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Article

Mineralogical Characterization and Provenance of Black Sand in the Xiahenan Area, Tarim Large Igneous Province

by
Songqiu Zhang
1,
Renyu Zeng
1,2,*,
Shigang Duan
3,
Jiayong Pan
1,2,
Dong Liang
4,
Jie Yan
1,2,
Jianjun Wan
1,2,
Qing Liu
1 and
You Zhang
1
1
State Key Laboratory of Nuclear Resources and Environment, East China University of Technology, Nanchang 330013, China
2
Jiangxi Provincial Key Laboratory of Genesis and Prospect for Strategic Minerals, East China University of Technology, Nanchang 330013, China
3
MNR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China
4
Xinjiang Geological Explration Institute of China Metallurgical Geology Bureau, Urumqi 830000, China
*
Author to whom correspondence should be addressed.
Minerals 2025, 15(8), 884; https://doi.org/10.3390/min15080884
Submission received: 15 July 2025 / Revised: 16 August 2025 / Accepted: 19 August 2025 / Published: 21 August 2025
(This article belongs to the Special Issue Mineralization and Metallogeny of Iron Deposits)
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Abstract

The Tarim Large Igneous Province (TLIP) in NW China hosts abundant Fe–Ti–V oxide deposits associated with mafic–ultramafic intrusions. In the Xiahenan area, on the western margin of the TLIP, a distinct magnetic anomaly is linked to widespread surface accumulations of black sand. However, the genesis and origin of these black sand grains remain unclear. Based on mineral assemblages, this study classifies the grains of the black sand into three types: (i) plagioclase (An10–90)–ilmenite–olivine–magnetite assemblage (Sand I), (ii) plagioclase (An0–10)-fine-grained magnetite assemblage (Sand II), and (iii) hornblende–magnetite highly complex assemblage (Sand III). Mineral geochemical studies demonstrate that magnetite in Sand I and Sand II is of magmatic origin, with protolith being basaltic magma. Magnetite in Sand III was eroded from veins formed by hydrothermal processes at 300–500 °C. Ilmenite in Sand I contains a high FeTiO3 component, representing basaltic ilmenite. Olivine in Sand I has a low Fo content (43.86–47.27), belonging to hortonolite olivine. Research indicates that Sand I and Sand II share similar mineral assemblages and mineral geochemical characteristics with basalts in the Xiahenan area, suggesting they are weathering products of Xiahenan basalts or their cognate magmas. In contrast, the veined magnetite of Sand III formed during post-magmatic hydrothermal events.

1. Introduction

Fe–Ti–V oxide deposits serve as the primary sources of V and Ti, predominantly occurring in mafic–ultramafic intrusions associated with Large Igneous Provinces [1,2,3,4,5]. The Tarim Large Igneous Province (TLIP) in NW China contains numerous Fe–Ti–V oxide deposits that are genetically related to Early Permian (between ~300 and 280 Ma) mafic–ultramafic intrusions and exhibit whole-rock mineralization features [6,7,8]. The Bachu area, located in the western part of the TLIP (Figure 1a,b), hosts two large-scale Fe–Ti–V oxide deposits: the Wajilitage deposit and the Xiaohaizi deposit [7,9,10]. On the 1:250,000 aeromagnetic anomaly map (Figure 1c), these deposits display magnetic characteristics dominated by negative and alternating positive-negative anomalies and strong variations, showing a south-negative and north-positive polarity contrast, which reflects the presence of reversely magnetized mafic–ultramafic rocks. In the Xiahenan area east of Wajilitag and Xiaohaizi, magnetic anomalies similar to those of known Fe–Ti–V oxide deposits have been identified. Field observations revealed abundant magnetic black sand on the surface, suggesting the magnetic anomalies are likely associated with these sands. Determining the mineral composition and sources of the black sand is crucial for interpreting the magnetic anomalies and guiding ore exploration in this area.

2. Geological Setting

Bounded by the Tianshan Mountains to the north and NW, the Kunlun Mountains to the SW, and the Altun Mountains to the SE (Figure 1b), the Tarim Basin is located in northwestern China and occupies an area of approximately 600,000 km2 [11]. Except for those covered by desert, the Precambrian crystalline basement is exposed mostly in the areas of the northern margin, southwestern area, and eastern area of the TLIP [13,14,15,16]. The TLIP and its surrounding areas contain extensive Late Carboniferous to Early Permian intraplate magmatic rocks [17]. The Early Permian basalts cover an area of approximately 25,000 km2 (Figure 1b) with an estimated volume of 15,000 km3, comparable in scale to the basalts of the Emeishan LIP [11,18]. Additionally, the western part of the TLIP hosts voluminous rhyolitic rocks (Figure 1b), covering an area of nearly 50,000 km2 [19,20]. The intrusive rocks in the region are predominantly mafic–ultramafic in composition and represent both the source rocks and host rocks for Fe–Ti–V oxide mineralization [6,7]. In recent years, studies have revealed that along the northern margin of the Tarim Large Igneous Province, in the Beishan area, mafic–ultramafic intrusive bodies related to Cu–Ni–PGE mineralization are also widely developed, such as the multi-stage composite complexes at Poyi and Hongnieshan. These intrusions record the activity of mantle-derived magmas in a post-subduction extensional setting, indicating that the area may have experienced multiple, multi-source magmatic events, some of which are associated with relatively primitive mantle-derived mafic magmas [21,22,23].
The Xiahenan area is located on the Bachu Uplift Belt in the western part of the TLIP. Due to intense Cenozoic uplift of the Bachu Uplift, the Lower Permian Bielangjin Formation of the Aqia Group is exposed at the surface in this area. This formation consists of silty mudstone, volcaniclastic rocks, and variegated sandstone interbedded with mudstone and contains multiple basalt layers [12,24]. The black sand mainly occurs above these basalts and in the surrounding desert (Figure 2a,b), exhibiting strong magnetic properties. The exposed basalts in Xiahenan can be divided into nine layers, each with a relatively thin outcrop thickness of approximately 1–5 m. The rocks are black to dark gray in color, displaying amygdaloidal structures and porphyritic textures. The lava bedding surfaces are gently inclined, dipping slightly southward (Figure 2c). Different basalt layers are separated by sedimentary interbeds with thicknesses ranging between 10 and 30 m.

3. Analytical Methods

3.1. TESCAN Integrated Mineral Analyzer (TIMA)

Mineral mappings were obtained on carbon-coated targets using a MIRA3 scanning electron microscope (SEM) equipped with two energy-dispersive X-ray spectrometers (EDS), an EDAX Element and a TESCAN Integrated Mineral Analyzer (TIMA), at Chengxin Geological Company, Langfang, China (Langfang, China). An acceleration voltage of 25 kV and a beam current of 9 nA were used. Disintegration analysis was employed to simultaneously collect backscattered electron (BSE) images and energy-dispersive X-ray spectrometers (EDS) data. BSE images were acquired with a pixel size of 1.5 µm in a lattice mode, and the EDS data were collected with a spacing of 7 µm. The analysis method classifies plagioclase based on mineral spectral data and a predefined database: compositions with anorthite content (An%) between 0 and 10 are identified as albite (Na-rich); those with An% between 90 and 100 are classified as anorthite (Ca-rich); and intermediate compositions (e.g., andesine, oligoclase, labradorite) (An10–90) are grouped under the general category of plagioclase.

3.2. Electron Probe Micro-Analyzer (EPMA)

The major elements and trace elements in magnetite, ilmenite, and olivine can be used to explore the genesis of minerals and the physicochemical conditions of their formation [25,26,27,28,29]. In this paper, in situ micro-area analyses were carried out on these minerals in the black sand. The analysis of major elements was conducted using a JXA-8530F Plus EPMA (Electron Probe Micro-Analyzer) in the State Key Laboratory of Nuclear Resources and Environment, East China University of Technology (Nanchang, China). During the operation, the acceleration voltage was set at 15 kV, the current at 20 nA, and the beam spot diameter at 1 μm or 2 μm. Natural minerals or synthetic metal national standards were used as reference samples, and the detected elements include Si, Ti, Al, Fe, Mn, Mg, Cr, Ni, etc. The data were corrected using the ZAF program implemented in the JEOL PC-EPMA software (version 11.2.0).

3.3. LA-ICP-MS Analysis of Magnetite

The analysis of trace elements in magnetite by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) was completed in the State Key Laboratory of Nuclear Resources and Environment, East China University of Technology (Nanchang, China). The analysis used a PerkinElmer NexION 1000 quadrupole ICP-MS, and the laser ablation device was an ESI NWR 193 nm excimer laser. For the laser ablation test data, a method combining internal standards and external standards was adopted. The iron (Fe) element was selected as the internal standard, and NIST-610 glass was used as the external standard. The offline processing and correction of the test data (including the selection of sample and blank signals, correction of instrument sensitivity drift, and calculation of element contents) were completed with the Iolite 4.0 software [30].

4. Mineral Composition and Classification of Grains from the Black Sand

The grains of the black sand have different mineralogical compositions. According to their composition, the analyzed grains can be grouped into three categories: Sand I, Sand II, and Sand III (Figure 3):
(1)
Sand I: It is mainly composed of plagioclase (An90–100), ilmenite, olivine, and a small amount of magnetite. Irregular Fe–Ti oxides and olivine fill the spaces between the feldspars (Figure 3c). The content of magnetite in Sand I is relatively low, and the surface of the magnetite particles is clean and flat. Ilmenite within it can be seen in long, blade-like and lattice-like forms exsolved parallel to the (111) plane of the magnetite (Figure 4a). The ilmenite particles in Sand I are relatively large, occurring in anhedral to subhedral grains, and they often coexist with magnetite (Figure 4a). Olivine mostly coexists with ilmenite and often develops a corrosion rim structure (Figure 4b). Locally, olivine can be seen distributed in a poikilitic texture within the relatively large ilmenite grains.
(2)
Sand II: It is mainly composed of plagioclase (An0–10), magnetite, and a small amount of ilmenite and apatite (Figure 3d). The magnetite is distributed in the plagioclase (An0–10) in the form of star-shaped dots and sparse disseminations. The interior of the particles is rough, and the surface has many pits (Figure 4c,d). The ilmenite has a small particle size and mostly coexists with magnetite (Figure 4c).
(3)
Sand III: It is mainly composed of minerals such as magnetite, hornblende, ilmenite, and plagioclase (An10–90) (Figure 3e). The magnetite occurs in a vein-like form, cutting through the hornblende, with a vein width of about 2–5 μm (Figure 4e). The surface of the magnetite is clean, without exsolution traces. Ilmenite often coexists with magnetite (Figure 4f).

5. Chemical Composition of Characteristic Minerals

5.1. Magnetite

The results of EPMA and LA-ICP-MS analyses of magnetite are shown in Appendix A, Table A1 and Table A2. The compositions of magnetite in different black sands vary significantly (Figure 5).
Magnetite in Sand I is enriched in TiO2 (15.45–25.31 wt.%) and Al2O3 (0.11–2.64 wt.%), while exhibiting relatively low SiO2 (0.20–0.32 wt.%) (Figure 5a–c). In terms of trace elements, it is relatively enriched in Pb, Mn, Co, and Ni but relatively depleted in Sn, Mg, V, and Cr (Figure 6a), with Co contents ranging from 4.47 to 17.29 ppm, Ni from 23.27 to 40.84 ppm, V from 0.70 to 36.70 ppm, Sn from 0.08 to 4.36 ppm, and Cr from 0.11 to 6.58 ppm (Figure 5). Compared with Sand I, magnetite in Sand II has slightly lower TiO2 contents (2.66–10.32 wt.%) but significantly higher MgO contents (0.31–4.84 wt.%). It is enriched in Pb, Sn, Ni, and V while being depleted in Ga, Co, and Cr (Figure 6a). Notably, Ni (39.52–159.74 ppm), V (368.61–546.54 ppm), and Co (21.05–41.88 ppm) contents are higher than those in Sand I (Figure 5). In contrast to Sand I and Sand II, magnetite in Sand III contains lower TiO2 (0.25–0.48 wt.%) and MgO (0.05–0.42 wt.%) contents. It is relatively enriched in Sn, Mn, V, and Ni but depleted in Ga, Mg, Co, and Cr (Figure 6a). Trace element concentrations such as Ni (9.82–28.16 ppm) and Cr (0.34–2.66 ppm) are generally lower than those in magnetite from Sand I and Sand II.
The chondrite-normalized rare earth element (REE) patterns of magnetite from the three sand types are shown in Figure 7b. Magnetite in Sand I and Sand II generally displays right-sloping patterns characterized by enrichment in light rare earth elements (LREEs) and relative depletion in heavy rare earth elements (HREEs). Some samples from Sand I exhibit slight negative Eu anomalies, which may indicate plagioclase fractionation [31]. In contrast, Eu anomalies in Sand II are negligible. The distribution patterns of magnetite in Sand I and Sand II are similar to those in the underlying Xiahenan basalt, suggesting a strong genetic relationship with the mafic magmatic system. In comparison, magnetite in Sand III shows overall lower REE abundances and relatively flat distribution curves, with a distinct positive Eu anomaly, implying crystallization associated with plagioclase accumulation. The REE patterns among Sand III samples vary significantly, indicating that the source rock bodies underwent a complex evolutionary process.
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Figure 6. (a) Bulk continental crust-normalized trace element variation diagram of three types of magnetite in Xiahenan (values of bulk continental crust after [32] (pp. 1–64). (b) Chondrite-normalized REE patterns (normalized values are from [33]; rare earth data of basalt are from [12]).
Figure 6. (a) Bulk continental crust-normalized trace element variation diagram of three types of magnetite in Xiahenan (values of bulk continental crust after [32] (pp. 1–64). (b) Chondrite-normalized REE patterns (normalized values are from [33]; rare earth data of basalt are from [12]).
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Figure 7. (a) Olivine type diagram (according to [34]). (b–d) Diagram of the relationship between Fo and MnO, SiO2, and Ni of olivine. Note: I—chrysolite; II—hyalosiderite; III—hortonolite; Ⅳ—ferrohortonolite.
Figure 7. (a) Olivine type diagram (according to [34]). (b–d) Diagram of the relationship between Fo and MnO, SiO2, and Ni of olivine. Note: I—chrysolite; II—hyalosiderite; III—hortonolite; Ⅳ—ferrohortonolite.
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5.2. Ilmenite

Ilmenite mainly occurs in black Sand I. Electron probe analyses were carried out on the ilmenite in Sand I, and the results and calculation results are shown in Table A3. The results show that ilmenite has TiO2 contents ranging from 49.85% to 51.84%, FeO contents ranging from 39.34% to 41.32%, MnO contents ranging from 0.49% to 0.57%, MgO contents ranging 2.30% to 3.64%. The contents of CaO, SiO2, NiO, Na2O, K2O, etc., are all relatively low, mostly below the detection limit.

5.3. Olivine

Olivine is only found in black Sand I. The results of electron probe testing are shown in Table A4, and the chemical composition characteristics are as follows: it has a low Fo value [Fo = molecular Mg/(Mg + Fe)], ranging from 43.86 to 47.27 mol%, and it is hortonolite olivine, which falls in the same area as the olivine in the layered basalt of the Xiahenan area (Figure 7a) (Table A4). Olivine has MgO contents ranging from 19.91% to 21.87%, FeO contents ranging from 42.33% to 44.25%, MnO contents ranging from 0.64% to 0.75%, and Ni content ranging from 79 to 817 ppm. As the Fo value increases, MnO in olivine decreases (Figure 7b), suggesting that the parental magma of the olivine underwent fractional crystallization [35].

6. Discussion

6.1. Genesis of Minerals

6.1.1. Magnetite Genesis

According to the magnetite genetic discrimination diagram proposed by Dare et al. (2014) [28], in the plot of magnetite trace elements normalized to continental crust values (Figure 6a), magnetite from the Sand I and Sand II samples falls within the evolutionary field of Fe–Ti–V type magmatic-hydrothermal deposits. The overall trace element enrichment in magnetite from the Sand III sample is significantly reduced, approaching the boundary of the high-temperature hydrothermal field, indicating characteristics of hydrothermal alteration.
In the Ti–Ni/Cr diagram of magnetite (Figure 8a), magnetite in Sand I and in Sand II both show magmatic origin, while the magnetite in Sand III has Ni/Cr ≥ 1, indicating a hydrothermal origin. In the TiO2-Al2O3-MgO diagram (Figure 8b), magnetite in Sand I and Sand II falls in the area of ultrabasic-basic-intermediate magmas. In addition, in the Ni/(Cr + Mn)-Ti + V diagram, magnetite in Sand I and Sand II are projected in the area of Fe–Ti–V type, which is quite similar to the Fe–Ti–V oxide deposit in Bachu, Tarim Large Igneous Province, also showing the characteristics of magmatic origin. While magnetite in Sand III falls in the area of Skarn-type origin, which further confirms that the magnetite vein has a hydrothermal origin.
Existing studies have shown that the distribution coefficient of elements between minerals and melts mainly depends on temperature. The contents of elements such as Ti and Al are directly positively correlated with temperature both in magmas and hydrothermal fluids [26]. Therefore, the (Al + Mn)–(Ti + V) diagram can be used to distinguish the formation temperature of magnetite. In the (Al + Mn)–(Ti + V) diagram for the ore-forming temperature of magnetite (Figure 8d), magnetite in Sand I, Sand II, and Sand III are distributed and projected at the junction of >500 °C, 300 °C–500 °C, >500 °C, and 300 °C–500 °C.
Based on the above characteristics, magnetite in Sand I and Sand II is of magmatic origin, and they were formed at relatively high temperatures, with the formation temperature of magnetite in Sand I being higher than that of Sand II. Magnetite in Sand III is of hydrothermal origin, and its formation temperature is lower than that of magnetite in Sand I and Sand II. Considering that magnetite in Sand III is distributed in a vein-like pattern, it is speculated that it was formed during the hydrothermal event after the magmatic period.

6.1.2. Ilmenite Genesis

In the Fe2O3-FeTiO3-MgTiO3 diagram (Figure 9, the ilmenite in black sand is distributed within the compositional range of ilmenite in granite and basalt. Combined with the coexistence of ilmenite and olivine, it indicates that ilmenite is formed in basic rocks. In addition, ilmenite is mainly a solid solution of ilmenite (FeTiO3), geikielite (MgTiO3) and hematite. The compositional variation in geikielite is closely related to the pressure (depth) conditions during formation. That is, the higher the MgTiO3 component, the greater the formation depth [36]. In this study, the MgTiO3 component of ilmenite in the black sandy detritus is low, indicating that it was formed at a shallow depth. In addition, the mass percentage of each mineral is calculated from the content (Figure 3a) and density of each mineral in the sand. The mass fraction of ilmenite in the sand is 11.84%. Multiplying this by the TiO2 content in ilmenite (averaging 50.4%) yields an ilmenite grade of 5.97%. This grade level is higher than the lower limit of the economic grade for ilmenite placer mining (typically requiring TiO2 > 5%) [37]. As shown in Figure 4, ilmenite mainly exists as euhedral to subhedral grains with a particle size mostly between 30 and 100 μm, clear boundaries, and few fractures, possessing good physical separation characteristics. Ilmenite exists in the sand, and its mining and beneficiation costs are relatively low. Therefore, we preliminarily believe that the black sand on the surface of Xiahenan has potential for industrial applications.
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Figure 8. (a–c) Discrimination diagrams of magnetite (a–c) and (d) temperature discrimination diagram of magnetite. (a) Ti-Ni/Cr diagram (according to [28]). (b) TiO2-Al2O3-MgO ternary magnetite discrimination diagram [38] (magnetite in basalt data from Yuan et al., unpublished). Note: I: sedimentary–metamorphic-contact metasomatic magnetite; II: ultrabasic–basic magnetite–intermediate-magmatic magnetite; III: acidic–alkaline magma magnetite. (c) Diagram of Ni/(Cr + Mn)–(Ti + V) [26,39] (pp. 1–874). (d) (Al + Mn)–(Ti + V) diagram [26].
Figure 8. (a–c) Discrimination diagrams of magnetite (a–c) and (d) temperature discrimination diagram of magnetite. (a) Ti-Ni/Cr diagram (according to [28]). (b) TiO2-Al2O3-MgO ternary magnetite discrimination diagram [38] (magnetite in basalt data from Yuan et al., unpublished). Note: I: sedimentary–metamorphic-contact metasomatic magnetite; II: ultrabasic–basic magnetite–intermediate-magmatic magnetite; III: acidic–alkaline magma magnetite. (c) Diagram of Ni/(Cr + Mn)–(Ti + V) [26,39] (pp. 1–874). (d) (Al + Mn)–(Ti + V) diagram [26].
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Figure 9. Diagram of ilmenite composition of different sources (according to [40]) (basalt data from Yuan et al., unpublished).
Figure 9. Diagram of ilmenite composition of different sources (according to [40]) (basalt data from Yuan et al., unpublished).
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6.1.3. Olivine Genesis

The olivine present in the black sand deposits from the Xiahenan area has Fo values ranging from 44.35 to 47.27, which are significantly lower than the typical range for olivine derived from primitive mantle sources (Fo > 88), indicating that these olivines crystallized from a highly evolved, iron-rich basaltic magma [41,42,43]. Electron probe microanalysis reveals that these olivines generally contain low Ni concentrations (<1000 ppm) and relatively high MnO contents (approximately 0.64–0.75 wt.%). Together with their common intergrowth with ilmenite and the presence of resorption textures, these features suggest that the olivines are unlikely to represent early crystallization phases from primitive mantle-derived basaltic melts but instead likely formed during late-stage crystallization from highly evolved, Fe-rich melts [43,44,45].
Considering the extensive distribution and multi-phase eruptive characteristics of basalts within the Tarim Large Igneous Province, previous studies have demonstrated that these basalts are predominantly of high-Ti type and exhibit strong fractional crystallization trends. During the late-stage magmatic differentiation, Fe-enriched intermediate-mafic dike assemblages can form, including gabbro, syenite, and Fe-rich intermediate dikes [7,46,47]. These rock units may represent crucial parental magma sources for the formation of low-Fo olivine.

6.2. Source of the Black Sand

In the TiO2-Al2O3-MgO ternary diagram for detrital magnetite from the black sand deposits in the Xiahenan area (Figure 8b), magnetite from both Sand I and Sand II plot within the ultramafic-mafic-intermediate magmatic magnetite field (Field II). Their compositional fields coincide with those of magnetite from the Xiahenan basalts, indicating a genetic relationship with basaltic magmatism. Among them, the magnetite in Sand I shows compositional characteristics closer to those of basaltic magnetite in the projection, characterized by higher TiO2 contents and relatively lower Al2O3 and MgO levels. These features reflect an early crystallization stage of primitive basaltic magma, likely formed in a magma environment with relatively enriched Ti and shallow crystallization [25,27,29]. In contrast, the magnetite in Sand II, although still located within field II, plots away from the projection position of basaltic magnetite from the Xiahenan area, with relatively lower TiO2 content and elevated MgO and Al2O3 concentrations. This geochemical trend suggests that the magnetite in Sand II may have formed during the evolved stage of basaltic magma after undergoing fractional crystallization. At this stage, Ti components in the parental magma were preferentially consumed by early-crystallizing Fe-Ti oxides such as titanomagnetite, resulting in relative enrichment of Mg and Al in the residual melt [28,29]. Meanwhile, the magnetite in both Sand I and Sand II exhibits similar rare earth element (REE) distribution patterns to that of magnetite from the Xiahenan basalts (Figure 6b). The composition of ilmenite is also comparable to that in the Xiahenan basalts, showing typical basaltic ilmenite characteristics and indicating formation at relatively shallow depths (Figure 9).
The silicate minerals in Sand I are mainly olivine. As the earliest crystallized mineral in magma, olivine records the most primitive magmatic information, so the elemental content of olivine can be used to determine the nature of the magma. Experimental petrology shows that the Fe-Mg distribution coefficient between olivine and melt during the crystallization process is fixed, that is, KdOl/melt = (FeO/MgO)Ol/(FeO/MgO)melt = 0.3 ± 0.03 [48], and the source of minerals can be determined through the olivine-melt equilibrium theory. The highest Fo value of olivine in the black sand is 47.27 mol%. Taking the Fe-Mg distribution coefficient as 0.3, the FeO/MgO of the coexisting melt is calculated to be 3.65. The TFeO/MgO of the whole rock of the Xiahenan basalt is 2.24–5.66 [12]. The TFeO/MgO of the coexisting melt of olivine in the black sand is 3.65, which is within the range of TFeO/MgO of the whole rock of the Xiahenan basalt. In addition, the basalts underlying the black sand in the study area contain olivine with Fo values ranging from 39.67 to 42.88, along with extremely low whole-rock Mg# values (as low as 22.73). In comparison, the olivine in the black sand detritus exhibits slightly higher Fo values (Fo 44.35–47.27) but still falls within a very low range. The mineralogical characteristics of magnetite, ilmenite, and olivine indicate that Sand I and Sand II share similar mineral chemical compositions with the Xiahenan basalts.
The magnetite in both Sand I and Sand II exhibits magmatic origin (Figure 8a). However, olivine is absent in Sand II, with plagioclase being the dominant silicate mineral. Research shows that there is fractional crystallization in the Xiahenan basalt [12]. In addition, as shown in the previous text, the protolith of Sand I has also experienced crystallization differentiation. The integrated compositional characteristics and mineral assemblage suggest that Sand II likely formed during the intermediate stage of basaltic magma differentiation, representing an evolved product formed under prolonged fractional crystallization. Sand III is mainly composed of hydrothermal magnetite and represents a product of post-magmatic hydrothermal events.
Combined with field geological observations, these detrital deposits overlie the basalt and exhibit strong magnetism and enrichment in Fe-Ti oxides, suggesting that the three types of black sand are all derived from the Xiahenan basalt or its cognate magma. Basalt formed during the early stage of magmatic evolution underwent weathering to produce Sand I. After fractional crystallization, the basalt weathered to form Sand II. During post-magmatic hydrothermal events, a large amount of magnetite-bearing vein rocks developed, which cut through the host rock and, upon weathering, produced Sand III. During the wind sorting process, detrital materials rich in titaniferous oxides were retained in place, which explains why the magnetic susceptibility of the detritus is significantly higher than that of the basalts from the Xiahenan area.

7. Conclusions

(1)
The black sand is composed of grains that were eroded from three different magmatic rocks: Sand I is composed of plagioclase, ilmenite, olivine, and magnetite; Sand II is composed of plagioclase and fine-grained magnetite; and Sand III is composed of hornblende and vein-like magnetite.
(2)
Magnetite is present in all three types of sands. The magnetite in Sand I and Sand II is of magmatic origin, being the products of the weathering of magmatic rock at different stages of differentiation of mafic–ultramafic rocks. The magnetite in Sand III is distributed in veins and is of hydrothermal origin. Meanwhile, ilmenite and olivine are mainly distributed in Sand I, both exhibiting characteristics of magmatic origin.
(3)
The geochemical characteristics of the mineral elements of magnetite, ilmenite, and olivine indicate that the three types of black sand are all derived from the Xiahenan basalt. Basalt generated during magmatic events weathered to form Sand I and subsequently Sand II. During the post magmatic hydrothermal events, fine veins of magnetite developed and cut through the basalt. These basalts with developed veins formed Sand III after weathering.

Author Contributions

Writing—original draft, visualization, S.Z.; methodology and writing (review and editing), R.Z. and J.P.; investigation, S.D.; resources, D.L.; review and editing, J.Y. and J.W.; data curation, Q.L. and Y.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Deep Earth Probe and Mineral Resources Exploration-National Science and Technology Major Project (Nos. 2024ZD1003403); the Jiangxi Provincial Natural Science Foundation (No. 20232BAB213061, 20242BAB27002); The China Uranium Industry Co., Ltd. East China University of Technology Innovation Partnership Foundation (2023NRE-LH-12); and the National Nature Science Foundation of China (Grants Nos. 42030809, 42262017, 42002095, 42162013).

Data Availability Statement

Data is contained in Appendix A.

Acknowledgments

We would like to thank the staff of the Nuclear Resources and Environment, East University of Technology, for their advice and assistance in the experimental analysis. In addition, we wish to thank the anonymous reviewers and editors for their insightful comments.

Conflicts of Interest

The authors declare no conflicts of interest.

Appendix A

Table A1. Results of electron probe analysis of magnetite in black sand from Xiahenan (wt%).
Table A1. Results of electron probe analysis of magnetite in black sand from Xiahenan (wt%).
StageSampleCaOMgOTiO2SiO2Al2O3FeOFe2O3MnOCr2O3NiONa2OK2OTotal
Sand ⅠMag Ⅰ-1b.d.l.0.1415.900.072.0544.0235.321.970.34b.d.l.0.060.0299.90
Mag Ⅰ-2b.d.l.0.2420.270.022.4247.4725.251.770.25b.d.l.b.d.l.b.d.l.97.69
Mag Ⅰ-3b.d.l.0.1518.050.051.7946.3331.221.370.290.070.040.0299.38
Mag Ⅰ-4b.d.l.0.0319.600.032.2547.9728.711.840.240.070.02b.d.l.100.76
Mag Ⅰ-5b.d.l.1.4016.230.042.6443.5333.780.400.240.060.020.0198.34
Mag Ⅰ-6b.d.l.1.5521.270.322.1747.1024.611.840.280.030.02b.d.l.99.17
Mag Ⅰ-7b.d.l.0.1725.310.192.0453.2816.541.270.220.110.030.0299.18
Mag Ⅰ-9b.d.l.0.2017.850.191.8546.0830.871.380.280.060.04b.d.l.98.80
Mag Ⅰ-10b.d.l. 2.0815.450.020.1141.7439.750.550.090.15b.d.l.b.d.l.99.92
Sand ⅡMag Ⅱ-10.220.313.140.270.2232.3359.730.150.010.020.020.0196.43
Mag Ⅱ-2b.d.l.0.733.531.260.1834.7659.310.10b.d.l.0.020.010.0499.96
Mag Ⅱ-30.133.998.680.001.2131.8752.841.090.06b.d.l.b.d.l.0.0399.90
Mag Ⅱ-4b.d.l.3.858.180.071.3331.3752.361.110.050.060.010.0398.42
Mag Ⅱ-50.134.119.460.021.2431.8850.401.170.030.090.010.0298.55
Mag Ⅱ-60.124.8410.320.040.5431.2048.800.990.020.030.030.0196.93
Mag Ⅱ-7b.d.l.1.274.670.330.1933.2558.690.21b.d.l.b.d.l.b.d.l.0.0298.64
Mag Ⅱ-80.040.653.810.370.2033.8160.430.060.01b.d.l.0.010.0399.42
Mag Ⅱ-90.020.342.661.330.3834.3159.980.21b.d.l.0.050.040.0299.36
Mag Ⅱ-10b.d.l.0.333.330.270.3232.6959.000.080.030.04b.d.l.0.0196.11
San ⅢMag Ⅲ-10.230.280.262.590.2434.2162.680.040.01b.d.l.0.060.02100.62
Mag Ⅲ-20.260.140.362.260.2333.7662.740.06b.d.l.0.030.040.0499.91
Mag Ⅲ-30.220.230.402.480.1932.6159.010.03b.d.l.b.d.l.0.050.0495.26
Mag Ⅲ-40.320.170.272.410.1732.4859.640.01b.d.l.b.d.l.0.040.0495.54
Mag Ⅲ-50.370.190.482.340.1632.6559.790.02b.d.l.b.d.l.0.130.0396.16
Mag Ⅲ-60.200.120.291.960.1833.6363.93b.d.l.b.d.l.b.d.l.b.d.l.0.03100.34
Mag Ⅲ-70.120.050.431.350.1333.4665.82b.d.l.b.d.l.b.d.l.b.d.l.0.03101.39
Mag Ⅲ-80.260.310.252.610.2334.0062.510.05b.d.l.0.040.030.04100.32
Mag Ⅲ-90.280.210.312.330.1933.7662.930.030.020.060.070.05100.20
Mag Ⅲ-100.300.420.282.700.1934.0762.600.050.03b.d.l.0.040.03100.72
Note: The Fe2O3 and FeO contents in all electron microprobe data were calculated based on the valence balance principle [49]. b.d.l: below detection limit.
Table A2. Trace element contents components of magnetite by LA-ICP-MS (ppm).
Table A2. Trace element contents components of magnetite by LA-ICP-MS (ppm).
Serial NumberSand ⅠSand ⅡSand Ⅲ
Mag1-1Mag1-2Mag1-3Mag1-4Mag1-5Mag1-6Mag2-1Mag2-2Mag2-3Mag2-4Mag3-1Mag3-2Mag3-3Mag3-4Mag3-5Mag3-6
Y8.448.1924.2928.8816.9117.9512.838.9319.654.962.130.911.4511.241.2514.78
Pb27.0123.1518.1817.2570.39108.0361.4337.84135.42115.3716.9212.8314.3829.8017.4539.54
Zr23.4043.3426.1418.0133.0250.41249.01336.92215.16231.5445.3638.6758.05120.1227.74108.54
Hf0.441.070.260.160.660.985.716.934.184.250.440.310.521.97110.221.32
Al0.500.54810.120.080.361.722.671.091.801.5510.470.262.182.010.283.14
Cu9.5122.91126.834.9736.9750.9518.566.0549.7329.378.052.4514.1812.544.4326.85
Sn0.110.320.110.084.244.3614.7414.2815.1615.093.22.606.983.5482.605.84
Ga1.071.051.121.231.163.9112.7605.747.926.071.770.752.805.680.978.37
Mn0.110.110.160.170.020.020.060.060.380.420.030.020.040.060.030.08
Mg0.860.880.931.260.130.171.420.651.701.450.240.130.640.720.110.49
Zn72.5972.5293.40100.8211.1518.34241.39124.40925.47934.5120.109.7921.7257.5413.07114.11
Co15.3015.2513.2617.274.486.4941.8826.9421.8921.053.961.495.909.751.7024.52
V3.023.770.880.7031.9336.70368.61400.25386.65546.5439.3076.9868.8278.5341.71195.03
Ni29.9527.9831.5940.8423.2729.1096.9939.52159.74149.4212.0510.3218.8018.209.8228.16
Cr1.461.130.110.493.326.583.8129.4215.969.911.010.570.340.910.512.66
La6.255.7922.0029.9840.5539.7139.5530.9857.4049.154.7492.723.2514.033.6714.71
Ce11.2310.2943.2959.0676.1280.1276.1655.6081.4466.785.023.083.8724.954.3818.05
Pr1.090.955.166.877.067.488.595.658.975.080.410.250.432.880.341.76
Nd3.723.1520.5928.1724.2526.2334.1621.4735.2615.931.590.871.6312.161.108.14
Sm0.72 0.664.205.274.474.426.473.685.762.010.230.090.232.530.15241.71
Eu0.130.160.660.971.451.681.770.952.290.960.160.080.150.730.101.30
Gd0.990.744.055.473.633.6714.9112.885.021.530.330.120.332.630.192.12
Tb0.180.150.630.820.650.510.590.380.630.250.050.020.050.380.030.30
Dy1.251.163.644.557663.523.382.881.873.491.310.310.140.332.040.192.14
Ho0.330.330.790.980.690.710.530.330.660.230.080.020.050.430.040.51
Er1.121.082.542.731.871.891.390.941.890.730.340.140.161.210.152.07
Tm0.200.180.360.400.260.310.180.140.280.100.060.020.030.160.030.35
Yb1.581.652.602.511.502.281.050.891.670.760.400.230.211.160.242.83
Lu0.240.280.400.350.290.330.140.170.270.150.090.040.040.170.040.54
Table A3. Electron probe test data of ilmenite in black sand from Xiahenan.
Table A3. Electron probe test data of ilmenite in black sand from Xiahenan.
Sample Number Ilm-1Ilm-2Ilm-3Ilm-4Ilm-5Ilm-6Ilm-7Ilm-8Ilm-9Ilm-10Ilm-11Ilm-12Ilm-13Ilm-14
CaOb.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.
MgO3.052.933.012.912.842.752.782.652.852.682.692.992.542.30
TiO250.2950.3650.2649.9350.3150.5950.7950.5550.0050.6250.6050.3351.5449.85
SiO20.05b.d.l.b.d.l.0.040.040.010.01b.d.l.0.010.040.020.030.010.03
Al2O30.020.050.050.060.050.080.060.110.080.080.090.050.060.08
FeO39.3439.5139.2439.2439.6140.0640.1740.2539.2240.0840.1039.3941.3240.13
Fe2O36.216.306.775.805.456.364.745.926.235.665.255.873.686.25
MnO0.510.540.530.540.520.530.550.490.550.590.510.580.490.52
Cr2O30.100.060.050.090.030.010.020.060.060.050.070.130.010.03
NiOb.d.l.b.d.l.0.01b.d.l.0.03b.d.l.b.d.l.0.010.040.040.02b.d.l.0.03b.d.l.
Na2Ob.d.l.b.d.l.b.d.l.b.d.l.b.d.l.0.01b.d.l.b.d.l.0.010.010.02b.d.l.b.d.l.0.02
K2Ob.d.l.0.010.02b.d.l.0.02b.d.l.b.d.l.b.d.l.0.020.010.01b.d.l.b.d.l.0.01
Total99.5599.7599.9498.6298.91100.3999.13100.0399.0699.8699.3899.3699.6999.21
The number of cations based on three oxygen atoms
Ti0.9400.9400.9360.9420.9470.9400.954 0.943 0.9400.9450.9490.9430.9640.939
Kb.d.l.b.d.l.0.001b.d.l.0.001b.d.l.b.d.l.b.d.l.0.001b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.
Si0.001b.d.l.b.d.l.0.0010.001b.d.l.b.d.l.b.d.l.b.d.l.0.0010.0010.001b.d.l.0.001
Fe2+0.8170.8200.8120.8230.8290.8270.8390.8340.8190.8320.8360.8200.8590.841
Mg0.1130.1080.1110.1090.1060.1010.1030.0980.1060.0990.1000.1110.0940.086
Mn0.0110.0110.0110.0110.0110.0110.0120.0100.0120.0120.0110.0120.0100.011
Cab.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.
Fe3+0.1160.1180.1260.1100.1030.1180.0890.1100.1170.1060.0990.1100.0690.118
Cr0.0020.0010.0010.0020.001b.d.l.b.d.l.0.0010.0010.0010.0010.002b.d.l.b.d.l.
Alb.d.l.0.0010.0020.0020.0010.0020.0020.0030.0020.0020.0030.0010.0020.002
Vb.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.
Znb.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.
Pb.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.
Cub.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.
Nab.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.0.0010.0010.001b.d.l.b.d.l.0.001
Pbb.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.b.d.l.
Nib.d.l.b.d.l.b.d.l.b.d.l.0.001b.d.l.b.d.l.b.d.l.0.0010.001b.d.l.b.d.l.0.001b.d.l.
Total2.0002.0002.0002.0002.0002.0002.0002.0002.0002.0002.0002.0002.0002.000
End-member composition/%
Fe2O311.6311.7812.6410.9810.2811.848.9311.0611.7110.609.8811.016.9011.82
FeTiO381.8582.1081.3782.5283.0682.8384.0183.6382.1983.4383.8482.1886.0584.30
MnTiO31.0831.131.111.151.111.121.171.021.171.251.081.221.041.10
MgTiO311.3110.8511.1110.9010.6310.1210.359.8110.649.9410.0211.129.448.60
Note: The Fe2O3 and FeO contents in all samples were calculated according to the electron balance principle [49]. b.d.l: below detection limit.
Table A4. Electron probe test data of olivine in black sand and basalt from Xiahenan.
Table A4. Electron probe test data of olivine in black sand and basalt from Xiahenan.
SampleSample NumberCaONiOSiO2FeOMnOMgOTotalFoFaNi (ppm)
SandOl-10.250.0234.6543.830.7019.9199.3644.3554.76141
Ol-20.300.0734.6544.030.7120.94100.6945.4853.64558
Ol-30.270.0634.3342.710.6620.9298.9446.2252.95464
Ol-40.220.0534.8042.520.6421.0099.2446.4452.75416
Ol-50.280.0934.6042.320.7021.1799.1446.7252.41723
Ol-60.220.0234.6143.190.7420.7999.5745.7553.32181
Ol-70.330.0234.7742.330.7121.5499.7047.1551.97141
Ol-80.250.0534.6742.800.7221.1299.6046.3852.72401
Ol-90.350.1034.5942.960.7020.8799.5746.0053.13817
Ol-100.300.0534.5642.520.6920.9599.0746.3552.78361
Ol-110.240.0534.6942.860.7121.3199.8546.5752.55361
Ol-120.300.0534.7443.570.7520.4399.8345.1153.96401
Ol-130.280.0134.7142.860.6420.5399.0345.6853.5079
BasaltOl-10.130.0733.6047.690.8117.90100.1939.6759.31519
Ol-20.150.0333.7646.540.8418.4599.7640.9757.98196
Ol-30.110.0233.7746.420.8118.4099.5340.9758.00181
Ol-40.160.0533.3746.430.7718.3799.1540.9658.06361
Ol-50.150.0733.5746.480.7718.6799.6941.3257.72519
Ol-60.150.1133.5146.100.7819.3499.9942.3756.66857
Ol-70.160.0633.9845.380.8119.4899.8742.9156.08503
Ol-80.220.0133.6447.330.8517.99100.0339.9558.9739
Ol-90.120.0333.7545.530.8419.5499.8042.8856.07244
Ol-100.130.0134.1846.170.8218.83100.1541.6757.31102

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Minerals 15 00884 g001
Figure 1. Regional geological setting of the study area. (a) Map of China to show the location of Xinjiang (square) (modified after [11]). (b) Structural location map of the Xiahenan area (modified after [12]. (c) Aeromagnetic anomaly map at a scale of 1:250,000 (adapted from internal materials).
Figure 1. Regional geological setting of the study area. (a) Map of China to show the location of Xinjiang (square) (modified after [11]). (b) Structural location map of the Xiahenan area (modified after [12]. (c) Aeromagnetic anomaly map at a scale of 1:250,000 (adapted from internal materials).
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Figure 2. (a) Black sand on the surface layer of Xiahenan; (b) Black sand particles; (c) Geological cross-section of layered basalt in Xiahenan (the horizontal and vertical proportions are different). For a more intuitive representation of the distribution characteristics of the basalt layer, the vertical scale is magnified by 20 times.
Figure 2. (a) Black sand on the surface layer of Xiahenan; (b) Black sand particles; (c) Geological cross-section of layered basalt in Xiahenan (the horizontal and vertical proportions are different). For a more intuitive representation of the distribution characteristics of the basalt layer, the vertical scale is magnified by 20 times.
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Figure 3. (a) Mineral assemblage of the black sand in Xiahenan. (b) TIMA image of the black sand. (c–e) Three types of sands. (Note: In the TIMA analysis, plagioclase (Pl) refers to An10–90, albite (Ab) to An0–10, and anorthite (An) to An90–100. Albite and anorthite are the end-member types of plagioclase and are collectively referred to as “plagioclase” in the text. Actinolite and ferrokaersutite are both collectively referred to as “hornblende” in the text).
Figure 3. (a) Mineral assemblage of the black sand in Xiahenan. (b) TIMA image of the black sand. (c–e) Three types of sands. (Note: In the TIMA analysis, plagioclase (Pl) refers to An10–90, albite (Ab) to An0–10, and anorthite (An) to An90–100. Albite and anorthite are the end-member types of plagioclase and are collectively referred to as “plagioclase” in the text. Actinolite and ferrokaersutite are both collectively referred to as “hornblende” in the text).
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Figure 4. Microscopic features of the black sand in the Xiahenan Area. (a) Microphotograph of black Sand I, showing that magnetite forms a coalesced body with ilmenite. (b) Olivine is embedded in ilmenite. (c) Microphotograph of black Sand II, with magnetite occurring as fine aggregates. (d) Microphotograph of black Sand II. (e,f) Black Sand III, with magnetite occurring with a veined pattern. Note: Hbl—hornblende; Ilm—ilmenite; Mag—magnetite; Ol—olivine; Pl—plagioclase.
Figure 4. Microscopic features of the black sand in the Xiahenan Area. (a) Microphotograph of black Sand I, showing that magnetite forms a coalesced body with ilmenite. (b) Olivine is embedded in ilmenite. (c) Microphotograph of black Sand II, with magnetite occurring as fine aggregates. (d) Microphotograph of black Sand II. (e,f) Black Sand III, with magnetite occurring with a veined pattern. Note: Hbl—hornblende; Ilm—ilmenite; Mag—magnetite; Ol—olivine; Pl—plagioclase.
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Figure 5. Box-whisker plots comparing major elements of three types of magnetite in Xiahenan. (a–d) Comparison of the main elemental content (TiO2, Al2O3, SiO2, MgO) of magnetite in the three types of sand; (e–i) Comparison of the trace elemental content (Co, Ni, V, Sn, Cr) of magnetite in the three types of sand. ⧫ Outlier: Extreme values that deviate from the main distribution of the data may be caused by special reasons or errors.
Figure 5. Box-whisker plots comparing major elements of three types of magnetite in Xiahenan. (a–d) Comparison of the main elemental content (TiO2, Al2O3, SiO2, MgO) of magnetite in the three types of sand; (e–i) Comparison of the trace elemental content (Co, Ni, V, Sn, Cr) of magnetite in the three types of sand. ⧫ Outlier: Extreme values that deviate from the main distribution of the data may be caused by special reasons or errors.
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MDPI and ACS Style

Zhang, S.; Zeng, R.; Duan, S.; Pan, J.; Liang, D.; Yan, J.; Wan, J.; Liu, Q.; Zhang, Y. Mineralogical Characterization and Provenance of Black Sand in the Xiahenan Area, Tarim Large Igneous Province. Minerals 2025, 15, 884. https://doi.org/10.3390/min15080884

AMA Style

Zhang S, Zeng R, Duan S, Pan J, Liang D, Yan J, Wan J, Liu Q, Zhang Y. Mineralogical Characterization and Provenance of Black Sand in the Xiahenan Area, Tarim Large Igneous Province. Minerals. 2025; 15(8):884. https://doi.org/10.3390/min15080884

Chicago/Turabian Style

Zhang, Songqiu, Renyu Zeng, Shigang Duan, Jiayong Pan, Dong Liang, Jie Yan, Jianjun Wan, Qing Liu, and You Zhang. 2025. "Mineralogical Characterization and Provenance of Black Sand in the Xiahenan Area, Tarim Large Igneous Province" Minerals 15, no. 8: 884. https://doi.org/10.3390/min15080884

APA Style

Zhang, S., Zeng, R., Duan, S., Pan, J., Liang, D., Yan, J., Wan, J., Liu, Q., & Zhang, Y. (2025). Mineralogical Characterization and Provenance of Black Sand in the Xiahenan Area, Tarim Large Igneous Province. Minerals, 15(8), 884. https://doi.org/10.3390/min15080884

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