Application of 3D Induced Polarization Method in the Exploration of a Pb–Zn Deposit in Northwestern Guizhou

2026/08/19

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1 Geological Setting and Geophysical Characteristics
1.1 Geological Setting
The study area is tectonically situated on the southwestern margin of the Yangtze Block, at the junction of the Tethys–Himalayan and CircumPacific tectonic domains, specifically on the northeastern edge of the triangular zone bounded by the Xiaojiang, Mile–Shizong, and Ziyun–Yadu deepseated faults. The region has undergone intense deformation, with dominant NWtrending faults and subordinate NEtrending faults (Fig. 1). Among these, F32 and the Tianqiao anticline serve as important orehosting and orecontrolling structures in the area.

1.2 Orebody Characteristics
Ore minerals are mainly sphalerite and pyrite, with gangue minerals dominated by calcite and dolomite. The orebodies occur mainly as stratoid, lenticular, and vein forms. The major chemical components are ZnS, PbS, FeS₂, CaO, CO₂, and Fe₂O₃, with minor MgO and MnO. The economically valuable components are lead and zinc, which occur predominantly as sulfides. Lead is mainly hosted in galena, while zinc is hosted in sphalerite.
2 Instrumentation and Array Layout
For this survey, the fullwaveform acquisition system (FW fullwaveform highpower IP instrument) was employed, as shown in the field photographs.

The 3D IP survey layout, combining gradient dipoledipole and poledipole configurations (Fig. 3 in the original text shows a schematic of the 1source, 6receiver measurement setup).

A total of five 3D IP sounding profiles were surveyed, numbered JD01 to JD05. With the designed verification borehole as the center, Array I was laid out with a station spacing of 100 m, line spacing of 100 m, and a line length of 800 m (receiver array), covering 300 m × 800 m with an azimuth of 42° and a total of 32 measuring points. Perpendicular to Array I, Array II was designed with the same station spacing (100 m), line spacing (100 m), and a line length of 400 m (receiver array), covering 400 m × 800 m at an azimuth of 132°, also with 32 points..The parameters are as follows：MN=50-100m、transmit cycle:16s、maximum AB=5.2km、maximum transmitted power：10 kW，One single transmission, with 16 channels receiving signals simultaneously.
3 Field Photographs

4 Induced Polarization Anomaly Characteristics
Based on the tests conducted over the typical deposit and the acquired data, an apparent polarizability threshold of 15 mV/V was selected as the lower limit for delineating IP anomalies in the study area. The 3D inversion visualization of apparent polarizability shows that the anomaly concentration centers are mainly distributed around stations 92–98 on Lines L4 and L5, with sporadic shallow nearsurface blocks and a larger ellipsoidal feature at intermediate depth [Fig. 5(a), Fig. 5(b)].

Slices along Lines L4 and L5 reveal more clearly that on Line L4, between stations 92–96 at depths corresponding to elevations of 900–1450 m, there is a highpolarizability, lowresistivity anomaly, with apparent polarizability of 15–20 mV/V [Fig. 6(a2)] and apparent resistivity of 60–400 Ω·m [Fig. 6(b2)]. Similarly, on Line L5, between stations 90–94 at elevations of 900–1950 m, the anomaly shows high polarizability (15–16 mV/V) [Fig. 6(a3)] and low resistivity (25–300 Ω·m) [Fig. 6(b3)]. Considering the magnitude, spatial distribution, and correlation of these highpolarization anomalies on Lines L4 and L5, together with stratigraphic thickness and the orebearing potential of the horizons, we interpret this anomaly as oreinduced.

5 Analysis of Anomaly Results
A borehole was drilled at station 94 on Line L4 for verification [Fig. 7(a)]. The drilling shows:
From 5 to 180 m depth (elevation 1920–1740 m), the strata belong to the Permian Qixia Formation, which is a Pb–Zn host horizon in the district. Lithologies are mainly micritic limestone and bioclastic limestone, with welldeveloped fractures and fissures on a large scale, containing reddishbrown ferruginous oxides.
From 440 to 480 m depth (elevation 1485–1445 m), the strata are the Carboniferous Baizuo Formation, with extremely developed fractures filled with abundant reddishbrown ferruginous oxides, and disseminated pyrite is common. Sphalerite occurs in pyritized and silicified dolomite, with Pb–Zn ore bodies reaching economic grade and thickness.
From 680 to 715 m depth (elevation 1245–1210 m), the strata are the Devonian Yaosuo Formation, consisting mainly of dolomite and limestone, with abundant disseminated and veintype pyrite. Sphalerite is hosted in pyritized layers.
The spatial positions of the pyriteenriched and Pb–Zn mineralized zones revealed by the borehole are encompassed by the 3D IP highpolarizability anomaly (15–19 mV/V) [Fig. 7(b)].