Posts Tagged Mira Geoscience

About 3d modelling on Mineral Exploration Roundup 2011 in Vancouver

Posted by on Friday, 7 January, 2011

Tuesday, January 25, 2011

Technical Session: Public Geoscience: Investing in Tomorrow’s Discoveries:

Regional 3D Inversion Modelling of Airborne Gravity, Magnetic, and Electromagnetic Data in British Columbia, Nigel  Phillips from Mira Geoscience/Geoscience BC

DARNLEY BAY – summer results and discoveries

Posted by on Tuesday, 14 September, 2010
Base Metal Targets
The exploration and drill targets for base metals, shown in Figure 1, were prepared from analysis and modelling of the recently completed gravity, electromagnetic and magnetic surveys flown over a large portion of its properties near Paulatuk, NT. The analysis was prepared in conjunction with mapped geology, topography, satellite imagery and previously acquired airborne and ground geophysical data.
The following provides a summary of the 41 separate base metal exploration targets selected as a result of the analysis and modelling:
Gravity (22 targets) 76 km2; Magnetic (7 targets) 108 km2; Electromagnetic (12 targets) 54 km2.
The methods indicate the data type where the target is most evident, although many targets incorporate coincident or complementary geophysical responses from at least two data types. The base metals targets are broken into several categories, depending on the nature of their responses and their estimated depths. Nine of these targets are designated for assessment by geological prospecting and sampling as they may outcrop.
Location map showing the 41 base metals targets on the 100%-owned properties of Darnley Bay Resources Limited. The red dashed outlines indicate the two areas of highest priority for follow-up.
3D Gravity Modelling
Geoscientists study the earth’s gravity field to determine the density of the rocks in the subsurface. Changes in density from surface to tens of kilometers in depth affect the gravity field that we measure. The more basic (mafic) classes of igneous and metamorphic rocks, and most metallic minerals, have higher densities and produce stronger gravity responses. The 132 mGal Darnley Bay gravity anomaly is perhaps the strongest of its kind in the world, reflecting an isolated intrusion.
In 2007, Darnley Bay contracted Mira Geoscience, through its Vancouver office, to apply 3D modelling to the ground gravity and airborne magnetic data available over the Darnley Bay anomaly and surrounding region. A 3D model of a large, deep-seated mafic/ultramafic intrusion was developed to explain the anomaly on a regional scale. The effect of this model was subtracted from the gravity and a more detailed model of the upper 10 km of the earth’s crust was prepared from the residual gravity field, to ascertain the shape of the anomaly source at depths of economic interest. The modelling in 2007 resulted in the reassessment of the geological models to explain the anomaly source and its mineral potential. Darnley Bay realized that it required gravity data in much greater detail before embarking on a drill program.
Northtech Drilling Ltd. commenced drilling Darnley Bay’s first 2010 base metals target on August 28.
Target EM-8 is currently being drilled, an electromagnetic anomaly with coincident magnetic response interpreted from the 2010 VTEM survey (see target map on the home page at It will be followed by target M-7, a magnetic anomaly with coincident electromagnetic response. Both drill holes are at 65° from the horizontal with a length of 300 m. Concurrently, other targets are being followed up on the ground with gravity and magnetic surveys, and geological prospecting, to prioritize targets for the continuing drill program.
The airborne gravity survey (Sander Geophysics) completed in April 2010 confirmed the size, shape and amplitude of the Darnley Bay anomaly and greatly improved the resolution and detail. Mira Geoscience was once again contracted to prepare a 3D model. Mira utilized the same regional model for the intrusive body and prepared a new model of the upper 10 km of the earth’s crust from the airborne survey’s residual gravity field. It utilized the free-air gravity field and incorporated a correction for the surface topography. Since the surface rocks incorporate a range of gravels and sediments with different densities, their effects cannot be fully corrected for and as a result, some topography is visible in the model.
The software used to prepare the new 3D model is Mira’s implementation of the GRAV3D module developed by the Geophysical Inversion Facility at the University of British Columbia.  The 3D inversion was constructed as follows:
1. Preparing a representation of the earth as a volume measuring 63.5 km E-W by 66.0 km N-S by 10.25 km vertically. The cells within the volume measure 500 m x 500 m x 250 m.
2. Implementing geological constraints, incorporating the sediments mapped on surface and their densities, and the log of Darnley Bay’s 2000 drillhole.
3. Applying the GRAV3D inversion, which determines a geologically reasonable density to each cell in the model while best-fitting the observed gravity data. This process takes several days of continuous iteration on a massively parallel computer.
The result is a 3D volume model where the density varies between each cell. For display purposes, a series of density surfaces are extracted from the model to better appreciate the geometry and concentrations of higher density material.
Darnley Bay Resources Limited and Diadem Resources Ltd. announce that they have completed the first phase of 2010 drilling on their 50/50 joint venture package of 33 claims on the Parry Peninsula, Northwest Territories. Of the four targets drilled, three have resulted in the discovery of new kimberlite pipes. These are in addition to the ten kimberlite pipes discovered in 2000, of which six have proven diamondiferous. The kimberlite material intersected in the 2010 drilling is being prepared for shipping to CF Mineral Research Ltd. in Kelowna BC for analysis.
Darnley Bay and Diadem are quite encouraged by the initial success of the drill program. Numerous high priority targets remain untested. The results of this first phase are being incorporated in planning for the second phase of 2010 drilling, as well as determining the targets that are better suited for drilling from frozen lakes in February-April 2011. Diadem is funding the 2010 program.
Hole MT112-01
This hole targeted a 1.7 ha ground magnetic low of 10 nT amplitude, partially covered by a lake. It intersected 15.35 m of kimberlite, hosted in dolomite. The kimberlite intersection is described as “Dark green to black, fine grained matrix consisting of dark green ferro-magnesian minerals and 10 to 35% green partially altered olivine and peridotite fragments, some being completely talc altered. Contains numerous greenish, subrounded possible mantle derived fragments to 100 mm.”
Hole MT102-01
This hole targeted a 3.6 ha ground magnetic low of 325 nT amplitude, partially covered by a lake. It intersected 7.6 m of kimberlite, hosted in dolomite. The kimberlite intersection is described as “Dark gray to blackish-green, massive, fine to medium grained kimberlite (micro breccia). The mass of the kimberlite comprises dark green 1-5 mm mafics in a white clay – calcite matrix.”
Hole MT10-03
This hole targeted a 10.2 ha ground magnetic low of 105 nT amplitude, partially covered by a lake. It intersected 0.6 m of kimberlite, hosted in dolomite. The kimberlite intersection is described as “Dark gray to black, loose packed, sub-rounded to sub-angular wall rock and some mantle derived fragments in a fine to medium grained matrix. Fragments consist of 1 to 25 mm black mudstone and chert, gray dolomite and some greenish-gray, rarely apple green, serpentinised mantle-derived xenoliths.”

To great resources with Mira

Posted by on Wednesday, 31 March, 2010

Mira Geoscience has held 4 days GOCAD training session in Toronto with support of MacDonald Mines and Energiser Resources.

The Gocad® Mining Suite is the most advanced, easy-to-use, and cost-effective 3D earth modelling system available to the mining, geotechnical, and environmental industries. It is an extension of Paradigm™ Gocad®, the earth modelling standard in the oil and gas industry.


Rock property database

Posted by on Thursday, 18 March, 2010

In this 2010 year the program Targeted Geoscience Initiative (TGI-3) is finishing. The Government of Canada committed $25M over five years to extend the mission of the Targeted Geoscience Initiative Program with a focus on base metal reserves in established mining communities. And through the TGI-3 program, additional petrophysical data will be added to the database for the TGI study areas (Southern B.C., Cantral Manitoba-Saskatchewan, Central Newfoundland, Abitibi, Ontario-Quebec, Bathurst, N.B.).

The National Rock Properties Database (NRPD) has been in development since 1998 and was initiated through a partnership between Noranda, Falconbridge, the Geological Survey of Canada, Quantec Geoscience Ltd, and Mira Geoscience Ltd. The result of the original development was a fairly complete data model and interface for the maintenance and query of rock property data collected using wireline geophysical methods. Through a partnership between McMaster University, MIRA Geoscience, and the GSC through the CAMIRO Project in 2004-05, the NRPD data model was extended to include rock property data measured on rock samples, definitions of universal lithology and alteration classifications for geological description.

The NRPD resides in an Oracle database. The database currently contains over 5 million rock property data records. Key parameters of each dataset include location coordinates, so that data can be queried by region, as well as geological attributes. The parameters currently available for query are Caliper, Conductivity, Density, Gamma, IP, Magnetic Susceptibility, Neutron porosity, Potassium, Resistivity, Self potential, Self potential gradient, Uranium, Temperature gradient, Temperature, Thorium and Acoustic velocity.