Lecture 2: Prospecting to Proving


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Prospecting, Exploration, Exploration Model, Mineral Resources and Mineral Reserve

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Lecture 2: Prospecting to Proving

  1. 1. Topic 2: Prospecting for a mineral deposit and proving it A short series of lectures prepared for the Fourth year of Geology 2010- 2011 by Hassan Z. Harraz hharraz2006@yahoo.com Prof. Dr. H.Z. Harraz Presentation 14 November 2011 1 Mining Geology, Introduction
  2. 2. Definitions Mining The activity that removes from the earth’s crust the abnormal concentration of metal found in the deposit Mine An opening or excavation of the earth from which minerals are extracted Prof. Dr. H.Z. Harraz Presentation 214 November 2011 Mining Geology, Introduction
  3. 3. Why do we mine minerals? Prof. Dr. H.Z. Harraz Presentation14 November 2011 3 Mining Geology, Introduction
  4. 4. STAGES IN THE LIFE OF A MINE  Prospecting;  Exploration to discovery;  Developing Ore Deposit;  Models for Mineral Deposit;  Drill;  Mining Methods;  Mining techniques;  Mineral Processing techniques;  Reclamation. Prof. Dr. H.Z. Harraz Presentation14 November 2011 4 Mining Geology, Introduction
  5. 5. Identifying Mineral Deposits (costs $$$$$ to find them…) • Aerial photos, • Radiation detectors, • Magnetometer, • Gravimeter, • Deep well drilling, • Seismic survey, • Chemical analysis. Prof. Dr. H.Z. Harraz Presentation 14 November 2011 5 Mining Geology, Introduction
  6. 6. PROSPECTING FOR A MINERAL DEPOSIT AND PROVING IT Before a mineral deposit can be worked, it must first be found and its industrial possibilities must be made clear. – The work of finding the deposit is called PROSPECTING. – The establishment of the basic parameters and elements of the deposit, its quality and quantity (reserves), the type of country rock,...etc., is called PROVING. No sharp boundary exists between prospecting and proving. Each merges into the other, forming different stages of mining-geological exploration, but can be divided into three stages: i) Prospecting, Increasing the coast ii) Exploration and iii) Proving. Prof. Dr. H.Z. Harraz Presentation14 November 2011 6 Mining Geology, Introduction
  7. 7. i) Prospecting  Finding deposits or any ore sign.  Determine basic Parameters of elements in the deposits, rock type.  Complete geochemical prospecting survey. Type of geochemical Prospecting Surveys:  Stream sediment samples.  Soil samples.  Bedrock samples. Prof. Dr. H.Z. Harraz Presentation14 November 2011 7 Mining Geology, Introduction
  8. 8. ii) Exploration Methods In increasing order of cost per square km, exploration methods are: • remote sensing (satellite imagery); • geological mapping;In increasingorder of • geophysical surveys;cost / km2 • geochemical surveys (bulk sampling), • drilling: The goal of drilling is to define an orebody model. Prof. Dr. H.Z. Harraz Presentation 14 November 2011 8 Mining Geology, Introduction
  9. 9. iii) Proving Methods A) Preliminary proving The purpose of preliminary proving is to find out:- the quality of mineral (reserves) and its quality in relation to the current requirements of industry in a particular area. The information from the preliminary proving should give an all-round description of the deposit which will enable the cost of its detailed exploration to be estimated as well as the cost of the project for exploiting it.The following points should be cleared up:- a) The shape and area of the deposit; b) Its depth and angles of dip and strike; c) Its thickness and variations in thickness along the dip and strike; d) The properties of the surrounding rock and overburden; e) The degree of uniformity of distribution of mineral within the deposit; f) Its quantity and distribution in the country rock; g) The mineralogical and chemical composition of the deposit; h) The change in quality of mineral with depth and area i) Larger scale maps Prof. 500 or 1: 100. 1: Dr. H.Z. Harraz Presentation 14 November 2011 9 Mining Geology, Introduction
  10. 10. When the thickness of overburden is More gently sloping beds under asmall (<4m) and the angle of dip is small thickness of overburden andsteep, trenches are used for exploration high topographic area are prospected by vertical pits In very gently sloping beds, boreholes are used for exploration because neither trenches nor pits can give results. Under thick overburden, exploration with pits andNovember 2011 14 trenches becomes inappropriate. Prof. Dr. H.Z. Harraz Presentation 10 Mining Geology, Introduction
  11. 11. Consequence Remove covering rocks or any overburden outcrop Quality and Trenches (0.25 Quantity - 0.50 m deep) Collect channel Prospecting bedrock pits samples Prof. Dr. H.Z. Harraz Presentation14 November 2011 11 Mining Geology, Introduction
  12. 12. B) Detailed proving  Make more deeper borehole,  Make geological cross sections,  Samples are taken throughout, is divided into quality grades for chemical and industrial tests.  Determine the mineral reserves,  Determine mine zone, place of open, method of mine,  The manner of extraction is also established,  Flotation system.i) Orebody Models: Thegoal of drilling is to definean orebody model. Drillingis time-consuming andexpensive Prof. Dr. H.Z. Harraz Presentation14 November 2011 12 Mining Geology, Introduction
  13. 13. Where to Explore? • Scale Sequence. • Continent and country selection: based on tectonics, known mineral provinces and political stability. • Province and district selection: based on known deposits, geoscientific databases, maturity of previous exploration, recent discoveries. • Prospect scale selection: based on previous exploration results, are there immediate drill targets or favourable previous drill results? Prof. Dr. H.Z. Harraz Presentation14 November 2011 13 Mining Geology, Introduction
  14. 14. Developing Ore Deposit Models for Mineral ExplorationComponents of an ore deposit model Research on known deposits. Empirical model = Exploration Model: (Geophysical characteristics; Geological characteristics and Geochemical characteristics).  Conceptual model = Genetic Model : (Trap, Transport and source). Prof. Dr. H.Z. Harraz Presentation14 November 2011 14 Mining Geology, Introduction
  15. 15. ConceptualEmpirical Figure shows Components of an ore deposit model Prof. Dr. H.Z. Harraz Presentation 14 November 2011 15 Mining Geology, Introduction
  16. 16. Critical elements for genetic model  Tectonics controls magmatism, volcanism, heat- flow, structure, sedimentation, and composition of source rocks.  Structure and permeability controls fluid pathways.  Chemistry of fluids and source rocks controls metals transported and metals deposited in ores.  Both the fluid chemistry and the effectiveness of the trap controls ore grades.  The longevity of the system and size of the hydrothermal cell controls the size of deposit. Prof. Dr. H.Z. Harraz Presentation14 November 2011 16 Mining Geology, Introduction
  17. 17. Prof. Dr. H.Z. Harraz Presentation14 November 2011 17 Mining Geology, Introduction
  18. 18. Examples to Standard genetic models Models for Zinc deposits Models for Gold deposits VHMS Zn-Pb-Cu  Epithermal Au-Ag SEDEX Zn-Pb-Ag  Mesothermal Au MVT Zn-Pb  Orogenic Au Irish style Zn-Pb-Ag  Intrusion-related Au Carbonate Replacement  Archaean Lode Au Deposits (CRD)  Slate belt Au Zn skarns  Carlin type Au Pb-Zn veins around granites  Porphyry Au-Cu  Witwatersrand Au (Paleo-placer gold) Prof. Dr. H.Z. Harraz Presentation 14 November 2011 18 Mining Geology, Introduction
  19. 19. Criteria for determining Source Rocks  Regional geological relationships.  Timing of mineralization wall rock potential sources -source rocks must be pre-or syn-mineralization.  Composition of source rocks (e.g., basalts are good source rocks for copper; Ultramafics are source rocks for Ni; Dacites are source rocks for Pb, reduced granites are source rocks for Sn).  Isotopic tracers can be used to help define source rocks (e.g., Pb, Sr, Nd/Sm, Re/Os, S, C, O, H).Relevance of Source Rocks are a critical part of the Genetic Model. are important at the Province Scale -does this province or district have source rocks for copper? or gold? or …..etc. are hotly disputed by academics, but less relevant to explorers. Prof. Dr. H.Z. Harraz Presentation 14 November 2011 19 Mining Geology, Introduction
  20. 20. Figure shows Source of metals and S in VHMS deposits? Prof. Dr. H.Z. Harraz Presentation14 November 2011 20 Mining Geology, Introduction
  21. 21. Controls on Transport of MetalsFluid pathways from source to trap: i) Plumbing system: hydrology of hydrothermal system; importance of faults and permeable rock units. ii) Pressure regime: free convection or gravity drive or over-pressured rock package or tectonic drive? iii) Basement structures commonly control fluid pathways in upper crust.Fluid chemistry controls metal solubility i) Metals are commonly more soluble under: Higher T, lower pH, higher salinity ii) Oxidation state of fluid is important. iii) Fluid -rock chemical interaction occurs along the fluid pathway and may change metal solubility.Metal Complexes Enhance Solubility i) Base metals are commonly transported as chloride complexes: CuCl- , ZnCl2, PbCl3-, FeCl2….etc. ii) Gold may transport as a bisulfide or chloride complex: Au (HS)2-, AuCl2- Prof. Dr. H.Z. Harraz Presentation 21 14 November 2011 Mining Geology, Introduction
  22. 22. The Trap EnvironmentMaximum metal deposition occurs when a condition of gross chemical or physical disequilibrium exists between the ore fluid and the host rock environment (trap).This may be caused by: o Rapid drop in temperature. o Reaction with a chemically different rock (e.g., limestone). o Mixing with a chemically different fluid. o Change in redox (e.g., organic-rich shale). o Change in pH. Prof. Dr. H.Z. Harraz Presentation14 November 2011 22 Mining Geology, Introduction
  23. 23. Temperature trap on seafloor Redox trap at sandstone/shale boundary14 November 2011
  24. 24. Models are never complete or ever perfect, we need……  New field observations, data and research.  Up-date deposit model.  Modify ground selection criteria,.  Modify target ore style.Developing Ore Deposit Models for Mineral Exploration Prof. Dr. H.Z. Harraz Presentation 14 November 2011 24 Mining Geology, Introduction
  25. 25. MINERAL RESOURCE AND MINERAL RESERVE Fig.11: Relationship between Mineral Resources and Mineral Reserves Prof. Dr. H.Z. Harraz Presentation14 November 2011 25 Mining Geology, Introduction
  26. 26. Ore volume may be divided into blocks by using shafts, adits, levels…etc.These ore blocks can be considered belong to one of the following category. There are three standard categories for quoting ore reserves: Measured Or Proven Ore category: - Later to open mines, - The ore is blocked out and thoroughly sampled, - This is often referred to as ore-in-sight (Outlined from 4 dimensions), - Sample information is all from ore productive units. Indicated or probable Ore category : -It should only be used for ore that has been clearly outlined in 3 dimensions by drilling, pitting, trenching, ….etc. - Sample information is all from "drill indicated ore". Inferred Ore category: implies a degree of uncertainty and is used in cases where there is good geological evidence for continuity, but only a limited amount of sample data such as a few widely spaced boreholes. Prof. Dr. H.Z. Harraz Presentation 14 November 2011 26 Mining Geology, Introduction
  27. 27. Prof. Dr. H.Z. Harraz Presentation14 November 2011 27 Mining Geology, Introduction
  28. 28. SOLID MINERAL RESERVESa) Morphology of Reserve • Lode rock: – Ore rock – Barren rock • Ore rock: mixture of – Ore of mine grade – Barren rock extracted with ore • Barren rock: is divided into:- – Barren rock extracted separately: A part of the barren rock hoisted to the surface separately from the ore. – Barren rock extracted with ore: A part of the barren rock gets mixed with the ore during stoping extracted with ore. Prof. Dr. H.Z. Harraz Presentation14 November 2011 28 Mining Geology, Introduction
  29. 29. Fig.9: Mineral reserves and mining losses. Prof. Dr. H.Z. Harraz Presentation14 November 2011 29 Mining Geology, Introduction
  30. 30. Prof. Dr. H.Z. Harraz Presentation14 November 2011 30 Mining Geology, Introduction
  31. 31. Ore EvaluationTonnage (Q) = Volume * Tonnage Factor (Specific. Gravity) ……. TonnesOre reserve calculations= average grade * Tonnage (Q)Ore Price = Ore Reserve * Price Prof. Dr. H.Z. Harraz Presentation 14 November 2011 31 Mining Geology, Introduction
  32. 32. Mine Geology Responsibilities “Utilise the Mineral Resource to Maximise Profitability”1. Understand & Communicate controls on mineralization (mapping).2. Ensure a representative sample is collected.3. Accurately model and estimate grade.4. Design most profitable ore blocks .5. Deliver the predicted grade and tonnage of the ore blocks to the ROM by minimizing ore loss and dilution.6. Manage Acid Mine Drainage (AMD) according to best practise to minimize environmental impact.7. Tonnes and grade reconciliation and feedback to Exploration and Mine Planning. Prof. Dr. H.Z. Harraz Presentation 14 November 2011 32 Mining Geology, Introduction