## 3 Data Acquisition and Processing  
### Data Acquisition  
The DZL area is located in a high-altitude, high-mountain region, with elevations ranging from 4560 m to over 5800 m, and an average elevation of 5200 m. The maximum relative height difference exceeds 700 m, and most of the working area has elevations above 5000 m, posing significant challenges for both ground-based and airborne geophysical work (Figure 4).  
To ensure the safety of the aerial survey, this project selected the AS350 (H125) helicopter, manufactured by Airbus Helicopter (Marignane, France), which has excellent high-altitude performance, as the flight platform. The airborne magnetic survey equipment was also chosen to be lightweight and compact. The airborne magnetic survey system used in this project consists of the AARC510 airborne compensation and recording system produced by RMS Instruments (Mississauga, ON, Canada), the CS-VL high-precision cesium vapor magnetometer produced by Scintrex (Concord, ON, Canada), the T34 radar altimeter produced by SmartMicro (Braunschweig, Germany), and the DL-4 navigation system produced by NovAtel (Calgary, AB, Canada). The equipment was installed on the helicopter using a rigid rod mounting system (Figure 5). To keep the magnetometer away from the aircraft and reduce interference, a hollow rod was installed under the belly of the aircraft, using a triangular bracket structure to make it more stable. A streamlined compartment at the front of the rod was used to house the magnetometer. The recording system and positioning navigation system were installed in the cabin, and the radar altimeter was installed under the belly of the aircraft. Researchers have studied the magnetic interference problem of the AS350 helicopter, and found that placing the magnetometer 4 m away from the rotor coverage area can reduce the interference to below 1 nT [21]. As a result, the length of the probe is 4.5 m outside the rotor range in this project. Magnetic interference  
Figure 3: A geological map and geological cross-section of the DZL deposit (modified from data provided by the client). (**a**) The geological map of the DZL deposit. Points “A” and “B” are the endpoints of the geological section in (**b**). (**b**) The geological section crossing the main mining body; the lithology of the geological section is controlled by drill holes, and the ore body develops in the skarn band on the south side of the intrusive rock.  
tests were conducted after the installation, and the static magnetic noise reached 1.45 pT, while the dynamic magnetic noise was 41.4 pT on the baseline.  
The geological structure of the mining area is mainly oriented in the NE and EW directions, so the survey lines were designed to be approximately perpendicular to the  
Figure 4: A satellite image of the study area with overlaid topographic contour lines. The contour interval is 100 m, the number at the star location represents the main peak, and the inverted triangle location represents the elevation of the valley lowlands. The dashed box represents the area of the geological map in Figure 3a.  
Figure 5: The helicopter-borne magnetic survey system used in this survey. CS-VL represents the high-precision cesium vapor magnetometer, GNSS represents the Global Navigation Satellite System, AARC510 is the airborne compensation and recording system used in the project, and Radar represents the radar altimeter.  
main structural direction, with an SN orientation. The line spacing was 100 m, and the tie lines were in the EW direction with a spacing of 2 km. This airborne magnetic survey covered an area of approximately 20 km \(\times\) 9 km around the DZL deposit, with a total flight distance of about 2000 km, an average flight height of 115 m, and an average deviation of 3 m.