In 2020, Aurora AG Limited successfully completed more than 10,000 line kilometers of high-precision detailed magnetic survey. The results allowed taking a fresh look at the mineral potential of the target areas and obtain a high-quality geophysical basis for designing follow-up exploration works.
Aurora field crew carried out the acquisition using high-tech magnetometers manufactured by GEM Systems (Canada). The Overhauser effect of these magnetometers allowed overcoming limitations typical to ground magnetic survey, at the same time maintaining high accuracy and productivity.
Final processing of the acquired data was performed using innovative techniques of geophysical field analysis, including:
- robust 3D inversion in VOXI cloud platform (Geosoft OM),
- Gridsluth depth estimation
- Multiscale Edge Analysis for calculating dip angles of sequences
- Data enhancement methods
A geophysical model built by Aurora AG specialists and geological materials provided by clients were used for a comprehensive geological and geophysical interpretation. As a result, we identified targets with the highest mineral potential (gold, polymetals, titanium).
Gold. Magnetic survey at one of potential gold areas was set to map ore-controlling massive ultramafic intrusion and delineate its contacts, where ore bodies are localized. Bedrocks in the area are under a thick regolith cover, which obstructs the geological mapping and prompts the use of geophysical methods.
Aurora AG Limited team achieved convincing results by performing high quality survey and applying advanced processing and interpretation techniques:
1.Optimized selection of parameters for 3D magnetic susceptibility inversion that mimics the ultramafic intrusion and is calculated by VOXI (Geosoft OM) lead to a robust physical and geological model of the deposit.
2.Exploration drilling, which was based on geological and structural analysis substantially supplemented by geophysics, intersected several lens-shaped mineralized zones at the contact of the ultramafic intrusion with quartz-metasomatic rocks. Identified deposit is related to listvenite ore formation with an average gold grade of up to 5 g/t.
As the result, the acquired data allowed distinguishing the patterns of gold orebodies localization within the area and, in turn, building search criteria for subsequent highlighting of high mineral potential zones. This case demonstrates successful application of geophysical services provided by Aurora AG Limited for the search of gold ore deposits.
Figure 1. Physical-geological model of the deposit: 1) 3D magnetic susceptibility inversion; 2) ore bodies with different gold grades (1-5 g/t); 3) future mine pit concept; 4) superimposed TMI map.
Base metals. The magnetic survey conducted by Aurora AG Limited has clearly demonstrated its efficiency in exploration of base metals deposits at Western Mugodzhary.
The results of quantitative interpretation, which was based on the study of known polymetallic occurrence, made it possible to target 3.9 km long area with multiple polymetallic Mo-W and Au mineralization objects (Figure 2).
The known ore occurrence is confined to the western exocontact of granite body with metamorphosed effusive-sedimentary sequence, where mineral structure of ore body comprises sulfides: galena, sphalerite, pyrite and pyrrhotite. Moreover, serpentinized listvenites of high gold content (up to 2 g/t) predicts gold potential as well.
Factors of practical interest of the identified magnetic anomalies:
- Identified patterns between the character of the observed physical fields and their confinement to certain geological formations;
- Mineral composition of ore bodies (pyrrhotite and serpentinite inclusions) with enhanced magnetic properties;
- Detected by VOXI 3D inversion group of near-surface objects (Figure 3), which has identical nature with the known ore occurrence and are located at favorable geological conditions.
Figure 3. Group of near-surface objects
The acquired data were sent for further verification by drilling and drift works. Thus, the magnetic surveys conducted by Aurora AG Limited once again provided geologists with an effective tool for mineral prospecting and exploration.
Titanium. Historical data reports a large number of occurrences of copper, gold, zinc, nickel, cobalt at one of the areas belonging to the metallogenic zone of the Upper Priirgiz. However, the most significant commodity among reported is titanium and associated with it titanomagnetite ores. In particular, in the area among the gabbro intrusive mafic and ultramafic composition there is a phenocryst of titanomagnetite, and, the content of titanium oxide up to 6%. The most important in the search for titanium ores are pyrogenetic deposits, genetically related to gabbro, gabbro-amphibolites - ilmenite-magnetite, ilmenite-titanomagnetite and various types of ilmenite stream gravels. In terms of exploration criteria, magnetite-ilmenite ore bodies are marked out by anomalies over 2000 nT.
Detailed magnetic survey identified the dipole anomaly of an intrusive nature (Fig. 4a), which has favorable properties for bearing titanomagnetite. 50k geological map (Fig. 4b) shows this zone as a junction of faults of different strike. Intensity ranges from -1400 nT at anomaly’s lower extremum, to 2300 nT at the maximum. High-frequency response (derived from TMI plots above the target (Fig. 4d) and at analytical signal map in Fig. 4c) indicates the target is relatively near to surface, and the dipole character along with vector magnetization are probably due to a younger origin relative to the main intrusive body. Listed properties indicate the object is a high potential for titanomagnetite.
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Figure 4. Searching for titanomagnetite |
Moreover, diurnal variations technique verifies the anomaly (one of the methods of magnetic exploration) has ore origin which explains the geomagnetic field over the object is more intense than where it is calm magnetic field. This suggests the likely inclusion of a larger amount of ilmenite than if the object was a waste rock of increased magnetic susceptibility.
