Age and Source of the Jinjingzui Skarn-Type Gold Deposit in the Southeastern Hubei Province, China

Abstract

The Jinjingzui gold (Au) deposit is located in the central part of Edong, China. The theoretical gold reserves are large with significant potential for mining and future development. This deposit is the only Au-bearing deposit discovered in the Middle-Lower Yangtze River Valley Metallogenic Belt, which has existing ore bodies that are mainly diorite. Re–Os dating of molybdenite from the Jinjingzui deposit confirm that the deposit formed in the Lower Cretaceous period, with an isochron age of 138.5 ± 2.7 Ma. The geochemical data of the rocks indicate that the diorite contains 54.75% to 56.66% SiO₂, 5.68% to 8.94% Fe₂O₃, 2.05% to 2.19% MgO, and 1.06% to 1.08% TiO₂, and with enrichment of large-ion lithophile elements (e.g., Rb and Ba). High-field-strength elements U-Nb–Ti displayed strong negative anomalies. Six pyrites from the Jinjingzui Au deposit δ³⁴S_V-PDB(‰) ranged from −2.4% to −8.4%, with an average value of −3.1%, and ²⁰⁶Pb~²⁰⁴Pb, ²⁰⁷Pb~²⁰⁴Pb, ²⁰⁸Pb~²⁰⁴Pb contents ranged from 17.77–18.58, 15.48–15.67 to 37.91–39.05, with average values of 18.14, 15.59 and 38.49, respectively. These values indicate that the metallic components originated from the upper mantle and lower crust. The Re concentrations in the molybdenites are significantly higher than those in other ores within the district (847.91~2018.58 × 10⁻⁶), suggesting a significant mantle component was involved in the mineralization process.

1. Introduction

The Middle-Lower Yangtze River Valley Metallogenic Belt (MLYRVB), located in Hubei Province, China, is one of the most significant porphyry-skarn Cu-Fe-Au-W-Mo belts in the country. It is renowned for its extensive metal resources [1,2,3]. The belt is comprised of seven ore clusters, namely Edong, Jiurui, Anqing-Guichi, Tongling, Luzhong, Ningwu, and Ningzhen (Figure 1), with these clusters having a long history of research and development [4,5,6,7,8,9,10,11,12,13]. The Edong ore cluster is located in the west segment of the MLYRVB, (Figure 1 and Figure 2), and previous studies have demonstrated that the primary metallogenic elements are Fe, Cu, Au and Mo. Fe and Fe-Cu deposits are identified in the northwest Edong district, including the Chengchao Fe deposit, the Jinshandian Fe deposit and the Tieshan Fe-Cu deposit. Cu(Au, Mo) and W-Cu deposits are typically located in the southeast, such as the Tonglushan Cu-Fe-Au ore deposit, the Jiguanzhui Cu-Au deposit, the Qianjiawan Cu-Au deposit, the Tongshankou Cu-Mo deposit and the Ruanjiawan W-Cu deposit.

The Jinjingzui Au ore deposit (Figure 2) is located in the central part of the Edong ore cluster, with large gold reserves and great metallogenic potential [16]. The gold deposits are primarily skarn type and located in association with Yanshanian granitoid intrusions. These ore bodies are typically in the contact zone between intermediate-acid intrusive rocks and wall rock, or in the carbonate stratum wall rock [7,11,17]. The ore body of the Jinjingzui deposit principally occurs in the altered fracture zone, located between the marginal and internal facies of the diorite pipe in the mining area. Early studies of the deposit’s geological characteristics indicate that mineralization is related to diorite, with the metallogenic type being altered diorite-type gold ore. Early studies indicated that the diagenetic processes and metallogenic materials might have a common source, but there was a lack of supporting isotope evidence [16]. However, recent studies have demonstrated that the deposit is a typical skarn-type deposit [18]. Few studies have systematically investigated the genesis of the Jinjingzui deposit, particularly regarding the geochronology of the host diorite intrusion and associated gold mineralization. This paucity of accurate geochronological data has significantly complicated efforts to establish a robust genetic model for understanding the metallogeny of the Jinjingzui deposit and its broader regional context within the western segment of the Middle-Lower Yangtze River Valley metallogenic belt (MLYRVB).

Accurate dating of the mineral deposit is critical for understanding the genesis of the Jinjingzui deposit and analogous mineral systems. This study aims to conduct an evaluation of selected variables that indicate ore genesis and summarize the regional metallogenic characteristics. Specifically, this paper presents sulfide mineral S-Pb isotopic compositions, geochemistry data of diorite, and Re–Os isochron dating of molybdenite. These data will constrain the sources of hydrothermal components and the relationship between Au mineralization and diorite.

2. Regional Geology and Ore Deposit Geology

2.1. Regional Geology

The Edong ore cluster is located in the west region of the MLYRVB (Figure 1). Tectonically, it is located along the northern margin of the Yangtze Craton, and the southeastern margin of the North China Craton and is adjacent to the Dabieshan orogenic belt [19]. It is bordered by the Xiangfan–Guangji Fault to the northwest and Shangma–Tuanfeng–Linagzihu Fault to the northeast [20]. The Cambrian to quaternary strata are widely exposed in this region, lacking middle and lower Devonian and upper Jurassic strata, among which the Triassic carbonate rocks are the primary host of skarn deposits in the area [15]. Regional diagenesis is proposed to be controlled by the Indosinian NW-NWW fault, with the Yanshanian fault characterized by the presence of the smaller-scale NE-NNE fault [21]. The Edong ore cluster, which mainly comprises diorite and quartz diorite [21], has six granitoid batholiths (including Echeng, Tieshan, Jinshandian, Lingxiang, Yinzu and Yangxin—see Figure 2). In addition, at Tongshankou and Fengshandong, there are several small granodiorite porphyry stocks (Figure 2). Geochronology studies indicated that the formation of all these intrusions took place during the late Jurassic to the early Cretaceous periods [1,22,23].

2.2. Local and Mine Geology

The Jinjingzui deposit is situated near Daye City, Hubei province. This ore cluster is severely covered with the Quaternary strata, comprising 80% of the material present. Drilling conducted by the Daye group exposed strata comprising thin/thick bedded marble, dolomite, and dolomitic marble. The intrusive rocks in the Jinjingzui deposit are typically diorite and diorite porphyry, which are mostly distributed at the edge of the pluton and have a phase change relationship with diorite. The main structural directions in the ore district are NE and NW. The diorite and gold ore bodies are located in structural convergence positions, controlled by the NNE reverse anticline and NW fault (Figure 3a). There are approximately eight discrete ore bodies in the Jinjingzui district. Among these, the No. 1 ore body between exploration lines 9–14 (elevation −374~7 m) has relatively large resources and is currently mined, having known Au reserves of nearly 8 tons. The No. 8 ore body is found in the contact zone situated at the apex of the intrusion, while the remaining ore bodies are positioned close to the interior of the smaller intrusive rocks, forming regular and irregular ring shapes, or appearing within the intrusions as veins. (Figure 3b).

Ore textures in the Jinjingzui deposit are mainly composed of disseminated and vein-like structures, with dense clumps and brecciform structures also partially identified (Figure 4a,b). Over 30 minerals were identified in the Jinjingzui Au deposit, including pyrite, marcasite, chalcopyrite, magnetite, pyrrhotite, altaite, chalcopyrite, malachite, galena, gold, silver, and sphalerite. The dominant gangue minerals are K-feldspar, quartz, hornblende, biotite, garnet, diopside, plagioclase, dolomite, calcite, montmorillonite, illite and sericite (Figure 4). Gold is present as microscopic, submicroscopic and dispersed particles, including native and small quantities of kustelite. The morphology of the microscopic gold includes sphere-, plate-, foliaceous, dendritic, angular, polyangular and irregular. Based on the relationship between gold and other minerals, the occurrence characteristics of microscopic gold can be categorized into two types: intergranular-crack gold and encapsulated gold. The former includes intergranular gold found in the spaces between mineral grains and crack gold present within the internal fractures of minerals. These gold particles are relatively coarse and can be readily liberated. Encapsulated gold is characterized by a small particle size and its difficulty in dissociating from pyrite, marcasite, altaite or other minerals. Wall-rock alteration related to Au mineralization includes skarnization and silicification. Based on field observations of cross-cutting relationships between veins, the occurrence of mineral assemblages and the textural/growth relationships of adjacent minerals and the crystallization sequence of ore-forming and skarn minerals can be divided into the following three stages: (i) skarn stage; (ii) sulfide-carbonate stage (as the temperature decreases, a significant quantity of sulfides commences to precipitate); and (iii) a supergene oxidation stage. The paragenetic sequence of minerals from these stages is shown in Figure 5.

3. Sampling and Analytical Methods

Zircon and rock powder were extracted from three fresh diorite samples (JJZ-7, JJZ-8, and JJZ-9), all sourced from the -280-m level footrill of the Jinjingzui skarn deposit. The fresh diorite has a gray to grayish-green color and has fine-grained, medium and massive textures (Figure 6). The mineral compositions mainly include plagioclase (60–80%), amphibole (3–8%), pyroxene (2–7%), biotite (3–5%), quartz (1–3%), and minor quantities of titanite, zircon and apatite (Figure 6). Molybdenite (Figure 7) and pyrite are separated from skarn and silicified altered diorite, respectively. (Figure 4).

The major trace and rare earth element concentrations of the samples were analyzed at Yanduzhongshi Testing Technology Co., LTD., Beijing, China. The concentrations of major elements were determined using X-ray fluorescence (XRF). Before XRF analysis, the powder sample was weighed, mixed with Li₂B₄O₇ (1:8) flux, and then heated to 1150 °C. Sample melts were poured into a gold-platinum crucible to cool, forming a uniform glass sheet. Glass sheets were directly analyzed via XRF spectrometry. The loss on ignition (LOI) was quantified by subjecting samples to heating in silica crucibles at 1000 °C for one hour, with subsequent measurement of weight reduction. Trace and rare earth elements concentrations were analyzed by inductively coupled plasma–mass spectrometer (ICP-MS) using a M90, Analytik Jena instrument. The error of the measured data is less than 5% based on repeated assay of the control sample GSR 2. The error of some volatile and trace elements is less than 10%.

The Re–Os isotope analysis of molybdenite was performed at Beijing Yandu Zhongshi Testing Technology Co., Ltd. (Beijing, China). The analysis utilized the isotope dilution method, with specific procedures including reverse aqua regia digestion using Carlo Erba tubes, conducted under sealed conditions at 220 °C for 24 h. Os was separated and enriched via direct distillation, while Re was extracted with acetone from an 8 mol/L sodium hydroxide solution. Isotope ratios were subsequently determined using ICP-MS (Thermo Fisher Scientific Triton Plus, MA, USA). In-house sulfide Re–Os isotope reference JCBY from the Jinchuan Cu-Ni deposit was used for quality control.

S and Pb isotopes were analysed at ALS Chemex (Guangzhou) Co., Ltd. (Guangzhou, China). First, the powder crushed to 60–80 mesh was selected under a binocular microscope to isolate pyrite minerals, ensuring a purity of approximately 99%. The sulfur analysing procedure is as follows: accurately weigh an appropriate amount of the pyrite powder sample and transfer it to a tin boat. Use the Costech ECS 4010 elemental analyzer in conjunction with the Finnigan MAT 253 stable isotope ratio mass spectrometer to determine the 34S/32S isotopic ratio in the sample. Lead isotope ratios were determined by taking a 0.5 g sub-sample and dissolving it sequentially with perchloric acid, hydrofluoric acid, nitric acid and hydrochloric acid. After digestion, the solution was evaporated by heating on an electric mantle, following which the residue was re-dissolved in hydrochloric acid; The cooled solution was volumetrically diluted to 25 mL with hydrochloric acid (10%) and analyzed by ICP-MS. Pb isotope standard material and internal standards were used to validate sample measurements.

4. Analytical Results

4.1. Major Elements and Trace Elements

The major and trace element compositions of the three diorite samples from the Jinjingzui deposit are listed in

Table 1. Composition of major elements (%), trace elements (ppm), and REE (ppm) of samples from the diorite.

Sample	SiO2	TiO2	Al2O3	TFe2O3	MnO	MgO	CaO	Na2O	K2O	P2O5	LOI	Total	Mg #	A/CNK	NaO2 + K2O
JJZ-7	53.74	1.08	17.7	8.49	0.10	2.15	7.71	4.21	2.49	0.5	1.82	99.98	31.08	0.75	6.7
JJZ-8	52.25	1.09	17.44	8.71	0.10	2.11	8.73	4.01	2.46	0.54	2.51	99.95	30.18	0.69	6.46
JJZ-9	55.22	1.06	17.6	5.53	0.06	2	7.45	3.96	4.07	0.52	2.47	99.94	39.17	0.72	8.03
Sample	Rb	Ba	Th	U	Nb	Sr	Zr	Hf	Yb	La	Ce	Pr	Nb	Nd	Sm
JJZ-7	63.12	643.36	12.38	0.17	17.22	1194.21	237.17	6.27	2.28	60.17	124.9	13.87	17.22	59.46	10.53
JJZ-8	62.68	657.32	13.52	0.22	17.51	1223.91	225.37	6.04	2.29	63.21	132.12	14.67	17.51	61.71	11.21
JJZ-9	105.69	752.81	11.95	0.38	17.91	1087.36	220.68	6.06	2.34	60.05	127.41	14.06	17.91	59.95	10.94
Sample	Eu	Gd	Tb	Dy	Ho	Er	Tm	Yb	Lu	Y	ΣREE	δEu	(La/Yb)N
JJZ-7	3.48	10.86	1.35	5.55	1.05	2.77	0.38	2.28	0.33	26.88	296.97	1	18.94
JJZ-8	3.73	11.79	1.41	5.71	1.13	2.93	0.38	2.29	0.32	27.64	312.61	0.99	19.8
JJZ-9	3.56	11.48	1.4	5.76	1.15	3.02	0.39	2.34	0.32	27.93	301.81	0.97	18.42

. Low SiO₂ concentrations (54.75–56.66%) were measured, with high concentrations of Fe₂O₃^T (5.68–8.94%), MgO (2.05–2.19%) and TiO₂ (1.06–1.08%) detected. Al₂O₃ and CaO content ranged from 17.89–18.05% to 7.64–8.96%, respectively. The alkali content (K₂O + Na₂O) was reported from 6.46 to 8.03%. Two samples (JJZ-7 and JJZ-8) plotted in the TAS diagram lie in the monzodiorite area, and one (JJZ-9) in the monzonite region (Figure 8a). The A/CNK ratio of the samples varies from 0.69 to 0.75, indicating a metaluminous composition (Figure 8b). In the SiO₂-K₂O diagram (Figure 8c), two samples (JJZ-7 and JJZ-8) fall into the high-K cal-alkaline area and one in the shoshonitic area.

Samples in this study are rich in large-ion-lithophile elements (LILE), Rb-Ba and high-field-strength elements (HFSE) Th. The samples exhibited subparallel chondrite-normalized REE patterns, characterized by strong fractionation between light and heavy REE, with barely perceptible Eu anomalies (δEu = 0.97~1.00) (Figure 9b). The total REE, LREE and HREE content of the samples are 296.97–312.61 μg/g, 272.41–286.65 μg/g and 24.56–25.96 μg/g, respectively (Table 1). LREE/HREE ratios range from 10.68 to 11.09 with the (La/Yb)_N ratio varying from 18.42 to 19.80.

4.2. Molybdenite Re–Os Dating

The molybdenite showed a lead-gray color in the hand specimens and occurred as a massive or impregnated structure in the Skarn samples (Figure 7). The samples reported high Re contents, with w(Re)ranging from 847.91 × 10⁻⁶–2018.58 × 10⁻⁶ (

Table 2. Re–Os isotopic data of molybdenites from the Jinjingzui Au deposit.

Samples	Weight (g)	w(Re) (×10−6)		w(Commons Os) (×10−9)		w(187Re) (×10−6)		w(187Os) (×10−9)		Age (Ma)
		Measured Value	Uncertainty	Measured Value	Uncertainty	Measured Value	Uncertainty	Measured Value	Uncertainty	Measured Value	Uncertainty
JJZ-1-1	0.00221	2018.58	26.76	0.1309	0.04	1268.72	16.82	2935.85	22.2	138.7	2.5
JJZ-1-2	0.00245	1926.52	28.06	2.5859	0.04	1210.86	17.64	2798.81	16.4	138.6	2.6
JJZ-4-1	0.00255	1775.82	24.35	1.0373	0.05	1116.14	15.31	2577.37	18.4	138.4	2.5
JJZ-4-2	0.00234	847.91	13.29	0.3173	0.02	532.93	8.35	1238.80	8.5	139.4	2.7
JJZ-4-3	0.00222	1813.77	29.09	0.6757	0.05	1139.99	18.29	2663.06	15.8	140.1	2.8

), and yielded relatively restricted model ages from 138.4 ± 2.5 to 140.1 ± 2.8 Ma, which correspond well with measured isochron ages of 138.5 ± 2.7 Ma (MSWD = 0.41) (Figure 10).

4.3. Sulfur and Lead Isotopic

Six pyrite samples from the Jinjingzui Au deposit δ³⁴S_V-PDB(‰) ranged from −2.4% to −8.4% (

Table 3. S-Pb isotopic data of pyrite from Jinjingzui Au deposit.

Sample	Mineral	δ34S (‰)	206Pb/204Pb	207Pb/204Pb	208Pb/204Pb	208Pb/206Pb	208Pb/207Pb	206Pb/207Pb
JJZ-10	pyrite	5.9	18.020	15.610	38.650	2.145	2.477	1.155
JJZ-11	pyrite	2.3	17.770	15.480	37.910	2.134	2.449	1.144
JJZ-12	pyrite	−2.4	17.930	15.570	38.300	2.136	2.460	1.151
JJZ-13	pyrite	2.2	18.170	15.620	38.510	2.119	2.465	1.163
JJZ-15	pyrite	2.2	18.580	15.670	39.050	2.101	2.492	1.186
JJZ-16	pyrite	8.4	18.350	15.590	38.540	2.101	2.473	1.176

), having an average value of −3.1%. ²⁰⁶Pb~²⁰⁴Pb, ²⁰⁷Pb~²⁰⁴Pb, ²⁰⁸Pb~²⁰⁴Pb contents ranged from 17.77–18.58, 15.48–15.67 to 37.91–39.05, with average values of 18.14, 15.59 and 38.49, respectively (Table 3).

5. Discussion

5.1. Petrogenesis

The samples obtained from the Jinjingzui deposit show low SiO₂ and high TiO₂, Al₂O₃, FeO^T and MgO concentrations, enrichment of LILE (Rb, Ba) and depletion of HFSE (U, Nb, Ti). The standard curve of chondrite and rare earth elements showed a right-leaning chondrite distribution curve with a strong differentiation of light REE (LREE) and heavy REE (HREE) with barely perceptible Eu anomalies (Figure 9a,b). All these geochemical characteristics are analogous to those of the coeval Echeng diorite within the ore cluster, and both display diagnostic signatures of arc-related magmatic rocks. This similarity can likely be attributed to the remote influence of the Mesozoic Pacific Plate, which induced lithospheric delamination and subsequently reactivated the source region containing Proterozoic arc magmatic materials, ultimately leading to the formation of ore-bearing magmas [20]. Based on the (Y + Nb)–Rb diagrams, the Jinjingzui deposit diorite samples lie in the volcanic arc-syn collision area (Figure 11a). The samples in this study showed a high concentration of Y (26.88–27.93ppm) and low Sr/Yb ratio (38.93–44.43), with all data points falling into the normal island arc area in the Y-Sr/Y plots (Figure 11b).

Jinjingzui diorite has a uniform distribution of ε_Nd(t) and ε_Hf(t), ranging from −5.24 to −4.76 and −12.2 to −6.5 [14]. These results are similar to Cu-Au skarn deposit ore-related intrusions [1,7,28]. These isotope characteristics indicate that these intrusions likely originated from the partial melting of an enriched mantle source, followed by crustal assimilation during the magmatic evolution. However, the zircon CL image demonstrates a clear ring of magmatic zircon oscillations, without core-mantle structure and ancient inherited zircons, suggesting a slight mixing of continental crust [14]. In addition, the Mg^# value of the Jinjingzui diorite (30.18–39.17) is significantly lower than that of mantle peridotite (70–80) [29]. The composition does not represent a melt in equilibrium with the original peridotite mineral assemblages. Therefore, it can be assumed that the diorite from the Jinjingzui deposit was not formed by the partial melting of mantle peridotite at low temperatures but originated from partial melting within an enriched mantle source region, resulting in the production of basaltic magma, which subsequently underwent magmatic evolution and differentiation.

Figure 11. (a) (Y + Nb)–Rb and (b) Y-Sr/Y diagrams of Jinjingzui diorites (modified from [30,31]). Syn-COLG—syn-collision granites; Post-GOLG—syn-collision granites; WPG—within plate granites; VAG—volcanic arc granites; ORG,—ocean ridge granites.

Figure 11. (a) (Y + Nb)–Rb and (b) Y-Sr/Y diagrams of Jinjingzui diorites (modified from [30,31]). Syn-COLG—syn-collision granites; Post-GOLG—syn-collision granites; WPG—within plate granites; VAG—volcanic arc granites; ORG,—ocean ridge granites.

5.2. Timing of Mineralization

Currently, molybdenite Re–Os isotopic systems are a reliable method for dating metal sulfide systems due to the high closed temperature (about 500 °C), which is not susceptible to hydrothermal, metamorphic and tectonic events [32,33,34,35]. In this study, molybdenite samples yield Re~Os model ages of 138.4 ± 2.5Ma ~140.1 ± 2.8Ma and a weighted mean age and an isochron age of 139.0 ± 1.1Ma and 138.5 ± 2.7Ma, respectively. This age likely represents the mineralization age of the samples collected from the Jinjingzui deposit. The zircon U–Pb geochronological data demonstrate concordance with molybdenite Re–Os isochron ages, substantiating a close temporal and genetic association between the mineralization event and dioritic magmatic activity [14].

5.3. Origin of Ore-Forming Materials

Based on this study, δ³⁴S_V-PDB(‰) values of pyrite in the Jinjingzui Au deposit range from −2.4% to −8.4%, with an average value of −3.1% (n = 6). These values coincide closely with the distribution of previously determined δ³⁴S_V-PDB data for mantle-derived fluids (±3%) [36]. Studies conducted previously reported that the sulfur isotopic components were generally uniform in the adjacent skarn Cu-Au deposit in Edong ore clusters [37]. Collectively, these sulfur isotopic compositions are suggested to indicate a deep magmatic source for the sulfur contained within the minerals of the Jinjingzui ore deposit.

Lead isotopic tectonic patterns can distinguish the sources of lead in different tectonic environments. In ²⁰⁷Pb/²⁰⁴Pb–²⁰⁶Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb–²⁰⁶Pb/²⁰⁴Pb diagrams (Figure 12), the data points fall near the lower crust and orogenic belt regions. The lead isotope evolution line has a high slope, intersecting with the crust-mantle lead isotope evolution line at a high angle, indicating that the lead provenance of Jinjingzui deposit has characteristics of a mixed source of upper mantle and lower crust.

Previous research suggested that the Re content from molybdenites with a mantle component has a significantly higher content than those derived from a crustal source [34,39].

Table 4. Re–Os isotopic data of molybdenites from the deposits in Edong district.

Deposit	Sample	w(Re) (×10−6)	w(Commons Os) (×10−9)	w(187Re) (×10−6)	w(187Os) (×10−9)	Cite
Jinjingzui Au deposit	JJZ-1-1	2018.58	0.13	1268.72	2935.85	This study
	JJZ-1-2	1926.52	2.59	1210.86	2798.81
	JJZ-4-1	1775.82	1.04	1116.14	2577.37
	JJZ-4-2	847.91	0.32	532.93	1238.80
	JJZ-4-3	1813.77	0.68	1139.99	2663.06
Tongshankou Cu-Mo deposit	TSK5	224.30	0.30	141.00	334.60	[40]
	TSK10	203.60	0.21	128.00	306.27
	TSK1	84.60	0.53	53.20	127.30	[7]
	TSK2	135.40	0.37	85.10	203.90
	TSK3	75.40	0.33	47.40	113.60
	TSK4	110.60	0.39	69.50	167.80
	TSK5	99.50	0.32	62.60	150.40
	TSK6	177.00	0.53	111.20	266.30
Tonglushan Cu-Fe-Au deposit	TLS3	665.40	0.53	418.20	961.39	[40]
	TLS4	305.70	0.27	192.10	442.69
	TLSB7	261.40	0.04	164.30	377.60	[10]
	TLSB7	263.70	0.04	165.70	387.10
	TLSB16	432.50	0.20	271.80	617.90
Qianjiawan Cu-Au deposit	QJW1	334.90	0.59	210.50	483.28	[40]
Ruanjiaran W-Cu deposit	RJW4	24.80	0.05	15.59	37.34
Fengshandong Cu-Mo deposit	FSD4	436.50	0.64	274.40	659.20
Jilongshan Cu-Au deposit	WJ247	383.00	0.54	240.70	600.00	[41]
	WJ267	817.40	0.08	547.70	1360.00
	WJ323	174.30	0.08	109.50	274.20
	WJ328	2419.60	0.26	1520.80	3845.00
	WJ602	764.70	0.02	480.60	1184.00
	ZK39-1	298.81	/	187.81	467.34	[17]
	ZK39-2	347.75	/	218.58	556.48
	210CM28-1	470.16	/	295.51	747.53
	210CM28-2	466.10	/	292.96	731.60
Jiguanzui Au-Cu deposit	JGZB96	425.70	0.13	267.50	619.30	[10]
	JGZB97	500.40	0.42	314.50	718.90
	JGZB100	1152.00	0.89	724.00	1673.50
	ZK2412-7	810.80	0.14	509.60	1173.00
	ZK2412-9	785.90	0.14	494.00	1138.00
Taohuazui Au-Cu deposit	JGZB146	1009.00	0.12	634.00	1464.00	[11]
	JGZB147	371.30	0.48	233.40	537.60

shows the Re content in molybdenites from selected gold-bearing skarn deposits in the Edong ore clusters. The Jinjingzui gold deposit Re concentrations in molybdenites are significantly higher than other ore samples in the district (847.91–2018.58 × 10⁻⁶), which infers that a higher mantle component is involved in the mineralization. These data, combined with the sulfur and lead isotopic composition from the Jinjingzui Au deposit, indicate that metallic components have a deep source and possibly originated from intermediate magmatism during the Yanshanian period.

5.4. Implications of Regional Mineralization

Xie et al. (2006, 2008) proposed that two significant mineralization events occurred in the Middle-Lower Yangtze River Valley, with mineralization ages concentrated in the ranges of 132–145 Ma and 123–125 Ma. The mineralization in the southeastern Hubei ore cluster primarily occurred during the first event [9,42,43]. The rock-forming and mineralization processes exhibit a clear temporal correlation, indicating their coeval formation. Zircon U–Pb dating (141 Ma) and molybdenite Re–Os dating (138.5 Ma) demonstrate that the Jinjingzui gold deposit formed during the Early Cretaceous, contemporaneous with other skarn-type deposits in southeastern Hubei and the broader Middle-Lower Yangtze River Valley [14]. This chronological consistency suggests these deposits share a common tectonic setting (

Table 5. Ages of deposits in Edong district.

Deposit	Mineral	Method	Age (Ma)	Cite
Jinjingzui Au deposit	molybdenite	Re–Os	138.5 ± 2.7Ma	This study
Tongshankou Cu-Mo deposit	molybdenite	Re–Os	143.8 ± 2.6	[7]
	phlogopite	40Ar-39Ar	143.8 ± 0.8
	phlogopite	40Ar-39Ar	143 ± 0.3	[44]
	molybdenite	Re–Os	142.9 ± 1.8	[11]
Tonglushan Cu-Fe-Au deposit	molybdenite	Re-Os	138.1 ± 1.8
		Re–Os	137.8 ± 1.7
		Re–Os	137.3 ± 2.4	[10]
	phlogopite	40Ar-39Ar	140.3 ± 1.1	[11]
Qianjiawan Cu-Au deposit	molybdenite	Re–Os	137.7 ± 1.7	[10,40]
Ruanjiaran W-Cu deposit	molybdenite	Re–Os	143.6 ± 1.7	[11]
Fengshandong Cu-Mo deposit	molybdenite	Re–Os	144.0 ± 2.1
Jilongshan Cu-Au deposit	molybdenite	Re–Os	150.8 ± 0.82	[17]
	molybdenite	Re–Os	149.5 ± 1.2	[41]
Jiguanzui Au-Cu deposit	molybdenite	Re–Os	138.2 ± 2.2	[10]
Tieshan Fe deposit	phlogopite	40Ar-39Ar	140.9 ± 1.2	[43]
Chengchao Fe deposit	phlogopite	40Ar-39Ar	132.6 ± 1.4
Jinshandian Fe deposit	phlogopite	40Ar-39Ar	131.6 ± 1.2
Taohuazui Au-Cu deposit	molybdenite	Re–Os	139.4 ± 2.0	[11]
	phlogopite	40Ar-39Ar	139.9 ± 1.1

).

There are divergent perspectives within the academic community regarding the tectonic background of rock formation and mineralization in the middle and lower reaches of the Yangtze River. Some scholars argue that this region’s tectonic setting is intraplate, while others propose a subduction-related tectonic setting [4,5,45,46,47]. Despite these differing views, an increasing body of evidence supports the formation of skarn-type polymetallic deposits in this area under conditions of lithospheric extension and thinning [48,49]. During the Late Jurassic to Early Cretaceous, the middle and lower reaches of the Yangtze River and the broader eastern China area experienced a significant transition from a north–south Indosinian tectonic regime to a northeast-oriented Paleo-Pacific tectonic regime [50]. Regional mineralization events during this period are likely closely associated with this major tectonic transformation. Geophysical data show that the primary metal deposits in the MLYRVB are located in areas of minimal crustal thickness, further corroborating the strong link between lithospheric extension and large-scale mineralization [9]. Through their analysis of deep seismic reflection profiles in the region, Lü et al. (2004) concluded that the delamination and extension of the lithospheric mantle triggered the underplating of mafic or ultramafic magmas [51].

The relatively uniform εNd(t) and zircon Hf isotopic compositions suggest that the Jinjingzui diorite likely originated from an enriched lithospheric mantle [28]. The Mg# values (30.18 to 39.17) are significantly lower than those of mantle peridotite equilibrium melts (70 to 80) [14,29], indicating that the diorite could not have been directly formed by low-temperature partial melting of mantle peridotite. Instead, it is more plausible that the diorite formed through partial melting of an enriched mantle source region, producing basaltic magma that subsequently underwent magmatic evolution and differentiation. Additionally, the absence of inherited zircons suggests that crustal contamination was minimal during the petrogenesis of the ore-forming rocks [14]. The Jinjingzui diorite is located within the post-collisional granite province, consistent with the major tectonic regime shift in the middle and lower reaches of the Yangtze River during the Late Jurassic to Early Cretaceous [28,44]. Moreover, the δ³⁴S values of pyrite (−2.4‰ to 8.4‰) and the Re content of molybdenite (847.91 × 10⁻⁶ to 2018.58 × 10⁻⁶) imply that the ore-forming materials primarily originated from the enriched lithospheric mantle. These characteristics collectively indicate that the petrogenesis and mineralization of Jinjingzui occurred in a tectonic setting characterized by lithospheric extension and thinning. Figure 13 presents a simplified diagram of the mineralization model.

6. Conclusions

(1)

Molybdenite Re–Os dating indicates that the deposit formed in 138 Ma in the age of Ore-bearing diorite, indicating that both the diorite and the Au mineralization at Jinjingzui formed during the Early Cretaceous period.

(2)

Geochemical and relatively uniform εNd(t) and zircon Hf isotopic compositions confirm that characteristics collectively indicate that the petrogenesis and mineralization of Jinjingzui occurred in a tectonic setting characterized by lithospheric extension and thinning.

(3)

S-Pb isotope components and high Re concentrations in the molybdenites suggest the metallic components originated from the upper mantle and the lower crust but with a higher mantle component involved in the mineralization than other deposits in the district.