It covers seismic method, gravity method, electromagnetic method, magnetic method and radiometric method. all these methods help in mineral exploration
This Lecture includes the Resistivity survey, field procedure, application advantage, limitaion, Apparant resistivity, VES (Vertical Electrical Sounding), Resistivity Profiling and IP Survey in brief.
Geological surveys are normally undertaken by private agencies, state government departs of mines and geology, and national geological survey organizations. They maintain the geological inventory of various formations, mineral deposits and resources. They keep all records for the advancement of knowledge of geosciences for the benefit of the nation. Geological mapping are parts of a geological survey. It involves certain procedures. This lesson highlights the methods and procedures of geological mapping.
Information about these fluids is an invaluable aid in mineral exploration.
Conventional academic methods of analysing fluid inclusions are too slow and tedious to be of practical application in typical mineral exploration activities.
However, the academic data from numerous studies does show that CO2 is an exceptionally important indicator when exploring for most types of gold deposit.
Because the baro-acoustic decrepitation method is a rapid and reliable method to measure CO2 contents in fluids, it can be used to study a spatial array of data and it is an invaluable and practical exploration method.
Measurements of temperatures of fluid inclusions does not usually help in mineral exploration as hydrothermal minerals deposit over a wide temperature range and there is no specific temperature which is indicative of mineralisation. However, if temperatures are available on a large spatial array of samples, then temperature trends may be a useful exploration method to find the hottest part of the system, which is presumably the location of the best economic mineralisation. Baro-acoustic decrepitation is the most practical method to determine temperatures of the large numbers of samples required.
Salinities of fluid inclusions are of limited use in exploration and are difficult to measure. However, they can be used to recognise intrusion related hydrothermal systems.
It covers seismic method, gravity method, electromagnetic method, magnetic method and radiometric method. all these methods help in mineral exploration
This Lecture includes the Resistivity survey, field procedure, application advantage, limitaion, Apparant resistivity, VES (Vertical Electrical Sounding), Resistivity Profiling and IP Survey in brief.
Geological surveys are normally undertaken by private agencies, state government departs of mines and geology, and national geological survey organizations. They maintain the geological inventory of various formations, mineral deposits and resources. They keep all records for the advancement of knowledge of geosciences for the benefit of the nation. Geological mapping are parts of a geological survey. It involves certain procedures. This lesson highlights the methods and procedures of geological mapping.
Information about these fluids is an invaluable aid in mineral exploration.
Conventional academic methods of analysing fluid inclusions are too slow and tedious to be of practical application in typical mineral exploration activities.
However, the academic data from numerous studies does show that CO2 is an exceptionally important indicator when exploring for most types of gold deposit.
Because the baro-acoustic decrepitation method is a rapid and reliable method to measure CO2 contents in fluids, it can be used to study a spatial array of data and it is an invaluable and practical exploration method.
Measurements of temperatures of fluid inclusions does not usually help in mineral exploration as hydrothermal minerals deposit over a wide temperature range and there is no specific temperature which is indicative of mineralisation. However, if temperatures are available on a large spatial array of samples, then temperature trends may be a useful exploration method to find the hottest part of the system, which is presumably the location of the best economic mineralisation. Baro-acoustic decrepitation is the most practical method to determine temperatures of the large numbers of samples required.
Salinities of fluid inclusions are of limited use in exploration and are difficult to measure. However, they can be used to recognise intrusion related hydrothermal systems.
Numerical
methods have been used to simulate epithermal gold
bearing ore systems models and their reflection in the MobileMT
data The current forward modeling covers 3 typical and
generalized epithermal systems models in a wide spectrum of
geoelectrical conditions, from resistive to conductive
Subsurface 2D Image Analyses of the Uyangha Basement Area, South-Eastern NigeriaIOSR Journals
Geo-electric soundings were made in Stella Maris Secondary School, in Uyangha, Nigeria to image
the subsurface and obtain thicknesses and resistivities of different layers. A quantitative interpretation of the
data obtained clearly reveals the presence of four (4) geo-electric sections which are interpreted to be dry
laterite, moist laterite, weathered basement, and saturated basement. The depth probed is about 100m. The
saturated basement is the aquifer unit. Depth to aquifer unit in the area is at about 65m to 80m.The thickness of
the aquifer unit ranges from 20m to 35m. For ground water exploitation, boreholes in the area should therefore
be drilled to the depth of 91m, for reasonable groundwater yield. The lateritic layer makes the study area
suitable for building construction in the area.
Determination of Thickness of Overburden in Basement Area Using Schlumberger ...iosrjce
The overburden thickness of Abuja (Lat. 70
12´N – 9
0 30´ N and Long. 50
24´E- 7
0
19´E)
has been estimated. The geophysical method used was the electrical resistivity and the electrodes
array was Schlumberger type. The equipment utilized were four electrodes, hammer, four reels of
wires, crocodile clips, measuring tape, global positioning systems(GPS) and a terrameter. The survey
was carried out in two locations and the average resistivity values of the first four geoelectrical layers
were from the surface, 590 Ωm, 1800 Ωm, 1900 Ωm and 760 Ωm. These layers were interpreted as
probably top soil, laterite, weathered basement rock and fairly weathered basement rock. The
average thickness of the overburden was found to be 5.43m
Evaluation of sub-soil geo-electric properties in a proposed power sub-statio...IJERA Editor
Electrical resistivity survey was carried out in a site proposed for the construction and installation of a Power sub-station. The project will involve subsurface installation of cables and other objects that easily conduct electricity. Extant laws including EIA also require knowledge of subsurface distribution of resistivity in construction projects that would involve burial of steel pipes and cables. The imperative of this is emphasized by the location of the project in an area of shallow groundwater conditions. Field resistivity measurements were undertaken using ABEM Terrameter SAS 1000, adopting Schlumberger configuration in vertical electric sounding at 12 locations within the study site. The results were used to generate geo-electric log models. Three geo-electric profile models (pseudo- profiles) were also taken NE-SW of the site. Interpretation of the models shows that the area is characterized by two geo-electric layers to the depth of 30m. The upper layer of lower resistivity occurs to a depth of 2-3m. This layer consists of lateritic to silty sands. The lower layer has a resistivity of between 900 - >2000 Ωm and represents fine to coarse sands and gravels. On the Soil Electrical Resistivity Classification (BS 1377), the subsoil falls within non-corrosive class. Objects installed in the soil are not likely to suffer corrosion soon. Similarly, subsurface electrical installations will pose minimal hazards and would require basic precautions to avoid electrical accidents.
Subsurface Determination Of Cavities In Limestone Rock Area By Geoelectric Me...IJERA Editor
Two Dimensional of geoelectric method can be used to find out the conductive formation in the earth surface. The purpose of this research is to give the description about the geological subsurface formation, that the high resistivity value is indicate the potential area of cave and void in the limestone rocks. The dipole dipolegeoelectric method is used in this research with the path of lines is 250 m with 10 m electrode spacing. The total lines is 7 and the azimuth is from east to west. Resistivity method is started with inject the electrical current into the earth by current electrode, then potential difference will arise and measured by potential electrode. Variation value of resistance for each layer rock can calculated by divided potential defference with current value. The existence of the cavity is known by the resistivity value is more than 2500 ohm-m, while the cracks have a resistivity of 1500 to 2500 ohm-m.
Resistivity Imaging of Shallow Sediments within University of Maiduguri Campu...iosrjce
Electrical resistivity imaging within University of Maiduguri campus shows varying resistivity values
and thicknesses for shallow sediments from one profile line to another. Sequence stratigraphy of the sediments
indicates they were deposited at different times and varying conditions. Structure of the medium of deposition
conditioned the lithological structures of the sediments. Basin or bowl-shapes of some resistivity structures are
characteristics of some gravelly and clayey sediments. In most cases where such structures are encountered,
gravels seem to host sands; while clays are located at the central parts. This situation may suggest that the
sediments were deposited at the same time, where heavier ones settled to the bottom of the stratigraphy.
Sometimes clayey sediments host sandy sediments; a situation that may be associated with different times of
deposition. Some sediments were laid horizontally, some inclined and others nosed into overlying ones.
Majority of the resistivity images indicate clayey sediments occupying the basal resistivity units. Lower
resistivity values associated with some clayey sediment suggest high degree of saturation. The water might have
been derived through infiltration of the overlying porous sediments. The clays may be followed upwardly by
sands, while gravels sometimes form the capping sediments. Few resistivity profiles host the three sediments at
the bottom of the resistivity structures. Stratigraphic thicknesses for the sediments vary both laterally and
vertically. These are associated with the structure of the medium and prevailing conditions at the time of
deposition
Research Inventy : International Journal of Engineering and Scienceinventy
Research Inventy : International Journal of Engineering and Science is published by the group of young academic and industrial researchers with 12 Issues per year. It is an online as well as print version open access journal that provides rapid publication (monthly) of articles in all areas of the subject such as: civil, mechanical, chemical, electronic and computer engineering as well as production and information technology. The Journal welcomes the submission of manuscripts that meet the general criteria of significance and scientific excellence. Papers will be published by rapid process within 20 days after acceptance and peer review process takes only 7 days. All articles published in Research Inventy will be peer-reviewed.
2. Electromagnetic Method which uses electrodes with current to create a
geophysical image
if charge has been stored inside a type of rock body we observe an overvoltage
effect
3. a potential difference measurement
Voltage Decay/Overvoltage: the decay of potential difference
as a function of time
(Glaser, 2007)
4. the effects of alternating currents on the measured value of resistivity
more often used than T.D. IP to locate ore bodies
The measurement between the phase shifts between the current
produced and the voltage observed (See Figure b, below)
(Glaser, 2007)
5. Phase angle & Critical frequency = Chargeability
Can be used to separate out zones of primary mineralization and the
texture of a body (variation in mineralization)
(Niederleithinger, 2003)
7. Intrusions and hydrothermal fluids
create alteration zones
Alteration zones differentiated by
different mineral assemblages
Assemblages often contain ore
deposits
(Farr, 2008)
Modified from Nelson,
2012
8. • Each zone has different resistivities
different IP responses
• High metallic content (Cu) = high
chargeability
(Oldenburg, 1997)
9. Use of spectral IP & Dipole-Dipole
Low FE = core of deposit (Potassic)
• Highly resistive core (potassic)= high apparent
resistivity
• High apparent resistivity = low Fe [(p0-p1)/p1]
High MF = high M = pyrite halo
Economic ore likely occurs between
Potassic and Phyllic zone (potassic core
has little sulfides, phyllic zone has high
sulfide due to pyritization)
200 million tons of 0.45% Cu
(Berger, 2008)
10. Isolation amplifier: secure data
acquisition from common mode
voltages
Transmitter: sends series of current
signals which are sampled by the
GDP-16
Shunt resistor: creates a small
resistive path to measure the
voltage from the transmitter
GDP-16: used to measure real/
complex resistivity and the phase
difference
11. Certain procedures are taken into
consideration before running tests on the
sample;
• Prevention of surface current
• Trimming of sample
• Damping of sample
12. Finds disseminated ores that have weak magnetic and gravity
responses
Good preliminary survey
Provides supplemental information to build model
13. Berger, B.R., Ayuso, R.A., Wynn, J.C., Seal, R.R., 2008, Preliminary model of porphyry copper deposits, U.S. Geological Survey Open-File Report, v. 1321, p.55
Farr, M.R., 2008, Exploring for Copper Deposits, University of Kansas <http://www.beloit.edu/sepm/Rocks_and_minerals/exploring_for_copper.html> accessed on
November 8, 2013
Fink, James B., 1990, Induced Polarization: Applications and Case Histories, Society of Exploration Geophysicists, Tulsa, Okla.
Fu, Lei, 2011, Induced Polarization Effect in Time Domain: Theory, Modeling and Applications, The University of Utah
Holliday, J.R., Cooke, D.R., 2007, Advances in geological models and exploration methods for copper+gold porphyry deposits, Ore deposits and exploration technology:
proceedings of exploration, p. 791-809
Morrison and Gasparikova, 2012, DC Resistivity and IP field systems, data processing and interpretation, <http://appliedgeophysics.berkeley.edu/dc/EM46.pdf> accessed on
November 6, 2013
Nelson, S.A., 2012, EENS 2120 Petrology: Magmatic Differentiation <http://www.tulane.edu/~sanelson/eens212/magmadiff.htm> accessed on November 8, 2013
Niederleithinger, E., 2003, Spectral Induced Polarization – a tool for non-destructive testing of soils and building materials, Federal Institute for Materials Research, Berlin,
Germany, <http://www.ndt.net/article/ndtce03/papers/v060/v060.htm> accessed October 30, 2013
Oldenburg, D.W., Li, Y.L., Ellis, R.G., 1997, Inversion of geophysical data over a copper gold porphyry deposit: a case history for Mt Milligan, Geophysics, v. 62, n. 5, p. 1419-
1431
Pelton, William H. and Smith, Peter K., 1976, Mapping Porphyry Copper Deposits in the Philippines with IP, Geophysics, v. 41, no. 1 p. 106-122
Reynolds, John M., 2011, An Introduction to Applied and Environmental Geophysics, 2nd Edition, Chichester, Wiley, 712 p.
Sharma, Prem V., 1997, Environmental and Engineering Geophysics, Cambridge, Cambridge University Press, 500 p.
Toovey, L.M., 2011, Copper exploration techniques: induced polarization surveys, Copper investing news http://copperinvestingnews.com/6465-copper-exploration-
techniques-induced-polarization-surveys.html > accessed on October 31st, 2013
Toovey, L.M., 2011, Porphyry copper: the world’s most valuable deposits, Copper investing news http://copperinvestingnews.com/6465-copper-exploration-techniques-
induced-polarization-surveys.html > accessed on October 31st, 2013
Wightman, Jalinoos, and Sirles, Induced Polarization. EPA.
<http://epa.gov/esd/cmb/GeophysicsWebsite/pages/reference/methods/Surface_Geophysical_Methods/Electrical_Methods/Induced_Polarization.htm> Accessed
November 4, 2013.
Editor's Notes
IP response is related to how well a unit is the subsurface can hold on to electrical charge
The conductivity depends on the amount of ore present and the conduction of the ore
Induced polarization is an electromagnetic method that uses electrodes with current to create a geophysical image. It is where a current is run through the ground by two electrodes and observed when the current is switched off. The voltage is then observed to have decayed, instead of instantaneously returning back to zero.
Current is supplied to the ground, the moving charges induce a response from chargeable grains in the subsurface. When the current is supplied, a charge builds up outside of the metallic grains. Since charge is free to move in the metals present in the subsurface (because they are conductors), the electrons will move to the side of the mineral grain where the positive current is present. This creates a temporary charge separation where the mineral grain acts as a small capacitor, creating a potential difference within itself (within the grain). When the current is switched off from our current electrodes, the total observed voltage drops instantaneously by the amount of current being supplied by the current electrodes (V) so the remaining voltage is only that of the potential difference that was induced in the metallic grains by the original current. It takes a while for this potential difference to disperse, leaving us with Vi, the overvoltage which decays over time. The decrease in this overvoltage over time is what is measured this is the IP response.
Current is supplied (V) by current electrodes
Charge builds up on metallic grains
Current induces a potential difference in the metallic grains (Vi) – this is the overvoltage
A voltage (VT) is observed at potential electrodes (where V + Vi=VT)
Current is switched off VT – V = Vi
Vi decays at a rate depending on the conductivity of the grain and the amount of time the grain was subjected to the current
Induced polarization (IP) is a potential difference measurement between the potential electrodes. When the current through the electrodes is switched off, the potential difference does not instantaneously drop to zero. The potential difference instead drops significantly at first, but then it slowly decays to zero after a short amount of time.
Apparent resistivity is observed at 2 different frequencies
Frequency (f0) = pa0
Frequency (f1) = pa1
Pa0>pa1
Studying the effects of alternating currents on the measured value of resistivity is another method of IP, in the frequency domain (Figure b). This method is done by locating portions of the earth where resistivity decreases, as the frequency of applied current is being increased. This form of IP method is more often used to locate ore bodies.
In a perfect earth we would expect to see the two curves matched up… instead we see a phase shift caused by a delay in time in when the supplied current is turned off/on and when that potential difference is measured
Time and Frequency domain IP methods can locate ore bodies, but they cannot give us a good estimate of the amount of mineralization in the subsurface. To do this, we can use Spectral IP
ρ0 = DC Resistivity
ω = 2πf = angular frequency
Μ = Vi/VT = Chargeability
τ= time constant
c = relaxation constant
i= √-1
IP response is related to how well a unit is the subsurface can hold on to electrical charge
The conductivity depends on the amount of ore present and the conduction of the ore
Phase angle & Critical frequency = Chargeability
Can be used to separate out zones of primary mineralization and the texture of a body
Spectral induced polarization (SIP) allows us to measure the variation in resistivity with different applied frequencies. This method allows us to see several resistivity measurements at different frequencies.
Spectral induced polarization aims to specifically distinguish material properties of the subsurface.
Spectral induced polarization (SIP) allows us to measure the variation in resistivity with different applied frequencies. This method allows us to see several resistivity measurements at different frequencies.
Spectral induced polarization aims to specifically distinguish material properties of the subsurface.
Dipole-Dipole is a commonly used set up for Induced polarization. It consists of two sets of electrodes, the current and potential electrodes. The pairs of current electrodes and pairs of potential electrodes are usually placed close to one another at equal distances. While the spacing between the pairs of each current and potential electrodes are spaced further apart at equal distances that are multiples of the spacing between the pairs of current electrodes and potential electrodes.
A primary advantage of the dipole-dipole electrode array is the ease of deployment in the field due to shorter wire lengths.
Why else would we use Dipole Dipole arrangement?
How Porphyry deposits form:
Large igneous intrusions develop at convergent boundaries
Magma begins to cool within the earth (i.e. intrusions)
Minerals begin to crystallize out of the magma, copper is not one of the first to crystallize since it is not able to fit into the crystal arrangement of the minerals present in the granite. Instead, it remains in solution this increases the concentration of Cu in the magma
Granitic intrusion (minus the Cu) cools, and and Cu is left in fluid, it is the last to crystallize
The remaining copper rich fluid is the last to crystallize and therefore it enters available fractures or fissures within the rock… or in the case of the Philippines a pre-existing fault line (the Philippine Fault which forms the Philippine Copper Belt)
porphyry copper is in the vein network at top, intrusion is cooling - they are the last things to crystallize and take advantage of fractures - they dont fit into the other minerals’ crystal systems that form in the intrusive granite so they don't crystallize with the other minerals. Instead they enter the fluids in the veins
alteration rim around the porphyry
forms around the top and sides of the magma chamber
explore where there is erosion so we can open-pit mine
andesitic to rhyolitic volcanic types
in subduction zones – since subduction related volcanism
Porphyry is not a massive sulphide – it is spread out in a or vein network
Since each zone has characteristic mineral assemblages, they will hold on to charges differently and for different amounts of time creating different IP responses
Same case history dr. eaton used as an example for how topography can complicate IP responses… but we’re not concerned with that in this case
Use of spectral IP & Dipole-Dipole
Low FE = core of deposit (Potassic)
Highly resistive core (potassic)= high apparent resistivity
High apparent resistivity = low Fe [(p0-p1)/p1]
High MF = pyrite halo
Economic ore likely occurs between Potassic and Phyllic zone (potassic core has little sulfides, phyllic zone has high sulfide due to pyritization)
200 million tons of 0.45% Cu
Tension fractures provide space for magma to move upwards
Deposits exist north of the Philippine Fault (known as Philippine Copper Belt) (Step 5. in porphyry formationThe copper rich fluid is the last to crystallize and therefore it enters available fractures or fissures within the rock… or in the case of the Philippines a pre-existing fault line (the Philippine Fault which forms the Philippine Copper Belt))
Copper fills fractures and disseminations in surrounding rock
Copper occasionally outcropped = targets are likely shallow (we like to look for shallow targets because 1. it makes for easy prospecting and tells us where to conduct geophysical surveys and 2. means we can likely easily open-pit mine (which is cheap)
Isolation amplifier: The isolation amplifier eliminates common mode voltage. Common mode voltage creates a noisy signal and by using an isolation amplifier it eases data interpretation.
Transmitter: sends series of current signals in square wave which are essential in finding our complex resistivities and phase difference
Shunt resistor: The shunt resistor is used when dealing with large currents. The current passes through a small resistive path that is controlled which leads us to measuring our voltagecreates a small resistive path to measure the voltage from the transmitter
Electrodes/Sample: This is where the rock sample lies, between the two electrodes which pass the current through it, and measure it’s properties.
