Geophysics review Flashcards
4 subdisciplines of geophysics
global, exploration, geotechnical & environmental, forensic
subdiscipline focused on the structure of the earth
global geophysics
3 sub-subdisciplines under exploration geophysics
mining, petroleum, hydrocarbon, groundwater studies, geothermal energy exploration
subdiscipline focused on detection of ore bodies
mining geophysics
subdiscipline focused on structures that trap oil
petroleum geophysics
subdiscipline focused on the depth and configuration of an aquifer
groundwater studies
3 focuses of geotechnical and environmental geophysics
site investigations, contamination studies, archeological investigations
focus of geotechnical & environmental geophysics that involves mechanical properties and depth
site investigations
focus of geotechnical & environmental geophysics that involves detection and flow direction
contaminant studies
subdiscipline that involves locating or detecting the presence of subsurface structures or bodies and determine their depth, size, shape and physical properties
exploration geophysics
what is being explored for in exploration geophysics?
features of bodies related to mineral deposits, energy or groundwater resources
what are the 6 geophysical methods?
gravity, magnetics, seismic reflection, seismic refraction, electrical (georesistivity, induced polarization), ground penetrating radar
the 3 anomaly profiles for magnetic geophysical method
poles, mid-latitude, equator
geophysical method that makes use of lines of current flow throughout the earth
electrical resistivity method
5 main physical properties involved in geophysical surveys
density, magnetics susceptibility, elasticity, conductivity, relative dielectric permittivity
what property is measured an @ what units for magnetic geophysical method?
magnetic susceptibility (dimensionless); magnetic field strength (Gauss = 10^-4 T, Gamma = nT
what property is measured an @ what units for gravity geophysical method?
density (kg/m^3, g/m^3); gravitational field strength (mGal = 10^-3 cm/s^2)
what property is measured an @ what units for seismic geophysical method?
velocity (m/sec, km/sec, m/sec)
what property is measured an @ what units for electrical geophysical method?
resistivity: ohm-meters
conductivity: mho/m = Siemens/m (S/m)
a physical property contrast (vertical or lateral)
geophysical anomaly
geophysical method that studies changes in strength of geomagnetic field
magnetic
geophysical method that studies the travel times of reflected or refracted seismic waves
seismic
geophysical method that studies resistance and potential differences
electrical
geophysical method that studies the changes in strength of the earth’s gravitational field
gravity
geophysical method that studies the reflection of electromagnetic waves
GPR
5 points in qualitative interpretation of anomalies
- distribution of highs and lows
- trend or orientation of highs and lows
- shape of anomalies (circular, linear)
- amplitude or wavelength of anomalies
- breaks or discontinuities in the anomalies
examples of minerals explored for in exploration geophysics
gold, copper, massive sulfides, iron, chromite, laterite
examples of hydrocarbons explored for in exploration geophysics
oil, gas, coal, gas hydrates
3 stages of geophysical surveys
reconnaissance, detailed exploration pt 1, detailed exploration pt 2
stage in geophysical surveys that use airborne geophysics or ground surveys
reconnaissance
stage in geophysical surveys that use ground geophysics and borehole logging
detailed exploration
5 mineral districts in the phils
Baguio-Mankayan Gold district
Paracale Gold district
Masbate Gold district
Surigao Gold district
Masara Gold district
5 kinds of mineral deposits in the phils
epithermal
porphyry Cu/Cu-Au
volcanogenic massive sulfides
nickel laterite
chromite
tectonic settings of mineral deposits in the phils
extensional, compressional, transtensional
depositional environment of mineral deposits
volcanic caldera, dome complex, oceanic terrane
age of mineralization of mineral deposits
Mesozoic, Cenozoic
host/associated rock types of mineral deposits
volcanic rocks, ultramafic rocks, acidic rocks
deposit forms of mineral deposits
veins, massive, replacement
ore controls of mineral deposits
hydrothermal breccia pipes, fractures, extensional faults
host/associated rock types of epithermal Au-Ag-Cu high sulphidation deposits
andesite to dacite and rhyodacite
deposit form of epithermal Au-Ag-Cu high sulphidation deposits
veins and massive sulphide replacement pods and lenses, stockwork and breccias
ore mineralogy of of epithermal Au-Ag-Cu high sulphidation deposits
pyrite, enargite/luzonite, chalcocite, covellite, bornite, gold, electrum
gangue mineralogy of epithermal Au-Ag-Cu high sulphidation deposits
pyrite and quartz predominate
alteration mineralogy of epithermal Au-Ag-Cu high sulphidation deposits
quartz, kaolinite/dickite/alunite/barite/hematite
ore controls of epithermal Au-Ag-Cu high sulphidation deposits
caldera ring, darial fractures, fracture serts and faults and breccias in and around intrusive centers
geophysical signature of epithermal Au-Ag-Cu high sulphidation deposits
magnetic lows in hydrothermally altered (Acid-leached) rocks, gravity contrasts may mark boundaries of structural blocks
other exploration guides for epithermal Au-Ag-Cu high sulphidation deposits
- deposits are found in 2nd order structures adjacent to crustal-scale fault zones, normal and strike-slip, as well as local structures associated with subvolcanic intrusions
usual lithology for mineral exploration
sedimentary rocks, volcanic rocks, intrusive complex, granitic plutons, gneiss and granite
what alterations indicated magnetic lows and magnetic highs in mineral deposits
magnetic low = hydrothermal alteration
magnetic high = potassic alteration
how does magnetite affect magnetic anomalies
magnetic highs = presence of magnetite
magnetic lows = alteration destroyed magnetite
what is studied in groundwater exploration
depth and configuration of aquifer
what is studied in petroleum exploration
structures that trap oil
what is studied in non-mineral exploration for environmental problems
leaking underground storage tanks and drunks;
contamination studies (detection, flow direction)
what is studied in forensic geophysics
locate missing buried bodies
locate clandestine graves or disturbed ground
locate buried weapons or evidence of crime
