![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)](https://image.slidesharecdn.com/oredepositclassification1-230114144037-3deca1f1/85/Ore-deposit-classification-1-ppt-26-320.jpg)
Ore deposit classification (1).ppt
- 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
- 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
- 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.
- 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
- 33. Origin Due to Surface Processes • Exhalative processes (volcanic and sedimentary) - exhalites
- 34. VMS Formation
- 37. Hydraulic Fracturing • Fracturing of rock by water under high pressure • Increases permeability • Transport and deposition of ores
- 38. Fracturing