Definition of 3D common earth models:

Géologie Québec proposes to produce 3D common-earth modelling with quantitative geological interpretations of Abitibi Subprovince mining camps. This approach is based on shared physical properties that permits the formation of a quantitative geoscientific link integrated into the 3D common-earth model. Consequently, it is possible to juxtapose the geological and geophysical models, particularly when physical properties (density and magnetic susceptibility measurements) are available for rock outcrops. A similar approach can be used to integrate geological interpretations and the lithogeochemical data. 3D common-earth models aim to fit the criteria defined by each of the disciplines involved within the project and support quantitative-geology applications. Therefore, the principal stakeholders involved in a project make reference to a single model using the same platform (Figure 1). A regional 3D common-earth model therefore acts as an integration and a processing platform for all available geoscientific data on a quantitative basis.

Data integration within 3D models depends on data availability, density and distribution, as well as the project objectives sought. To ensure the success of 3D common-earth modelling, the following data must be available:

1. Surface data (2D):

• Topographic elements (digital elevation points, hydrography)
• Mining and road infrastructures
• Main lithological and stratigraphical contacts (key horizons marker)
• Faults and folds traces, planar and linear structural measurements
• Systematic sections covering the entire study area
• Lithogeochemical analyses, alteration indexes and economic assays
• Geophysical survey data
• Physical rock properties (magnetic susceptibility measures, density)

2. Drilling information available in 3D:

• All available drilling data (collar, deviation, geology, mineralized intersections, alteration indexes, magnetic susceptibility measures, densities, etc.)

3. Ground-based, drilling-related and airborne geophysical surveys:

• Seismic data
• Magnetic data
• Gravimetric data
• Electric methods (DC, IP)

The 3D common-earth model of the Joutel mining camp (Figure 2) was used as an initial project for this new type of dynamic, queryable, and upgradable product. Production of this model required an optimal use of public digital database as well as the recovery of major databases from mining companies. Also, validation exercises (ex: poll survey) done on the Joutel 3D common-earth model were used to define the mining exploration industry’s needs in regard to 3D products. Finally, the multidisciplinary approach used in the 3D geological modelling for the Joutel mining camp demonstrates that this new digital regional product (1/20 000) can also be used as an exploration tool.

A second project is currently under way in the Destor-Porcupine region (Figure 3). The main objectives of this 3D common-earth modelling were to:

1. Produce a regional 3D common-earth model (11.4 X 4.0 X 1.0 km) integrating all of the geoscientific data (geology, geophysics, lithogeochemistry, drilling, mineralization, alteration index, etc.) available in this mining camp;
   
2. Define the 3D gold distribution in function of the diamond drill hole data available;
   
3. Establish queries on the basis of geological, geophysical and geochemical data in order to establish new exploration targets.

The compilation of multidisciplinary data for the 3D modelling of Destor-Porcupine took place during the summer of 2002. Data integrated within the gOcad® modules was primarily acquired from exploration companies currently active within the Duparquet mining camp, from the SIGÉOM and from a purchased lithogeochemical database from Jean Descarreaux. A total of 1,746 drillholes, including 50,348 economic assays and 3,638 lithochemical analyses, were imported into the 3D model.

Inversion of the magnetic data indicates that the Duparquet Formation is locally shallow and that certain geological contacts must be reverified. In addition, integration of the drillholes gave us a better idea of the geology as well as the gold distribution and alteration.