Ore Genesis of the Jiawula Pb–Zn–Ag Deposit, Inner Mongolia: Constraints from C–H–O Isotopes, In Situ S Isotopes, Fluid Inclusions, and LA-ICP-MS Analysis of Chalcopyrite

Abstract

The Jiawula large-scale Pb–Zn–Ag deposit occurs within Jurassic volcanic rocks, structurally controlled by NW-trending faults. This study integrates systematic analyses of chalcopyrite trace elements, fluid inclusions, and stable isotopes (C–H–O–S) to elucidate its ore-forming fluid evolution and mineralization processes. Fluid inclusion analyses reveal an evolutionary trajectory from an early H₂O–NaCl–CO₂ system to a late H₂O–NaCl–CH₄ system. Carbon isotopes indicate that magmatic degassing-derived CO₂ dominated the early stage (δ¹³C = −6.34‰), with subsequent methane input contributing to the late stage (δ¹³C = −16.73‰). Hydrogen–oxygen isotopes demonstrate that the ore-forming fluids represent mixtures of deep-sourced magmatic water and meteoric water. In situ sulfur isotopes (δ³⁴S = −0.1‰ to 5.2‰) suggest a predominantly magmatic sulfur source. Combined characteristicsincluding low-temperature (298.8–197.2 °C), low-salinity (<5 wt % NaCl eq) fluids, chalcopyrite trace-element signatures, mineral assemblages, and pore-filling texturesclassify the Jiawula deposit as an epithermal deposit. In contrast, adjacent porphyry-type Mo–Cu mineralization represents a distinct, subsequent overprinting event.

1. Introduction

The Jiawula large Pb–Zn–Ag deposit is situated in the southwestern segment of the Derbugan metallogenic belt within the Erguna Block, eastern Central Asian Orogenic Belt. It contains proven reserves exceeding 1.93 million tons of Pb–Zn metals with average grades above 5 wt % and associated silver reserves surpassing 2300 tons, averaging 150–200 g/t. The No. 2 orebody constitutes the largest known mineralization, accounting for 80% of total reserves. − This deposit has become a crucial base for China’s nonferrous metal industry.

Research on ore-forming fluids at the Jiawula Pb–Zn–Ag deposit reveals divergent views regarding fluid sources, physicochemical characteristics, and metallogenic mechanisms. Fluid provenance debates focus on magmatic vs meteoric contributions. Zhai Degao et al. (2013) and Yang Jinghong et al. (1989) advocate a mixed-source model, where early fluids are magmatic, later overprinted by meteoric water (δD: −166‰ to −103.4‰; δ¹⁸O_H2O: −11.8‰ to +13.09‰). In contrast, Pan Longju et al. (1990) argue for magmatic dominance in adjacent areas, while Xie Chengbo and Liu Ming (2001) emphasize meteoric control.

Fluid inclusion analysis confirms that the Jiawula deposit represents a gradually cooling, medium- to low-salinity H₂O–NaCl system. Han Shiqing (2013) highlighted spatial heterogeneity and CO₂-rich volatiles in early fluids. Zhai Degao et al. (2010) and Li Tiegang (2016) emphasized fluid immiscibility and magmatic–meteoric mixing as key processes, while Yang Mei (2017) identified a meteoric-dominated fluid in the late stages based on thermometry and Raman data.

Genetic models remain debated. Wu Guang (2006) classifies the deposit as epithermal vein-type, while Pan Longju and Sun Enshou (1992), Geng Wenhui et al. (2000), and Zhai Degao et al. (2013) favor a volcanic–subvolcanic hydrothermal origin, linked to mantle magmatism. Li Tiegang (2016), Yang Mei (2018), and Hui Kaixuan et al. (2021) integrate both, proposing a porphyry–epithermal system where Cu is deposited from boiling magmatic fluids at depth and Pb–Zn–Ag from mixed meteoric–magmatic fluids at shallow levels.

Persistent debate over fluid sources and genetic classification underscores the need for further isotopic, fluid inclusion, and metallogenic mechanism constraints. We conducted field geological surveys and ore petrographic studies to reveal the structural framework and mineral assemblage characteristics of the deposit. The ore-forming mechanisms and deposit features were investigated through trace element analysis of chalcopyrite using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Additionally, fluid inclusion and multiisotope analyses were employed to explore the sources of ore-forming fluids and materials.

2. Geological Setting

The Northeastern Inner Mongolia region of China lies within the Central Asian Orogenic Belt (Figure a), the world’s largest accretionary orogenic belt. , The Derbugan metallogenic belt, situated in the Erguna Block of its eastern portion, represents one of the most significant polymetallic metallogenic belts in Northeast China and adjacent territories, boasting remarkable mineral resources and tectonic research value. Spanning northeastern Inner Mongolia, western Heilongjiang, and Russia’s Transbaikal region, this belt hosts numerous large to superlarge deposits, including the Wunugetushan porphyry Cu–Mo deposit, Jiawula Pb–Zn–Ag deposit, Chaganbulagen Pb–Zn–Ag deposit, and Erentaolegai Ag deposit. ,,, It exhibits distinct temporal and genetic links with the Central Asian Metallogenic Domain (e.g., Mongolia’s Oyu Tolgoi Cu–Au deposit) and the Circum-Pacific Metallogenic Belt while developing unique tectonic-magmatic mineralization systems. Located at the intersection of the Paleo-Asian Ocean and Mongol-Okhotsk tectonic domains, this region experienced significant tectonic activity from the Late Paleozoic to Mesozoic, influenced by the closure of the Mongol-Okhotsk Ocean and regional crustal reorganization. , These processes led to widespread Jurassic-Cretaceous intermediate-acid magmatic rocks, , showing spatial–temporal correlations with Pb–Zn–Ag mineralization.

1.

(a) Northeast Inner Mongolia in the eastern part of the Central Asian Orogenic Belt (modified after Chen et al., 2024). (b) Northeastern Inner Mongolia, showing the location of the Jiawula deposit (modified after Feng et al., 2019).

The Jiawula Pb–Zn–Ag deposit is located in the southwest section of the Derbugan metallogenic belt in the Eerguna block (Figure b). The area is dominated by outcrops of Mesozoic and Cenozoic strata, with large areas of outcrops of Jurassic terrestrial volcanic strata, including conglomerates, sandstones, and mudstones of the Middle Jurassic Wanbao Formation (J₂ wb); andesite and andesite basalt of the Middle Jurassic Tamulangou Formation (J₂ tm); and tuffaceous sandstones, siltstones, etc., of the Upper Jurassic Manitu Formation (J₃ mn).

Structurally, the area is predominantly controlled by NE- and NW-trending fault systems. , Major structures include the NE-striking Derbugan deep fault, Genhe deep fault zone, Hulun fault, and NW-trending Muhaer and Hanigou fault zones. These deep-seated fractures governed the distribution of Mesozoic volcanic-intrusive magmatism and exerted critical influences on episodic mineralization events.

The region experienced multistage intense magmatic activities, encompassing Hercynian, Indosinian, Early Yanshanian, and Late Yanshanian intrusions. Late Yanshanian intrusions, characterized by shallow emplacement (medium- to coarse-grained granite, biotite granite, plagiogranite, porphyritic granite, and monzogranite), show strong genetic associations with Late Mesozoic mineralization.

3. Ore Deposit Geology

The stratigraphic sequence of the Jiawula deposit is mainly composed of sandstone, conglomerate, and carbonaceous slate of the Upper Permian Laolongtou Formation; andesite, basalt, and rhyolite of the Middle Jurassic Tamulangou and Wanbao Formations; as well as the Upper Jurassic Manitou Formation. Quaternary marble and silicified marble form the cap rock (Figure ). The Laolongtou, Tamulangou, and Wanbao Formations constitute the principal host strata for the Pb–Zn–Ag mineralization; fault structures play essential roles in ore formation, where the NNW-striking Muhaer Fault and the NWW-trending Jiawula–Chaganbulagen Fault exert critical control over deposit genesis. The radial fault system also contributes to controlling the distribution of ore bodies; mineralization occurs primarily as veins and stockworks. Wall-rock alteration is characterized by chloritization as the dominant type with propylitization, silicification, and quartz-sericitization occurring locally. In the southern sector of the deposit, concealed porphyry-style Cu–Mo mineralization exhibits potassic alteration, silicification, and quartz-sericitization.

2.

Geological map of the Jiawula Pb–Zn–Ag deposit (modified after Hui et al., 2021).

4. Sample Description

4.1. Mineral Paragenesis

Based on the ore type and mineral association (Figure ), we divided the Jiawula deposit into three mineralization stages (Figure ). Figure shows the typical mineral characteristics of each mineralization stage. The ore minerals are mainly hosted in the propylitic alteration zone and the chlorite zone, occurring in vein-like patterns. The following is a description of the characteristics of each mineralization stage in the deposit.

3.

Typical samples of different mineralization stages of the Jiawula deposit: (a–c) Stage I, (d–f) Stage II, and (g–i) Stage III.

4.

Mineral symbiosis sequence of the Jiawula deposit.

Stage I (Figure a–c) occurs in propylitized andesite. The primary mineral assemblage comprises pyrite, sphalerite, and chalcopyrite (Ccp-I), with sericite and quartz as the gangue minerals. Chalcopyrite (Ccp-I) occurs as chalcopyrite disease within sphalerite, accounting for approximately 5% of the host sphalerite’s area.

Stage II (Figure d–f) is hosted in chloritized andesite. The mineral association includes pyrite, chalcopyrite, sphalerite, and arsenopyrite, with quartz as the dominant nonmetallic mineral. Chalcopyrite exhibits two distinct microtextures: (1) residual texture (Ccp-IIA) coexisting with quartz, arsenopyrite, pyrite, and sphalerite and (2) anhedral aggregates (Ccp-IIB) intergrown with abundant pyrite.

Stage III (Figure g–i) develops in chloritized andesite. The mineral assemblage is dominated by sphalerite, galena, and pyrrhotite, with minor silver-bearing minerals forming veinlets crosscutting sulfides. Gangue minerals include quartz and diorite with localized fluorite occurrences. Chalcopyrite (Ccp-III) exhibits veinlet textures embedded within pyrrhotite and sphalerite.

4.2. Fluid Inclusions

Quartz-hosted fluid inclusions in the Jiawula deposit (Figure ) are classified into three types: liquid-rich (L-type), vapor-rich (V-type), and solid-bearing (S-type). L-type inclusions range from 3 to 15 μm, V-type from 5 to −20 μm, and S-type from 10 to 25 μm.

5.

Microphotograph of quartz fluid inclusions in different mineralization stages of the Jiawula deposit: (a,b) Stage I, (c,d) Stage II, and (e,f) Stage III.

Stage I (Figure a,b) contains large, irregularly shaped fluid inclusions. Coexisting L- and V-type inclusions within the same field of view (Figure a) exhibit nearly identical homogenization temperatures, indicative of fluid boiling during this stage.

Stage II (Figure c,d) is characterized by smaller elliptical to polygonal L-type inclusions.

Stage III (Figure e,f) features elongated and streaky L-type inclusions with reduced dimensions.

5. Methods

5.1. Sulfide In Situ Microarea Analysis (LA-ICP-MS)

The main and trace element analysis of sulfide in situ microareas was completed using the LA-ICP-MS technology platform at Wuhan SampleSolution Analytical Technology Co., Ltd., Wuhan, China. For detailed instrument parameters and analysis procedures, see Zong et al. (2017). The experimental system consists of a GeolasPro laser ablation device (integrated COMPexPro 102 193 nm ArF excimer laser source and MicroLas optical system) coupled to an Agilent 7700e mass spectrometer. High-purity helium and compensation argon are used for introduction, and a signal homogenization device is used to optimize plasma stability. The experimental setup was a 32 μm beam spot and a 5 Hz repetition rate. The multiple external standard method without internal calibration was used. NIST 610 silicate glass was used as the calibration material, and the USGS MASS-1 sulfide standard was used simultaneously to verify the accuracy of the method. The raw data was processed by the ICPMSDataCal software package.

5.2. In Situ S Isotope

The isotopic microzone in situ analysis was carried out using a RESOlution-S155 193 nm ArF excimer laser ablation system coupled to a Nu Plasma II multicollector inductively coupled plasma mass spectrometer at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Wuhan). A 33 μm laser beam spot diameter and a 5 Hz pulsed ablation frequency were used, and the laser energy density was maintained at 2 J/cm². The carrier gas path was injected into the mass spectrometer after optimization by a He–Ar–H2 ternary mixed gas system. The analysis sequence included 120 s: 20 s background determination, 40 s effective signal acquisition, and 60 s system purging. Data normalization was performed using WS-1 (δ³⁴S_V‑CDT = 0.30 ± 0.10‰) as the reference substance.

5.3. C–H–O Isotopes

C–H–O isotopes were analyzed at Wuhan SampleSolution Analytical Technology Co., Ltd., Wuhan, China. The carbon isotopes of CO₂ in quartz fluid inclusions were tested using the following process: 2 g of the 40–60 mesh inclusion sample was taken and baked continuously at 105 ± 2 °C for 4 h. The inclusion was broken using an automatic online thermolysis system with an elemental analyzer Flash EA: the inclusion gas was fully released in a 550 °C pyrolysis tube for 5 min, water vapor was adsorbed in a water trap containing the dehydrating agent Mg­(ClO₄)₂, and a reducing nickel catalyst tube was simultaneously used to achieve the conversion of CH₄ cracking. When the system gradient was raised to 960 °C and the mass spectrum baseline stabilized, the gas sample was introduced into the isotope mass spectrometer. The measurement results were calibrated using the international reference material GBW04417 (δ¹³C_V‑PDB = −6.06‰).

Method of hydrogen isotope analysis of inclusions: 10–20 mg of a single mineral sample of quartz (40–60 mesh, 0.25–0.42 mm particle size) was weighed accurately and dried in vacuum for 12 h. The analysis was performed using a thermal cracking coupled mass spectrometry system (253plus, Thermofisher), where the high-temperature reaction chamber (1420 °C) preloaded with glass carbon filler instantaneously cleaves the water molecules in the inclusion to generate a H₂/CO mixture, which is transported to the chromatographic column by a high-purity helium carrier gas (5N) for component separation. The mass spectrometry detection process refers to international standards, including USGS57 (biotite, δD_VSMOW = −91‰), USGS58 (muscovite, δD_VSMOW = −28‰), and IAEA-CH7 (polyethylene, δD_VSMOW = −100.3‰).

Oxygen isotope analysis was performed using 200 mesh (particle size ≤ 75 μm) samples. After being weighed precisely to 6 mg of pure quartz or equivalent silicate (conversion standard based on total oxygen molar mass), the samples were dried at 105 °C for 12 h. The BrF5 chemical method was used. The sample was heated with the BrF5 reagent in a vacuum reaction system at a constant temperature of 580 °C for 12 h to generate oxygen molecules, and the gas was purified and captured by a 5 Å molecular sieve. Mass spectrometry analysis was performed using a Thermofisher 253Plus isotope mass spectrometer.

5.4. Microscopic Temperature Measurement of Fluid Inclusions

The microthermometry of quartz fluid inclusions was carried out at the fluid inclusion laboratory of the Collaborative Innovation Center for Exploration of Strategic Mineral Resources, China University of Geosciences (Wuhan). The temperature measurement was carried out using a Linkam THMS 600 hot and cold stage from the UK. Before the temperature of the sample was measured, the hot and cold stage was calibrated using a synthetic fluid inclusion standard sample from Fluid Inc. in the United States. The heating and cooling rates were 5–30 °C/min, and the heating rate near the phase transition point was between 0.1 and 0.5 °C/min.

6. Results

6.1. Trace Element Data of Chalcopyrite

A 14-point minor element geochemical study of typical samples at different mineralization stages was carried out using LA-ICP-MS, and the data are shown in Table and the box-and-whisker plot (Figure a). In Stage I, chalcopyrite exhibits a diseased texture with grain sizes less than 25 μm, which is smaller than the 32 μm diameter of the LA-ICP-MS laser beam. As a result, trace elemental analysis could not be performed.

1. Trace and Major Element Concentrations (ppm) of Chalcopyrite in the Jiawula Deposit Analyzed by LA-ICP-MS.

			K	Ca	Ti	FeS	CuS	Zn	Ga	Ge	As	Ag	Cd	In	Sn	Sb	Pb
No.	samples	stage	ppm	ppm	ppm	wt %	wt %	ppm	ppm	ppm	ppm	ppm	ppm	ppm	ppm	ppm	ppm
1	JWL-13B-9	Ccp-IIa	93.01	72.62	5.76	44.59	55.14	430.55	0.21	5.27	486.19	504.94	11.24	17.25	20.53	4.27	2.33
2	JWL-13B-10		49.48	83.51	5.78	46.29	52.77	3713.29	0.13	3.85	516.33	584.54	49.25	9.09	5.92	1.13	2.08
3	JWL-13B-6		29.28	0.00	9.20	45.61	53.67	4044.28	0.27	5.87	151.46	470.96	42.94	69.64	37.39	0.00	1.50
4	JWL-13B-7		40.37	0.00	6.49	46.04	53.47	2462.01	0.00	0.63	148.22	411.26	14.38	28.91	5.60	2.84	24.58
5	JWL-13B-8		39.40	254.18	6.45	46.27	53.11	699.81	0.31	1.11	157.11	439.50	4.02	2.56	2.26	3.00	45.45
6	JWL-13B-9		10.80	812.71	6.21	46.89	52.60	488.93	0.33	4.14	165.95	544.20	2.37	34.04	12.44	0.00	1.35
7	JWL-13B-10		18.93	0.00	3.82	47.83	51.56	270.09	0.20	4.17	154.80	534.12	2.70	24.64	8.64	0.29	1.83
8	JWL-13A-3	Ccp-IIb	9.54	262.25	2.00	45.98	53.75	246.36	0.13	2.31	184.95	302.38	1.18	3.78	0.35	0.00	5.25
9	JWL-13A-4		0.00	191.20	3.93	46.48	52.96	351.20	0.09	4.79	190.63	300.03	2.30	0.43	0.28	0.00	1.72
10	JWL-13A-5		0.36	195.16	8.23	46.83	52.85	314.73	0.01	3.72	173.52	288.62	2.24	2.15	0.21	0.00	0.44
11	JWL-2B-01	Ccp-III	37.85	398.68	4.45	57.43	40.95	229.76	1.60	6.53	621.13	198.65	9.70	1.23	63.44	151.84	642.92
12	JWL-2B-02		36.03	274.00	4.41	44.20	55.39	178.83	0.00	5.56	374.69	191.17	5.42	1.86	69.48	4.09	20.71
13	JWL-2B-03		8.10	369.98	4.39	45.65	53.20	234.51	0.02	5.23	359.00	198.56	2.48	2.01	40.14	14.98	478.55
14	JWL-2B-04		10.84	240.02	4.14	43.46	55.80	78.53	3.25	6.84	821.72	512.50	2.38	0.00	0.63	1286.78	199.60

6.

(a) Chalcopyrite sulfide trace box-plot. (b,c) Representative time-resolved analysis signal diagram for LA-ICP-MS analysis of Stage II–III chalcopyrite.

The trace elements enriched in the chalcopyrite of the Jiawula deposit are Zn, Ag, As, Ca, Sb, Pb, K, Sn, In, and Cd. The elements Ga, Co, Ni, Mn, and Mg are deficient. The characteristics of the data are as follows:

• (1)It is not difficult to see from the etching signal diagram (Figure b,c) that the Fe, Cu, and S signals in the Stage II–III chalcopyrite are smooth, indicating that these elements are evenly distributed and exist stably in the chalcopyrite in the form of crystal lattice bonding. However, there is a spike in the Zn element in Stage II, indicating the presence of sphalerite inclusions in the Stage II chalcopyrite.
• (2)The Zn element in chalcopyrite shows great variability, with a decreasing trend in its mean value from 1730 ppm (Ccp-IIA) to 304 ppm (Ccp-IIB) and 180 ppm (Ccp-III). There is also a downward trend for Ag (499 ppm–297 ppm–275 ppm) and In (27 ppm–2 ppm–1 ppm); Ge shows a slight upward trend (3.58 ppm–3.61 ppm–6.05 ppm).

6.2. In Situ S Isotopes

In five typical samples at different mineralization stages (including arsenopyrite, chalcopyrite, galena, pyrite, and sphalerite), 52 in situ S isotope data were obtained, as shown in Table and Figure . The δ³⁴S of the Jiawula deposit shows a narrow range of −0.1–5.2‰. Among them, the δ³⁴S of Stage I is 2.3‰–4.0‰, with an average value of 2.8‰. The δ³⁴S of Stage II is −0.1‰-5.2‰, with an average value of 2.9‰. The δ³⁴S of Stage III is 0.6–3.9‰, with an average value of 2.3‰. The δ³⁴S of chalcopyrite ranges from −0.1 to 3.4‰, the δ³⁴S of pyrite ranges from 2.2 to 2.8‰, the δ³⁴S of arsenopyrite shows 2.0 to 2.9‰ for Stage II, the δ³⁴S of galena shows 0.6 to 1.3‰, and the δ³⁴S of sphalerite shows 2.3 to 5.2‰.

2. In Situ Sulfur Isotope Data of Different Sulfides in the Jiawula Deposit.

no.	sample no.	mineral	stage	δ34SV‑CDT (‰)
1	23JWL-11A-1	sphalerite	Stage I	4.0
2	23JWL-11A-2	sphalerite	Stage I	2.3
3	23JWL-11A-3	sphalerite	Stage I	3.1
4	23JWL-11A-4	sphalerite	Stage I	3.0
5	23JWL-11A-5	sphalerite	Stage I	2.7
6	23JWL-11A-6	sphalerite	Stage I	2.5
7	23JWL-11A-7	pyrite	Stage I	2.5
8	23JWL-11A-8	pyrite	Stage I	2.3
9	23JWL-11A-9	pyrite	Stage I	2.5
10	23JWL-11A-10	pyrite	Stage I	2.8
11	23JWL-11A-11	pyrite	Stage I	2.8
12	23JWL-11A-12	pyrite	Stage I	3.4
13	23JWL-13-1	arsenopyrite	Stage II	2.0
14	23JWL-13-2	arsenopyrite	Stage II	2.9
15	23JWL-13-3	arsenopyrite	Stage II	2.4
16	23JWL-13-4	arsenopyrite	Stage II	2.6
17	23JWL-13A-1	chalcopyrite	Stage II	–0.1
18	23JWL-13A-2	chalcopyrite	Stage II	0.9
19	23JWL-13A-3	chalcopyrite	Stage II	2.3
20	23JWL-13B-1	chalcopyrite	Stage II	3.1
21	23JWL-13B-2	chalcopyrite	Stage II	3.4
22	23JWL-13B-3	chalcopyrite	Stage II	2.2
23	23JWL-13B-4	galena	Stage II	1.3
24	23JWL-13B-5	galena	Stage II	0.7
25	23JWL-5A-1	sphalerite	Stage II	3.7
26	23JWL-5A-2	sphalerite	Stage II	3.4
27	23JWL-5A-3	sphalerite	Stage II	3.7
28	23JWL-5A-4	sphalerite	Stage II	4.5
29	23JWL-5A-5	sphalerite	Stage II	4.8
30	23JWL-5A-6	sphalerite	Stage II	4.6
31	23JWL-5A-7	sphalerite	Stage II	4.7
32	23JWL-5A-8	sphalerite	Stage II	5.2
33	23JWL-1B-1	sphalerite	Stage III	2.5
34	23JWL-1B-2	sphalerite	Stage III	3.0
35	23JWL-1B-3	sphalerite	Stage III	3.3
36	23JWL-1B-4	sphalerite	Stage III	3.1
37	23JWL-1B-5	sphalerite	Stage III	3.8
38	23JWL-1B-6	sphalerite	Stage III	3.9
39	23JWL-2B-4	pyrite	Stage III	2.6
40	23JWL-2B-5	pyrite	Stage III	2.2
41	23JWL-2B-6	pyrite	Stage III	2.8
42	23JWL-1B-7	galena	Stage III	1.3
43	23JWL-1B-8	galena	Stage III	0.6
44	23JWL-1B-9	galena	Stage III	1.2
45	23JWL-2B-1	chalcopyrite	Stage III	1.2
46	23JWL-2B-2	chalcopyrite	Stage III	3.4
47	23JWL-2B-3	chalcopyrite	Stage III	1.5
48	23JWL-2A-1	chalcopyrite	Stage III	2.0
49	23JWL-2B-7	galena	Stage III	0.7
50	23JWL-2B-8	galena	Stage III	0.8
51	23JWL-2A-2	pyrite	Stage III	2.9
52	23JWL-2A-3	pyrite	Stage III	2.8

7.

In situ sulfur isotope histogram of the Jiawula deposit.

6.3. Fluid Inclusions

6.3.1. Fluid Inclusion Temperature Measurement

Fluid inclusion thermometry was performed on typical samples selected from the three metallogenic stages (Table ; Figures and ), and the salinity of the aqueous solution inclusions of the two phases was calculated according to the formula provided by Bodnar (1993), and the metallogenic pressure and metallogenic depth were calculated according to the empirical formula of Shao Jielian and Mei Jianming (1986).

3. Microscopic Temperature Measurement Data of Fluid Inclusions.

no.	stage	mineral	type	T m,ice (°C)	T h,v (°C)	salinity (wt %)	H (km)	P (bar)
1	Stage I	quartz	V-type	–0.4	234.8	0.70	0.79	146.5
2			V-type	–2.8	219.2	4.65	1.14	179.3
3			V-type	–1	217.3	1.74	0.88	147.4
4			V-type	–1.1	230.5	1.91	0.90	158.3
5			V-type	–0.5	223.4	0.88	0.81	141.5
6			V-type	–0.5	241.9	0.88	0.81	153.2
7			L-type	–0.8	234.1	1.40	0.85	154.7
8			L-type	–2.3	232.4	3.87	1.07	181.8
9			L-type	–1.3	236.8	2.24	0.93	166.6
10			L-type	–2.8	245.7	4.65	1.14	200.9
11			L-type	–0.5	221.4	0.88	0.81	140.2
12			L-type	–1.1	249	1.91	0.90	171.0
13			L-type	–0.7	260.3	1.22	0.84	169.6
14			L-type	–0.6	200	1.05	0.82	128.5
15			L-type	–3.5	298.8	5.71	1.23	258.2
16			L-type	–1.2	239.2	2.07	0.91	166.3
17			L-type	–1.1	238	1.91	0.90	163.5
18			L-type	–0.7	229.6	1.22	0.84	149.6
19			L-type	–1.5	239.4	2.57	0.95	172.4
20			L-type	–2.6	273.8	4.34	1.11	220.0
21			L-type	–1.4	253.4	2.41	0.94	180.4
22			L-type	–2.1	254.6	3.55	1.04	195.3
23			L-type	–1.9	249.9	3.23	1.01	187.9
24			L-type	–2.2	265.4	3.71	1.05	205.6
25			L-type	–1.9	271.6	3.23	1.01	204.2
26			L-type	–1.8	253.1	3.06	1.00	188.3
27			L-type	–2.1	265.2	3.55	1.04	203.5
28			L-type	–1.5	274.5	2.57	0.95	197.7
ave.				–1.5	244.8	2.54	0.95	176.2
19	Stage II	quartz	L-type	–1.2	170	2.07	0.91	118.2
20			L-type	–1.2	192.4	2.07	0.91	133.8
21			L-type	–1.5	224.9	2.57	0.95	162.0
22			L-type	–2.9	247.5	4.80	1.15	204.1
23			L-type	–2.3	238.7	3.87	1.07	186.7
24			L-type	–1.5	204.1	2.57	0.95	147.0
25			L-type	–1.4	156.5	2.41	0.94	111.4
26			L-type	–2	217.7	3.39	1.03	165.4
27			L-type	–1.9	206.9	3.23	1.01	155.6
28			L-type	–0.6	221.2	1.05	0.82	142.2
29			L-type	–1.3	216.7	2.24	0.93	152.5
30			L-type	–0.7	229.1	1.22	0.84	149.3
31			L-type	–0.3	178.9	0.53	0.78	110.0
32			L-type	–2.4	224.1	4.03	1.08	176.9
33			L-type	–0.1	213.1	0.18	0.75	126.9
34			L-type	–0.1	234.3	0.18	0.75	139.5
35			L-type	–0.2	177.9	0.35	0.76	107.6
36			L-type	–0.3	176.4	0.53	0.78	108.4
ave.				–1.2	207.2	2.07	0.91	144.3
37	Stage III	quartz	L-type	–0.3	211.7	0.53	0.78	130.1
38			L-type	–0.1	205.1	0.18	0.75	122.1
39			L-type	–0.9	209.1	1.57	0.87	140.0
40			L-type	–1	212.1	1.74	0.88	143.9
41			L-type	–0.8	271.1	1.40	0.85	179.1
42			L-type	–0.6	203.4	1.05	0.82	130.7
43			L-type	–1.2	208.3	2.07	0.91	144.8
44			L-type	–0.6	248.3	1.05	0.82	159.6
45			L-type	–0.7	255.1	1.22	0.84	166.3
46			L-type	–0.7	202.8	1.22	0.84	132.2
47			L-type	–0.8	197.2	1.40	0.85	130.3
48			L-type	–1.4	214.8	2.41	0.94	152.9
49			L-type	–0.5	207.5	0.88	0.81	131.4
50			L-type	–0.7	200	1.22	0.84	130.3
51			L-type	–0.6	203.2	1.05	0.82	130.6
52			L-type	–0.7	209.3	1.22	0.84	136.4
53			L-type	–0.8	210.3	1.40	0.85	138.9
54			L-type	–1	208.2	1.74	0.88	141.2
ave.				–0.7	215.4	1.30	0.84	141.2

T _m,ice, temperature of final ice melting; T _h,v, homogenization temperature of V-type and L-type fluid inclusions or the disappearing temperature of bubbles for S-type fluid inclusions. The depth of mineralization (H) and pressure (P) are determined using the empirical formula proposed by Shao Jielian and Mei Jianming. (1986): P = P ₀ × T _h/T ₀, H = P × 1/300 × 10⁵; where P ₀ = 219 + 2620 × S, T ₀ = 374 + 920 × S.

8.

(a,c,e) Temperature histogram of quartz fluid inclusions. (b,d,f) Salinity histogram of quartz fluid inclusions.

9.

Binary plot of salinity–temperature for quartz fluid inclusions.

The T _m,ice of Stage I ranges from −3.5 to −0.4 °C, corresponding to a salinity of 0.70 to 5.71 wt % NaCl eq. The homogeneous temperature T _h value ranges from 200.0 to 298.8 °C; the corresponding ore depth is 0.95 km, and the ore-forming pressure is 176.2 bar.

The T _m,ice of Stage II ranges from −2.9 °C to −0.1 °C, corresponding to a salinity of 0.18 to 4.80 wt % NaCl eq. The uniform temperature T _h ranges from 156.5 to 247.5 °C. The corresponding ore-forming depth is 0.91 km, and the ore-forming pressure is 144.3 bar.

The T _m,ice of Stage III ranges from −1.4 to −0.1 °C, corresponding to a salinity of 0.18 to 2.41 wt % NaCl eq. The uniform temperature T _h ranges from 197.2 to 271.1 °C; the corresponding ore-forming depth is 0.84 km, and the ore-forming pressure is 141.2 bar.

6.3.2. Laser Raman Spectroscopy

The laser Raman spectroscopy of fluid inclusions in the Jiawula deposit (Figure ) all show a strong H₂O peak, among which Stage I and Stage II show a certain intensity of the CO₂ peak, which is especially obvious in Stage II; at the same time, Stage II and Stage III show different degrees of the CH₄ peak. All of this evidence indicates that the metallogenic stage of the Jiawula deposit is transitioning from an oxidizing environment to a reducing environment.

10.

Laser Raman spectroscopy analysis of fluid inclusions in the Jiawula deposit.

6.4. C–H–O Isotopes

C–H–O isotope data for fluid inclusions were obtained from three samples from the three metallogenic stages (Table ). The δ¹³C values (Figure a) of the Jiawula deposit range from −6.34 to −16.73‰; δD (Figure b) ranges from −120.1 to −131.7‰. The values of δ¹⁸O_H2O were determined using the fractionation equation (δ¹⁸O_H2O = δ¹⁸O_{quartz‑water}-3.38 × (10⁶ × T^–2) + 3.40) according to Clayton et al. (1972) and O’Neil et al. (1969). The δ¹⁸O values (Figure b) of the Jiawula deposit range from 0.31 to 4.1‰, and the δ¹⁸O_H2O values range from −10.93 to −5.53‰.

4. Carbon, Hydrogen, and Oxygen Isotope Composition of the Jiawula Deposit.

no.	sample	stage	mineral	Th/°C	δD/‰	δ18OV‑SMOW/‰	δ18Owater/‰	δ13CV‑PDB/‰	reference
1	23JWL-10	Stage I	quartz	245	–132	4.10	–5.10	–11.99	this study
2	23JWL-20	Stage II	quartz	207	–129	0.31	–10.93	–6.34
3	23JWL-1	Stage III	quartz	215	–120	0.47	–10.29	–16.73
4	NJ-65	early stage	quartz	353	–141	–4.5	–9.7		Li Tiegang (2016)
5	NJ-73	early stage	quartz	353	–141	–4	–9.2
6	NJ-11	middle stage	quartz	271	–155	–4.6	–12.5
7	NJ-13	middle stage	quartz	271	–142	–4.8	–12.7
8	NJ-14	middle stage	quartz	271	–133	–5.5	–13.4
9	NJ-15	middle stage	quartz	271	–160	–5	–12.9
10	NJ-17	middle stage	quartz	271	–134	–4.7	–12.6
11	NJ-53	middle stage	quartz	271	–133	–5.2	–13.1
12	NJ-55	middle stage	quartz	271	–143	–4.9	–12.8
13	NJ-56	middle stage	quartz	271	–147	–4.8	–12.7
14	NJ-57	middle stage	quartz	271	–161	–4.2	–12.1
15	NJ-70	middle stage	quartz	271	–166	–4.9	–12.8
16	NJ-77	middle stage	quartz	271	–133	–1.2	–9.1
17	NJ9–1	late stage	quartz	209	–145	–2.2	–13.3
18	NJ9–2	late stage	quartz	209	–145	–1.6	–12.7
19	08jw-06		quartz	212	–133.6	–3.4	–16.75		Zhai Degao et al. (2013)
20	08jw-09		quartz	235	–129.9	–4.2	–15.96
21	08jw-11		quartz	237	–138.2	–5.5	–17.13
22	08jw-08		calcite	235	–120.5	–2.2	–11.27
23	08jw-12		calcite	196	–103.4	12.5	1.08
24	J–HO–1		quartz	235	–139.7	–7.2	–18.96		Han Li et al. (1998)
25	J–HO–7		quartz	235	–109.58	3.65	–8.11
26	J–HO–8		quartz	235	–130.48	–0.29	–12.05
27	7		quartz	280	–109.58	8.65	1.00		Han Shiqing et al. (2006)
28	8		quartz	280	–130.48	13.09	5.44

11.

(a) Carbon isotope composition of the Jiawula deposit. (b) Hydrogen and oxygen isotope composition of the Jiawula deposit (after Sheppard, 1977). Gray symbols represent data compiled from Li Tiegang (2016), Zhai Degao et al. (2013), Han Shiqing (2006), and Han Li (1998).

7. Discussion

7.1. Mechanism of Chalcopyrite Mineralization

The Se–Ni–Cd ternary diagram (Figure a) can be used to effectively distinguish the chalcopyrite in the Jiawula deposit as mostly hydrothermal chalcopyrite. In hydrothermal deposits, In and Sn are characterized by cotransport and enrichment. , The significant positive correlation between In and Sn in the chalcopyrite of the Jiawula deposit (Figure c) suggests that the two may enter the crystal lattice through isomorphic substitution (e.g., Sn⁴⁺ replacing Cu⁴⁺/Fe³⁺ or In³⁺ replacing Fe²⁺).

12.

(a) Trace Se–Ni–Cd ternary diagram of chalcopyrite in the Jiawula deposit. (b–d) Trace binary diagram of chalcopyrite elements in the Jiawula deposit (the gray data comes from George et al., 2018, and Tao Hong et al., 2021).

The Ag in the chalcopyrite from the Jiawula deposit was more enriched in the early stage, while Sn increased in the later stage and showed a linear negative correlation of Ag–Sn (Figure d), which suggests that there may have been a substitution mechanism for Ag and Sn during the precipitation of chalcopyrite in the Jiawula deposit. The difference in the valence state and radius between Ag⁺ (ion radius 1.15 Å) and Sn⁴⁺ (0.69 Å) may limit the coexistence of the two in the chalcopyrite (CuFeS₂) crystal lattice. Ag may preferentially substitute for Cu⁺ (radius 0.77 Å) by isomorphism or occupy interstitial sites, while the substitution of Sn⁴⁺ needs to be combined with a vacancy of Fe³⁺ or coupled with other cations (e.g., Cu²⁺ → Sn⁴⁺ + □). Due to the complexity of charge compensation, Ag and Sn may form a competitive substitution relationship.

The Cd–Zn relationship in sulfide deposits has long served as a significant indicator of mineralization mechanisms. Cook (2009) identified a Cd²⁺ ↔ Zn²⁺ substitution mechanism in sphalerite. Although the Cd/Zn ratio cannot directly constrain the temperature, pH, or genetic type of deposit, numerous studies have demonstrated that high-temperature deposits typically exhibit elevated Cd/Zn ratios. , This pattern extends to chalcopyrite mineralization, where the Cd/Zn ratio serves as a critical parameter for estimating crystallization temperatures, with individual deposits maintaining relatively constant Cd/Zn values. The Jiawula deposit displays a strong Cd–Zn correlation (Cd/Zn ≈ 0.01; Figure b), which is close to that of the Toroiaga epithermal Zn–Pb–Ag–Au deposit in Romania (0.017) but notably lower than the Baita Bihor skarn-type Zn–Pb deposit, also in Romania (0.04), and the Yulekenhalasu porphyry-type Cu–Mo deposit in China (0.2). This geochemical signature strongly supports an epithermal origin for the Jiawula deposit rather than a porphyry-type affinity.

7.2. Ore-Forming Fluids and Material Sources

Research on fluid inclusions (Table ; Figures and ) indicates that the ore-forming fluids exhibit moderate-to-low temperatures (156.5–298.8 °C) and low salinities (0.18–5.71 wt % NaCl eq). Calculated mineralization depths are all <1 km (Table ). The fluid during the early deep mineralization stage has higher temperatures (200.0–298.8 °C) and salinities (0.70–5.71 wt % NaCl equiv), accompanied by boiling phenomena (Figure a). In contrast, the late stage shows a preferential decrease in salinity without significant temperature variation, indicating that fluid evolution was primarily controlled by mixing processes rather than extensive cooling or boiling. Specifically, an influx of low-salinity meteoric water likely diluted the original high-salinity magmatic-hydrothermal fluids. This is similar to the W–Mo ore deposits in the Ningshan-Zhen’an area, also exemplified by the Tashvir and Varmazyar deposits in Iran and the Sanshandao gold deposit in the Jiaodong Peninsula, Eastern China. Furthermore, reactivation or formation of new fluid pathways during late mineralization may have facilitated further dilution by external fluids without substantially altering the thermal regime. The progressive shift from early magmatic water to late-stage mixing with meteoric fluids, as evidenced by δD−δ¹⁸O_water data (Figure b), is further supported by previously published data sets (gray symbols) from Li Tiegang (2016), ZHAI Degao et al. (2013), Han Shiqing (2006), and Han Li (1998).

Laser Raman spectroscopy analysis (Figure ) demonstrates that gaseous components in quartz-hosted fluid inclusions exhibit a transition from early-stage CO₂ to late-stage CH₄. The CO₂ enrichment likely originated from deep-seated magmatic degassing or mantle-derived fluid input, the presence of which effectively buffered the fluid’s oxidation state. This facilitated the stabilization of molybdenum (transported as MoO₄ ^2–) under highly oxidized conditions. In contrast, late-stage inclusions show the disappearance of CO₂ with a significant enhancement in CH₄ Raman signals. Consequently, we infer that the ore-forming fluids in the Jiawula deposit evolved from an early H₂O–NaCl–CO₂ system to a late H₂O–NaCl–CH₄ system. This transition reflects a decrease in oxygen fugacity within the mineralization environment, controlling a shift in carbon speciation pathways from C + 2H₂O → CO₂ + 2H₂ to CO₂ + 4H₂ → CH₄ + 2H₂O.

In situ sulfur isotope analyses in the Jiagwula deposit yield a narrow δ³⁴S range (−0.1–5.2‰). This range aligns closely with values reported by Li Tiegang (2016) (δ³⁴S = 1.2–8.4‰) and ZHAI Degao et al. (2013) (δ³⁴S = 1.37–4.10‰) but is slightly lower. While supporting a predominantly magmatic sulfur source, this difference reflects localized fluid mixing and isotopic fractionation. Specifically, the sampling location likely incorporated deeper or reduced sulfur sources, possibly influenced by boiling, mixing, and the resultant isotopic fractionation during mineralization. Carbon isotope data provide strong corroboration: δ¹³C values shift from −6.34‰ (early) to −16.73‰ (late), indicating early dominance of magmatically degassed CO₂, progressively overprinted by oxidation of organic matter and mixing with meteoric water–organic carbon sources under volcanic–subvolcanic influences.

7.3. The Relationship between Ore Deposit Genesis and Porphyry-Type Cu–Mo Mineralization

Porphyry–epithermal systems (e.g., Grasberg deposit, Baguio District, Yanacocha deposit) are predominantly characterized by magmatic waters, featuring high-salinity fluid inclusions (10–50 wt % NaCl eq), elevated temperatures (>350 °C), and high mineralization pressures, with intrusive bodies typically emplaced at 2–5 km depths, transitioning to epithermal domains around 1.5–2.5 km. Conversely, epithermal deposits (e.g., Hishikari deposit, El Peñón deposit, Comstock mining district) exhibit meteoric- or groundwater-dominated fluids, with H–O isotopes indicating meteoric or magmatic–meteoric mixed signatures, alongside low temperatures (150–250 °C), low salinity (<5 wt % NaCl eq), minimal mineralization pressures, and depths ranging from 0 to 1.5 kmcharacteristics consistent with those of the Jiawula deposit.

In terms of ore deposit chronology (Figure ; Table ), ,,,,− previous studies reveal a molybdenite Re–Os age of 135 ± 3 Ma for porphyritic Cu–Mo mineralization, distinctly postdating the zircon U–Pb age of the Jiawula deposit (145 ± 5 Ma) and the sulfide Rb–Sr-constrained Pb–Zn mineralization epoch (142–153 Ma). This temporal gap (approximately 10 Myr) exceeds reasonable time scales for evolution within a unified magmatic–hydrothermal system, suggesting separate mineralization events in geologically distinct phases.

13.

Data on the mineralization age of the Jiawula deposit.

5. Isotopic Ages of Rocks and Minerals from the Jiawula Deposit.

no.	sample descriptions	dated material	methods	ages (Ma)	reference
Jiawula Pb–Zn–Ag deposit
1	quartz porphyry	whole-rocks	K–Ar	122	Wang and Pan (1992)
2	feldspar porphyry	whole-rocks	K–Ar	117	Wang and Pan (1992)
3	granodiorite	whole-rocks	K–Ar	124.15	Yang et al. (1998)
4	quartz porphyry	whole-rocks	K–Ar	121	Geng (2005)
5	quartz monzonite porphyry	whole-rocks	K–Ar	138	Geng (2005)
6	quartz monzonite porphyry	zircon	U–Pb	143 ± 2	Li et al. (2016)
7	granite porphyry	zircon	U–Pb	143.1 ± 3.9	Yang et al. (2017)
8	granite porphyry	zircon	U–Pb	146.4 ± 1.4	Yang et al. (2017)
9	quartz porphyry	zircon	U–Pb	150.1 ± 1.8	Niu et al. (2017)
10	syenite porphyry	zircon	U–Pb	148.8 ± 2.2	Niu et al. (2017)
11	monzonite porphyry	zircon	U–Pb	145.3 ± 1.9	Niu et al. (2017)
12	quartz monzonite porphyry	zircon	U–Pb	152.2 ± 1.5	Liu et al. (2018)
13	granite porphyry	zircon	U–Pb	141.9 ± 0.5	Cao and Liu (2020)
14	quartz monzonite porphyry	zircon	U–Pb	141.9 ± 2.4	Hui et al. (2021)
15	quartz monzonite porphyry	zircon	U–Pb	138.7 ± 1.8	Wang (2021)
16	quartz monzonite porphyry	zircon	U–Pb	139 ± 1.8	Wang (2021)
17	quartz-pyrite-sphalerite-galena veins	sphalerite	Rb–Sr	143 ± 2	Li et al. (2014)
18	quartz-pyrite-sphalerite-galena veins	pyrite	Rb–Sr	142 ± 3	Li et al. (2014)
19	ore	sphalerite	Rb–Sr	153 ± 2	Cao et al. (2018)
20	altered andesite	muscovite	Ar–Ar	133 ± 0.7	Niu et al. (2020)
Cu–Mo mineralization
21	monzonite porphyry	molybdenite	Re–Os	135.4 ± 2.3	Hui et al. (2021)
22	quartz monzonite porphyry	molybdenite	Re–Os	134.6 ± 3.8	Wang (2021)

Consequently, the Jiawula deposit is determined to represent an epithermal deposit formed during the Early Cretaceous (∼145 Ma). A potential linkage to underlying porphyry systems is conceivable; however, metallochronological constraints preclude a genetic relationship with the currently exposed porphyry intrusions, instead indicating superimposed relationships from multiple magmatic intrusions and mineralization episodes.

8. Conclusions

The Jiawula deposit formed during the Early Cretaceous period (∼145 Ma). C–H–O–S isotope data indicate that the ore-forming materials were primarily derived from deep-seated magmatic sources. Following fluid boiling, late-stage meteoric water input became increasingly involved in fluid evolution. Fluid inclusion and laser Raman spectroscopy analyses provide further constraints on the nature of the ore-forming fluids: the system evolved from an early H₂O–NaCl–CO₂ fluid, dominated by magmatic degassing-derived CO₂ (δ¹³C = – 6.34‰), to a late-stage H₂O–NaCl–CH₄ fluid, characterized by the involvement of meteoric water and CH₄-bearing carbon sources (δ¹³C = −16.73‰). This transition reflects a decrease in oxygen fugacity within the mineralization environment and a corresponding shift in carbon reaction pathways from C + 2H₂O → CO₂ + 2H₂ to CO₂ + 4H₂ → CH₄ + 2H₂O.

Mineral assemblages, the low-temperature and low-salinity fluid characteristics, and trace element signatures in chalcopyrite collectively indicate that the Jiawula deposit represents a typical epithermal deposit. In contrast, the porphyry-style Cu–Mo mineralization, with a metallogenic age approximately 10 million years younger than that of the Jiawula deposit, is interpreted as the result of subsequent multiphase magmatic intrusions and superimposed mineralization events.

The authors declare no competing financial interest.