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

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. 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
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14 November 2011 Mining Geology, Introduction

3. Why do we mine minerals?
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Mining Geology, Introduction

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.
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Mining Geology, Introduction

5. Identifying Mineral Deposits (costs $$$$$ to find them…)
• Aerial photos,
• Radiation detectors,
• Magnetometer,
• Gravimeter,
• Deep well drilling,
• Seismic survey,
• Chemical analysis.
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Mining Geology, Introduction

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.
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Mining Geology, Introduction

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.
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Mining Geology, Introduction

8. ii) Exploration Methods
In increasing order of cost per square km, exploration methods are:
• remote sensing (satellite imagery);
• geological mapping;
In increasing
order of • geophysical surveys;
cost / km2
• geochemical surveys (bulk sampling),
• drilling: The goal of drilling is to define an orebody model.
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Mining Geology, Introduction

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.
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Mining Geology, Introduction

10. When the thickness of overburden is More gently sloping beds under a
small (<4m) and the angle of dip is small thickness of overburden and
steep, 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.
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Mining Geology, Introduction

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
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Mining Geology, Introduction

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: The
goal of drilling is to define
an orebody model. Drilling
is time-consuming and
expensive
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Mining Geology, Introduction

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?
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14. Developing Ore Deposit Models for Mineral
Exploration
Components 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).
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Mining Geology, Introduction

15. Conceptual
Empirical
Figure shows Components of an ore deposit model
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Mining Geology, Introduction

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.
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Mining Geology, Introduction

17. Prof. Dr. H.Z. Harraz Presentation
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Mining Geology, Introduction

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)
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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.
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Mining Geology, Introduction

20. Figure shows Source of metals and S in VHMS deposits?
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Mining Geology, Introduction

21. Controls on Transport of Metals
Fluid 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-
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Mining Geology, Introduction

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.
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Mining Geology, Introduction

23. Temperature trap on
seafloor
Redox trap at
sandstone/shale
boundary
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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
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Mining Geology, Introduction

25. MINERAL RESOURCE AND MINERAL RESERVE
Fig.11: Relationship between Mineral Resources and Mineral Reserves
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Mining Geology, Introduction

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.
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Mining Geology, Introduction

27. Prof. Dr. H.Z. Harraz Presentation
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28. SOLID MINERAL RESERVES
a) 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.
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Mining Geology, Introduction

29. Fig.9: Mineral reserves and mining losses.
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30. Prof. Dr. H.Z. Harraz Presentation
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Mining Geology, Introduction

31. Ore Evaluation
Tonnage (Q)
= Volume * Tonnage Factor (Specific. Gravity) ……. Tonnes
Ore reserve calculations= average grade * Tonnage (Q)
Ore Price = Ore Reserve * Price
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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.
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