Geo helpful study

1. Lecture 2 - Ore Deposit Classification
and Ore Reserves
Dr. Solomon Buckman
Rm P1-39
Email: solomon.buckman@unisa.edu.au
Field Mapping and Economic Geology
EART 4002 (012999)

2. Mineral Resources and Ore Reserves
Go to http://www.jorc.org/main.php?action=4 to download a copy of the JORC
Code and Guidelines for reporting Mineral Resources and Ore Reserves
JORC Code

3. JORC Code
• Who has heard of the JORC Code?
• Why is the classification and public reporting of ore reserves so
important?
• The main principles governing the operation and application of
the JORC Code are transparency, materiality and
competence.
– Transparency requires that the reader of a Public Report is provided
with sufficient information, the presentation of which is clear and
unambiguous, to understand the report and is not misled.
– Materiality requires that a Public Report contains all the relevant
information which investors and their professional advisers would
reasonably require, and reasonably expect to find in the report, for the
purpose of making a reasoned and balanced judgement regarding the
Exploration Results, Mineral Resources or Ore Reserves being reported.
– Competence requires that the Public Report be based on work that is
the responsibility of suitably qualified and experienced persons who are
subject to an enforceable professional code of ethics.
• As an exploration or mining geologist you must be familiar with
this code for reporting purposes. It is also a good guide for
writing geological reports in general.

4. Joint Ore Reserves Committee
(JORC) Code

5. Reporting of Exploration Results

6. Reporting of Exploration Results

7. Misleading
reporting

8. Mineral Resources and Ore Reserves
• 20. A 'Mineral Resource' is a concentration or occurrence of material of intrinsic economic
interest in or on the Earth's crust in such form and quantity that there are reasonable
prospects for eventual economic extraction. The location, quantity, grade, geological
characteristics and continuity of a Mineral Resource are known, estimated or interpreted
from specific geological evidence and knowledge. Mineral Resources are sub-divided, in
order of increasing geological confidence, into Inferred D21 , Indicated D22 and Measured
D23 categories.
• 29. An 'Ore Reserve' is the economically mineable part of a Measured or Indicated Mineral
Resource. It includes diluting materials and allowances for losses which may occur when the
material is mined. Appropriate assessments, which may include feasibility studies, have
been carried out, and include consideration of and modification by realistically assumed
mining, metallurgical, economic, marketing, legal, environmental, social and governmental
factors. These assessments demonstrate at the time of reporting that extraction could
reasonably be justified. Ore Reserves are sub-divided in order of increasing confidence into
Probable Ore Reserves D30 and Proved Ore Reserves D31 .
• 30. A 'Probable Ore Reserve' is the economically mineable part of an Indicated, and in
some circumstances Measured Mineral Resource. It includes diluting materials and
allowances for losses which may occur when the material is mined. Appropriate
assessments, which may include feasibility studies, have been carried out, and include
consideration of and modification by realistically assumed mining, metallurgical, economic,
marketing, legal, environmental, social and governmental factors. These assessments
demonstrate at the time of reporting that extraction could reasonably be justified.
• A Probable Ore Reserve has a lower level of confidence than a Proved Ore Reserve.
• 31. A 'Proved Ore Reserve' is the economically mineable part of a Measured Mineral
Resource. It includes diluting materials and allowances for losses which may occur when the
material is mined. Appropriate assessments, which may include feasibility studies, have
been carried out, and include consideration of and modification by realistically assumed
mining, metallurgical, economic, marketing, legal, environmental, social and governmental
factors. These assessments demonstrate at the time of reporting that extraction could
reasonably be justified.
• 32. The choice of the appropriate category of Ore Reserve is determined primarily by the
classification of the corresponding Mineral Resource and must be made by the Competent

9. Classification of Ore Deposits
• No two ore deposits are the same!
However, they can be divided into broad
classes eg syngenetic (BIF) vs epigenetic
(vein)

10. Discordant Orebodies
• Regularly shaped bodies
– Tabular – veins, faults. Divides footwall and hanging
wall
– Tubular – pipes or chimneys (vertical) and mantos
(horizontal)
• Irregularly shaped bodies
– Disseminated deposits eg diamonds in kimberlites,
closely spaced veins called a stockwork
– Irregular replacement deposits eg magnesite
replacement of limestone, skarn

11. Concordant Orebodies
• Sedimentary host rocks
– particularly important for base metals and
iron.
– Parallel to bedding and limited development
perpendicular to it, thus strataform. Not to be
confused with stratabound, which refers to
type of orebody, concordant or discordant,
which is restricted to a particular part of the
stratigraphic colomn

12. Stratiform
Deposits

13. Sedimentary host rocks
• Limestone hosts
– Very common host for base metal sulfide deposits
– Due to their solubility and reactivity they become
favourable horizons for mineralisation
• Argillaceous hosts
– Shale, mudstone, argillites and slates
– Eg Kupferschiefer copper bearing shale, 1m thick
over 136 km2.
• Arenaceous hosts – next slide
• Rudaceous hosts
– Alluvial gravels and conglomerates often host placer
deposits of gold, PGE’s and Uranium
• Chemical sediments
– Iron, manganese, evaporite and phosphorite
formations

14. Arenaceous
Hosts
• Heavy minerals
in beach sands
eg Crowdy
Head, NSW
• Unconsolidated,
easy to process
using gravity
settling
techniques
• Formed by
marine
regressions and

15. Igneous Host Rocks
• Volcanic hosts
– Volcanic-associated massive sulfide (VMS)
deposits. Important source of base metals.
Consist of >90% pyrite and generally
stratiform bodies.

16. Igneous Host Rocks
• Plutonic hosts
– Layered mafic intrusions
• Rythmic layering in the form of alternating bands of
mafic and felsic minerals
• Host to chromite, magnetite, ilmenite and PGE’s
• Stratiform, great lateral extent eg Bushveld
– Komatiites
• Nickel-copper sulfide ores formed by the sinking of
an immiscible sulfide liquid to the bottom of a
magma chamber or lava flow. Liquation deposits.
• Sulfides usually accumulate in hollows at the base of
the magma forming conformable sheets or lenses

17. Residual Deposits
• Formed by the removal of non-ore
material from proto-ore.
• Eg leaching of silica and alkalis from a
nepheline syenite may leave behind a
surface capping of hydrous aluminum
oxides, called bauxite.
• Eg weathering granite – kaolinite
• Eg laterite can enrich nickel from
peridotites

18. Supergene Enrichment
• Groundwater circulation can lead to
redistribution of metals above the water
table

19. Textures and Structures of
Ore and Gangue Minerals

20. Terminology – Ore Deposits
• Ore
• Gangue
• Waste
• Grade
• Cut-off
• Reserves
• Host rock
• Country rock
• Hydrothermal
• Alteration *
• Metamorphism *
• Vein
• Replacement
• Massive sulphide
• Skarn
• Epigenetic
• Syngenetic
• Gossan

21. Terminology - Deposit Scale
Structure
• Concordant
• Discordant
• Stratiform
• Stratabound
• Footwall
• Hangingwall
• Fault
• Shear zone
• Lode, shoot
• Breccia
• Stockwork
• Chimney
• Manto

22. Terminology - Hand specimen scale structure
• Banding
Banding may represent small scale sedimentary layering in a syngenetic
deposit such as a massive sulphide or repeated pulses of mineralization in a
vein.
• Crustiform banding
When minerals grow within a vein, they often grow inwards from the vein
wall. Several layers of different types of minerals, representing different
pulses of hydrothermal fluids passing through the structure, may be
observed in a single vein. These bands are often aligned symmetrically
away from the center of the vein.
• Comb structure
When minerals crystallize inwards from opposite walls of a vein, they often
meet in the center to form an interdigitating pattern of crystals, usually
quartz, which has an appearance similar to a rooster's comb.
• Vug
This is an open space or cavity, usually within a vein.
• Cockscomb
This is a crustiform banding when it surrounds breccia fragments.

23. Crustiform banding

24. Fluid Inclusions
• Formed during crystal growth and provide us with a
sample of the ore forming fluid
• Yield crucial geothermometric data and tell us about
the physical state of the fluid eg boiling
• Most fluid inclusion work carried out on transparent
minerals such as quartz, fluorite and sphalerite
• Principle matter is water and carbon dioxide.
• 4 groups of inclusions
– Type 1 – two phase, principally water with some vapour
– Type 2 – two phase, principally vapour with some water
– Type 3 – three phase, water-vapour-halite, contain daughter
mineral that have crystallised from solution
– Type 4 – CO2-rich inclusions, CO2 liquid.

25. Fluid inclusions
• Fluids trapped in small crystal imperfections
• Can reveal information about the nature of ore
forming fluids ie exceedingly strong brines form at
depth indicating chloride in hydrothermal solutions is
a potent solvent of metals through the formation of
metal-chloride complex ions (ligands)

26. Wall Rock Alteration
• Argillic – clay minerals (dickite, kaolinite, pyrophylite,
montmorillonite)
• (Na,Ca) 0.33(Al,Mg) 2Si4O10(OH)2·nH2O
• Sericitization
3KAlSi3
O8
+ 2H+  KAl3
Si3
O10
(OH)2
+ 6SiO2
+ 2K+
K-feldspar Sericite Silica
[Ca, Na]AlSi3
O8
+ K+ + 2H+  KAl3
Si3
O10
(OH)2
+ 6SiO2
+ 3[Na+, Ca+]
Plagioclase and Albite Sericite Silica
• Propylitic - Characterized by chlorite, calcite and minor epidote. Mafic
minerals highly altered and plagioclase less so
• Chloritisation
4H+ + 2K(Mg,Fe)3(Si3Al)O10(OH)2  Al(Mg,Fe)5(Si3Al)O10(OH)8 + (Mg,Fe)2+ + K+ + 3SiO2
Biotite Chlorite Quartz
• Carbonatisation – ppt’n of carbonates (calcite, dolomite,
magnesite, siderite)
• Potassic – secondary biotite, orthoclase, chlorite
• Silicification – addition of silica (Quartz, chalcedony)

27. Figure 3-3 Photograph of thin section 17 showing chloritisation
and associated opaques in this case most likely Fe oxides (f.o.v
1mm / PPL).

28. Theories of Ore Genesis
• Internal Processes
– Magmatic crystallisation
• Diamonds in kimberlites, feldspar in pegmatites
– Magmatic segregation
• Fractional crystallisation
• Liquation
– Hydrothermal processes
• Sources of the solutions and their contents
– Meteoric water
– Sea water
– Deeply penetrating ground water
– Metamorphic water
– Magmatic water
• Means of transport (ligands)
– Lateral secretion
– Metamorphic processes

29. Fluid
Sources

30. Geothermal
Systems

31. Lateral Secretion

32. Metamorphic Processes

33. Origin Due to Surface
Processes
• Exhalative processes (volcanic and
sedimentary) - exhalites

34. VMS Formation

35. VMS Fluid Circulation

36. Stages of
VMS
Develop-
ment &
Zoning

37. Hydraulic Fracturing
• Fracturing of rock by water under high
pressure
• Increases permeability
• Transport and deposition of ores

38. Fracturing