Introduction

Titanium, atomic number 22, is relatively lightweight yet possesses high strength compared to other metals. Owing to these properties, titanium is widely used across advanced industries, including the aerospace, space, and defense industries. However, South Korea currently relies on imports for approximately 99.8% of its titanium alloys, rendering the supply chain highly vulnerable. Accordingly, the Korean government designated titanium as one of 33 critical minerals requiring management from the perspective of resource security.

The Myeonsan titanium deposit, located in the Taebaeksan Basin of South Korea, is one of the most prospective domestic titanium occurrences and has been interpreted as a paleo-placer deposit hosted by the Cambrian Myeonsan Formation. The deposit occurs within conglomeratic sandstone in the lower part of the Myeonsan Formation, where titanium-bearing minerals such as rutile, ilmenite, and hematite are concentrated. These ore minerals are considered to have originated from the weathering and erosion of Precambrian basement rocks and were subsequently deposited and enriched during sedimentary processes (Cheong 1969; Kim and Cheong 1987; Kim 1991; Woo et al. 2006; Park et al. 2022; Yu et al. 2023). The titanium-bearing horizons are surrounded by various lithologies, including clastic sedimentary rocks, limestone, intrusive dykes, and Precambrian granite, providing an appropriate geological setting for evaluating the relationships between mineralization and measurable physical properties. Consequently, the Myeonsan deposit offers an excellent natural laboratory for investigating the capability of integrated physical property measurements to discriminate ore-bearing rocks from host lithologies.

Laboratory characterization of rock properties plays a fundamental role in understanding the relationships between mineral composition and measurable physical responses. Quantitative measurements of density, magnetic susceptibility, electrical resistivity, and polarization behavior provide valuable information for evaluating geological materials and distinguishing ore-bearing rocks from surrounding lithologies. Because individual physical properties are influenced by different mineralogical and textural factors, a single measurement rarely provides a complete description of a geological system. Consequently, integrated measurements of multiple physical properties have become increasingly important for improving material characterization and reducing ambiguity in the interpretation of subsurface resources. In mineral exploration, laboratory-derived physical property datasets serve as reference criteria for interpreting geophysical anomalies and assessing the diagnostic capability of different measurement techniques. Such datasets are particularly valuable for titanium-bearing deposits, where complex associations of oxide minerals and host rocks can generate diverse physical responses.

Among various physical property measurements, polarization-based electrical methods have received considerable attention because of their sensitivity to mineral composition and interfacial charge-transfer processes. Time-domain induced polarization (TDIP) characterizes the transient voltage response following current interruption, whereas electrochemical impedance spectroscopy (EIS), referred to as spectral induced polarization (SIP) in geophysical applications, evaluates frequency-dependent electrical responses over a broad spectral range. These measurements provide complementary information on charge storage, transport mechanisms, grain-scale mineral interactions, and pore-fluid effects. Previous studies have demonstrated the effectiveness of polarization-based measurements for characterizing ore-bearing rocks and identifying mineralized zones. For example, SIP measurements successfully discriminated skarn ore minerals from surrounding host rocks (Park et al. 2016), and frequency-dependent polarization responses have been applied to characterize molybdenum skarn deposits (Shin 2021a). In titanium exploration, Wynn (1988) reported that polarization measurements provided greater sensitivity to titanium mineralization than conventional magnetic methods, while Bérubé et al. (2019) showed that spectral responses are influenced not only by ore mineral content but also by mineral texture and grain-scale relationships. These studies demonstrate the potential of TDIP and EIS (SIP) measurements for quantitative characterization of mineralized geological materials. Furthermore, artificial intelligence (AI) and machine-learning-based approaches have demonstrated the potential of integrating multiple physical and chemical parameters to identify complex relationships and establish quantitative predictive frameworks for material characterization (Huang et al. 2025, 2026; Wu et al. 2025, 2026a). Such data-driven approaches may provide a useful framework for integrating multiple petrophysical and electrical parameters to improve the quantitative discrimination of mineralized rocks from their host lithologies.

Comprehensive datasets integrating multiple physical property measurements of titanium-bearing ores and associated host rocks remain limited. In particular, quantitative relationships among density, magnetic, electrical, electrochemical, geochemical, and petrographic characteristics have not been systematically evaluated for sedimentary titanium deposits. Such information is essential for establishing reliable discrimination criteria between ore-bearing and host lithologies and for understanding the physical mechanisms responsible for their measured responses.

Therefore, this study presents an integrated characterization of representative rocks collected from the Myeonsan titanium deposit using density, porosity, magnetic susceptibility, direct-current electrical resistivity, time-domain induced polarization (TDIP), electrochemical impedance spectroscopy (EIS; spectral induced polarization, SIP, in geophysical applications), portable X-ray fluorescence (p-XRF), and petrographic observations. The objectives of this study are to (1) quantify the physical property contrasts between titanium-bearing ores and host rocks, (2) evaluate the diagnostic capability of individual and complementary measurement techniques, and (3) establish measurement-based criteria for the characterization of titanium-bearing rocks and their application to mineral exploration.

Geological setting and titanium mineralization

Figure 1 shows the geological map of the Myeonsan area and the location of borehole KDMS 2023-10. The study area is located in the Taebaeksan Basin of South Korea, where Cambrian sedimentary strata of the Joseon Supergroup unconformably overlie the Precambrian Hongjesa Granite (Kwon et al. 2019). Among these units, the Myeonsan Formation hosts economically significant titanium mineralization.

The Myeonsan Formation is composed mainly of sandstone, conglomeratic sandstone, siltstone, and shale. Titanium mineralization is concentrated within the conglomeratic sandstone of the lower Myeonsan Formation, where rutile, ilmenite, and hematite occur as the principal ore minerals, locally accompanied by magnetite. These minerals are interpreted to have originated from the weathering of Precambrian basement rocks and were subsequently concentrated through sedimentary processes, forming a paleo-placer titanium deposit (Cheong 1969; Kim and Cheong 1987; Kim 1991; Woo et al. 2006; Park et al. 2022; Yu et al. 2023).

The titanium-bearing horizons are associated with several surrounding lithologies, including limestone, clastic sedimentary rocks, intrusive dykes, and granite. This geological setting provides an opportunity to compare the physical properties of ore-bearing and host rocks and to evaluate their diagnostic characteristics through integrated laboratory measurements.

Fig. 1
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Geological map of the Myeonsan area

Rock sampling and specimen preparation

Rock samples were collected from borehole KDMS 2023-10, which penetrates the titanium-bearing Myeonsan Formation and surrounding lithological units (Fig. 2). The borehole intersects basement granite, titanium-bearing conglomeratic sandstone, clastic sedimentary rocks, limestone, and locally developed intrusive dykes. Titanium mineralization is concentrated within the lower part of the Myeonsan Formation.

A total of 39 representative samples were selected to capture the lithological variability encountered in the borehole. Based on lithology and mineralization characteristics, the samples were classified into five groups: Myeonsan ore (MO), limestone (LS), dyke (DY), clastic sedimentary rock (CS), and granite (GR). The dataset consists of 9 titanium ores, 12 limestones, 4 dykes, 11 clastic sedimentary rocks, and 3 granites. Particular attention was given to collecting titanium-bearing ores together with their surrounding host rocks to enable quantitative comparison of physical property responses associated with mineralization.

All samples were prepared as cylindrical specimens for laboratory measurements. The upper and lower surfaces of each specimen were cut and polished to ensure reproducible physical property measurements. Cylindrical specimens are particularly advantageous for electrical measurements because they promote a relatively uniform current-density distribution within the rock interior and facilitate the calculation of a geometric factor required for resistivity and polarization measurements (Shin 2021b).

For titanium-bearing ores, half-core specimens were additionally prepared as semi-cylindrical samples because of limited core availability. The prepared specimens were subsequently used for density, porosity, magnetic susceptibility, direct-current electrical resistivity, time-domain induced polarization (TDIP), electrochemical impedance spectroscopy (EIS; spectral induced polarization, SIP, in geophysical applications), portable X-ray fluorescence (p-XRF), and petrographic analyses.

Fig. 2
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Columnar section with position of rock obtained from holes of KDMS 2023-10

Laboratory experiment

An integrated laboratory measurement workflow was applied to characterize the physical, electrical, geochemical, and mineralogical properties of the rock specimens. The measurements included density, porosity, magnetic susceptibility, direct-current electrical resistivity, time-domain induced polarization (TDIP), electrochemical impedance spectroscopy (EIS; spectral induced polarization, SIP, in geophysical applications), portable X-ray fluorescence (p-XRF), and petrographic observations. The geometric factor required for electrical measurements was calculated from the dimensions of each specimen. The resulting dataset was used to evaluate the relationships between lithology, mineralization, and measurable physical properties.

Density and porosity

Density and porosity provide quantitative information on the mineral composition and pore structure of geological materials. These properties were determined using the Archimedes buoyancy method following the procedures recommended by the International Society for Rock Mechanics (ISRM 1979).

Prior to saturation, the rock specimens were dried in an oven at 110 °C for 24 h and weighed to obtain the dry mass (Mdry). Water saturation was achieved by placing the specimens in a water-filled desiccator and applying a vacuum (< 6 Torr) for 24 h to remove air from the pore spaces and ensure complete saturation. The temperature, electrical resistivity, and pH of the water were 24.3 °C, 51.7 Ω·m, and 6.9, respectively.

The saturated mass (Msat) was measured after removing excess surface water with a damp cloth, whereas the submerged mass (Msub) was measured while the specimen was immersed in water (Fig. 3a). All measurements were performed using an electronic balance with a resolution of 0.01 g.

The apparent volume (V), saturated density (ρsat), and porosity (n) were calculated using Eqs. (1)–(3), respectively.

The volume of the rock specimen is calculated using Eq. (1) as below:

$$\:\begin{array}{c}V=\frac{M_{sat}-M_{sub}}{{\rho\:}_w}\approx\:M_{sat}-\\M_{sub}\:(\because\:{\rho\:}_w\approx\:1\:g/{cm}^3)\end{array}$$
(1)

The density of the rock specimen is calculated using Eq. (2) as below:

$$\begin{array}{c}{\rho\:}_{sat}=\frac{M_{sat}}V\approx\\\frac{M_{sat}}{M_{sat}-M_{sub}\:}\end{array}\:\:$$
(2)

The porosity of the rock specimen is calculated using Eq. (3) as below:

$$\:n=\frac{{M}_{sat}-{M}_{dry}}{{M}_{sat}-{M}_{sub}}\times\:100$$
(3)

where \(\:V\) is the apparent volume of the specimen (cm³), \(\:{M}_{sat}\) is the mass of the saturated specimen (g), \(\:{M}_{sub}\) is the mass of the saturated specimen measured in water (g), \(\:{\rho\:}_{w}\) is the density of water (g/cm³), \(\:{\rho\:}_{sat}\) is the density of the saturated specimen (g/cm³), \(\:n\) is the porosity (%), and \(\:{M}_{dry}\) is the mass of the dried specimen (g).

Magnetic susceptibility

Magnetic susceptibility quantifies the ability of a material to become magnetized under an external magnetic field and is primarily controlled by the abundance and type of magnetic minerals. Measurements were performed using an MS-3 susceptibility meter equipped with an MS-2E sensor (Bartington Instruments, UK), and data acquisition was controlled using Bartsoft software (Fig. 3b). Prior to measurement, the instrument was calibrated in air following the manufacturer’s recommended procedure. The sensor was then placed in direct contact with the specimen surface to obtain susceptibility readings (Shin et al. 2013).

Because rock specimens may exhibit mineralogical anisotropy, magnetic susceptibility can vary depending on the measurement direction. To minimize directional bias while preserving the integrity of the specimens, measurements were performed at six locations on each sample, including the upper, lower, and side surfaces. The arithmetic mean of the six measurements was used as the representative magnetic susceptibility value for each specimen.

Direct-current resistivity, TDIP, and EIS measurements

Figure 3c shows the experimental setup used for direct-current electrical resistivity, time-domain induced polarization (TDIP), and electrochemical impedance spectroscopy (EIS; spectral induced polarization, SIP, in geophysical applications) measurements. Electrical resistivity quantifies the resistance of a material to electric current flow, whereas induced polarization reflects delayed electrical responses caused by charge accumulation at mineral–fluid interfaces, grain boundaries, and pore structures.

Because subsurface rocks are generally saturated with groundwater, all specimens were fully saturated with water prior to electrical measurements. After saturation, the specimens were removed from water, and excess surface moisture was gently wiped off with a damp cloth. To minimize drying during measurement, each specimen was quickly fixed in an acrylic holder. Electrodes consisting of filter paper and copper mesh were installed at both ends of the specimen and connected to Solartron SI1287 and SI1260 instruments. Water was placed at the bottom of the holder, and the holder was sealed to maintain a saturated atmosphere during the measurements (Kim and Choi 1999; Park 2004).

Direct-current resistivity and TDIP measurements were performed first. A square-wave current was applied with an injection time and relaxation time of 4 s each. Electrical resistivity was calculated from the measured potential difference and current under steady-state conditions using the geometric factor determined from the specimen dimensions.

The resistivity was calculated as follows:

$$\:\rho\:=\frac{V_p}I\:\times\:\:\frac AL$$
(4)

where ρ denotes the electrical resistivity (Ω⋅m), Vp is the average potential difference (V) measured between the two potential electrodes, I is the average current (A) measured between the two current electrodes, A is the cross-sectional area of the sample (m2), and L is the length of the sample (m), and A/L represents the geometric factor.

TDIP measurements were conducted by recording the voltage decay after current interruption. The decay curve was fitted using an exponential function:

$$\:V_{off}\left(t\right)=\:V_s{\:exp}^{-t/\tau\:}$$
(5)

where Voff is the voltage decay after current interruption, t is the elapsed time (s), Vs is the extrapolated voltage at t = 0 (V), and \(\:\tau\:\) is the relaxation time (s).

Chargeability was calculated as the ratio of Vs to Vp and expressed in mV/V. The relaxation time represents the characteristic time scale of voltage decay and is related to charge storage and release processes in the rock.

After the TDIP measurements, EIS measurements were performed by applying a sinusoidal excitation voltage of 1000 mV over a frequency range from 0.1 Hz to 10 kHz. The phase and impedance responses were measured as functions of frequency and used to evaluate frequency-dependent polarization behavior. In geophysical terminology, this measurement is commonly referred to as spectral induced polarization (SIP). Compared with TDIP, which records transient voltage decay after current shutoff, EIS directly measures the frequency-dependent electrical response under continuous sinusoidal excitation. Therefore, TDIP and EIS provide complementary information on polarization mechanisms associated with pore structure, mineral composition, and ore-related conductive or semiconductive minerals.

Portable X-ray fluorescence (p-XRF)

Portable X-ray fluorescence (p-XRF) measurements were conducted to evaluate variations in elemental composition among the different lithological groups and to assess their relationships with the measured physical properties. Particular attention was given to the distribution of titanium and associated elements that may influence density, magnetic susceptibility, and electrical polarization responses.

Elemental analyses were performed using an XL3t portable X-ray fluorescence analyzer (Thermo Scientific, USA) (Fig. 3d). The instrument determines elemental composition by measuring characteristic fluorescent X-rays emitted from the specimen following X-ray excitation. Prior to the analysis of the rock specimens, detector calibration was performed using the instrument’s built-in calibration procedure. Following detector calibration, a certified reference material (CRM), 1–1/4Cr 1/2Mo (UNS K11572), was measured to evaluate the analytical performance of the instrument before specimen measurements. One representative location was selected on each specimen, and the measurement time was set to 30 s. The resulting elemental data were subsequently compared with the physical property measurements and petrographic observations to identify compositional controls on the observed geophysical responses.

Fig. 3
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Laboratory measurement instruments of rock samples for data acquisition of density/porosity (a), magnetic susceptibility (b), resistivity/chargeability (c) and portable X-ray fluorescence (d)

Results and discussion

Figure 4 summarizes the mean values and standard deviations of density, porosity, magnetic susceptibility, electrical resistivity, and chargeability for the five lithological groups. These results provide a basis for evaluating which physical properties are most diagnostic for distinguishing titanium-bearing ores from host rocks.

The density results show the clearest contrast between the Myeonsan ore (MO) samples and the other lithologies. The mean density of MO was 3.17 g/cm³, which is higher than those of limestone (LS, 2.74 g/cm³), dyke (DY, 2.73 g/cm³), clastic sedimentary rock (CS, 2.84 g/cm³), and granite (GR, 2.68 g/cm³) (Fig. 4a). This high density is attributed to the abundance of heavy ore minerals such as rutile, ilmenite, and hematite in the MO samples. The standard deviation of MO density was also larger than those of most host rocks, indicating heterogeneous ore-mineral contents within the mineralized interval. In contrast, LS, DY, CS, and GR showed relatively small density variations, reflecting more uniform lithological compositions within each group.

Porosity showed a different pattern from density. The mean porosities were 0.49% for MO, 0.46% for LS, 1.06% for DY, 0.36% for CS, and 1.19% for GR (Fig. 4b). Although DY and GR exhibited relatively higher porosities, porosity did not provide a clear distinction between titanium-bearing ores and host rocks. The low porosities of the sedimentary rocks, including MO, LS, and CS, may reflect pore reduction associated with compaction, cementation, and diagenetic pore filling. Therefore, porosity appears to influence the electrical properties of some lithologies but is not itself a direct indicator of titanium mineralization.

Magnetic susceptibility also showed limited diagnostic capability for identifying the titanium-bearing ores. The mean magnetic susceptibilities were 2.82 mSI for MO, 0.90 mSI for LS, 10.00 mSI for DY, 0.54 mSI for CS, and 0.08 mSI for GR (Fig. 4c). Although MO contains ore minerals, it did not exhibit the highest susceptibility. This result is consistent with the mineralogical characteristics of the ore assemblage, in which rutile is weakly magnetic and hematite is antiferromagnetic. The relatively high susceptibility of DY suggests that magnetic minerals in intrusive rocks can produce stronger magnetic responses than the titanium-bearing ores. Thus, magnetic susceptibility alone may be insufficient for discriminating MO from host lithologies in this deposit.

Electrical resistivity showed considerable variability among lithologies. The mean resistivities were 4,732 Ω·m for MO, 11,129 Ω·m for LS, 1,923 Ω·m for DY, 10,222 Ω·m for CS, and 2,572 Ω·m for GR (Fig. 4d). Although ore minerals may reduce resistivity because of their semiconductive behavior, MO did not show the lowest resistivity. Instead, DY and GR exhibited lower resistivities, likely reflecting their higher porosities and enhanced pore-fluid conduction under saturated conditions. Conversely, LS and CS showed relatively high resistivities, consistent with their low porosities. These results indicate that resistivity is strongly controlled by pore structure and saturation state, and therefore its ability to directly indicate titanium mineralization is limited.

In contrast, chargeability provided the strongest electrical discrimination between titanium-bearing ores and host rocks. The mean chargeability of MO was 91.57 mV/V, markedly higher than those of LS (5.64 mV/V), DY (3.41 mV/V), CS (4.62 mV/V), and GR (6.56 mV/V) (Fig. 4e). This contrast suggests that polarization processes associated with ore minerals are much stronger in MO than in the surrounding lithologies. The large standard deviation of MO chargeability further indicates variable ore-mineral abundance and texture among the ore samples. Together with the density results, the chargeability data demonstrate that density and induced polarization are the most effective physical properties for distinguishing titanium-bearing ores from host rocks in the Myeonsan ore deposit.

Overall, the multi-parameter results indicate that not all measured properties contribute equally to ore discrimination. Density and chargeability show clear diagnostic contrasts related to ore mineralization, whereas porosity, magnetic susceptibility, and resistivity are more strongly influenced by lithology, pore structure, and non-ore mineral assemblages. These findings support the value of integrated physical property measurements for identifying the most reliable indicators of titanium-bearing rocks.

Fig. 4
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Bar plots of geophysical properties by laboratory measurement results showing (a) density, (b) porosity, (c) magnetic susceptibility, (d) resistivity, and (e) chargeability

Figure 5 presents the phase and AC resistivity spectra obtained from the EIS (SIP) measurements of the rock specimens. Compared with the AC resistivity spectra, the phase spectra more clearly reveal frequency-dependent polarization behavior and provide greater discrimination among the lithological groups. According to previous studies, spectral variations below approximately 100 Hz are primarily associated with interfacial polarization occurring between semiconductive minerals and pore fluids, whereas spectral responses at higher frequencies are commonly influenced by dielectric polarization and relaxation processes within mineral grains (Pelton et al. 1978; Revil et al. 2014).

Several Myeonsan ore (MO) specimens, particularly MO1, MO2, MO5, and MO9, exhibit relatively strong phase responses at low frequencies, followed by a gradual decrease with increasing frequency. This spectral behavior is consistent with induced polarization effects generated by ore minerals and is interpreted to reflect charge accumulation at mineral–fluid interfaces. These specimens also correspond to samples showing high TDIP chargeability values, suggesting that the low-frequency phase responses and chargeability measurements reflect related polarization mechanisms.

In contrast, MO3, MO4, MO6, MO7, and MO8 exhibit phase spectra characterized by increasing phase values toward higher frequencies. Similar spectral behavior is observed in the host-rock specimens, indicating that these samples are influenced by dielectric polarization processes in addition to ore-related polarization effects. The coexistence of both spectral patterns within the MO group suggests heterogeneity in ore-mineral abundance and mineralogical composition among the titanium-bearing samples.

The surrounding lithologies generally show weak low-frequency polarization responses and increasing phase values at higher frequencies. This behavior is interpreted to be associated with dielectric polarization and relaxation processes within electrically insulating minerals. Most host rocks are dominated by silicate and carbonate minerals, which possess limited electronic conductivity but can store electrical energy through polarization of bound charges under an alternating electric field. Consequently, dielectric relaxation becomes increasingly significant at higher frequencies, resulting in the observed phase increase. Although minor variations are present in some specimens, such as CS8 and CS11, the overall spectral characteristics of the host rocks differ from those of the strongly polarized ore samples.

These results indicate that EIS measurements provide complementary information to TDIP and enable discrimination between samples dominated by ore-mineral polarization and those controlled primarily by dielectric mineral responses. Therefore, frequency-dependent phase measurements can serve as an additional indicator for characterizing titanium-bearing rocks and evaluating mineralization.

Figure 6 presents representative photomicrographs of the investigated lithologies. The MO specimens are dominated by opaque ore minerals with minor amounts of quartz (Fig. 6a). Reflected-light observations reveal the presence of rutile, ilmenite, and hematite as the principal ore minerals (Fig. 6b). In contrast, the LS specimens are composed predominantly of calcite (Fig. 6c), whereas the DY specimens contain quartz, feldspar, amphibole, and minor opaque minerals (Fig. 6d). The CS specimens are characterized by alternating coarse-grained quartz and fine-grained silicate minerals (Fig. 6e), and the GR specimens contain quartz, feldspar, mica, and tourmaline (Fig. 6f). Sericitization of feldspar observed in the DY and GR specimens indicates that these rocks were affected by hydrothermal alteration.

The petrographic observations support the interpretation of the physical property and EIS results. The abundance of rutile, ilmenite, and hematite in the MO specimens is consistent with their high density, elevated chargeability, and strong low-frequency polarization responses. In contrast, the host rocks are dominated by electrically insulating silicate and carbonate minerals, which are consistent with the dielectric polarization characteristics observed in the high-frequency phase spectra. Therefore, the contrasting spectral responses between ore and host rocks can be directly linked to differences in mineral composition and texture, demonstrating that the integrated physical property measurements successfully capture the mineralogical controls on geophysical responses.

Fig. 5
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Bode plots of spectral induced polarization by laboratory measurement of rock samples showing (a) Myeonsan ore, (b) limestone, (c) dyke, (d) clastic sedimentary rock, and (e) granite

Fig. 6
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Photomicrographs of thin sections observed under plane-polarized light (PPL) and reflected light. (a) Myeonsan ore, PPL; (b) Myeonsan ore, reflected light; (c) limestone, PPL; (d) dyke, PPL; (e) clastic sedimentary rock, PPL; and (f) granite, PPL. Abbreviations: Amphibole = Amp, Calcite = Cal, Hematite = Ht, Ilmenite = Ilm, Muscovite = Ms, Plagioclase = Pl, Quartz = Qtz, Rutile = Rt, Tourmaline = Tur

Table 1 summarizes the physical properties and portable X-ray fluorescence (p-XRF) results of all specimens. For the EIS measurements, the phase and AC resistivity values at 0.1 Hz were extracted because induced polarization effects were most pronounced at low frequencies. The detection limits for Ti and Fe were 0.06 wt% and 0.1 wt%, respectively. Overall, the titanium-bearing ore (MO) specimens exhibit higher density, chargeability, and low-frequency phase responses than the surrounding host rocks. These contrasts are generally accompanied by elevated Ti and Fe contents, suggesting that ore minerals contribute significantly to the observed geophysical responses.

Table 1 Summary of geophysical properties and p-XRF results measured in this study
Full size table

Among the MO specimens, MO1, MO2, MO5, and MO9 exhibit strong chargeability and phase responses together with relatively high Ti (> 3.11 wt%) and Fe (> 8.82 wt%) contents. These samples correspond to the spectral group characterized by pronounced low-frequency polarization behavior. The consistency among density, chargeability, phase response, and elemental composition suggests that ore-mineral enrichment is an important factor controlling the measured physical properties.

An interesting exception is MO3, which exhibits the highest Ti (9.85 wt%) and Fe (24.27 wt%) contents among all specimens but shows weaker polarization responses than MO1, MO2, MO5, and MO9.

This discrepancy highlights an important limitation of portable X-ray fluorescence (p-XRF) measurements. Because portable X-ray fluorescence (p-XRF) analysis was conducted at a single location on each specimen, the measured elemental contents may not fully represent the bulk composition of heterogeneous ore samples. The rock properties may be controlled not only by the concentrations of specific elements but also by the mineralogical characteristics and interactions of coexisting metal oxides (Wu et al. 2026b). Complementary mineralogical and geochemical analyses would therefore provide further constraints on these relationships. However, because the specimens were provided through a mining project and had to be preserved intact, destructive analyses requiring additional crushing, such as XRD and ICP-MS, could not be performed.

In contrast, density, TDIP, and EIS measurements integrate responses over a much larger volume of the specimen. Therefore, local elemental concentrations measured by portable X-ray fluorescence (p-XRF) could be useful for indirectly identifying the occurrence of metallic minerals rather than serving as direct predictors of bulk polarization behavior.

Conclusions

This study presented an integrated physical property characterization of titanium-bearing ores and associated host rocks from the Myeonsan titanium deposit, South Korea. A total of 39 representative specimens were analyzed using density, porosity, magnetic susceptibility, direct-current electrical resistivity, time-domain induced polarization (TDIP), electrochemical impedance spectroscopy (EIS; spectral induced polarization, SIP, in geophysical applications), portable X-ray fluorescence (p-XRF), and petrographic observations.

The results demonstrate that titanium-bearing ores can be distinguished from surrounding host rocks primarily by their higher density, elevated chargeability, and pronounced low-frequency phase responses. In contrast, porosity, magnetic susceptibility, and electrical resistivity showed limited capability for directly discriminating ore-bearing rocks from host lithologies. The EIS measurements further revealed contrasting frequency-dependent polarization behaviors between ore and host rocks. Several ore specimens exhibited strong low-frequency polarization responses associated with ore-mineral-related induced polarization effects, whereas most host rocks were characterized by dielectric polarization responses at higher frequencies.

Overall, this study demonstrates that integrated physical property measurements provide a quantitative framework for characterizing titanium-bearing rocks and distinguishing ore-bearing intervals from surrounding lithologies. The results highlight the complementary value of density, TDIP, and EIS measurements and support their application in the characterization and exploration of titanium mineral resources.