Services offered by GHM include survey design, data acquisition, processing, modelling, inversions, data compilation and interpretation. Depending upon project requirements and targets, a variety of surface survey methods including Induced Polarization (IP) and DC Resistivity, Electromagnetics, Magnetic, Seismic and Gravity are used.
Our technical team includes well trained and registered professionals capable of performing QA/QC on the data, processing the results and providing the best possible geological and model target solution to the client.
The interpretation results are provided and discussed with the client in a timely and professional manner.
o Drill Target Generation
o Ore Delineation
o Geological Mapping
o Focus Drilling
o Bedrock Mapping
o Overburden Study
o Ground Validation
o GIS & Query
o Physical Properties Analysis
o Base Metals Prospecting
The purpose of carrying out geophysical surveys is to find out something about the rocks in the survey area. Geophysical methods all depend on measuring a physical property of rocks.
Geophysical surveys generally look for concentrations of anomalously high values of the property being measured.
The results of the survey are used to identify a target of interest, or to correlate the spatial variation of values of the property with variations in the geology.
The primary reasons to do geophysics are to get information on geology, and possibly to find targets of economic interest (W.J. Scott, Ph.D., P.Eng., P.Geo, 2014).
o Lode Gold Deposits
A lode Au deposit is a hydrothermal deposit whose principal commodity is Au. Dubé and Gosselin (2007) provide a comprehensive synthesis of this deposit type and its various subcategories including 1) shear- and fault-zone-related deposits, principally greenstone-hosted quartz-carbonate vein deposits (orogenic, mesothermal, lode gold, shear-zonerelated quartz-carbonate or gold-only deposits) associated with collisional tectonics, 2) intrusion-related deposits associated with felsic plutons of subaerial, oceanic, and continental setting, and 3) epithermal deposits (high- and low-sulphidation) associated with subaerial and shallow-marine environments (Lydon et al., 2004).
o Volcanogenic Massive Sulphides
Volcanic massive sulphide (VMS) deposits form by discharge of hydrothermal solutions onto the seafloor, commonly near plate margins. A comprehensive synthesis of VMS deposits is provided by Galley et al. (2007). VMS deposits typically develop in the form of a concordant lens that is underlain by a discordant stockwork or stringer zone comprising vein-type sulphide mineralization located in a pipe of hydrothermally altered rock.
VMS deposits typically have density, magnetic, conductivity, and acoustic velocity properties that differ significantly from those of their host rocks.
There is, therefore, enormous potential for direct detection of orebodies using geophysical methods that measure these properties.
The most common sulphide mineral in VMS deposits is pyrite, which may be accompanied by subordinate pyrrhotite, chalcopyrite, sphalerite, and galena (Galley et al., 2007). Magnetite, hematite, and cassiterite are common nonsulphide metallic minerals, and the gangue mineral barite may also be present. Densities of these minerals range from 4.0 to 7.5 g/cm3
o Sedimentary Ehalative Sulphide Deposits
SEDEX deposits (Pb-Zn) are found in sedimentary basins, usually in the form of conformable to semiconformable sheets or tabular lenses of stratiform sulphides (Lydon, 1995; Goodfellow and Lydon, 2007). Such bodies have typical aspect ratios of 20, maximum thicknesses of 5 to 20 m (Lydon, 1995), and may extend over a distance of more than 1 km (Goodfellow and Lydon, 2007).
The principal ore inerals are sphalerite and galena. Chalcopyrite is sometimes concentrated in feeder zones of SEDEX deposits, but only rarely attains concentrations of economic interest. Pyrite is the most abundant sulphide, and pyrrhotite may be common.
The physical and chemical properties of SEDEX deposits make them amenable to detection by several geophysical techniques. In the Purcell Basin, southeastern British Columbia, sulphide mineralization associated with the Sullivan and smaller North Star and Stemwinder Pb-Zn-Ag deposits is reflected by strong finite conductors and positive magnetic anomalies (Lowe et al., 2000).
o Mississippi Valley Pb-Zn-Cu-U
Mississippi Valley-type (MVT) Pb-Zn deposits are typically stratabound, some are prismatic pipe-shaped bodies, hosted by limestone or dolomite in platform carbonate sequences (Sangster, 1995) and occur in clusters. Sphalerite and galena are the dominant ore minerals that characteristically occupy open spaces in carbonate breccias; replacement of host rocks is relatively rare.
Most deposits or MVT districts occur below unconformities or nonconformities, related probably to minor uplift or warping, but few deposits have been affected by subsequent deformational events. Dimensions of the one hundred known orebodies in the Pine Point district vary from 60 to 2000 metres in length, 15 to 1000 metres in width, and 0.5 to 100 metres in thickness (Hannigan, 2007).Additional information on various aspects of MVT deposits may be found in Dewing et al. (2007), Hannigan (2007), Paradis and Nelson (2007), and Paradis et al. (2007).
o Porphyry Copper Deposits
Porphyry deposits are a major source of production for Cu, Mo, and Re, and an important source forAu,Ag, and Sn. Sinclair, (2007) provides a comprehensive synthesis of porphyry deposits. Porphyry-style base and precious metal mineralization is spatially and genetically related to high level, epizonal and mesozonal felsic to intermediate porphyritic intrusions and adjacent host rocks.
Mineralization may be in the form of stockwork quartz veins and veinlets, fractures, disseminations, and replacements containing pyrite, chalcopyrite, bornite, and magnetite. Deposit forms are quite variable and range in size from hundreds to thousands of metres laterally and with depth, and are commonly zoned with barren cores and generally concentric metal zones surrounded by barren pyritic haloes.
Alteration associated with porphyry deposits is typically zoned from an inner potassic (biotite and/or K-feldspar) alteration zone, closely associated with mineralization, to a more extensive propylitic alteration zone consisting of quartz, chlorite, epidote, calcite, albite, and pyrite, which surrounds the inner potassic zone. Zones of phyllic and argillic alteration may occur between and overlap with the inner potassic and outer propylitic alteration zones. Minerals relevant to geophysical detection include magnetite, pyrite, chalcopyrite, biotite, K-feldspar, and sericite.
o Uranium Deposits
Unconformity-related uranium deposits are the most significant high-grade, low-cost source of uranium in the world (Jefferson et al., 2007). In Canada, notable targets for exploration are the mid-Proterozoic sedimentary Athabasca and Thelon basins in the northwestern Canadian Shield.
The deposits occur typically along or near unconformities between metamorphic basement rocks, commonly containing graphitic pelitic units, and overlying undeformed sedimentary successions consisting mainly of quartzose sandstone. Graphitic units provide a lithological control on mineralization (Ruzicka, 1995), acting as a reductant.
Additional deposit types include: Olympic Dam, Magmatic Nickel Copper PGE, Kimberlite Diamond Deposits, Chromite Deposits, Skarn Deposits, Mantos Deposits, Redbed Copper Deposits, Layered Intrusion Ni-Cu, Iron Sedimentary Deposits, Tin Vein-Stockwork Deposits, Intrusive-hosted Breccia REE
Environmental geophysics is primarily used to identify, map or predict the presence and potential movement of surface water and groundwater and to identify contaminants in the soil within the upper 10 to 50 m of the Earth's surface (https://cseg.ca/student/careers/enviro.htm. 2018).
In environmental investigations, geophysical surveys provide depth images of the physical property variations in the soils and rocks, which are further associated to subsurface contamination. Geophysics is a useful tool for reducing the risks and costs of detecting and characterization of contaminated areas.
Mapping and monitoring contaminated soils.
The risks associated with contaminated soils, sediments and other environmental pollutants are basically related to the number of people potentially exposed to the contaminated areas and the risk of expansion of contamination to other subsurface and groundwater reservoirs.
DC Resistivity Imaging, Seismics, EM profiling and sounding, Self Potential and Gradient magnetics are commonly used to map those sites and to estimate-monitor the contamination levels for further environmental assessment and remediation (examples are concentrations of metals, agricultural contaminants, petroleum contaminated soils).
Hazardous waste site investigations
DC resistivity imaging, Seismics and EM methods are used to map anomalous zones associated to hydraulic conductivity variations within the bedrock in the waste disposal sites.
Contaminant Plume mapping
Contaminants dissolved in the groundwater will alter the physical and chemical properties of soils, rocks and groundwater. Contaminant plume mapping is done by geophysical mapping of natural features that will control contaminant migration (pathways of preferential permeability), homogeneous geologic settings permit the interpretation of contaminants. DC resistivity imaging, Seismics and EM methods are used to map anomalous zones associated to contaminant plumes.
Mapping and monitoring pollutants in groundwater.
The assessment of the degree and extent of pollution in groundwater involve bedrock characterization and mapping, fracture analysis, and hydraulic property estimation (conductivity, permeability, etc). The application of seismic refraction surveys, electrical imaging and borehole resistivity are essential in groundwater pollution mapping and monitoring.
Soil salinity evaluation.
Agricultural properties subject to irrigation can be compromised as water evaporates and formerly dissolved materials remain in the soil as salt deposits. Over time, this accumulation can remove the soil from productive agricultural use. Monitoring and mapping the soil conductivity can modify irrigation practices modified to reduce the soil salinity. Seismic refraction surveys, Electrical imaging, VES and EM are essential in soil salinity evaluation.
Landfill Imaging/ Boundary Mapping/Delineation
Evaluating the inhomogeniety of the landfill materials (usually chemical waste materials) and mapping its geometry is a common task resolve by geophysicists. 1D Electrical methods have been successfully applied to map the bottom of landfills and delineating subsurface waste areas. Electrical 2D Resistivity imaging provides depth estimation and internal structure and composition of landfills. Electromagnetic (EM) methods are commonly used in delineating lateral extend of landfills. Discrimination between metallic and non-metallic waste areas within landfills is also provided.
Surface and borehole geophysical methods are used for measuring subsurface physical property changes; including profiling of bedrock topography and structure, mapping of the water table, delineation of fracture systems, estimation of permeability of aquifers, mapping salt water-fresh water boundaries, estimation of groundwater contamination, imaging confining layers, and migration pathways.
Geophysics is an important tool in aquifer management when targeting areas for detailed investigation and well location for water supply. Surface geophysical methods include; seismic refraction, electromagnetic conductivity profiling and sounding, 2D resistivity imaging, 1D resistivity sounding, magnetic and self-potential. Borehole geophysical methods include; borehole resistivity and fluid resistivity.
Ground Water Resource Exploration
Groundwater resource investigations can be made more efficient through the use of geophysical methods, which permit an assessment of a large area to refine target locations to manageable levels. Geophysical methods include VES, Electrical profiling, EM and Seismics.
Groundwater flow velocity and direction estimation.
Well location for water supply
Geophysics can be used to estimate aquifer parameters such as transmissivity and permeability. VES, Electrical profiling, EM and Seismics methods are frequently used to identify areas of preferential groundwater permeability to establish optimal drilling locations.
Depth To Groundwater
The estimation of the water table depth is important for drilling activities, environmental investigations, and hydro-geological and engineering studies. VES, Electrical profiling, EM and Seismics methods are used to identify the depth to the water table.
Salt-water intrusion mapping
The presence of saltwater intrusion in fresh aquifers is a serious concern for many communities in coastal areas. Ionic dissolution of salt in fresh groundwater causes a decrease of electrical rock resistivity in the areas where salt intrusion is taking place. The resistivity contrast created by the salt intrusion is well measurable using 2D electrical resistivity imaging, resistivity profiling or conductivity EM methods.
Geophysics is used in engineering geology for profiling of bedrock topography and structure, location of voids, sinkholes and old mineshafts, mapping of the water table, and integrity testing of various surface and underwater structures.
Geophysical methods include gradient magnetometry, induced polarization, EM conductivity profiling and sounding, 1D resistivity sounding, 2D resistivity imaging, self-potential, seismic refraction and induced polarization, .
Location of Underground storage tanks /buried drums and utilities
Identifying the location of buried drums is often an important part of environmental investigations. Use of electromagnetic techniques and magnetometer has all provided successful results. Detail Seismic surveys are used to delineate subsurface features such as underground storage tanks, buried drums, and utilities.
Inducing a signal onto a subsurface utility and tracing the signal as it moves along or within the utility map underground pipes and utilities. Inductive locating is a method for locating unknown or lost conductors.
Soil classification and property analysis.
Determination of soil properties can be a fundamental objective of a geological investigation (eg. location of clays or sand soils). For geotechnical investigation shear and compressional velocity information can be used to establish the Poisson's ratio for the soils and combined with soil densities to estimate Young's modulus, shear modulus and dynamic modulus properties of the soils. EM conductivity and Seismic refraction methods are used.
Depth of topsoil estimation
In agriculture, the estimation of the depth of topsoil is an important issue. The areas that show very shallow topsoil are correlated to low-productivity rates. Deep topsoil corresponds to higher productivity. Seismics refraction, Electrical Sounding and 2D Electrical Imaging are used in the estimation of the topsoil depth.
Location of septic systems
Locating septic systems can be done to facilitate repair or investigation of environmental impacts. Detailed Seismic surveys or conductivity methods are used.
Location of burial trenches
Location of former burial trenches can be an important part of many environmental investigations. Geophysical methods provide an excellent method to identify and map these features. EI, MAG and Seismics and EM are used to measure changes in the physical properties of subsurface materials.
Reservoirs Leakage Detection
Leakage of water through a dam poses a serious safety hazard to public and environment in the adjacent areas. Spontaneous Potential methods measure the natural electrical potential generated by the water flowing through fractures and cracks in the dam and/or reservoir structure. Electrical resistivity methods are used to evaluate the saturation within dams as well as mapping fractures below the dam and reservoirs.
Geomembrane Leakage Location
Geomembrane leak location surveys involve applying an electrical potential either side in order to identify holes and tears of synthetic membranes. The method has been used to locate small holes below protective covers.
Karsts investigations/ Sinkholes and cavities
Karts cavities can cause damage to a homes and constructions.
Electrical Imaging (EI) and Seismics are used for Karts investigations and location of karst-related voids in the subsurface.
Rock Rippibility Studies
Rippability investigations include estimation of the depth to bedrock and water table; to characterize rock type and degree of weathering; and to locate fractures, faults, and buried channels. A refraction seismic survey is used to measure compressional-wave velocities in order to evaluate the rippability of the subsurface. Individual subsurface layer depths and thickness can be calculated based on the analysis of sonic wave arrival times.
Fracture zone mapping, delineation and evaluation
The precise location of fault zones can influence the results of engineering and environmental investigations. Applications include locating high yield wells, or the identification of potential seismic hazards. DC resistivity, Electrical Imaging and Seismic profiling can be used to locate fault systems and the fault dip and direction.
Geologic Hazards Investigations.
Seismic shear velocity measurements performed on site using conventional refraction methods is the most common method used for geologic hazard investigations. Rock and Soil Properties estimation (Elastic Moduli And Shear Wave Velocities).
Seismic methods are used to investigate sites that require an assessment of engineering properties in the subsurface. The dynamic moduli can be fully calculated after measuring seismic velocities on site. Given measurements of seismic velocities and an estimate of soil density, calculations of the Poisson Ratio, Shear Modulus, Young's Modulus and Bulk Modulus for a site can be easily done. These properties can be applied to significant engineering projects with great percent of accuracy.
Seismic surveys are used to identify variations in depth to bedrock, as well as changes in velocity and elastic properties within the bedrock potentially indicative of physical rock property variations.
Power System Grounding
High quality grounding surveys required by the utility industry are performed with standard geophysical resistivity equipment. Geophysical methods include EI, EM and VES.
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