Final Report - Geoscience BC

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2. What is Measured?Measured physical rock property data are a means of linking geophysical surveys to subsurfacegeology. The advent of forward modeling and inversion of geophysical data along with theability to rapidly compute large amounts of data on desktop computers now enables us tonumerically modify geophysical data in 3D that approximates the geometry of geological bodies.To inform these computer models it is important to redraw geological maps and cross-sections interms of the geophysical properties of the geological units. These geological – geophysicalreference maps should be simplified to emphasize units with distinct densities and / or magneticproperties and boundaries with physical contrasts. Other parameters such as resistivity,conductivity and chargeability may be mappable parameters. Direct rock property measurementsof this type of data are less available. Reference maps can then guide the computer models toselect a forward model or inversion that best fits the geology.Solutions for forward models and inversions of geophysical data are non-unique, in other wordsseveral geological geometries can explain a geophysical anomaly. Preferred geometric solutionscan be identified by preparing a likely geological geometry that corresponds to the knowndistribution of physical rock properties for rock units. Data for density and magneticsusceptibility are more commonly measured and available. Also inversions for gravity (densitycontrasts) and magnetics are more easily computable with existing codes. Rock property data forresistivity, chargeability and conductivity are less commonly measured. Also the computing timeand complexity for electrical properties and conductivity are a greater challenge. Geophysicalcontract companies do provide these services however.Sulphide geochemical analyses can be used as a proxy for chargeability. Electrical conductivityof samples can be directly measured in laboratories. Density is commonly measured by retrievalof a rock sample and measurement by weight in air – weight in water technique. An alternativeindirect measurement of relative density is by borehole measurement of gamma-gamma andmise-a –la-masse. It is also common to measure seismic velocities and acoustic properties ofrocks. Spectral gamma logs are means of correlation of rock units with radiometric surveys.Field spectral measurements are used to constrain airborne gamma spectral surveys. Table 1 listsa number of physical properties that are measured.3
3. Physical PropertiesProperty Method of Measurement UnitsMagnetic susceptibility susceptibility meter x 10 -3SIKoenigsberger ratio measured from oriented core Kn = remanence/ ms x fieldDensity wgt in air – wgt in water; spectral gamma gamma; g/cm3gravity meter; borehole gravity meterConductivity mhos/m; siemens/m (S m -1 )Resistivity apparent resistivity with applied current ohm meters x 104 or ohm mChargeability transient voltage millivolt/voltGamma Ray MeV gamma rays; calculate eUranium, eThorium; eThorium v ePotassium (ppm)Spectrometry ePotassium % potassiumSeismic velocity elastic wave velocity km/sec = vAcoustic impedance z = v x ρPorosity %Temperature measure degrees centigrade milliKelvin/m; ºc/mGradientNatural Gamma cps4
Page 3 and 4: … modelling the earth310 Victoria
Page 5 and 6: … modelling the earthList of Figu
Page 7 and 8: 1. IntroductionPhysical rock proper
Page 9 and 10: 2. Project DeliverablesDeliverables
Page 11 and 12: GSC in the Fraser Delta region (dat
Page 13 and 14: (c)Data Summary by LocationArea of
Page 15: directories: ‘Input Data’, ‘O
Page 18 and 19: 4. RPDS Application4.1. General Ove
Page 20 and 21: Wireline DataRPDSSample DataProcess
Page 22 and 23: 4.3. Web InterfaceAll data within R
Page 25 and 26: Appendix 1 - Rock Properties Worksh
Page 27 and 28: Appendix 2 - DVD Data ArchiveSee at
Page 29 and 30: … modelling the earthTable of Con
Page 31 and 32: … modelling the earth
Page 33: geophysical data. The geophysical m
Page 37 and 38: surveys have excellent resolution o
Page 39 and 40: surveys are commonly calibrated by
Page 41 and 42: 5. Case Study of Mt. Milligan Porph
Page 43 and 44: merge into the background. Deposits
Page 45 and 46: Mount Milligan geologyFrom Jago (20
Page 47 and 48: Susceptibilty data for rock types m
Page 49 and 50: 4 1 9 . 7 12 55 07 51 0 01 2 51 5 0
Page 51 and 52: Mount Milligan synthetic models for
Page 53 and 54: Unconstrained synthetic model inver
Page 55 and 56: Detection of other targets - lower
Page 57 and 58: Detection of other targets - buried
Page 59 and 60: Mt. Milligan - unconstrained invers
Page 61 and 62: Constrained Inversion:Unconstrained

Final Report - Geoscience BC

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