Geoscience
GIS Map Gallery
Geographic Information System
Manitoba’s Integrated Anomaly Map
Introduction
The search for diamonds in Manitoba is at a relatively early stage with exploration active for approximately 6 years. Kimberlites have been discovered to the east in Ontario, west in Saskatchewan and north in Nunavut, but to date only one small kimberlite has been discovered in Manitoba.
Extensive study has revealed many characteristics associated with kimberlite intrusion. From what is known about these associations there appears to be no fundamental reason that would indicate that kimberlites do not occur in Manitoba. It must be recognized however that portions of Manitoba are covered with a thick cover of Quaternary sediments. This is the case for northern and northeastern Manitoba, which is currently the focus of diamond exploration by industry.
In order to help promote diamond exploration the Manitoba Geological Survey has undertaken a program of compiling and synthesizing data that may help to focus exploration into favourable regions. The process involves such diverse functions as compiling all available kimberlite indicator mineral survey data (see the adjacent post) to various research projects into geochronology, crustal structure and tectonics and Quaternary stratigraphic studies. This presentation deals with a project to compile diverse data sets using a Geographic Information System in an attempt to produce a map that can help identify structural and petrologic anomalies that can have some bearing on kimberlite exploration. The data types include geophysical maps, structural and lineament studies and the compilation of documented anomalous occurrences such as carbonatite and syenite intrusions and structures that involve both the Precambrian and the overlying Phanerozoic rocks. This process is at an early stage and the current map is a preliminary presentation.
The Rationale
Study of diamondiferous kimberlite and lamproite bodies worldwide has identified many associations or controls on their distribution including:
- thick lithosphere,
- old (Archean), cold lithosphere,
- lithospheric extension,
- locations on cratonic margins,
- association with extension structures such as grabens, mafic dike swarms and crustal-scale faulting,
- spatial association with alkaline intrusions, syenites and carbonatites,
- based on known occurrences near Manitoba the likely age of kimberlite intrusions would be Jurassic to Cretaceous.
The information layers included in this compilation were chosen to help identify associations between these features. Included are:
- provincial scale gravity data,
- aeromagnetic trends and breaklines,
- major faults,
- surface lineaments,
- mafic dike swarms,
- point locations of a unique geological character such as the Wekusko kimberlite, Eden Lake carbonatite and Cinder Lake nepheline syenite,
- results of KIM surveys.
The Map
This presentation combines a number of direct data observations with interpreted information derived from other data sets. The theme near the bottom of the legend called ‘Gravity over shaded magnetics’ is an example of fusion of data sources where colour polygons that form the background represent the provincial gravity map ranging from blue for low to red for gravity high. The shadowgram behind the gravity data is derived from the 1:1 000 000 residual total field aeromagnetic map.
Magnetic trend lines on the map were derived from careful examination of the total field data and represent 3 basic types:
- breaklines that mark a transition from one type of magnetic pattern to a visually different pattern (terrane boundaries and major lithostratigraphic breaks)
- narrow linear traces that can represent faults or mafic dikes
- linear magnetic lows that cross all other feature.
Surface lineaments were identified using a 90 metre digital elevation model (DEM). Elevation shadowgrams were produced with 3 different illumination directions to ensure that all possible lineaments were identified.
For both the magnetic linear and surface lineament studies slope aspect analysis was used to help separate linear from curvilinear trends. It is assumed that long, straight, linear trends are likely to young structures.
Major faults and mafic dike swarms (Mackenzie and Molson) were derived from existing geologic maps. The dike swarms were also extrapolated using aeromagnetic maps.
The process of identifying anomalous locations has just started and a representative selection is included on the map. These locations include both unique rock occurrences (kimberlite, syenite, Cretaceous volcanism) and structural anomalies (faulting in the Paleozoic). The KIM distribution database can also be displayed on top of the anomaly map.
Development of this compilation map will continue with the addition of further data sets such as updated geochronology information (regions of ancient crust) and additional geophysical and interpreted data that may help delineate areas of crustal thickening.
The data on kimberlite indicator mineral occurrences is derived from the Manitoba Kimberlite Indicator Mineral Database version 1.1 (Open File report OF2004-1).
