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GLE 2024 (Day 3) > GEOPHYSICS (MAGNETIC SKEMANG) > Flashcards

GEOPHYSICS (MAGNETIC SKEMANG) Flashcards

1
Q

a passive method which measures variation in the existing magnetic field strength oldest and most widely used geophysical tool in mineral exploration

A

Magnetic

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2
Q

deposits that are applicable to be sujected to Magnetic

A

Iron Ore Sulfides
Ni-Cu-PGEs

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3
Q

This provides regional coverage of large areas at a comparatively low cost specialy in delineating target areas during reconnaissance

A

Airborne Potential field sirveys

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4
Q

used as a magnetic sensor fixe to a string in the tail of an aircraft

A

Bird

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5
Q

Used to tow a sensor behind a ship to remove te magnetic effects of the vessel

A

Fish

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6
Q

Where is marine potenrial survey used?

A

Ocean Floor Polymetallic Nodules

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7
Q

The curved orientations of lines in a magnetic field

A

Lines of Force

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8
Q

Flux of density due to magnetic pole of strength m at dustance R and expressed as the force exerted on a unit positive pole at point P

A

Magnetic Field B

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9
Q

Units of Magnetics intensity?

A

Gamma (y) = 10^-9 T or= 1nT

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10
Q

Magnetic intensity at the poles

A

60,000 y or 60,000 nT

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11
Q

Magnetic intensity at the equator

A

30,000 y or 30,000 nT

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12
Q

How many degrees is the declination of the geomagnetic poles tp geopgraphical poles?

A

11.5 deg

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13
Q

The Angle between the Magnetic and Geograhic North

A

Declination

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14
Q

The Angle made by the point with respect to the horizontal

A

Inclination

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15
Q

What causes Magnetic Anomaly?

A

Superimposed presence of magnetic minerals and rocks on the normal geomagnetic field

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16
Q

Rocks’ magnetic suscpetibiloty is depedent on?

A

Proportion of rock forming ienrals with are either nonmagnetic or very feebly magnetic

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17
Q

Highly Magnetic Minerals

A

Magnetite, Ilmenite, Pyrrhotite

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18
Q

Hmeatite with a crystal form of Magnetite

A

Maghemite

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19
Q

Which type of igenous rocks are usually more magnetic due to higher magntite content

A

Mafic-Ultramafic

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20
Q

Magnetic propoerty of metamorphic rocks

A

Varying

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21
Q

Magnetic of property of sed rocks

A

Non magnetic unless enriched with magnetite bearing sulfide

22
Q

the response signaled by the causative bodyover regional trends of country rocks

A

Magnetic Anomaly

23
Q

Temperature above which magetic minerals lose their magnetic property (Curie Temo)

A

600 deg cel

24
Q

?No electrons are unpaired, lahat may ka pair
?Magnetic susceptibility is negative (Non Magnetic)
?When magnetic field is applied, magnetization is induced but reuces to zero when the field is removed
?Will be repelled when placed near a magnet

A

Diamagnetic Subastance

25
Q

?Magnetic field exists due to the spin of unpaired electrons
?Magnetic Susceptibility is Positive and Small (Weakly Magnetic)
?Tend to line up in the presence of magnetic field
?Magnetization depende linearly and reduces to zero on removal of the field
?Will be weakly attracted to Magnet
?Can be observed only at relatively low temp

A

Paramagnetic

26
Q

?Dipoles are PARALLEL to the magnetic domains
?Strong Spontaneous Magnetization w/c can exist even w.o external magnetic field
?Magnetic Susceptibility is very High (Strongly Magnetic)

A

Ferromagnetic

27
Q

?Dipoles are ANTI-PARALLEL w. equal number of dipoles in each direction
?There is noexternal magnetic field effects due to self cancellation
?Defects in crystal lattice may caused small magnetization caled Parasitic Antiferromagnetism (Non magnetic low temps but can be magnetic at higher temps until Neel Temp)

A

Antiferromagnetic

28
Q

?Dipoles are ANTI-PARALLEL w. unequal strength of dipoles thus no self cancellation
?Weakly attracte to magnet
?Can be transformed into Paramagnetism upon heating

A

Ferrimagnetism

29
Q

The temperature at which ferromagnetic or ferrimagnetic materials becomes paramagnetic on heating and lose their magnetic property

A

Curie temp (570 deg cel)

30
Q

Inherited Magnetization remaining after the removal of applie field

A

Remanent or Permanent Magnetization

31
Q

Type of remanent magentization whrein igenous rock solidifes and cools thtough the curie temp of its magnetic minerals

A

Thermoremanent Magnetization (TRM)

32
Q

The Magnetic particles of a sediment align within the Earth;s Field during sedimentation

A

Detrital Remanent Magnetiztaion (DRM)

33
Q

Magnetic Minerals recrystallize or grow during diaganesis or metamorphism

A

Chemical Remanent Magnetization (CRM)

34
Q

Develop slowly in an ambient magnetic field (Cool) as the domain magnetization relax ito the direction of the field

A

Viscous Remanent Magnetization (VRM)

35
Q

Path of Magnetiztaion

A

Hysterysis Loop

36
Q

Common causes of Magnetic Anomaly

A

1) Dykes (vertical)
2) Faulted, Folded or truncated sills and lava flows (Horizontal0)
3) Massive Basic Intrusion
4) Met Basement Rocks
5) Magnetite Ore Bodies

37
Q

Theory which states that Earths Magnetic Field is created continously within the outer core through an intense current loop due to friction caused by earth’s rotation

A

Dynamo Theory

38
Q

Magnetic survey instrument used to measure geomagnetic elements based on priniples of a suspended bar magnet in Earth’s Field

A

Magnetic Variometer

39
Q

Standard instrument in magnetic surverys which provides reading every 0.1 of a second

A

High Sensitivity Cesium Vapor Magnetometer

40
Q

Differential Magnetormeters

A

Magnetic Gradiometers

41
Q

Long term variatons in yhe main magnetic field caused by fluid motion in the Earth;s outer core but will not complicatie data reduction efforts

A

Secular Variations

42
Q

How can the longterm regional variations in magnetic field be corrected?

A

Used the IGRF Formula

43
Q

Cyclical Daily variations in magnetic field strength ranging from 20-60 nT

A

Diurnal Variations

44
Q

Maxmimum and Minimum of such daily variations

A

10 am max
4pm min

45
Q

How can the effect of diurnal variation be correcte?

A

Periodic calibration of insturemnts at a fixed base station

46
Q

Streams of high energy particles associated with sunsport activties striking the upper atmosphere and enormously increasing ionisphere currents

A

Magnetic Storms

47
Q

How can this be corrected?

A

Delay the Survey

48
Q

Recommended Flight heights for Airborne Magnetic

A

100-200 m Low Flight

49
Q

Maps produced by magnetic surveys which can give qualitative existense of the ore bodies

A

Isocontour Maps

50
Q

Mining and Econ Geol

A

Metallic Mineral
Iron Ore with higher magnetite and hematite
Massive Sulfide deposits (w/ EM)

51
Q

Structural

A

Extent of Sed Basins for Petroleum Explo
Faulting in Bed rocks
Used to define structural features

GLE 2024 (Day 3) (48 decks)

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