿床至少由一个矿体组成,也可以由两个或多个,甚至十几个乃至上百个矿体组成。由地质作用形成的、有开采利用价值的有用矿物的聚集地。包括地质的和经济的双重含义。矿床是地质作用的产物,但又与一般的岩石不同,它具有经济价值。矿床的概念随经济技术的发展而变化。19世纪时,含铜高于0.5%的铜矿床才有开采价值,随着科技进步和采矿加工成本的降低,含铜0.4%的铜矿床已被大量开采。

From wiki:

The mineral pyrite or iron pyrite, also known as fool’s gold, is an iron sulfide with the chemical formula FeS2 (iron(II) disulfide). Pyrite is considered the most common of the sulfide minerals.

Lec 2


Ore Textures

You will encounter these in labs.

  • Iron oxide ore minerals
    • Hematite - Fe_2O_3
    • Magnetite - Fe_3O_4
  • Sulphide orminerals
  • Copper one minerals
    • Chalcocite - Cu_2 S
    • Digenite - Cu_9 S_5
  • Other sulphide orminerals
    • Arsenoprite
  • Other ore minerals
    • Cobaltite - CoAsS (bonus mark)

Other minerals you already know: Rutile, Epidote, Calcite..

Ore mineral identification

  • Cleavage
  • Streak
  • Colour
  • Hardness
  • Density (specific gravity)

Unless you have a pristine and large minerals, these properties are hard to determine.

Reflected light microscopy

Many ore minerals are opaque in transmitted light.

  • start with low power
  • polarizer: will explore in lab

Mount preparation

  • Polished surface: need to be flat. Need Specimen levelling press to create flat surface.


High/low relief

Important Properties

With analyzer

  • Colour
  • Reflectance
  • Shape or Habit
  • Zoning
  • Cleavage
  • Hardness
  • Bireflectance: reflectivity change in plane polarized light as the state is rotated. Best example: Covellite

Without analyzer

  • Anisotropic v. isotropic
  • Polarization colours
  • internal reflection

Textures represent the spatial relationships within and between grains.

Paragenetic sequence: Relative sequences of ore mineral growth.

  • Inclusion/host relationships
  • Replacement texture

Hydrothermal Alteration (an intro)

hot water.

Alteration: a huge subject.

Gossan: rusty coloured alteration.

Sericite: Easy to recognize under the microscope.

Chlorite: Soft and green powder when scratched.

Epidote: ‘pistachio’ green color

Hydrothermal Alteration

  • Lots of jargon and loosely used terminology

Alternation names:

  • may be regional (dalmationite (bad name))
  • Field terms


  • Propylitic: green colour
  • Argillic (e.g. clay)
  • Silicic
  • Greisen: Commonly found in Australia

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