Geophysics Program Design 

The final survey design and line plan takes into account various factors, such as geology, commodity being targeted, target size, target orientation etc. The line spacing can vary from several 100m to several 10’s of metres. The reading station intervals are also variable from metres to 100’s of metres. 

 Survey Design – example of ground magnetics survey line plan over an iron ore deposit.

Survey Design – example of ground magnetics survey line plan over an iron ore deposit.

 Survey Design – example of gravity survey line plan over a basin target.

Survey Design – example of gravity survey line plan over a basin target.

Survey Types 

Commodity Exploration (List Commodities): 

Technique

Commodity Uses

Magnetics

Air

Lode Gold
Shear or Vein Hosted Gold
Diamonds
VMS & SEDEX
Porphyry Cu
Fe Ore
Structural Mapping
Oil

Ground

Lode Gold
Shear or Vein Hosted Gold
Diamonds
VMS & SEDEX
Porphyry Cu
Fe Ore
Structural Mapping

Electro-Magnetics

Air

VMS & SEDEX
Diamonds
Ni-sulphides & PGE’s
Structural Mapping

Ground

VMS & SEDEX
Ni-sulphides & PGE’s
Structural Mapping
MVT’s

Gravity

Air

Kimberlites
VMS & SEDEX
Fe Ore
Oil

Ground

Kimberlites
VMS & SEDEX
Fe Ore
VMS

Resistivity

 

Diamonds
VMS & SEDEX
Shear or Vein Hosted Gold
MVT’s

Induced Polarization (IP)

 

VMS & SEDEX
Lode Gold
Shear or Vein Hosted Gold
Ni-sulphides & PGE’s
MVT’s

Ground Penetrating Radar (GPR)

 

Alluvial Gold/Diamonds

Mapping

Geological mapping is an essential process in all mineral exploration projects. However, mapping the surface geology and structure only provides facts for 2 dimensions. The 3rd dimension is constructed from interpretational cross-sections. Geophysics provides independent information of the 3rd dimension: depth. In addition geophysical techniques are able to “see through” overburden. This is particularly useful when attempting to map areas where outcrop is sparse due to forest, desert or thick soil profiles. The variety of geophysical methods available can provide both regional and deposit specific information. 

The following are examples of how geophysics can be used along side mapping to aid exploration:

  • Magnetic maps are excellent for seeing structural information such as faults and shears. They can also show magnetic variation in rock types, which is useful for mapping, and be used directly to target commodities where there are magnetic by-products e.g. residual magnetite in kimberlites, Archaean hosted gold-bearing shears etc.  
  • Ground Penetrating Radar (GPR) can be used to map depths up to and below the water table by showing the contrast between different rocks and sub-stratum types. This is particularly useful for mapping palaeo-channels in alluvial gold and diamond exploration. 
  • Gravity surveys can show the contrast in different rock type densities. Metaliferous deposits are generally of a higher density than the surrounding host rocks and can be mapped on both a regional and deposit scale. 
 Regional aero-magnetics and geological interpretation of GreenStone Belt overlay.

Regional aero-magnetics and geological interpretation of GreenStone Belt overlay.

Field data collection Quality Assurance and Quality Control (QA/QC) 

New Era Geophysics is dedicated to offering the highest quality of service. In order to achieve this we operate strict QA/QC procedures throughout the data collection, processing and interpretation stages. 

The key to effective QA is planning and a good plan should identify the framework of steps that will result in quality data being collected. The following are aspects that should be considered in the initial stage of planning:

  • What is the purpose of the geophysical study?
  • What geophysical technique is best for the investigation?
  • What parameters associated with the chosen technique will show the target in the best way?
  • What are the likely errors to occur given the parameters of the project and what are the acceptable margins of error?
  • What are the limiting factors on site? E.g. location, access, topography, vegetation 
  • What are the boundaries of study? E.g. geographical extent, time, budget.

Once these questions are answered a detailed data collection plan can be tailored for the individual project. It should ensure that best practice is adhered to or exceeded in every aspect of the data collection. 

QC should take place in at least four stages during geophysical work:

  1. Planning 
  2. Field collection of data
  3. Data processing and 
  4. Interpretation. 

However, regardless of QC procedures or advanced data processing techniques, there is no way to remedy low-accuracy, poor quality data that has been collected in the field. Therefore, the key area of QA/QC must be the initial data collection. At New Era Geophysics we pride ourselves in the abilities of our team and the quality of the field data we collect, even in challenging environments. 

QC, like QA, comes down to planning. Effective QC at each stage comes from having a documented plan of procedures and then following that plan and documenting all work carried out.  Field teams fill in logbooks detailing every aspect of a day’s field work and highlight potential problems in the field. Each night the data, plus log, is sent to New Era’s geophysicist, who has 25 years of field experience. The data are reviewed in line with best practices relevant to the survey being undertaken. Geosoft Oasis Montaj is used for the QC process. Any errors or repeat readings required are communicated to the field teams nightly. By the end of the survey, the field data has been reviewed constantly by the geophysicist, and processed and plotted in real time. The field team is required to stay on site until the go ahead is received that all data is error-free and within specification.

Processing and Interpretation 

Once high quality data has been collected and checked, processing and interpretation are undertaken by New Eras geophysicist, using Geosoft Oasis Montaj. Data is processed in line with global best practice, using the newest techniques on the market, as well as the tried and tested. Communication with the client is paramount and the client’s wishes are taken into account daily. Once the processed products are in place, modelling and interpretation are the final stages before report-writing. Interpretation is taken to the level of detail according to the contract and the client’s wishes. All available data such as geological mapping, geochemical datasets, remote sensing datasets, and drilling are taken into account, and the resulting geophysical interpretation is as ‘geological’ as possible, drawing upon the decades of exposure and experience at New Era’s disposal. Structural interpretations are one of New Era’s strengths, and targeting using structural information is a seasoned product. Usually geological or structural maps are the final GIS product, with a set of targets and recommended boreholes- depending on the commodity being explored for and the objectives of the survey. Both of them are catered for in terms of the final products, images of the geophysical survey results, as well as the final interpretation.

For modelling New Era has a range of 2D gravity and magnetics forward modelling packages, as well Maxwell EM plate modelling software. For 3D inversion, New Era has access to a number of packages including Mginv3D and Geosoft’s VOXI and MVI. EM and AMT 3D inversion is still outsourced at this stage but magnetics, gravity, IP, and resistivity can all be carried out in-house. The final output from modelling is either a table of locations, sizes and depths of modelled bodies, as well as GIS output (e.g. MapInfo or ArcGIS formats) containing the modelled bodies, or 3D dxf shells of the  inverted bodies- which may then be imported into any 3D package for further analysis and drill planning.

Report writing is in line with the client’s wishes, ranging from full logistical and/or field reports, to lengthy and detailed interpretation reports, or short summary reports listing only the major findings. Again, global best practice is followed and client satisfaction is the major objective.