Study guide
6.2 Geophysical Exploration Methods in Mining Geology
PRC Mining Engineer Licensure Examination Philippines
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1 Chapter 1: Surface Mining Methods & Pit Optimization
1.1 Surface Mining Unit Operations & Method Selection 1.2 Bench Geometry, Slope Stability & Geotechnical Pit Design 1.3 Cut-Off Grade Optimization & Lerchs-Grossmann Pit Limits
2 Chapter 2: Underground Mining Methods & Strata Control
2.1 Underground Mining Method Classification & Selection 2.2 Rock Mechanics, Stress Analysis & Strata Control 2.3 Underground Ground Support Systems & Excavation Design
3 Chapter 3: Materials Handling, Equipment & Mine Economics
3.1 Drilling, Blasting & Explosives Engineering 3.2 Mine Loading, Haulage & Materials Handling Systems 3.3 Mine Capital (CAPEX), Operating Costs (OPEX) & Financial Evaluation
4 Chapter 4: Mine Safety, Ventilation & Philippine Mining Laws
4.1 Mine Ventilation Network Analysis & Environmental Quality 4.2 Philippine Mine Safety Rules, Health & Disaster Prevention 4.3 Philippine Mining Act of 1995 (RA 7942), DAO 2010-21 & Mining Ethics
5 Chapter 5: Physical Geology, Mineralogy & Philippine Deposit Types
5.1 Structural Geology, Tectonics & Ore Controls 5.2 Igneous, Metamorphic & Sedimentary Ore Mineralogy 5.3 Major Philippine Ore Deposit Models
6 Chapter 6: Mineral Exploration, Geophysics & Core Logging
6.1 Geochemical & Remote Sensing Exploration Techniques 6.2 Geophysical Exploration Methods in Mining Geology 6.3 Diamond Drilling, Core Logging & QA/QC Protocols
7 Chapter 7: Geostatistics, Resource Estimation & PMRC Code
7.1 Ore Body Block Modeling & Spatial Variography 7.2 Inverse Distance & Ordinary Kriging Grade Estimation 7.3 Philippine Mineral Reporting Code (PMRC 2020) & Resource Classification
8 Chapter 8: Comminution, Sizing & Physical Mineral Separation
8.1 Crushing, Grinding & Bond Work Index Calculations 8.2 Particle Screening, Hydrocyclone Classification & Sizing 8.3 Gravity Concentration & Magnetic/Electrostatic Separation
9 Chapter 9: Froth Flotation & Extractive Hydrometallurgy
9.1 Froth Flotation Chemistry, Reagents & Cell Kinetics 9.2 Leaching Technologies (Heap, Agitation & Tank) 9.3 Precious Metal Recovery: CIP, CIL, Merrill-Crowe & Electrowinning
10 Chapter 10: Process Plant Flowsheets & Environmental Tailings Management
10.1 Metallurgical Plant Flowsheets & Pulp Mass Balances 10.2 Tailings Storage Facility (TSF) Design & Dam Safety 10.3 Acid Mine Drainage (AMD) Mitigation & Environmental Protection (EPEP/FMR/DP)
11 Chapter 11: 2025 PRC Blueprint, Prospecting Tools & Exploration Decisions
11.1 Official 2025 TOS, Three-Paper Structure & Exam Strategy 11.2 Prospecting Instruments, Base Maps & Surface Geological Mapping 11.3 Integrating Direct and Indirect Evidence for Exploration Decisions
12 Chapter 12: Mine Infrastructure, Sustainable Development & Climate
12.1 Power, Water, Drainage & Support-Facility Selection 12.2 Sustainable Development, Progressive Rehabilitation & Community Impact 12.3 Mining, Climate, Reforestation, Coal & Energy-Transition Minerals
13 Chapter 13: Mine Valuation, Financial Analysis & Due Diligence
13.1 Time Value of Money, Future Value & Present Value 13.2 Financial Statements, Mine Economics & External Price Drivers 13.3 Exploration Provenance, Technical Review & Legal Due Diligence
14 Chapter 14: Mine Organization, Communication & Accountable Leadership
14.1 Line and Staff Functions in a Mining Organization 14.2 Communication With Superiors, Peers & Subordinates 14.3 Authority, Responsibility, Delegation & Safety Accountability
15 Chapter 15: Philippine Mining Law, Indigenous Rights & Professional Ethics
15.1 Legal Hierarchy, Mineral Tenure & Compliance Analysis 15.2 Constitutional Participation, IPRA, FPIC & Ancestral Domains 15.3 RA 4274, Professional Scope, Ethics & Document Integrity
16 Chapter 16: Applied Mathematics & Mine Surveying
16.1 Engineering Mathematics for Safe, Efficient Mine Decisions 16.2 Survey Control, Instruments, Traverses & Error Adjustment 16.3 Topographic Maps, Underground Set-Out & Survey Timeliness
17 Chapter 17: Feasibility Studies, Data Quality & Project Decisions
17.1 Scoping, Pre-Feasibility & Final Feasibility Study Maturity 17.2 Data Accuracy, Assumption Control & Go/No-Go Decisions 17.3 Multidisciplinary Integration, Interfaces & Independent Review
18 Chapter 18: Mining Computer Applications, Digital Control & Global Developments
18.1 Computer Functions, Office Applications & Data Governance 18.2 Geological Modeling, Mine Planning, Scheduling & Valuation Software 18.3 Real-Time Control, Critical Minerals & Regional Mining Developments
19 Chapter 19: Earth Systems, Geologic Time & Philippine Hazards
19.1 Solar-System Origin, Earth Interior & Atmospheric Layers 19.2 Rock Cycle, Landforms & the Geologic Time Scale 19.3 Philippine Tectonics, Geologic Hazards & Mitigation
20 Chapter 20: Metallurgy, Foundry Practice & Assaying
20.1 Extractive, Physical & Adaptive Metallurgy Principles 20.2 Foundry Materials, Casting, Solidification & Defects 20.3 Sampling, Fire Assay, Cupellation, Parting & Assay Calculations
21 Chapter 21: Solid–Liquid Separation, Environmental Law & Mine Ecology
21.1 Thickening, Filtration & Solid–Liquid Separation 21.2 Philippine Air, Water, Waste & Hazardous-Substance Controls 21.3 Mine Ecology, Closure, Tailings, Waste & Community Livelihood
6.2 Geophysical Exploration Methods in Mining Geology
Key Takeaways Explain This Topic AI
Induced Polarization (IP) chargeability measures electric charge storage in disseminated sulfur/metallic minerals, distinguishing disseminated sulfide halos from non-conductive country rocks.
Electrical Resistivity Tomography (ERT) maps subsurface electrical resistivity contrasts, differentiating conductive metallic sulfides or water-saturated clay-rich laterites from high-resistivity unweathered bedrock.
TMI processing must account for field inclination and remanence: RTP can center simple induced anomalies but becomes unstable near the magnetic equator, where stabilized transforms, reduction-to-equator, analytic signal, or forward/inverse modeling may be preferable.
Ground and airborne gravity surveys detect bulk density anomalies, targeting dense Volcanogenic Massive Sulfide (VMS) bodies, chromite pods, and structural basement horsts.
Airborne Radiometrics (gamma-ray spectrometry) measures K, U, and Th radioelement concentrations, identifying potassic alteration zones (K enrichment) associated with intrusive ore systems.
Last updated: August 2026
Geophysical exploration measures physical property contrasts between mineral deposits, host rock units, and structural zones. By detecting anomalies in Earth's electrical, magnetic, gravitational, radiometric, and electromagnetic fields, geophysics provides non-destructive 3D subsurface imagery that guides structural mapping and drill hole placement.
Electrical Methods: Induced Polarization & Resistivity
Electrical geophysical methods exploit contrasts in electrical conductivity ( σ \sigma σ , measured in S/m \text{S/m} S/m ) or electrical resistivity ( ρ = 1 / σ \rho = 1/\sigma ρ = 1/ σ , in Ω ⋅ m \Omega\cdot\text{m} Ω ⋅ m ) and chargeability ( M M M , in mV/V \text{mV/V} mV/V or milliseconds).
1. Induced Polarization (IP) Chargeability
Induced Polarization measures the transient decay of voltage in the ground after an applied direct current is interrupted. This charge storage phenomenon occurs via two principal mechanisms:
Electrode Polarization : Occurs at interfaces between metallic mineral grains (e.g., chalcopyrite, pyrite, galena, graphite) and pore fluids. Current flow causes charge buildup across the metallic-electrolyte boundary.
Membrane Polarization : Occurs in clay-rich rocks where narrow pore passages restrict ion movement.
Exploration Application : IP chargeability is often useful for detecting disseminated polarizable minerals , including sulfides, but no geophysical method is universally most effective. Porphyry systems may produce chargeability anomalies where sulfides are disseminated, yet response magnitude depends on mineralogy, texture, alteration, clay, water, array, instrument, and processing; a fixed mV/V threshold is not diagnostic of ore.
2. Electrical Resistivity Tomography (ERT)
ERT measures apparent resistivity ( ρ a \rho_a ρ a ) by injecting current through ground electrodes and measuring potential differences across receiving pairs.
High-Resistivity Targets ( > 1 , 000 Ω ⋅ m > 1,000\text{ }\Omega\cdot\text{m} > 1 , 000 Ω ⋅ m ) : Quartz veins, silicified breccia zones, unweathered crystalline intrusive rocks, and massive limestone units.
Low-Resistivity / Conductive Targets ( < 50 Ω ⋅ m < 50\text{ }\Omega\cdot\text{m} < 50 Ω ⋅ m ) : Water-saturated fault zones, clay-altered argillic halos, graphite beds, and metallic sulfide bodies.
Array Geometries : Dipole-Dipole arrays provide high horizontal resolution for vertical structures; Pole-Dipole arrays offer deeper penetration depth ( > 300 m > 300\text{ m} > 300 m ) with superior signal-to-noise ratios.
Philippine Laterite Application : ERT effectively maps the depth of weathered nickel laterite profiles, differentiating conductive water-saturated saprolite/clay zones ( 10 – 50 Ω ⋅ m 10\text{--}50\text{ }\Omega\cdot\text{m} 10 – 50 Ω ⋅ m ) from underlying high-resistivity unweathered ultramafic bedrock ( > 500 Ω ⋅ m > 500\text{ }\Omega\cdot\text{m} > 500 Ω ⋅ m ).
Magnetic Surveying: Total Magnetic Intensity & Reduced to Pole
Magnetic surveys measure local perturbations in the Earth's main magnetic field caused by spatial variations in rock magnetic susceptibility ( χ \chi χ ). Magnetic susceptibility depends primarily on magnetite content ( F e 3 O 4 Fe_3O_4 F e 3 O 4 ) and, to a lesser extent, pyrrhotite ( F e 1 − x S Fe_{1-x}S F e 1 − x S ).
1. Total Magnetic Intensity (TMI) & Dipolar Complexity
Ground magnetometers or airborne sensor arrays record Total Magnetic Intensity (TMI) in nanoTeslas ( nT \text{nT} nT ). At non-polar geomagnetic latitudes, Earth's inclined magnetic field induces dipolar anomalies (a paired magnetic high and magnetic low) offset laterally from the causative subsurface body.
2. Low-Latitude Magnetic Transformations
Reduced-to-Pole (RTP) recalculates an induced magnetic response as if the inducing field were vertical. For a simple body with known induced magnetization this can reduce dipolar asymmetry, but conventional RTP becomes numerically unstable as inclination approaches zero and can amplify noise. Remanent magnetization, anisotropy, topography, and interacting sources also prevent a unique “peak equals source” interpretation.
For Philippine low-latitude data, test field direction and remanence and compare stabilized RTP, reduction-to-equator, total gradient or analytic-signal products, tilt derivatives, and forward or inverse modeling. Choose the method from synthetic tests and geology; never make RTP a mandatory preprocessing step before drilling.
3. Application in Porphyry & Skarn Systems
Potassic Core Highs : High-temperature potassic alteration cores of porphyry deposits feature hydrothermal magnetite-biotite assemblages, producing prominent RTP magnetic highs.
Phyllic Magnetite-Destructive Lows : Outlying quartz-sericite-pyrite (phyllic) alteration destroys primary magmatic magnetite, converting it to non-magnetic pyrite and producing distinct magnetic low rings surrounding the intrusive core.
Magnetite Skarns : Intrusions contacting carbonate rocks form massive magnetite skarns (e.g., Larap, Camarines Norte), generating extreme magnetic anomalies ( > 5 , 000 nT > 5,000\text{ nT} > 5 , 000 nT ).
Gravity Surveys & Bulk Density Contrasts
Gravity surveys measure variations in Earth's gravitational acceleration ( g g g , in mGal \text{mGal} mGal , where 1 mGal = 10 − 5 m/s 2 1\text{ mGal} = 10^{-5}\text{ m/s}^2 1 mGal = 1 0 − 5 m/s 2 ) resulting from subsurface bulk density ( ρ \rho ρ ) contrasts.
1. Bouguer Gravity Anomaly & Corrections
Field observations are corrected for latitude, elevation (Free-Air correction), slab mass (Bouguer correction), and surrounding topography (Terrain correction) to yield the Complete Bouguer Anomaly : Δ g Bouguer = g obs − g theoretical + Δ g FA − Δ g Bouguer slab + Δ g Terrain \Delta g_{\text{Bouguer}} = g_{\text{obs}} - g_{\text{theoretical}} + \Delta g_{\text{FA}} - \Delta g_{\text{Bouguer slab}} + \Delta g_{\text{Terrain}} Δ g Bouguer = g obs − g theoretical + Δ g FA − Δ g Bouguer slab + Δ g Terrain
2. Density Contrasts ( Δ ρ \Delta \rho Δ ρ ) & Mineral Applications
Massive Sulfides & Chromite : Chromite ( ρ = 4.2 – 4.8 g/cm 3 \rho = 4.2\text{--}4.8\text{ g/cm}^3 ρ = 4.2 – 4.8 g/cm 3 ) and Volcanogenic Massive Sulfides (VMS, ρ = 4.0 – 5.0 g/cm 3 \rho = 4.0\text{--}5.0\text{ g/cm}^3 ρ = 4.0 – 5.0 g/cm 3 ) exhibit strong positive density contrasts ( Δ ρ > + 1.0 – 1.5 g/cm 3 \Delta \rho > +1.0\text{--}1.5\text{ g/cm}^3 Δ ρ > + 1.0 – 1.5 g/cm 3 ) relative to host volcanic or ultramafic rocks ( ρ = 2.7 – 3.2 g/cm 3 \rho = 2.7\text{--}3.2\text{ g/cm}^3 ρ = 2.7 – 3.2 g/cm 3 ). High-precision gravity surveys detect positive mGal anomalies overlying concealed chromite lenses in ophiolite terranes (e.g., Zambales Ophiolite Complex).
Barite & Iron Ore : Direct detection of dense hematite/magnetite bodies and massive barite veins.
- Radiometric & Electromagnetic (EM) Methods
- 1. Radiometrics (Gamma-Ray Spectrometry)
Radiometric surveys measure gamma radiation emitted during the radioactive decay of Potassium ( 40 K ^{40}K 40 K ), Uranium ( 238 U ^{238}U 238 U ), and Thorium ( 232 T h ^{232}Th 232 T h ) in the upper 30 cm 30\text{ cm} 30 cm of soil and rock.
Potassic Alteration Mapping : Hydrothermal potassic alteration introduces secondary K-feldspar and biotite, sharply elevating potassium concentrations relative to thorium ( K / T h K/Th K / T h ratio anomaly). This provides a direct geochemical-geophysical footprint for porphyry centers.
2. Airborne Electromagnetic Methods (EM & VTEM)
Airborne Versatile Time-Domain Electromagnetic (VTEM) systems induce secondary eddy currents in conductive subsurface bodies using a transmitter loop towed by a helicopter.
Massive Conductors : VTEM rapidly screens large areas for highly conductive, connected massive sulfide bodies (VMS, nickel-copper sulfides) buried beneath conductive overburden.
Matrix of Geophysical Methods by Exploration Target
Method Physical Property Measured High-Response Target Low-Response Target Primary Mining Application
Induced Polarization (IP) Chargeability ( M M M , mV/V \text{mV/V} mV/V ) Disseminated sulfides ( F e S 2 , C u F e S 2 FeS_2, CuFeS_2 F e S 2 , C u F e S 2 ) Unmineralized silicate rock Porphyry & epithermal gold-copper
Resistivity (ERT) Electrical Resistivity ( Ω ⋅ m \Omega\cdot\text{m} Ω ⋅ m ) Quartz veins, dry bedrock Faults, clay caps, saprolite Laterite thickness, epithermal veins
Magnetics (TMI and validated derived products) Magnetic Susceptibility ( χ \chi χ ) Magnetite skarns, potassic core Phyllic alteration zones Porphyry intrusive centers & skarns
Gravity Bulk Density ( ρ \rho ρ , g/cm 3 \text{g/cm}^3 g/cm 3 ) Chromite pods, VMS orebody Salt domes, weathered karst voids Direct massive sulfide & chromite targeting
Radiometrics Gamma radiation ( K , U , T h K, U, Th K , U , T h ) Potassic alteration ( K K K -biotite) Leached quartz-clay zones Porphyry & unconformity uranium