GEOPHYSICS (ELECTRICAL SKEMANG) Flashcards
Electrical Conductivity
Ability to let energy flow
Electrical Resistivity
Ability to deflect energy flow
Electrical Potential
Work done by moving a charge particle from infinity to other point
Electric Potential Difference
Work done in carrying a unit positive charge from A to B while keeping the charge in equilibrium
What is measured in Electrical Surveys?
Potential Difference through
Magnitude of current introduced and the variation in the receiving electrodes
Conductive Causative Bodies
?Massive Sulfides
?Graphite Rich Beds
? Fractured/Altered zones with Confined water containig dissolved salts and clay
High resistive body
Quartz Veins
Three types of Geoelectrical Survey
?Electric Resistivity
?Induced Polarization
?Self Potential
Used in the study of horizontal and vertical discontinuities in the electrical properties of the ground and the detection of 3D bodies of anomalous electrical donductivities
Resisitivity Method
Resistance between opposite faces of unit cube and is one of the extremely variable physical properties of rocks
Resisivity
Electrical Resistivity Formula
Resistance = (Resistivity*Length)/Cross Area
Most rock forming minerals are (Conductors or Insulators)
Insulators
How is electric current carried through a hard rock?
Through pore waters
Properties which govern reisitivity of rock
Porosity (Inverse)
Degree of Saturation (Direct)
Electrode configuration in which Current and Potenrial eletrodes are kept along a STRAIGHT LINE-EQUAL ARRAY SPACING “a”
Used in studying lateral variations most conveneient
Werner Array (C1-a-P1-a-P2-a-C2)
Electrode Configuration in which distance between Potential Electrodes are smaller than that between Current Electrodes with the Ps sitting between or inside Cs
Schlumberger Array (C1—P1-P2—-C2)
Electrode configuratio in which Potential Electrodes are outsie the Current electrodes with both pair having equal distance
Dipole Dipole (C1–C2——-P1–P2)
Type of Configuration in which the outer current electrodes are fixed and far apart while the Closer inner electrodes are moved together
Gradient Arrays
Three types of Electrode Configuration
1)Werner
2) Schlumberger
3) Dipole Dipole
A type of Electrical Resistivity surverying wherein current and potential electrodes are retained in a straight line at same relative spacing around a fixed central Points point pressuming that current penetrates continuously deeper
Useful for determining loose horizontal overburden thickness over hard rocks
Vertical Electrical Sounding or Electrical Drilling
A type of Resistivity survey wherein an electrode spread (A setup of Current and Potential electrodes) is progressively moved while maintaing electrode separation along a traverse line.
Employed in mineral exploration to locate faults and shear zones
Constant Separation Technique.Traversing / Electrical Profiling
Type of Electrical Resitivity Surveys
Vertical Electrical Sounding or Electrical Drilling
Constant Separation Technique
both a current meter and voltmeter
Resistivity Meter
What can resistivity survey detec?
Very Low Levels of Resistance with high accuracy
Frequency for Shallow probes
100 hz
Frequence for deeper probes
10 Hz
Units of Resitivity?
Ohm-Meter
Economics of resisitivy surveys
Light, Portable, INEXPENSIVE, Felxible at minimal fixed expense
Interpretation of Data
Rapid and Straghtforward
Is Electrical Resistivity suitable for reconnaissance, Why or Why not?
No because laborious
Mineral that are electrically polarized which can make rocks containing them highly conductive even when slightly moist
Clay
Base Metal Sulfide that are not so conductive
Sphalerite
Natural electric current on the ground that flow parallel to the Earths surface and caused regional potential Gradients
Telluric Current
Imaging Technique that identified ELECTRICAL CHARGEABILITY of subsurface Materials (Ore Bodies)
Induced Polarization
The measurement of Decaying volatage (as the ground acts as a capacitor and becoms electrically polarized) over a certain time interval
Time-Domain Induced Polarization
In an induced low frequency alternating current, resisitivity of subsurface decreaseases as frequence is increased (Resitivity down, AC frequency Up)
Frequency-Domain Induced Polarizaion
Effect in which Non Metallic Minerals, upon imposition of external current flow becomes additionally charged and such voltage decays as the source is switched off
Membrane/Electrolytic Polarization
Effect in Metallic Minerals upon imposition of external current flow through pore fluids caused transitory decaying voltage
Electrode Polarization or Overvoltage
Type of Ore that is perfect to be subject under Induced Polarization since Electrode Polarization will be more efficient in large surface area orebodies
Disseminated Sulfide Ore Body
Measured Parameter
Chargeability (ms)
Units of measurement of Chargeability
milliseconds
Common method of presenting IP Data
Pseuosection
Electrode configuration usually used in IP Reconnaissance
Gradient
A method that is base on natural potential differences resulting from electrochemical reactions in the subsirface and is unique because it is passive, non instrusive, non destructive and does not require introduction of external current
Self Potential or Spontaneous Polarization
What is the requirement of SP?
Causative Body must be near the water table
What part of the causative body especially metallic ore deposits are negatvely charge or acts as negative terminal?
Top of the orebody
What type of anomaly is expected over metallic ore deposits?
Central Negative Anomaly
Survey equpiments
Pair of NonPolarizing Porous Pot Electrode
Connected via a millivoltmeter
Electrodes are composed of simple metal spikes immersed in solution of its own salt
Mining and Econ Geol
Massive sulfide Orebodies (Magnetite or Graphite)
Reconnaissance for Base Metals
Prospecting for Geothermal
Downhole logging in Oil industry
Hydrogeol
Hydrogeo effetiveness of water engg remedial emasures
Environmental and Engg
Identification of seepages in dams and reservoirs
Finding leaks in Cancal Enbankments
Mining and Econ Geol
Exploration for sulfide deposits (Massive Cu, Ni, Au-g)
Extents of Deposit of Bulk Minerals (Clay and Gravel)
Geotthermal Resource
Structural
Overburden Thickness
Hydrogeol
Hydrogeological Investigation
Environmental and Engg
Engg Geological inbestigation before construction
Mining and Econ Geol
?Low-grade Ore Deposits (disseminated) PCDs
?Placer Deposits
?Base Metal Exploration (Both massive and disseminated)
Hydrogeol
Hydrogeophysical
Environmental and Engg
Environmental
Geotechnical
