Genesis and Tectono-Metallogenetic Setting of the Dongwujiiazi Gold Deposit, NE China: Insights from Whole-Rock Geochemistry and H–O–S–Pb Isotopes

Abstract

The Dongwujiiazi deposit is a structurally controlled orogenic gold deposit situated in the eastern part of the Chifeng–Chaoyang gold belt along the northern boundary of the North China Craton. This study establishes a comprehensive metallogenic model for the Dongwujiiazi gold deposit by integrating whole-rock geochemistry (major and trace elements), in situ trace elements and REEs in zircon, multi-isotope systems (H, O, S, Pb), and precise zircon U–Pb geochronology. Five types of intrusive and associated rocks are identified within the main biotite-pyroxene gneiss host of the Dongwujiiazi gold deposit: mylonitized granitic pegmatite, mylonitized porphyritic monzogranite, propylitized fine-grained quartz monzodiorite, quartz monzonite, and porphyritic dolerite. The gold-bearing polymetallic sulfide ores are composed of pyrite, chalcopyrite, sphalerite, galena, digenite, and native gold. Zircon grains in the Dongwujiiazi gold ore (2502 ± 15 to 2539 ± 18 Ma) are inherited from surrounding Neoarchean gneiss, recording older crustal sources rather than forming contemporaneously with the gold mineralization. H–O isotopes indicate that the ore-forming fluids were mixed in origin, involving both magmatic and metamorphic components. S and Pb isotopes suggest that the mineralizing sulfur was mainly derived from a magmatic source, while lead originated predominantly from lower crustal materials associated with the surrounding high-grade metamorphic rocks. In this study, we present a new metallogenic model for the Dongwujiiazi gold deposit, in which slab-derived and lower-crustal metamorphic fluids interacted with ascending magmas, resulting in fluid mixing and gold precipitation within structurally controlled zones of gneissic host rocks. Combined geochemical and isotopic evidence (H–O, S, Pb) indicates contributions from both magmatic and metamorphic sources, supporting formation as an intracontinental orogenic gold system in an active continental margin.

1. Introduction

The North China Craton (NCC) represents one of the Earth’s most ancient continental cores and records a long and intricate history of tectonic reworking, marked by repeated episodes of collision and accretion. Its northern margin, in particular, constitutes a highly prospective metallogenic zone, where extensive gold mineralization is concentrated within the Chifeng–Chaoyang belt. This region is regarded as one of China’s principal gold-producing provinces and provides an exceptional geological framework for examining the formation of orogenic gold systems within an intracontinental regime. Within this belt, the Dongwujiazi gold deposit occupies a position in its eastern segment and forms part of a broader cluster of more than 200 documented gold occurrences [1]. Notable deposits in this metallogenic province include Jinchanggouliang and Xiaotazigou [2], highlighting the regional-scale significance and continuity of gold mineralization.

Most gold deposits are widely recognized as orogenic in origin [3,4]. They are interpreted to have formed in convergent tectonic environments, particularly during the late stages of craton evolution when tectono-magmatic activity wanes [3,5,6]. These deposits are typically epigenetic and structurally controlled, occurring within deformed metamorphic belts across a wide range of crustal levels. They are most commonly associated with greenschist facies conditions and are frequently hosted by metamorphosed volcanic rocks [3,4,7,8,9].

Orogenic gold deposits commonly occur in rocks that have experienced metamorphism ranging from lower to upper greenschist facies [10]. The precise source of hydrothermal fluids responsible for transporting gold remains a topic of ongoing debate and investigation. Over the years, several mechanisms have been proposed to explain the origin of auriferous fluids in orogenic gold systems. According to [11], these include (1) release of fluids from greenstone rocks during progressive regional metamorphism, (2) fluid release from the lower and/or middle crust, with or without contributions from the mantle [3,12,13,14], (3) magmatic fluids derived from widespread or localized granitic intrusions, (4) addition of fluids during crystallization of lamprophyric magmas enriched with gold [12,15,16], and (5) extensive infiltration and deep circulation of meteoric fluids within the crust [17].

Nevertheless, the literature on orogenic gold deposits worldwide suggests that the most reasonable sources are metamorphic fluids generated through devolatilization reactions and fluids derived from felsic magmatic sources [8,11,18]. This perspective is particularly relevant for intracontinental orogenic settings, where interactions between lower crustal metamorphic fluids and magmatic contributions likely play a central role in ore formation.

This study aims to unravel the origin and evolution of the Dongwujiiazi gold deposit by integrating whole-rock geochemistry, H–O–S–Pb isotopes, and zircon U–Pb dating. It focuses on constraining the sources of metals and fluids, evaluating the role of lower crustal metamorphic and magmatic processes, and elucidating fluid migration and gold deposition within gneissic host rocks, providing new insights into intracontinental orogenic gold formation.

2. Geologic Setting

The Dongwujiiazi gold deposit is located along the northern edge of the North China Craton (NCC). It lies at the boundary between the Yanliao Depression Zone and the Inner Mongolia Uplift, and is controlled by the Chifeng–Kaiyuan and Chengde–Beipiao fault zones (Figure 1a). Regionally, the study area is underlain by Archean metamorphic rocks belonging to the Jianping Group, which are extensively distributed across the Chifeng–Chaoyang region [19]. These rocks constitute an ancient crustal basement and form the principal host for gold mineralization (Figure 1b). Lithologically, the metamorphic assemblage is mainly composed of gneiss, amphibolite, and banded magnetite–quartzite. Magmatic activity is represented predominantly by granitoid intrusions emplaced within the metamorphic basement. Structurally, the region is characterized by a well-developed fault system, with dominant trends in the NE and N–S directions, reflecting strong tectonic control on both magmatism and mineralization (Figure 1c).

The study area is characterized by a crystalline basement dominated by gneissic rocks intruded by multiple intrusive rocks. Field observations indicate that the gneiss exhibits well-developed foliation and ductile deformation features, suggesting a high-grade metamorphic origin and subsequent tectonic overprinting (Figure 2a–c). It is composed mainly of pyroxene, biotite, feldspar and quartz, which define the overall mineral assemblage of the rock. Quartz is found in the form of recrystallized crystals, and in some areas, in the form of veins. Minor accessory opaque minerals, mainly magnetite and pyrite, are sparsely distributed. The contact between the gneiss and quartz monzonite is clearly exposed and locally sharp, although minor transitional zones may occur, reflecting magmatic emplacement into pre-existing metamorphic rocks. The quartz monzonite is typically massive and medium- to coarse-grained, showing a relatively homogeneous texture compared to the surrounding foliated gneiss (Figure 2d,e).

Hydrothermal activity is widely distributed throughout the study area, mainly in the form of quartz veins that cut across both the gneiss and quartz monzonite (Figure 2f–i). These veins vary in thickness and are commonly associated with sulfide mineralization. The sulfides occur as disseminations (Figure 2f), vein infillings (Figure 2g), and locally massive aggregates within the quartz veins (Figure 2h). Their distribution suggests multiple stages of fluid flow and mineral precipitation.

The mineral assemblage observed in the veins includes abundant sulfides, with visible metallic minerals such as galena occurring locally (Figure 2i). The presence of galena, along with other sulfides, indicates a polymetallic hydrothermal system. Textural relationships, such as sulfides filling fractures and occurring along vein margins, suggest that mineralization postdates both deformation and magmatic intrusion.

Overall, the geological features of the area point to a multi-stage evolution system, involving (1) formation of the metamorphic basement (gneiss); (2) emplacement of multiple intrusive rocks within the gneissic basement; and (3) subsequent hydrothermal activity responsible for quartz veining and sulfide mineralization. This sequence reflects a structurally controlled hydrothermal system, where faults and fractures acted as conduits for mineralizing fluids, ultimately leading to the formation of ore-bearing quartz veins.

3. Petrography of Dongwujiiazi Gold Deposit

3.1. Host Rocks

Six types of host rocks and intrusions are identified in the Dongwujiiazi gold deposit, including (1) mylonitized granitic pegmatite; (2) mylonitized porphyritic monzogranite; (3) propylitized fine-grained quartz monzodiorite; (4) quartz monzonite; (5) biotite-pyroxene gneiss; (6) porphyritic dolerite.

The mylonitized granitic pegmatite exhibits a combination of mylonitic and pegmatitic textures, with a distinct banded structure in certain portions. The rock is dominated by K-feldspar (~50%), forming subhedral tabular-prismatic crystals, with grain sizes range from 0.2 to 30 mm (Figure 3a). Some feldspar occurs as granular aggregates, with argillic alteration and sericitization. Plagioclase (~15%), interpreted as andesine, occurs as subhedral tabular-prismatic crystals, with grain sizes range from 0.2 to 15 mm and some recrystallized portions form granular aggregates. It is locally oriented in banded aggregates, with signatures of argillic alteration and sericitization. Quartz (~35%) is present as anhedral granular crystals (0.5 to 12 mm grain size range), displaying undulose extinction. Minor accessory minerals include magnetite and apatite. The rock preserves evidence of strong ductile deformation, manifested in its mylonitic texture.

The mylonitized porphyritic monzogranite has mylonitic, porphyritic, and banded textures, with a fine-grained hypidiomorphic granular groundmass and localized metasomatic pseudomorphic textures (Figure 3b,c). Porphyroclasts, including K-feldspar, quartz, and hornblende, are embedded in the fine-grained groundmass. K-feldspar (~10%; grain size: 1.5 to 5 mm) occur as subhedral tabular-prismatic crystals, with argillic alteration and sericitization. Quartz (~10%; grain size: 1.5 to 5 mm) is elongated and occurs as banded and irregular crystals, with undulose extinction. Hornblende (~6%; grain size: 1.5 to 5 mm) is present as subhedral prismatic-columnar and irregular crystals, almost completely replaced by actinolite and epidote, showing metasomatic pseudomorphic textures. The groundmass (~74%; grain size: 0.1 to 1.5 mm) of porphyritic monzogranite exhibits a fine-grained hypidiomorphic granular texture, consisting mainly of plagioclase, K-feldspar, and quartz, with minor epidote and actinolite formed during alteration. Minor accessory minerals include magnetite, limonite, apatite, and zircon.

The propylitized fine-grained quartz consists of plagioclase, hornblende, biotite, and K-feldspar (Figure 3d). Plagioclase (~44%, grain size: 0.2 to 2.0 mm), predominantly of andesine composition, occurs as medium-sized subhedral tabular-prismatic crystals, with argillic alteration, sericitization, and epidotization. Hornblende (~25%; grain size: 0.2–2.0 mm, with a few reaching 2.5 mm.) occurs as subhedral prismatic to columnar crystals. Most grains are extensively altered to epidote and actinolite. Biotite (~10%; grain size: 0.2 to 1.5 mm) occurs as subhedral to irregular flakes that partially altered to chlorite and epidote, and contains exsolved sphene (titanite) as an accessory mineral. K-feldspar (~10%; grain size: 0.2 to 1.5 mm) occurs as subhedral to anhedral tabular-prismatic and granular crystals, with argillic alteration. Quartz (~10%; grain size: 0.2 and 1.5 mm) is present as anhedral granular to irregular crystals, showing graphic intergrowths with K-feldspar, resulting graphic texture (Figure 3d). Minor accessory minerals (<1%) include magnetite, sphene (titanite), and apatite.

The quartz monzonite displays a porphyritic texture with microcrystalline groundmass (Figure 3e). Phenocrysts include plagioclase, biotite, and hornblende, set in a fine-grained groundmass of feldspar and quartz microlites forming oriented bands. Plagioclase (andesine; ~14%; grain size: 0.2 to 1.8 mm) is euhedral to subhedral, with evidence of argillic alteration and clear polysynthetic twinning. Biotite (~4%; grain size: 0.2 to 2 mm) and hornblende (~2%; grain size: 0.2 to 1 mm) are partially altered, with hornblende exhibiting metasomatic replacement. The groundmass (~78%; grain size: less than 0.2 mm) composed of fine feldspar and quartz, and minor accessory minerals (~2%), including magnetite and limonite, are observed.

The biotite-pyroxene gneiss exhibits gneissose texture, defined by the oriented arrangement of major minerals (Figure 3f,g). Pyroxene (augite, ~20%; grain size: 0.1 to 1.5 mm) occurs as subhedral to anhedral prismatic and granular crystals, and locally altered to chlorite. Biotite (~10%), K-feldspar (~28%), plagioclase (~20%), and quartz (~20%) are all oriented as granular aggregates, collectively defining the gneissic fabric. Quartz locally displays myrmekitic intergrowths with plagioclase, and larger grains represent early quartz vein occurrence. Minor accessory minerals (~2%) include magnetite, pyrite, apatite, and zircon.

The porphyritic dolerite is characterized by ophitic and sub-ophitic textures, and locally amygdaloidal structures (Figure 3h). Phenocrysts consist mainly of plagioclase (~4%; grain size: 0.5 to 1.5 mm), euhedral to subhedral, with argillic alteration and sericitization. The groundmass (~90%, grain size: 0.1 to 0.5 mm) displays the characteristic diabasic texture, composed of tabular plagioclase laths, with interstitial chlorite and epidote derived from pyroxene alteration. Amygdules (~4%; grain size: 0.5 to 5.0 mm) are irregular, filled with chalcedony, calcite, and epidote. Minor accessory minerals (~2%) include magnetite, limonite, and apatite.

3.2. Gold-Bearing Polymetallic Sulfide Ore

The gold-bearing polymetallic sulfide ore comprises pyrite, chalcopyrite, sphalerite, galena, digenite, and native gold (Figure 4). Pyrite occurs predominantly as euhedral to subhedral granular crystals, displaying cubic to pyritohedral forms, with occasional anhedral grains (Figure 4b–d). Grain sizes range from 0.001 to 4.0 mm and are unevenly distributed within the mineralized quartz veins, with an estimated content of ~5%–14%. Most pyrite grains are fractured or fragmented, exhibiting brecciation (Figure 4b–d). Chalcopyrite, galena, and sphalerite commonly replace and enclose pyrite along fractures, forming fine veinlets and networks, indicative of a metasomatic corrosion texture. A few late-stage fine pyrite veinlets (Py II) replace sphalerite, representing post-formation hydrothermal remobilization.

Chalcopyrite (~8%–20%) occurs as anhedral to irregular grains with sizes ranging from 0.001 to 20 mm, and is unevenly distributed within quartz and sulfide veins (Figure 4a,e). It commonly occurs in association with galena and sphalerite and locally appears as fine blebs and intergrowths within sphalerite.

Sphalerite (~40%) also occurs as anhedral to irregular grains with sizes ranging from 0.01 to 20 mm, and is disseminated within sulfide veins. It is commonly intergrown with chalcopyrite. Locally, chalcopyrite occurs as fine inclusions and thin veinlets along grain boundaries of sphalerite, indicating late-stage replacement.

Galena (~10%–18%; grain size: 0.01 to 15 mm) occurs as anhedral granular to irregular crystals, unevenly distributed in the mineralized quartz and metal sulfide veins and often intergrown with chalcopyrite (Figure 4d,f). Star-like and wedge-shaped replacements of chalcopyrite by galena are common, and local fracturing indicates at least two deformation events. Digenite occurs as anhedral granular to irregular crystals, with grain sizes range from 0.01 to 0.3 mm and are mostly intergrown with chalcopyrite. Star-like and wedge-shaped replacements of chalcopyrite by digenite are observed, reflecting post-crystallization metasomatic modification. The mineral occurs in minor amounts within the polymetallic sulfide veins. Native gold (grain size: 0.01 to 0.3 mm) occurs as anhedral granular to irregular crystals (Figure 4c,f–h). It is typically intergrown with chalcopyrite, or hosted within transparent minerals, sphalerite, or fractures in pyrite, occurring in minor amounts within the polymetallic sulfide veins.

4. Analytical Methods and Results

4.1. Analytical Methods

Whole-rock major, trace, and rare earth element compositions were analyzed at the Analytical Laboratory using X-ray fluorescence (XRF) and ICP-based techniques. Major elements were determined by XRF following fusion preparation of powdered samples into glass beads under high-temperature conditions (~1150–1250 °C). Trace and rare earth elements were measured by ICP–OES after acid digestion of powdered samples using HF–HNO₃ in sealed vessels at elevated temperatures (130–185 °C). These analytical procedures ensured complete sample dissolution and high-precision elemental determinations (for detailed methodological descriptions, see Supplementary Text S1).

In situ sulfur isotope compositions of sulfides were determined by LA–MC–ICP–MS at Beijing Kehui Testing Technology Co., Ltd. (Beijing, China) using a 193 nm laser system coupled with a Neptune Plus instrument (Thermo Fisher Scientific Inc., Waltham, MA, USA). Analyses were performed under controlled laser conditions, and isotopic ratios were corrected using matrix-matched standards and standard–sample–standard bracketing.

Hydrogen (δD) and oxygen (δ¹⁸O) isotopes were analyzed using a Thermo Scientific 253 Plus IRMS coupled with a Flash EA elemental analyzer (Thermo Fisher Scientific Inc., Waltham, MA, USA) and Conflo IV interface at Beijing Kehui Testing Technology Co., Ltd. (Beijing, China). Samples were dried at 90 °C, pyrolyzed at 1380 °C, and the released gases were separated and measured under high-purity helium flow, with isotopic compositions calibrated against international standards.

Lead isotopes were measured using a Neptune Plus multi-collector ICP–MS in static mode following chemical purification at Beijing Kehui Testing Technology Co., Ltd. (Beijing, China). Instrumental mass bias was corrected using Tl normalization, and analyses were calibrated against NIST 981 Pb standard [21] with optimized plasma and ion lens settings to ensure high precision.

U–Pb zircon dating and trace/REE analyses were performed by LA–ICP–MS at Createch Testing (Tianjin) Technology Co., Ltd. (Beijing, China). using a 193 nm laser ablation system coupled with an ICP–MS, with He as the carrier gas and Ar as a make-up gas. Data reduction and age calculations were carried out using Iolite 4, with zircon GJ-1 used for external calibration and Plesovice for quality control.

4.2. Results

4.2.1. Whole-Rock Major and Trace Elements

Major Oxides

Samples from both ore and host rocks were analyzed. Geochemical classification of the studied host rocks was carried out using the SiO₂ versus (Na₂O + K₂O) diagram (Figure 5a) proposed by [22]. The Dongwujiiazi host rocks plot within the fields of monzodiorite, monzonite, diorite, quartz monzonite, granodiorite and granite (Figure 5a). The host rocks contain SiO₂ (42.69–73.11 wt.%), K₂O (1.03–8.39 wt.%), Na₂O (0.41–4.92 wt.%), MgO (0.43–5.46 wt.%; except some gneiss samples with 8.72–10.61 wt.%) and CaO (0.22–5.14 wt.%; gneiss: 6.04–8.67 wt.%). MnO and P₂O₅ are 0.21 and 0.44, respectively (

Table 1. Representative major (wt.%) and trace elements (ppm) abundances of host rocks and gold ore of the Dongwujiiazi gold deposit, NE China.

Rock Type	Monzodiorite		Quartz Diorite		Biotite-Pyroxene Gneiss		Fine-Grained Diorite		Diorite		Porphyritic Diorite		Gold Ore
Sample #	DWJ012	DWJ013	DWJ017	DWJ020	DWJ022	DWJ026	DWJ027	DWJ031	DWJ032	DWJ034	DWJ037	DWJ041	DWJ009	DWJ010	DWJ011
SiO2	59.81	60.31	72.43	72.68	54.01	67.72	55.68	56.08	73.11	68.78	66.91	69.6	30.43	60.81	76.83
TiO2	0.6	0.63	0.17	0.18	0.71	0.066	0.95	0.97	0.039	0.047	0.33	0.31	0.048	0.029	0.028
Al2O3	14.85	14.96	12.96	13.02	15.28	9.42	16.95	17.3	13.35	15.48	16.5	15.38	0.97	0.57	0.42
Na2O	3.6	3.36	3.66	3.79	3.21	1.37	4.88	4.92	2.48	2.49	4.5	4.18	0.13	<0.1	<0.1
Fe2O3(t)	8.63	6.99	5.32	5.19	11.01	13.33	8.25	8.19	3.33	3.98	3.15	2.89	43.97	26.29	15.8
MgO	4.92	5.46	1.44	1.41	5.32	3.12	2.49	2.42	0.7	0.61	0.99	0.43	1.53	0.76	0.63
MnO	<0.02	<0.02	<0.02	<0.02	<0.02	0.21	<0.02	0.088	<0.02	<0.02	<0.02	0.025	<0.02	<0.02	<0.02
CaO	4.06	4.2	0.43	0.35	4.32	2.82	3.27	2.82	0.54	0.42	2.06	1.88	0.5	0.43	0.69
K2O	2.51	2.59	3.34	2.81	3.01	1.03	3.98	3.37	6.23	8.01	3.96	3.7	0.2	0.18	0.13
P2O5	0.17	0.19	0.058	0.063	0.29	0.18	0.38	0.41	0.033	0.024	0.14	0.12	0.034	0.017	0.024
LOI	0.83	1.31	0.24	0.53	2.84	0.75	3.17	3.44	0.21	0.23	1.5	1.48	22.22	10.92	5.37
Total	99.98	100.00	100.05	100.02	100.00	100.02	100.00	100.01	100.02	100.07	100.04	100.00	100.032	100.006	99.922
Li	29.9	36.2	31.3	32.7	21	9.85	8	26.9	1.55	1.86	19.8	25.3	1.55	3.14	<1.0
Cs	2.29	2.58	2.84	2.75	2.06	2.06	1.98	0.88	11.2	0.42	0.86	1.02	0.19	0.2	0.12
Rb	65.4	102	71.6	43	85.8	26.2	26.7	69.1	256	224	107	106	<10	<10	<10
Be	1.75	1.87	2.37	3.59	1.74	0.58	<0.5	1.41	3.9	0.73	2.18	2.13	<0.5	<0.5	<0.5
Ba	626	773	784	904	1022	299	285	1242	346	1926	1098	1196	64.1	97	51.4
Th	8.14	8.85	15.5	8.74	<2.0	9.67	7.75	3.17	<2.0	<2.0	6.02	5.9	<2.0	<2.0	<2.0
U	1.69	1.92	2.5	1.26	0.2	0.41	0.4	0.52	0.67	<0.1	0.75	1.07	<0.1	0.16	<0.1
Nb	5.35	6.1	6.74	5.66	8.62	2.26	2.27	7.84	6.38	2.14	10.4	10.2	<2.0	<2.0	<2.0
Ta	0.66	0.49	0.75	0.55	0.36	0.23	0.086	0.46	0.62	0.16	0.73	0.68	0.073	<0.05	<0.05
Sn	1.61	1.48	1.52	2.45	1.38	1	1.42	1.42	1.21	<1.0	1.35	1.05	<1.0	1.26	1.11
Pb	12.2	23.4	8.53	3.51	13.5	7.09	6.43	9.9	21	20.2	12.2	15.6	42.8	691	23.8
Sr	549	576	127	65.9	634	229	229	564	190	398	304	312	19.1	14.2	19.4
Zr	127	166	121	77.2	129	55.6	64.9	177	8.02	4.3	194	195	6.99	2.96	3.11
Hf	4.18	4.92	4.62	3.78	4.38	2.16	2.11	5.18	0.6	0.17	5.82	5.82	0.28	0.11	0.13
Tl	0.53	0.64	0.55	0.52	0.45	0.3	0.27	0.57	0.96	0.86	0.4	0.4	<0.1	<0.1	<0.1
Y	12.3	14.3	7.22	4.06	16.5	60.8	59.7	20.2	7.3	2.47	14.8	13.4	2.05	1.81	2.18
La	21	25.8	28	12.5	29.2	33.9	31.9	37.6	11.4	12.6	40.3	39.9	<5.0	<5.0	<5.0
Ce	37.9	51.1	49.8	25.5	65.7	61.4	56.9	64.3	15.8	12.5	60.4	59.2	2.17	1.74	2.46
Pr	5.07	6.02	4.26	1.9	8.56	6.11	5.58	8.4	1.46	0.95	8.29	8.29	0.31	0.23	0.36
Nd	19.6	23.3	13	5.72	35.9	22.1	19.4	33.6	4.47	2.6	28.2	28.6	1.21	0.89	1.47
Sm	3.76	4.58	1.91	0.84	7.1	4.46	4.09	6.19	0.92	0.33	4.33	4.32	0.22	0.16	0.27
Eu	1.14	1.36	0.56	0.5	1.78	0.86	0.8	1.95	0.59	1.64	1.3	1.3	0.085	0.097	0.1
Gd	3.27	3.9	1.84	0.9	5.42	5.46	5.02	5.18	0.9	0.38	3.71	3.55	0.2	0.14	0.22
Tb	0.49	0.56	0.22	0.14	0.74	1.36	1.15	0.77	0.18	0.027	0.5	0.45	0.066	0.049	0.064
Dy	2.62	3.01	1.2	0.61	3.86	9.04	8.14	4.27	1.13	0.12	2.8	2.55	0.15	0.074	0.18
Ho	0.51	0.57	0.23	0.16	0.69	2.08	1.93	0.82	0.23	0.02	0.55	0.49	0.075	0.066	0.079
Er	1.32	1.57	0.69	0.36	1.88	6.76	7.46	2.33	0.7	0.064	1.68	1.52	0.08	0.049	0.089
Tm	0.21	0.25	0.11	0.062	0.27	1.31	1.18	0.35	0.13	<0.02	0.28	0.26	<0.02	<0.02	<0.02
Yb	1.27	1.47	0.75	0.42	1.59	9.46	8.59	2.26	0.83	0.043	1.87	1.72	0.072	0.04	0.081
Lu	0.19	0.24	0.13	0.062	0.25	1.52	1.38	0.34	0.14	0.034	0.32	0.29	<0.016	<0.016	<0.016
Sc	15.8	16.2	3.72	2.41	17.5	15.8	18.1	13.6	1.14	1.31	3.96	4.12	3.14	<1.0	<1.0
V	91.3	120	31.5	28.2	174	47.7	48.5	141	13.3	13.6	36.3	28.6	18.9	16.1	14.9
Cr	229	247	45.7	55.3	310	103	<5.0	<5.0	11.3	6.81	<5.0	<5.0	<5.0	<5.0	<5.0
Co	21.2	23.9	6.94	9.89	31.5	19.7	20.2	15.7	2.7	2.11	2.87	2.97	202	131	74.8
Ni	109	135	27.9	23.2	102	41.3	43.5	4.64	8.47	3.07	6.72	4.52	57	46.5	146
Cu	40	26.1	59.8	40.1	105	108	115	17.2	4.37	4.8	4.82	5.59	256	8964	1094
Zn	72.2	85.9	59.7	37.5	93.8	41.6	42.1	89.3	<4.0	4.57	52.3	62.8	15.2	282	13.3
Ga	17.4	19.5	16	12	20.7	8.89	9.14	20	14.9	11.8	17.3	17.2	<2.0	<2.0	<2.0
ΣREE	98.35	123.73	102.7	49.67	162.94	165.82	153.52	168.36	38.88	31.32	154.53	152.44	9.69	8.58	10.41
ΣLREE	88.47	112.16	97.53	46.96	148.24	128.83	118.67	152.04	34.64	30.62	142.82	141.61	9	8.12	9.66
ΣHREE	9.88	11.57	5.17	2.71	14.7	36.99	34.85	16.32	4.24	0.7	11.71	10.83	0.69	0.46	0.75
LREE/HREE	8.95	9.69	18.86	17.33	10.08	3.48	3.41	9.31	8.17	43.74	12.196	13.08	13.04	17.65	12.88
LaN/YbN	11.86	12.59	26.78	21.35	13.17	2.57	2.66	11.93	9.85	225.95	15.46	16.64	51.24	89.66	44.83
δEu	0.97	0.96	0.9	1.75	0.84	0.53	0.54	1.02	1.96	14.12	0.97	0.99	1.29	1.99	1.22
δCe	0.87	0.97	1	1.15	1.01	0.97	0.96	0.85	0.81	0.65	0.77	0.76	0.29	0.24	0.32

, Supplementary Table S1). The host rocks are generally fresh, although some samples exhibit alteration, as indicated by low loss on ignition (LOI) values (0.24–3.44 wt.%), with a few samples showing higher values of 5–11.6 wt.% (Table 1, Supplementary Table S1).

Gold ore samples exhibit a high Fe₂O_3(t) content, reaching up to 43.97 wt.% (Table 1). SiO₂ ranges from 30.43 to 76.83 wt.%, while Na₂O (0.13 wt.%), K₂O (0.2 wt.%), MgO (1.53 wt.%), CaO (0.69 wt.%), and MnO (>0.02 wt.%) occur at relatively low concentrations (Table 1). They are characterized by high LOI values, reaching up to 22.22 wt.%, indicating a significant volatile content in the gold ore. This likely reflects intense alteration and/or the presence of hydrous minerals, carbonates, or oxidized sulfides.

Trace and REEs

Barium (Ba), strontium (Sr), and zirconium (Zr) are highly enriched in the Dongwujiiazi host rocks, reaching concentrations of up to 2043, 881, and 200 ppm, respectively (Table 1, Supplementary Table S1). These rocks display moderate total REE contents (ΣREE = 119.39 ppm, on average), characterized by enrichment in LREEs (ΣLREE = 111.26 ppm) relative to HREEs (ΣHREE = 8.13 ppm) (Table 1, Supplementary Table S1). There is a positive correlation between La and Yb (Figure 5b).

Gold ores exhibit elevated copper (Cu) concentrations, reaching up to 8964 ppm. Cobalt (Co) shows moderate enrichment, ranging from 74.8 to 202 ppm, whereas nickel (Ni) is comparatively lower, with values between 46.5 and 146 ppm. The gold ore is very poor in REEs, ranging from 3.55 to 5.37 ppm. LREEs (3.26–4.88 ppm) are enriched relative to HREEs (0.28–0.49 ppm) (Table 1).

Chondrite-normalized REE patterns of the studied host rocks (Figure 6a) show a pronounced LREE-enriched and HREE-depleted trend with gently sloping patterns and positive Eu anomalies. Primitive mantle-normalized trace element patterns indicate enrichment in Pb and depletion in Dy and Yb (Figure 6b). In the gold ore samples (Figure 6c,d), REE and trace element patterns are characterized by LREE and Pb enrichment, with depletion of HREE.

4.2.2. Mineral Chemistry

In Situ Trace and REEs in Zircon

The concentrations of rare earth elements in zircon are presented in Supplementary Table S2. The chondrite-normalized REE patterns of zircon from gold ore (Figure 7) show strong enrichment in HREEs (Tb–Lu) and depletion in LREEs (La–Gd). The patterns display a smooth increase from LREEs to HREEs, with a pronounced positive Ce anomaly and a distinct negative Eu anomaly. The zircon REE pattern is similar to those of crustal zircon [24].

4.2.3. H–O Isotopes

The δD values of the studied quartz samples from the Dongwujiiazi deposit range from −63.9 to −94.6‰, while the calculated δ¹⁸Ofluid values range from approximately 10 to 11.5‰ (

Table 2. H–O isotopes of quartz from Dongwujiiazi gold deposit, NE China.

Sample No.	Name	δDV-SMOW‰	δ18OV-SMOW‰	Temperature	δ18Ofluid‰
DWJ003	Quartz	−65.1	12.49	300	10
DWJ003		−63.9	-	300	-
DWJ004		−94.4	13.43	300	11
DWJ004		−94.6	-	300	-
DWJ005		−70.8	14.08	300	11.5
DWJ005		−71.1	-	300	-
DWJ006		−80.4	12.52	300	10
DWJ006		-	12.26	300	10

Temperature values of orogenic gold deposit are taken from [26].

). The hydrogen isotopic composition of the ore-forming fluids was directly obtained from the host minerals, whereas the oxygen isotopic composition was calculated from quartz, considering the estimated mineralization temperature of 300 °C, as reported by [26]. These isotopic signatures indicate that the ore-forming fluids were predominantly derived from magmatic–metamorphic sources, with minimal contribution from meteoric water.

4.2.4. S Isotopes

The δ³⁴S values of the sulfide minerals from the Dongwujiiazi deposit range from 2.06 to 3.98‰ (

Table 3. Sulfur isotopes of sulfides, Dongwujiiazi deposit.

Sample No.	Sample Name	δ34SV-CDT‰
DWJ003	Sulfides	2.06
DWJ004		2.23
DWJ005		3.89
DWJ005		3.98
DWJ006		2.08
DWJ006		2.07

). These relatively narrow values indicate a homogeneous sulfur source, suggesting that the ore-forming sulfur was primarily derived from the magmatic–metamorphic host rocks rather than from external or sedimentary sources.

4.2.5. Pb Isotopes

The Pb isotopic compositions of gold ore are presented in

Table 4. Lead isotopes of gold ore from Dongwujiiazi gold deposit.

Sample No.	Name	206Pb/204Pb	2σ	207Pb/204Pb	2σ	208Pb/204Pb	2σ
DWJ003	Gold ore	15.9882	0.0004	15.2294	0.0004	36.1892	0.0011
DWJ003		15.9940	0.0004	15.2304	0.0005	36.1942	0.0012
DWJ004		15.7776	0.0003	15.1639	0.0004	35.9297	0.0012
DWJ005		15.6183	0.0003	15.1534	0.0004	35.7950	0.0010
DWJ006		15.6823	0.0004	15.1452	0.0004	35.8193	0.0010
206Pb/204Pb = 16.9412 ± 0.0010 (2SD, n = 46)
207Pb/204Pb = 15.4988 ± 0.0006 (2SD, n = 46)
208Pb/204Pb = 36.7232 ± 0.0017 (2SD, n = 46)

, with ²⁰⁶Pb/²⁰⁴Pb ratios ranging from 15.6183 to 15.9940, ²⁰⁷Pb/²⁰⁴Pb from 15.1452 to 15.2304, and ²⁰⁸Pb/²⁰⁴Pb from 35.7950 to 36.1942. These relatively restricted isotopic ranges suggest a homogeneous lead source.

4.2.6. Zircon U-Pb Age Dating

Measured ²⁰⁷Pb/²³⁵U ratios in zircon range from 5.6743 to 38.7263 (Supplementary Table S3), indicating a wide range of ages, with higher ratios corresponding to older ages. U-Pb zircon dating using the conventional Concordia method yielded four ages corresponding to the upper and lower intercepts, ranging from 2502 ± 15 and 2539 ± 18 Ma (Figure 8). Cathodoluminescence (CL) images of representative zircon grains separated from the gold ore reveal euhedral to subhedral prismatic crystals, typically 80–150 µm in length. Most grains exhibit well-preserved oscillatory zoning, indicative of a magmatic origin, while some domains display homogeneous overgrowths and minor recrystallization features, suggesting localized thermal metamorphism or alteration. A few grains contain inclusions and fractures, predominantly along the rims (Figure 9).

5. Discussion

5.1. Provenance of Zircon in Gold Ore

Zircon is an uncommon accessory mineral in gold ore deposits; however, it provides invaluable insights into the timing and source of ore-forming processes. Its robust crystal structure preserves geochemical and isotopic information, making it ideal for U–Pb age dating [27]. In the studied gold ore from the Dongwujiiazi deposit, zircon crystals were identified. Therefore, to constrain the provenance of zircon, in situ trace element and REE analyses, along with U–Pb dating, were conducted.

As mentioned above, the gold ore occurs within the intrusions (Figure 1 and Figure 2). The North China Craton (NCC) experienced multiple, successive stages of hydrothermal alteration, as indicated by ages of 1720–1703 Ma and approximately 1648 Ma. In contrast, the zircons studied here yield ages of 2502 ± 15 Ma and 2539 ± 18 Ma (Figure 8), which clearly predate the emplacement of the intrusions hosting the gold mineralization. Therefore, these zircons cannot represent the age of the ore-bearing intrusions, but instead reflect inheritance from older crustal sources.

Zircon grains separated from the gold ore are euhedral to subhedral, prismatic, and range from 80 to 150 µm in length. CL imaging shows that most grains possess well-defined oscillatory zoning, characteristic of magmatic crystallization, whereas some domains exhibit homogeneous overgrowths and minor recrystallization, indicating localized thermal metamorphism. Several grains also contain inclusions and fractures, particularly along the rims (Figure 9). Overall, these textures and internal structures suggest that the zircons originated from pre-existing metamorphic rocks, reflecting a crustal inheritance rather than formation contemporaneous with the gold mineralization. The REE distribution in the zircon closely resembles that observed in crustal zircons (Figure 7).

The primary host rocks of the ore are Neoarchean metamorphic rocks, particularly gneiss. Textural and geochemical evidence indicates that zircon grains were derived from the surrounding gneiss and subsequently transported into the ore, suggesting mobilization from the country rock during metamorphic processes rather than in situ formation within the ore.

5.2. H–O Isotopic Evidence for Fluid Origins

Hydrogen and oxygen isotopes are commonly used to trace the sources of ore-forming fluids [28,29,30,31]. In the δD–δ¹⁸O diagram, the ore-forming fluids of the Dongwujiiazi gold deposit plot within both the primary magmatic and metamorphic water fields (Figure 10), indicating contributions from multiple fluid sources. These results reveal that the mineralizing fluids were mixed in origin, reflecting interaction between magmatic and metamorphic components. Field and petrographic investigations (Figure 2 and Figure 3) reveal transitional alteration zones and interactions between altered rocks, including chloritized and sericitized domains, and surrounding granites. These features suggest the possible mixing of magmatic and metamorphic fluids during mineralization, and the transfer of zircon crystals from gneiss to gold ore is strong evidence of this mixing.

5.3. Sulfur and Lead Origins

At temperatures below 350 °C and under reducing conditions, where H₂S dominates, the δ³⁴S values of sulfide minerals reflect the overall sulfur composition of the hydrothermal fluid [33]. Since the Dongwujiiazi deposit is located adjacent to the Xiaotazigou gold deposit, it is likely that the ore-forming fluids experienced similar conditions, forming from reducing, medium–low temperature NaCl–H₂O–CO₂ hydrothermal solutions [2]. Mineralogical observations show that the ores are dominated by pyrite, chalcopyrite, and sphalerite, which typically form under reducing conditions. The absence of sulfate minerals further supports a reduced hydrothermal environment. Accordingly, the average δ³⁴S values of the sulfide minerals can be considered representative of the sulfur isotopic composition of the ore-forming fluid.

The δ³⁴S values of sulfide minerals from the studied gold ores range between 2.06‰ and 3.98‰. These values are comparable to those reported for the Dongpuzi deposit (δ³⁴S = +2.39‰ to +7.99‰; [34]) and fall within the typical range of magmatic sulfur (0‰ ± 3‰; [33]). In contrast, they are significantly lower than the values reported for schist and granulite rocks (+10.0‰ to +17.0‰; [35]). This isotopic signature suggests that sulfur in the studied ores was mainly sourced from a magmatic reservoir, with a minor contribution from metamorphic materials.

The Pb isotopic compositions of the studied sulfides, when plotted on the ²⁰⁶Pb/²⁰⁴Pb versus ²⁰⁷Pb/²⁰⁴Pb diagram, cluster predominantly within the lower crust field. This distribution indicates that the lead was mainly derived from a lower crustal source rather than from the mantle or upper crust. The relatively low Pb isotopic ratios suggest a contribution from evolved U- and Th-depleted crustal materials, which are characteristic of deep crustal reservoirs. Such signatures are commonly associated with ancient, high-grade metamorphic rocks, which are biotite-pyroxene gneiss that host mineralization in the study area (Figure 11).

5.4. Tectonic Setting of the Dongwujiiazi Deposit

Ref. [2] identified the Xiaotazigou gold deposit, located in close proximity to the present study area, as an orogenic gold system developed in an intracontinental orogenic setting following the collision between the North China Craton and the Siberian Plate. This close spatial and tectonic relationship suggests that the studied mineralization was likely formed under similar geodynamic conditions and may share a comparable genetic origin.

On the Ta/Yb versus Th/Yb diagram, the Dongwujiiazi host rocks plot within the field of active continental margins (Figure 12a), while the (Yb + Ta)–Rb and Yb–Ta diagrams show their affinity to volcanic arc granites (Figure 12b,c), collectively suggesting that the host rocks were emplaced in an active continental margin setting and formed through arc-related magmatism.

The La/Sm versus Ba/Th diagram (Figure 13a) shows that the studied samples follow two trends related to slab dehydration and sediment melting, indicating the involvement of both slab-derived fluids and partial melting of subducted oceanic sediments in magma generation. In addition, the Nb/Zr versus Th/Zr diagram (Figure 13b) reveals a trend of fluid metasomatism, suggesting that metasomatic fluids played an important role in modifying the mantle source. Furthermore, the positive correlation between La and Yb (Figure 5b) reflects coupled enrichment of LREEs and HREEs, consistent with magma evolution involving mixed mantle and crustal/sedimentary contributions. These combined features indicate interaction between mantle-derived melts and crustal/sedimentary components, and collectively support a subduction-related tectonic setting, consistent with formation in an active continental margin and an intracontinental orogenic environment.

5.5. Metallogenic Model

The formation of the Dongwujiiazi gold deposit can be interpreted within a subduction-related tectonic setting involving fluid generation, migration, and gold precipitation (Figure 14). During subduction, dehydration of the oceanic slab and associated sediments released H₂O- and CO₂-rich fluids into the overlying mantle wedge, leading to metasomatism and partial melting. These processes generated magmas enriched in volatile components and metals, including Au, S, and Pb. Simultaneously, high-grade metamorphism within the lower crust, particularly in gneissic rocks, produced additional metamorphic fluids through dehydration reactions. These fluids interacted with the ascending magmas, altering their composition and enhancing metal enrichment, as supported by Pb and H–O isotopic signatures indicating a lower crustal source with mixed magmatic–metamorphic characteristics.

The ore-forming fluids subsequently migrated upward along deep-seated faults and shear zones, driven by tectonic deformation and thermal gradients. During ascent, interaction between magmatic and metamorphic fluids led to fluid mixing and chemical evolution, and some zircon crystals were transported from gneiss into the ore fluid. Gold precipitation occurred in structurally controlled zones within the upper crust, particularly in fractured and altered gneissic host rocks, where changes in temperature, pressure, and fluid composition led to mineral deposition. Overall, this model (Figure 14) highlights a coupled system involving slab-derived processes, lower crustal fluid generation, and upward fluid transport, consistent with an intracontinental orogenic gold system formed in an active continental margin setting.

6. Conclusions

• The Dongwujiiazi deposit represents a structurally controlled orogenic gold system, hosted mainly in biotite-pyroxene gneiss.
• Five types of intrusions were identified in the deoposit: mylonitized granitic pegmatite, mylonitized porphyritic monzogranite, propylitized fine-grained quartz monzodiorite, quartz monzonite, and porphyritic dolerite.
• The ore consists of polymetallic sulfides including pyrite, chalcopyrite, sphalerite, galena, digenite, and native gold.
• Zircon grains in the gold ore are inherited from surrounding Neoarchean gneiss, with age of 2502 ± 15 to 2539 ± 18 Ma.
• Isotopic data (H–O, S, Pb) indicate that ore-forming fluids were derived from a mixture of magmatic and lower-crustal metamorphic sources.
• A metallogenic model is proposed in which slab-derived and lower-crustal fluids interacted with ascending magmas, resulting in fluid mixing and gold precipitation along structurally controlled zones, consistent with formation as an intracontinental orogenic gold system in an active continental margin.
• This study refines previous metallogenic models for orogenic gold systems by demonstrating that gold mineralization in the Dongwujiiazi deposit is not solely metamorphic- or magmatic-driven, but results from a hybrid system involving interaction between slab-derived fluids, lower crustal metamorphic components, and ascending magmas. This integrated interpretation provides a more complete understanding of gold precipitation processes in active continental margin settings.