A Late Jurassic Epithermal Pb-Zn Deposit: Insights from Rb-Sr Dating of Quar tz -Hosted Fluid Inclusions and Sphalerite Chemical Composition

: The Kangjiawan Pb-Zn deposit, situated within the Shuikoushan polymetallic ore ﬁ eld in Changning, Hunan Province, China, is a large-scale Pb-Zn deposit unearthed in 1976. Based on detailed geological ﬁ eld investigations, this study presents the results of the Rb-Sr isotopic dating, electron probe microanalyses (EPMAs), and LA-ICP-MS analyses of the Kangjiawan Pb-Zn deposit in order to determine the ore-forming age and the occurrence of trace elements in sphalerite and thereby constrain the genesis of the deposit. The Rb-Sr dating of quar tz -hosted ﬂ uid inclusions yielded an Rb-Sr isochron age of 150 ± 4 Ma, with an initial 87 Sr/ 86 Sr ratio of 0.71101 ± 0.00008 (MSWD = 1.1), suggesting that the Pb-Zn mineralization of the Kangjiawan deposit took place during the Late Jurassic, coeval with the magmatic activities within the ore ﬁ eld. EPMA and LA-ICP-MS analyses showed that Fe, Mn, and Cd were primarily incorporated into the sphalerite la tt ice through isomorphous substitution. Speci ﬁ cally, Fe and Mn substituted for Zn, whereas Cd replaced both Fe and Zn. Other elements such as Cu, Sb, and Sn occurred within the sphalerite la tt ice through mineral micro-inclusions or isomorphic substitution. EPMAs and LA-ICP-MS results showed that the FeS contents in sphalerite were less than 14.33%, with corresponding ore-forming temperatures below 259 °C. The LA-ICP-MS results showed that sphalerites from the Kangjiawan Pb-Zn deposit had relatively high Ga/In ratios ranging from 0.01 to 144, providing further support for medium-to-low-temperature mineralization. The trace element compositions of sphalerites from the Kangjiawan Pb-Zn deposit exhibit skarn-type characteristics, suggesting a potential association with contemporary magmatic activities within the Shuikoushan ore ﬁ eld. During the Late Jurassic, extensive granitic magmatic activities occurred in the study area. At the late stage of magma crystallization, hydro-thermal ﬂ uid containing Pb and Zn precipitated at medium-to-low temperatures and generated the Kangjiawan Pb-Zn deposit.


Introduction
Southern Hunan is an important source of nonferrous metals, rare earth metals, and radioactive minerals in China.It is also an important part of the Nanling metallogenic belt, which is rich in W, Sn, Mo, Bi, Be, Pb, Zn, REE, Nb, Ta, and others.The Kangjiawan Pb-Zn deposit, located within the Shuikoushan polymetallic ore field in Changning, Hunan Province, is a large, concealed deposit discovered relatively recently with the highest annual output in the Shuikoushan ore field [1,2].The ore bodies primarily occur in laminated and lenticular forms within a strongly silicified and fractured breccia zone, situated between the Permian Dangchong Formation marlstone and Qixia Formation limestone [3,4].Therefore, some scholars believe that the deposit might be of a sedimentary genesis and controlled via stratigraphy, lithology, petrography, and folding-fracture factors.However, the mineralization process and the genesis of the deposit are still under debate, in particular, the relationship between mineralization and magmatic activity [1,5], the source of ore-forming materials [6][7][8], and the properties and evolution of ore-forming fluids [1,6,[9][10][11][12]. Several views on the genesis of the deposit have been proposed as follows: magma hydrothermal metasomatic filling [5,[12][13][14]; polygenetic compound stratum [6,7]; and sedimentation-exhalation [9].Recent studies on H-O and S isotopes from the area suggest that the Kangjiawan Pb-Zn deposit was a metasomatic deposit filling in silicified breccias [14].At present, the deepest hole drilled in the deposit has reached 1500 m.However, no pluton related to mineralization has been found [15].Hence, further investigation is necessary to elucidate the metallogenic process and origin of the Kangjiawan Pb-Zn deposit.
In this paper, we present a study of the geochronology and geochemistry of the Kangjiawan Pb-Zn deposit based on detailed geological field work, with new results from quartz Rb-Sr dating and data on sphalerite chemical compositions, in an attempt to constrain the deposit's ore-forming age and mineralization process.

Ore Field Geological Setting
The Shuikoushan ore field is situated on the northwest margin of the Cathaysia Block, covering an area of ca.240 km 2 (Figure 1).It is a large-scale polymetallic ore field renowned for its abundant reserves of metals such as Pb, Zn, Au, Ag, etc.The ore field encompasses multiple deposits, including the Kangjiawan Pb-Zn deposit, the Shuikoushan Pb-Zn deposit, the Longwangshan gold deposit, the Xianrenyan gold deposit, and the Shi'aoling Pb-Zn deposit (Figure 1b).In recent years, new discoveries of metal mineral resources, including Fe, Cu, and Mo, have been made in the ore field.It stands as one of China's most crucial sources for the production of nonferrous metals and precious metals.
The Shuikoushan ore field primarily contains strata from the Paleozoic Devonian to the Cenozoic, with a total sedimentary thickness exceeding 3 km [16].The strata below the Upper Triassic are predominantly shallow marine carbonates interbedded with ironand coal-bearing coastal plain sands and shales; meanwhile, the Upper Triassic to the Cretaceous strata are primarily composed of terrestrial clastic molasses.Among them, the Permian Qixia Formation comprises a series of thick-bedded limestones, exhibiting fracturing in its middle and upper sections due to the presence of flint and carbonaceous rocks.The lower section of the Permian Dangchong Formation is characterized by thin-to medium-bedded marlstones, whereas the upper section is comprised of Mn-bearing siliceous rocks, intermittently interrupted by thin layers of shale.These two formations are the main ore-bearing strata in the ore field.
Structures are actively developed within the Shuikoushan ore field, with fold hinges predominantly exhibiting a near-SN orientation, and fault structures primarily striking close to SN, followed by NE, NW, and EW (Figure 1b).These structures influence magmatic activity and mineralization processes within the ore field, closely associated with the widespread silicified breccias in the area.
Magmatic rocks are widely exposed in the Shuikoushan ore field, comprising a total of 72 identified plutons and occupying an area of ca.4.8 km 2 (Figure 1b).These rocks consist of granodiorite, quartz diorite, rhyodacite, and dacite porphyry, followed by granodiorite porphyry, granite porphyry, and intermediate-acid lava rocks, with emplacement timing primarily attributed to the Late Jurassic [2,[17][18][19].They exhibit metaluminous to weak peraluminous characteristics, falling within the high-K calc-alkaline series with Itype affinities.It is proposed that the magmatic activity in the Shuikoushan ore field might originate from a mixture of the depleted mantle and the lower crust of South China and might be related to the extension in the lithosphere induced by the subduction of the Paleo-Pacific plate over 150~160 Ma [5,19,20].

Deposit Geology
The Kangjiawan Pb-Zn deposit is located in the northeastern part of the Shuikoushan ore field, approximately 3 km from the southwest Shuikoushan Pb-Zn deposit (Figure 1b) and serves as the ore field's primary mining site for Pb-Zn.The ore bodies are primarily situated within the interbedded silicified breccias, occurring between the marlstone of the Permian Dangchong Formation and the limestone of the Qixia Formation (Figure 2).The predominant geological structure of the ore bodies is stratabound, with secondary occurrences of lenticular and vein-like structures.To date, a cumulative total of 61 ore bodies have been delineated, among which seven are recognized as the principal deposits.The Kangjiawan Pb-Zn deposit is a large-scale Pb-Zn deposit characterized by metal reserves of about 220,000 tons of Pb, 240,000 tons of Zn, 750,000 tons of sulfur, 2 tons of Au, and 15 tons of Ag, with average ore grades of 3.92% for Pb, 4.50% for Zn, 2.68 g/t for Au, and 86.80 g/t for Ag.

Sampling and Analytical Methods
All samples were collected from Kangjiawan from underground stopes.Suitable samples were prepared as polished sections, which were subsequently subjected to mineralogical observations employing both reflected and transmitted light.Six samples from ore-bearing quartz veins were used for the Rb-Sr dating of fluid inclusions.Seven ore samples were designated for electron probe microanalysis (EPMA) on sphalerite, while five ore samples were allocated for the LA-ICP-MS spot analysis of trace elements in sphalerite.All the samples mentioned above belong to the main mineralization stage.The Rb-Sr analyses were carried out at the Isotopic Laboratory, Wuhan Geological Survey Center, China Geological Survey, while EPMAs and LA-ICP-MS analyses were conducted at the Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration, Guilin University of Technology, China.
Six quartz samples of ore-bearing quartz veins were collected from the Kangjiawan Pb-Zn deposit.The samples were crushed into small specimens (less than 0.4 mm in diameter) and hand-picked carefully from each sample under a binocular microscope.The Rb-Sr analyses in this study were carried out using a MAT-261 mass spectrometer (Thermo Scientific, Waltham, MA, USA) following the methods of Li et al. [23].During the analysis, repeat measurements on the standard NBS 987 sample yielded mean 87 Sr/ 86 Sr ratios of 0.71025 ± 6 (2σ); on NBS 607, they yielded mean 87 Sr/ 86 Sr ratios of 1.20035 ± 10 (2σ); and on GBW0411, they yielded mean 87 Sr/ 86 Sr ratios of 0.76006 ± 15 (2σ) [23].The total analytical blanks for Rb and Sr were 1-4 pg and 1-2 pg, respectively.The decay constant used for 87 Rb was 1.42 × 10 −11 a −1 .
The EPMAs were performed with a JEOL JXA-8300 electron microprobe (JEOL Ltd., Tokyo, Japan).Prior to analysis, the specimens underwent uniform carbon coating with a coating thickness of 20 nm.The analytical parameters were as follows: a 15 kV accelerating voltage, a 20 nA beam current, and a 2 µm spot size.Matrix correction was implemented through the ZAF correction program (Ver.1.14.0), resulting in a precision exceeding 1%.The elements measured included Zn, S, Fe, Mn, Cd, Pb, Cu, In, Co, As, Bi, Nb, Sn, Ti, Mo, Sb, Ga, and Ni.
The LA-ICP-MS analysis employed the GeoLas Pro HD laser ablation system (Geo-Las Systems GmbH, Aschau im Chiemgau, Germany), featuring a laser beam spot diameter of 35 µm and a laser ablation frequency of 10 Hz.The laser fluence was 3.5 J/cm 2 , with a repetition rate of 6 Hz.The ICP-MS utilized was the Agilent 7500 Series (Agilent Technologies, Santa Clara, CA, USA), which was calibrated using the NIST 610 standard glass (National Institute of Standards and Technology, Gaithersburg, MD, USA) to achieve a low oxide production rate.Each time-resolved analytical dataset comprised a 20 s blank signal and a 50 s sample signal.Helium carrier gas at a flow rate of 0.7 L/min was introduced into the cup, and the resulting aerosol was subsequently blended with Ar make-up gas at a rate of 0.89 L/min.The elements subjected to measurement included Ti, Mn, Fe, Co, Ni, Cu, Ga, Ge, Mo, Ag, Cd, In, Sn, Sb, Au, Tl, and Pb.The Zn content, as determined via EPMA, served as the internal standard, and outliers were excluded from the analysis.

Rb-Sr Dating of Fluid Inclusions in Quartz
The analytical Rb-Sr isotopic data of quartz-hosted fluid inclusions from the Kangjiawan Pb-Zn deposit are given in Table 1.Six samples exhibit 87 Rb/ 86 Sr ratios ranging from 0.272 to 2.759.The isochron ages and initial 87 Sr/ 86 Sr ratios were calculated using GeoKit software [24], with a 2% error for the 87 Rb/ 86 Sr ratios and a 0.1% error for the 87 Sr/ 86 Sr ratios (2σ).Six samples from the ore-bearing quartz veins yielded an Rb-Sr isochron age of 150 ± 4 Ma, with an initial 87 Sr/ 86 Sr ratio of 0.71101 ± 0.00008 (MSWD = 1.1) (Figure 5).   1.

EPMAs of Sphalerite
Seven sphalerites from the Kangjiawan Pb-Zn deposit were analyzed, and the results are listed in Table 2. Note: "-" represents a result below the detection limit.
The content of Zn in sphalerite ranges from 54.57 to 66.20 wt.%, with an average of 61.67 wt.%; the S content ranges from 32.06 to 33.54 wt.%, averaging 32.82 wt.%; the Fe content ranges from 0.03 to 8.00 wt.%, with an average of 3.02 wt.%; the Mn content ranges from 0.42 to 3.81 wt.%, averaging 1.82 wt.%; the Cd content ranges from 0.04 to 0.22 wt.%, averaging 0.08 wt.%; and the Ga content ranges from 0.01 to 0.10 wt.% (one sample was below the detection limit), averaging 0.05 wt.%.
It is noteworthy that the dispersed elements Cd and Ga present in sphalerites from the Kangjiawan Pb-Zn deposit meet their respective industrial-grade specifications (Cd: 0.01~0.09%;Ga: 0.01~0.02%)[25].Consequently, particular consideration should be given to the comprehensive utilization of Cd and Ga during the mining operations.

Ore-Forming Age
Comprehensive geological dating studies conducted over the past decade have constrained the timing of magmatic activities in the Shuikoushan ore field to the Early Jurassic.For example, Zhen et al. [17] obtained an age of 156 ± 1.2 Ma for the Xianrenyan granite porphyry via zircon LA-ICP-MS U-Pb dating; Zuo et al. [18] reported an age of 156.7 ± 1.6 Ma for the emplacement of the Laomengshan rhyodacite, also determined via zircon LA-ICP-MS U-Pb dating; Yang et al. [19], using SIMS zircon U-Pb dating, proposed that the Shuikoushan granitoid was intruded at 158.3 ± 1.2 Ma.
The precise dating of mineral deposits is crucial for constraining the mineralization process and the associated tectonic setting.Compared to the abundant magmatic timing data, there have been relatively few reports on the ore-forming age of the Shuikoushan ore field.Previous research has mostly speculated that the ore field's mineralization was contemporaneous with its magmatic activity, based on structural features, ore body attitudes, and relationships between ore bodies and magmatic rocks.However, due to the lack of precise isotopic dating analyses, these speculations have not garnered unanimous acceptance.The ore-forming age within the Shuikoushan ore field remained undetermined until 2015, when Huang et al. [20] conducted Re-Os isotopic dating on molybdenite from the Shuikoushan Pb-Zn deposit, obtaining an isochron age of 157.8 ± 1.4 Ma.The ore-forming age of the Kangjiawan Pb-Zn deposit has not been reported thus far.Furthermore, the latest drilling exploration data from the deposit indicate that no pluton related to mineralization was discovered at a depth of 1500 m, which limits the assessment of its ore-forming mechanism and of its relationship with magmatic activities in the ore field.
Many studies have implied that fluid inclusion Rb-Sr dating is suitable for obtaining accurate ore-forming ages [26,27].Although neither Rb nor Sr occurs in the quartz lattice, they could be trapped interstitially in crystal defects, such as in fluid inclusions found in quartz, as indicated in previous studies [28].For example, Rb and Sr concentrations in quartz-hosted aqueous fluid inclusions from the Pingshui gold deposit, Zhejiang Province, China, are 0.60-14.5 ppm and 6.55-33.9ppm, respectively [29]; Rb and Sr concentrations in fluid inclusions in quartz from the Xujiacun gold deposit, Heilongjiang Province, China, are 1.33-9.45ppm and 11.1-75.3ppm, respectively [30].Fluid inclusions in quartz from the Kangjiawan deposit have Rb and Sr concentrations of 0.222-1.009ppm and 0.232-10.710ppm, respectively, and yielded an Rb-Sr isochron age of 150 ± 4 Ma, implying that the Kangjiawan Pb-Zn deposit mineralized during the Late Jurassic, coeval with the magmatic activities within the Shuikoushan ore field.

Trace Element Occurrence in Sphalerite
Trace elements in geological bodies commonly exist in the following forms: independent minerals, isomorphic inclusions, non-isomorphic inclusions (including solid melt inclusions, mechanical inclusions, micro-particles, or elements existing in the interstices or other voids within mineral crystals in the form of ions, molecules, gases, or liquids), adsorptions, and inclusions associated with organic matter [31][32][33].The inter-relationships among various trace elements in minerals can serve as indicators of their occurrence, where isomorphism corresponds to a negative correlation and non-isomorphism corresponds to a positive correlation [34,35].
During the crystallization of sphalerite, Zn 2+ in the lattice is often replaced by other ions with similar properties, such as Fe 2+ , Mn 2+ , In 3+ , Cd 2+ , etc.Among these, Fe 2+ and Zn 2+ share similar geochemical properties, with equal ionic radii and the same valence in tetrahedral coordination, making Fe 2+ the primary ion for substituting Zn 2+ in sphalerite.
In conditions characterized by elevated temperature and low oxygen fugacity, the iron in the fluid predominantly manifests as Fe 2+ , facilitating a substantial substitution of Zn 2+ in the sphalerite lattice by Fe 2+ , consequently inducing the darkening of the sphalerite's color.As the temperature decreases and oxygen fugacity increases, iron gradually transforms from Fe 2+ to Fe 3+ , preventing its entry into the sphalerite lattice.Cd 2+ then takes the place of the previous Fe 2+ in the lattice positions, causing the color of sphalerite to lighten.Therefore, in conditions marked by elevated temperature and low oxygen fugacity, sphalerite tends to exhibit a relatively greater enrichment of Fe 2+ , whereas, in contrasting conditions, it demonstrates a relatively greater enrichment of Cd 2+ , resulting in a negative correlation between Fe and Cd [34,35].In other words, the presence of light-colored sphalerite indicates lower Fe content and relatively lower ore-forming temperatures [36].
In sphalerite from the Kangjiawan Pb-Zn deposit, both Fe and Mn exhibit a conspicuous negative correlation with Zn (Figure 6a,b), implying that Fe and Mn primarily incorporate into the sphalerite lattice through isomorphous substitution, displacing Zn.A broader negative correlation between Cd and Fe content indicates that Cd engages in isomorphous substitution within the sphalerite lattice, displacing Fe (Figure 6c).Notably, a distinct negative correlation between Cd and Zn is evident in sphalerites with higher Zn contents (i.e., the light-colored sphalerite) (Figure 6d), indicating the isomorphous substitution of Cd for Zn.Consequently, Cd in light-colored sphalerite replaces both Fe and Zn through isomorphous substitution.Time-resolved profiles acquired through LA-ICP-MS analysis can effectively serve as indicators for elucidating the forms in which trace elements occur.A relatively flat appearance in the time-resolved spectrum of a specific element implies it has an isomorphic presence, whereas the presence of multiple peaks in the time-resolved spectrum for a given element signifies its occurrence in the form of mineral micro-inclusions [36][37][38][39].In the LA-ICP-MS time-resolved profiles of sphalerites from the Kangjiawan Pb-Zn deposit (Figure 7), the time-resolved spectra for Fe, Mn, Cd, and In exhibit predominantly flat characteristics in the two representative samples, suggesting their prevalent isomorphic occurrence within the sphalerite matrix.Conversely, elements such as Cu, Sb, and Sn exhibit notable fluctuations in the curves of sample K21-01-06 (Figure 7a), while presenting smoother profiles in sample K21-01-01 (Figure 7b).In contrast, Pb exhibits an inverse pattern, displaying a smooth curve in sample K21-01-06 (Figure 7a) and pronounced fluctuations in sample K21-01-01 (Figure 7b).These observations suggest a coexisting state for these elements, indicating both the presence of mineral micro-inclusions and the potential for isomorphic substitution within the sphalerite lattice [40].

Ore-Forming Temperature
The concentrations of trace elements in sphalerite exhibit a close correlation with the ore's formation temperature.Consequently, ore-forming temperatures can be ascertained by analyzing the trace element concentrations and their corresponding ratios in sphalerite [41][42][43][44].For instance, sphalerite formed at elevated temperatures tends to exhibit greater enrichment in Fe, Mn, and In, while sphalerite formed under lower temperatures typically displays greater enrichment in Cd, Ga, Ge, and Zn.Therefore, the FeS content within sphalerite could serve as an indicative parameter for discerning ore-forming temperatures [45,46].In the Kangjiawan Pb-Zn deposit, 79 EPMA data points and 48 LA-ICP-MS data points exhibited that the molar content of FeS in sphalerite ranged from below 0.01% to 14.33%.Notably, only 49 data points (consisting of 39 EPMA and 10 LA-ICP-MS data points) were plotted on the temperature evolution curve and obtained valid temperatures of 175 °C to 259 °C (Figure 8).Meanwhile, the remaining 78 data points failed to provide precise temperatures due to their significantly low FeS contents.It is evident that the formation temperatures of these low-iron sphalerites (i.e., the light-colored sphalerites) are significantly lower than high-iron ones (i.e., the dark-colored sphalerites) (Figure 8).Previous microthermometric analyses of fluid inclusions revealed that the transparent, lightcolored sphalerites from the Kangjiawan Pb-Zn deposit precipitated at 120 °C to 140 °C [47].These findings suggest that the sphalerites from the Kangjiawan Pb-Zn deposit formed under medium-to-low temperatures (lower than 259 °C).Furthermore, the Ga/In ratio in sphalerite can serve as an additional criterion for assessing ore-forming temperatures.At low temperatures, the Ga/In ratio typically falls within the range of 1 to 100; at medium temperatures, it ranges from 0.01 to 5; and at high temperatures, the ratio is less than 0.01 [41,48].The LA-ICP-MS results reveal that the Ga/In ratios in sphalerite from the Kangjiawan Pb-Zn deposit range from 0.01 to 144, providing further support for classifying mineralization as occurring under medium-tolow temperatures.

Genesis of the Deposit
The genesis of the Kangjiawan Pb-Zn deposit has been subject to debate for a long time, with several prevailing viewpoints currently put forward.These theories state that the genesis of the deposit is of the middle-temperature, hydrothermal contact, metasomatic type [1], the shallow-sourced, low-temperature, hydrothermal type [49,50], the paleokarst type [51], the silicification-reconstructed diatreme type [52], the normal sedimentary type [53], the stratabound type [7,54], or the skarn type [13].Different Pb-Zn deposits of varying genetic origins exhibit distinct fluid properties and physicochemical conditions, resulting in notable differences in the trace element contents of the sphalerite [36,38].Previous researchers have established discrimination diagrams for genetic types based on the compositional characteristics of sphalerite in Pb-Zn deposits of different types [36,38] (Figure 9).In the majority of these diagrams, data points from the Kangjiawan Pb-Zn deposit primarily fall within or in close proximity to the range of skarn-type deposits, distinctly differentiating them from Mississippi Valley-type (MVT) and Volcanogenic Massive Sulfide (VMS) deposits (Figure 9a-c).This indicates that this deposit exhibits skarn-type affinities, implying a potential link to magmatic processes.However, in certain diagrams, deviations from the range of skarn-type deposits are observed (Figure 9d), possibly attributable to contamination by strata material or external fluids [44,55].The trace element composition of sphalerite can effectively serve as an indicator for discerning the genesis of Pb-Zn deposits.Previous studies have shown that deposits associated with magmatic or volcanic activities typically exhibit a relative enrichment of Fe, Mn, and In within sphalerite, while elements such as Ge and Tl tend to be depleted.Conversely, deposits related to basin brines show the opposite trend [36,38].LA-ICP-MS analysis results indicate that the dark-colored sphalerites from the Kangjiawan Pb-Zn deposit exhibit significantly higher contents of Fe, Mn, and In (with average contents of 42,185 ppm, 5582 ppm, and 2.63 ppm, respectively), while the light-colored sphalerites yield lower contents of Fe, Mn, and In (with average contents of 9.29 ppm, 0.03 ppm, and 0.25 ppm, respectively).All the sphalerites have low contents of Ge (with an average content of 0.22 ppm) and Tl (with an average content of 0.14 ppm, most of which are below the detection limit), suggesting a potential association with magmatic-hydrothermal activities during their mineralization process, especially the dark-colored sphalerites.
Previous studies indicated that Pb-Zn deposits associated with magmatic-hydrothermal processes exhibit specific characteristics in the trace element ratios of sphalerite, including Cd/Mn < 5 and Cd/Fe < 0.1 [48,[56][57][58].LA-ICP-MS analyses reveal that the darkcolored sphalerites from the Kangjiawan Pb-Zn deposit display low Cd/Mn ratios, ranging from 0.07 to 3.76, and low Cd/Fe ratios, ranging from 0.03 to 0.48.In contrast, the lightcolored sphalerites demonstrate extraordinarily high Cd/Mn ratios, surpassing 12,000, and Cd/Fe ratios, exceeding 23.These data further support the inference that the mineralization of the Kangjiawan Pb-Zn deposit, particularly during the initial stages of main mineralization, was associated with magmatic-hydrothermal activities.Subsequently, as the mineralization temperature decreased, it may have been contaminated by other external substances.
In general, the comprehensive analyses of the aforementioned evidence suggest a mixed origin for the Kangjiawan Pb-Zn deposit.During the Late Jurassic, the deposit originated from a skarn-type environment, associated with contemporary magmatic activities within the Shuikoushan ore field, characterized by relatively high temperatures.Subsequently, the deposition of dark-colored sphalerites with higher Fe contents occurred under medium temperatures, while the precipitation of light-colored sphalerites with lower Fe contents took place under lower temperatures.The decrease in mineralization temperature may be attributed to the mixing of different fluids, such as meteoric water or strata water [2].

Conclusions
(1) The Rb-Sr dating of quartz-hosted fluid inclusions suggests that Pb-Zn mineralization of the Kangjiawan deposit took place during the Late Jurassic, with a Rb-Sr isochron age of 150 ± 4 Ma.
(2) Fe, Mn, and Cd primarily incorporate into the sphalerite lattice through isomorphous substitution.Specifically, Fe and Mn substitute Zn, whereas Cd replaces both Fe and Zn.Other elements such as Cu, Sb, and Sn occur within the sphalerite lattice through mineral micro-inclusions or isomorphic substitution.
(3) The Kangjiawan Pb-Zn deposit formed under medium-to-low-temperature conditions (<259 °C), as indicated by the relatively low FeS contents and high Ga/In ratios in sphalerite.
(4) The trace element compositions of sphalerites from the Kangjiawan Pb-Zn deposit exhibit skarn-type characteristics, suggesting a potential association with contemporary magmatic activities occurring within the Shuikoushan ore field.

Figure 2 .
Figure 2. Geological profile of the Kangjiawan Pb-Zn deposit, (a) plan view, (b) elevation view.The dashed line in Figure 2a shows the trace of the section in Figure 2b.

Figure 3 .
Figure 3. Underground ore photographs (a,b) and hand specimen images (c,d) for the Kangjiawan Pb-Zn deposit: (a) sphalerite vein of stage II; (b) quartz veins of stage III crosscut galena of stage II; (c) hand specimen of stage I; and (d) sphalerite of stage II.Sp-sphalerite; Gn-galena; Py-pyrite; Qz-quartz.

Figure 5 .
Figure 5. Rb-Sr isochron of fluid inclusions in quartz from ore bodies in the Kangjiawan Pb-Zn deposit.MSWD-Mean Standard Weighted Deviation.The numbers 1-6 represent the sample No. in Table1.

Figure 6 .
Figure 6.Diagrams of Fe vs. Zn (a), Mn vs. Zn (b), Cd vs. Fe (c), and Cd vs. Zn (d) for sphalerites from the Kangjiawan Pb-Zn deposit.All data presented in this figure are EPMA data.

Figure 8 .
Figure 8.The diagram of temperature vs. molar content of FeS in sphalerite from the Kangjiawan Pb-Zn deposit (modified after Lu[45]).The red vertical line is the projection auxiliary line for EPMA data, while the black vertical line is the projection auxiliary line for LA-ICP-MS data.

Table 1 .
The analytical Rb-Sr isotopic data of quartz-hosted fluid inclusions from the Kangjiawan Pb-Zn deposit.