UAV-based magnetic survey in rugged topography area
ELECTROMAGNETIC PROSPECTION
The use of UAV/UAS (unmanned aerial vehicles/unmanned aerial systems for mineral prospecting)
Workflow
Equipment
Effective use of UAV-based magnetometer survey
Data comparison
Advantages
The Ground-based magnetometer has higher noise
levels than the UAV-based magnetometer.
Provide high quality data
Our system allows performing high-precision
aeromagnetic surveys at low altitudes, in flat terrain ,
and complicated landscape conditions.
More efficient, cost effective and safer
The UAV- based magnetometer is more efficient,
cost-effective, and safer than other methods.
• at the prospecting stage when studying the features of the geological structure of gold-bearing areas covered with loose sediments
• to localize promising areas for detailed geophysical and drilling operations
• in the study of loose sediments and the relief of bedrocks
• to determine the primary sources of gold
The method of electrotomography is gradually being introduced into the practice of work in prospecting and prospecting for placers of gold, but the possibilities of the method remain not fully disclosed. The use of induced polarization makes it possible to locate the sites of sulfide mineralization, that is, to determine the sources of gold
Experience of using electrotomography in geological exploration for placer gold
The principle of electrotomography
About the method
Electrotomography (ERT) is based on the difference between electrical resistivity of rocks.
Induced polarization (IP) measures the transient response and aims to determine the subsurface chargeability properties.
Principles of Geological Interpretation Electrical properties of rocks
Geological Substantiation of Interpretation Criteria The structure of the alluvial placer
Geological Substantiation of Interpretation Criteria An example of allocation of sediments of the channel facies
Geoelectric section along the exploratory trench (a) and its interpretation (b) with account for geological data
1 — mining allotment boundaries; 2 — top of the main bottom according to the geophysical and overburden data; 3 — loose deposits of the channel facies; 4 — weathering crust of the main bottom, crushed rock; 5 — sandstones; 6 — crumbling sandstones of the fault zone; 7 — faults: a — main fault, б — edge fault.
An example of prospecting works
Method of work:
Profile length - from 235 m to 955 m.
Measurement step along the profile (inter-electrode dictance) - 5 m.
Instrument - Skala 48k12 (SibER48k12).
Arrays - dipole-dipole, Schlumberger.
An example of prospecting works Experimental work at the technological test site
An example of prospecting works Channel and valley placers
1 - channel alluvium; 2 - massive and layered limestones; 3 - shales, sandstones, siltstones; 4 - weathered bedrock; 5 - base of alluvial deposits (bedrock roof); 6 - the boundaries of the promising area for mining the placer.
Thickness of alluvial deposits 5.5-9.5 m Bedrock - shale, sandstone, siltstone.
An example of identifying promising areas in a wide valley
On the 945 m long profile, two promising anomalies of increased resistivity 60 m wide, associated with paleochannels, were identified. Within these anomalies, it is necessary to conduct areal studies to map them in plan.
1 - channel alluvium (pebble); 2 - Devonian sandstones, siltstones, limestones; 3 - Silurian clay shales, siltstones; 4 - weathering crust of bedrock; 5 - base of alluvial deposits (roof of the raft); 6 - boundaries of promising areas of placer mining.
Bedrock - shales and sandstones, siltstones, limestones The thickness of the alluvial deposits is 8 -11 m
An example of identifying promising areas in a wide valley
1 - channel alluvium; 2 - massive and layered limestones; 3 - shales, sandstones, siltstones; 4 - weathered bedrock; 5 - base of alluvial deposits (bedrock roof); 6 - the boundaries of the promising area for mining the placer.
Thickness of alluvial deposits 5.5-9.5 m Bedrock - shale, sandstone, siltstone.
An example of prospecting works Channel and valley placers
1 - pebble; 2 - sand and pebble deposits; 3 - bedrock; 4 - contact-altered rocks, fractured; 5 - base of alluvial deposits (bedrock top).
An example of prospecting works Channel and valley placers
The thickness of the alluvial deposits is 6 - 8 m. Bedrock - limestones Л. 16 Л. 48
An example of prospecting works Channel and valley placers
The length of the profiles is from 355 to 1315 m
Inter-electrode distance - 5 m
Instrument - Skala 48k12 (SibER-48k12)
Installation – pole-dipole
The depth is not less than 70 m
Measured parameters - resistivity, IP
Gold in the region is known mainly as alluvial gold. Placers are alluvial deposits. In the upper part of the section, they consist of yellow-brown loams, under which are usually found rivers, represented by coarse sands and a large number of pebbles. Below the pebbles, there are more or less uniform gray, sometimes yellowish-gray sands with a small number of pebbles. The thickness of the entire section is from 3 to 5 m.
An example of prospecting works
Examples of areal studies Channel and valley placers
Geological characteristics of the site
The geological structure includes shales, phyllites, metamorphosed sandstones and gravelstones of the Lower Proterozoic.
The formation of zones of sulfide mineralization is associated with tectonic activity and magmatism.
They are controlled by tectonic dislocations of the northeastern strike, are characterized by increased gold content and, apparently, served as the main sources of metal during the formation of placers.
Examples of areal studies Channel and valley placers
- 21 profiles with an interval of 50 m.
- Inter-electrode distance 5 m.
- The length of the profiles was 235 m.
- The measurements were carried out by a multichannel electrical prospecting station "Skala-48k12“ (SibER-48k12).
- The sequence of connecting the electrodes corresponded to the symmetrical Schlumberger array.
- The polarizability of the rocks was measured in the time range of 20-100 ms.
- Chargeability parameter (m) of rocks is the ratio of the integral of the voltage measured in the time interval after turning off the current pulse to the voltage measured at the end of the current pulse.
- Data processing was carried out using the Res2Dinv and Res3Dinv programs. The inversion used the robust method.
Channel and valley placers
Channel and valley placers
Map of calculating blocks of indicated resources
Sources of gold
Channel and valley placers
Diagram of the distribution of the chargeability parameter (m) of rocks at a depth of 10 m according to 3-D inversion data
Dump placer
1 - soil-vegetation layer, 2 - Quaternary deposits, loams, 3 - brown clays, 4 - alluvial sand-gravel-pebble deposits with clay cement, 5 - sand lenses, 6 - sand-gravelpebble deposits with clay cement and boulders , 7 - bedrock, shale with zones of sulfide mineralizat
Channel and valley placers
1 - soil-vegetation layer, 2 - loams, 3 - sand-gravel-pebble deposits with clay cement, 4 - gold-bearing layer, 5 - shales, 6 - amphibolites, 7 - roof of the bedrock
Conclusión
- The method of electrotomography makes it possible to confidently determine the boundary of loose sediments and bedrocks, and to identify pockets in the base.
- When distinguishing the channel facies of alluvium, the criterion for interpretation is its abnormally high resistivity.
- Additional information on the polarizability of rocks makes it possible to identify mineralized zones in the bedrock, which are sources of metal in the placer.
- Based on the results of the areal ET data, taking into account the borehole testing, it is possible to calculate the indicated resources of the category and even the probable reserves if there is data on the metal content in the reservoir.
Photo of work process
