Geochronology of the Magmatic Rocks in the Duobaoshan Porphyry Cu-Mo Deposit in the Great Xing’an Range: Implication for the Metallogenic Epochs and Related Geodynamics

Abstract

The Duobaoshan porphyry copper–molybdenum deposit is located in the Great Xing’an Range, eastern segment of the Xing-Meng orogenic belt. It is the largest porphyry Cu-Mo deposit in NE China. Based on the contact relations of intrusive rocks and the results of LA-ICP-MS zircon U-Pb ages, we found that there were five stages of magmatism in the mining area, including the Early Ordovician (478.1 ± 3.2 Ma) granodiorite, the Middle Ordovician (462.1 ± 3.3 Ma, 459.5 ± 2.3 Ma) granodiorite porphyry, the Late Triassic (226.3 ± 0.4 Ma) oligoclase granite, the Middle Jurassic (170.1 ± 5.6 Ma) andesitic porphyrite, and the Early Cretaceous (118.1 ± 6.6 Ma) diorite. The Early and Middle Ordovician granodiorite and granodiorite porphyry are the principal host rocks for the mineralization in the deposit. However, Cu-Mo mineralization was also observed within the Late Triassic oligoclase granite, indicating that there are two stages of Cu-Mo mineralization in the Duobaoshan deposit. Combined with the previously reported Late Triassic skarn Cu mineralization occurring in the Xiaoduobaoshan deposit, and the Early Jurassic skarn Cu mineralization in the Sankuanggou and Yubaoshan deposits, we conclude that there are four metallogenetic stages in the Duobaoshan ore-concentration area. Regionally, there are five stages of Cu-Mo mineralization occurring in the northern Great Xing’an Range, including the Ordovician, Late Triassic, Early Jurassic, Late Jurassic, and Early Cretaceous. After discussing the tectonic setting for the generation of these deposits, we propose that the Duobaoshan ore-concentration area was influenced by the subduction of the Paleo-Asian Ocean, Mongol-Okhotsk, and Paleo-Pacific Plates during the Phanerozoic.

1. Introduction

The northern Great Xing’an Range is an accretionary continental margin on the southeastern margin of the Siberian Plate and structurally belongs to the joint of the Paleo-Asian Ocean metallogenic domain, the Okhotsk Ocean metallogenic domain and the Paleo-Pacific metallogenic domain. Porphyry deposits are the prominent deposit type found in this area (Figure 1, Table 1), and they are dominated by porphyry copper–molybdenum deposit, such as the Duobaoshan–Tongshan and the Wunugetushan large-scale copper–molybdenum deposits as well as the Badaguan and the Taipingchan small- and medium-scale copper–molybdenum deposits, followed by porphyry molybdenum deposits, such as the Chalukou super-large-scale molybdenum deposit and the Yili medium-scale molybdenum deposit. The Duobaoshan–Tongshan deposit with predicted copper resources of 10 million tons [1], proved copper resources of 3.35 million tons and molybdenum resources of 0.15 million tons [2], the Wunugetushan porphyry copper–molybdenum deposit with proved copper resources of 1.16 million tons and molybdenum resources of 0.362 million tons [3], and the Chalukou molybdenum deposit with proved molybdenum resources of 1.34 million tons [4] reveal that the study area presents appreciating metallogenetic potential and is expected to become an important non-ferrous metal base in China [5].

The Duobaoshan deposit is a prominent super-large porphyry copper–molybdenum deposit in the northeastern segment of the Xing-Meng orogenic belt, 150 km to the north of Nenjiang County, Northeast China [10]. Its geographical coordinates are 49°40′00″~50°40′00″ N and 125°30′00″~127°00′00″ E. For a long time, the metallogenetic geological background of the Duobaoshan mining area has been debated as the ages of the Paleozoic and Mesozoic geological intrusions vary between 175~521 Ma. Most scholars considered that the crystallization age and metallogenic epoch of the Duobaoshan copper–molybdenum deposit was the Late Paleozoic [11,12,13], while some scholars believed that it was the Early Paleozoic [7,14,15,16,17]. In terms of geodynamic background, some scholars argued that it was formed under a subduction-related arc environment during the Early Ordovician [17,18]. The Duobaoshan and Tongshan mining areas were under the post-collisional environment of the Erguna and Xing’an Blocks in the Early Ordovician [19,20], and the post-collisional extensional environment of the Xing’an and Songnen Blocks [21].

Table 1. Geochronology of the porphyry Cu and Mo deposits in the Great Xing′an Range, NE China.

No	Deposits	Geographic Location	Commodity	Host Igneous Rock Zircon U-Pb Age (Ma)	Mineralization Age (Ma)	References
1	Calukou	51°10′ N, 123°52′ E	Mo	Quartz porphyry (152.15.6 ± 0.47)	146.9 ± 0.8 (Molybdenite Re-Os)	[4]
2	Daheishan	51°08′ N, 123°52′ E	Mo	Granodiorite (147 ± 1)		[22]
3	Xiaokele	51°38′ N, 124°30′ E	Cu	Granodiorite porphyry (149.6 ± 1.0)		[23]
4	Guzhonggonglu	50°52′ N, 124°30′ E	Mo	Admellite (146.3 ± 2.5)	142.3 ± 2.0 (Molybdenite Re-Os)	[24]
5	Huoluotai	51°50′ N, 122°24′ E	Cu	Granodiorite (144.33 ± 0.81)		[25]
6	Yili	49°58′ N, 125°32′ E	Mo	Syengranite (132.43 ± 0.61)	131.8 ± 1.5 (Molybdenite Re-Os)	[26]
7	Taipingchuan	51°28′ N, 120°27′ E	Cu-Mo	Granodiorite porphyry (202 ± 5.7)	203 (Molybdenite Re-Os)	[27]
8	Badaguan	49°58′ N, 119°08′ E	Cu-Mo	Granodiorite porphyry (230.6 ± 2.8)	228.7 ± 3.1 (Molybdenite Re-Os)	[28]
9	Wunugetushan	49°25′ N, 117°17′ E	Cu-Mo	Monzogranite porphyry (178.2 ± 9.2)	179 (Molybdenite Re-Os)	[29]
10	XinZhangfang	50°39′ N, 120°45′ E	Mo		134 ± 2.0 (Molybdenite Re-Os)	[30]
11	Ershiyizhan	52°53′ N, 124°55′ E	Cu	Granodiorite porphyry (127 ± 2)		[31]
12	Binnan	50°47′ N, 126°31′ E	Mo	Admellite (155 ± 1.5)		[32]
13	Duobaoshan	50°14′ N, 125°25′ E	Cu	Granodiorite (478.1 ± 4.1), Granodite porphyry (474.8 ± 4.7)	475.1 ± 5.1 (Molybdenite Re-Os)	[17]
14	Tongshan	50°14′ N, 125°49′ E	Cu	Tonalite (461 ± 1)		[33]
15	Taipinggou	49°18′ N, 118°10′ E	Mo	Granite porphyry (131.5 ± 1.1)	129.4 ± 3.9 (Molybdenite Re-Os)	[34]
16	Xing’an	50°40′ N, 123°32′ E	Cu-Mo	Admellite porphyry (129 ± 1.0)		[35]
17	Xiaoduobaoshan	50°14′ N, 125°25′ E	Cu	Granodiorite (232.8 ± 1.7), Granite porphyry (226.6 ± 1.7)		[36]
18	Sankuanggou	50°15′ N, 125°24′ E	Cu-Fe	Granodiorite (175.9 ± 1.1)		[37]
19	YeZhuGou	49°48′ N, 125°52′ E	Mo	Granite porphyry (175 ± 1.3)		This study

Table 1. Geochronology of the porphyry Cu and Mo deposits in the Great Xing′an Range, NE China.

No	Deposits	Geographic Location	Commodity	Host Igneous Rock Zircon U-Pb Age (Ma)	Mineralization Age (Ma)	References
1	Calukou	51°10′ N, 123°52′ E	Mo	Quartz porphyry (152.15.6 ± 0.47)	146.9 ± 0.8 (Molybdenite Re-Os)	[4]
2	Daheishan	51°08′ N, 123°52′ E	Mo	Granodiorite (147 ± 1)		[22]
3	Xiaokele	51°38′ N, 124°30′ E	Cu	Granodiorite porphyry (149.6 ± 1.0)		[23]
4	Guzhonggonglu	50°52′ N, 124°30′ E	Mo	Admellite (146.3 ± 2.5)	142.3 ± 2.0 (Molybdenite Re-Os)	[24]
5	Huoluotai	51°50′ N, 122°24′ E	Cu	Granodiorite (144.33 ± 0.81)		[25]
6	Yili	49°58′ N, 125°32′ E	Mo	Syengranite (132.43 ± 0.61)	131.8 ± 1.5 (Molybdenite Re-Os)	[26]
7	Taipingchuan	51°28′ N, 120°27′ E	Cu-Mo	Granodiorite porphyry (202 ± 5.7)	203 (Molybdenite Re-Os)	[27]
8	Badaguan	49°58′ N, 119°08′ E	Cu-Mo	Granodiorite porphyry (230.6 ± 2.8)	228.7 ± 3.1 (Molybdenite Re-Os)	[28]
9	Wunugetushan	49°25′ N, 117°17′ E	Cu-Mo	Monzogranite porphyry (178.2 ± 9.2)	179 (Molybdenite Re-Os)	[29]
10	XinZhangfang	50°39′ N, 120°45′ E	Mo		134 ± 2.0 (Molybdenite Re-Os)	[30]
11	Ershiyizhan	52°53′ N, 124°55′ E	Cu	Granodiorite porphyry (127 ± 2)		[31]
12	Binnan	50°47′ N, 126°31′ E	Mo	Admellite (155 ± 1.5)		[32]
13	Duobaoshan	50°14′ N, 125°25′ E	Cu	Granodiorite (478.1 ± 4.1), Granodite porphyry (474.8 ± 4.7)	475.1 ± 5.1 (Molybdenite Re-Os)	[17]
14	Tongshan	50°14′ N, 125°49′ E	Cu	Tonalite (461 ± 1)		[33]
15	Taipinggou	49°18′ N, 118°10′ E	Mo	Granite porphyry (131.5 ± 1.1)	129.4 ± 3.9 (Molybdenite Re-Os)	[34]
16	Xing’an	50°40′ N, 123°32′ E	Cu-Mo	Admellite porphyry (129 ± 1.0)		[35]
17	Xiaoduobaoshan	50°14′ N, 125°25′ E	Cu	Granodiorite (232.8 ± 1.7), Granite porphyry (226.6 ± 1.7)		[36]
18	Sankuanggou	50°15′ N, 125°24′ E	Cu-Fe	Granodiorite (175.9 ± 1.1)		[37]
19	YeZhuGou	49°48′ N, 125°52′ E	Mo	Granite porphyry (175 ± 1.3)		This study

In light of the above discrepancies, we performed LA-ICP-MS zircon U-Pb dating on the intrusive rock masses in the Duobaoshan mining area with an aim of establishing the geological and geodynamic setting which led to the generation of such a high-grade non-ferrous ore-concentration area in the Great Xing’an Range, Northeast China. Our study has significantly contributed to the existing gaps in the research about the metallogenetic and geological back ground of the Duobaoshan porphyry copper–molybdenum deposit and other such types of deposit in the Great Xing’an Range. In this study, the Late Jurassic and Early Cretaceous rock masses are discovered for the first time, and new mineralization stages which occurred during the Middle Ordovician and Late Triassic were also identified.

2. Regional Geology

A large number of non-ferrous metal deposits such as Au, Ag, Cu and Mo metal deposits are discovered in the northern Great Xing’an Range in the Xing-Meng orogenic belt. According to the statistics, more than 10 super-large deposits, including Ouyu Tolgoi deposit and more than 30 large deposits, are discovered in Mongolia, Russia and the other neighboring areas of China [30], indicating that there is great prospecting potential in the Greater Khingan Range in the eastern segment of the Xing-Meng orogenic belt.

The Duobaoshan mining area in Nenjiang County, Heilongjiang Province, a famous ore-concentration area in the Northeast China, is also the focus for geological prospecting and metallogenic research. The outcrops in the Duobaoshan area consist of the formations which formed during the Ordovician, Silurian, Devonian, and Cretaceous. The Ordovician strata are composed of the lower andesites interbedded with acid volcanic rocks and upper siltstone and sericite slate. The Silurian strata consist of the siltstone and argillite, interbedded with andesite and dacite. The Devonian strata are composed of fine-grained sandstone and greywacke. The Early Cretaceous formations consist mainly of volcanic rocks, including lower andesite, andesitic tuff, and upper dacite, dacitic and rhyolitic tuff.

Caledonian, Variscan, and large-scale Indosinian and Yanshanian magmatism occurred in the Duobaoshan ore-concentrated area. The magmatic activity related to mineralization is mainly the granodiorite and granodiorite porphyry magmatism during the Caledonian Ordovician, followed by granitite magmatism which occurred during the Indosinian Triassic and Yanshanian Jurassic.

The Duobaoshan ore-concentrated area is located in the NW-trending arc tectonic belt which is held by the NNE trending Nenjiang fault and the NE trending Xinkailing fault. The two faults control the tectono-magmatic–hydrothermal activity and distribution of the strata (Figure 2).

There are four large- and medium-sized deposits including the Duobaoshan Cu-Mo, Tongshan Cu, Zhengguang Au and Erdaokan Ag deposits, as well as some smaller ore deposits, including the Sankuanggou and Xiaoduobaoshan deposits. These deposits are either porphyry-, epithermal- or skarn-type. The Duobaoshan porphyry copper–molybdenum deposit is a typical representative in the ore-concentrated area which shows very complex metallogenic mechanisms of multi-stage tectono-magmatic superimposition.

3. Ore Deposit Geology

3.1. Strata

The outcropped strata in the Duobaoshan deposit include the Ordovician and Silurian formations. Significantly, mineralization is observed in the Lower Ordovician Duobaoshan Formation where Cu content is obviously higher than that in the crust. Therefore, previous studies proposed that the Duobaoshan Formation is an important source layer for the Cu mineralization [2,11].

3.2. Structure

The prominent structure in the area is the Duobaoshan inverted anticline, and the deposit is located in the southwestern flank of the Duobaoshan inverted anticline near the core. Faulting is observed to be extensive before and after mineralization. Before mineralization, the NW-trending structures are dominated followed by NE-trending structures. These structures show multi-phased and inheritance characteristics in the mining area [38]. The orebodies are mainly controlled by the NW-trending structures and are arranged as an echelon shape (Figure 3), so they mostly represent lenticular, strip-like and vein-like shapes due to the reformation of the NW trending ductile shear zones. A number of NW-trending ductile shear zones penetrate the ore-bearing porphyry and Duobaoshan Formation. As a result, the ore-bearing granodiorite (porphyry) and Duobaoshan strata are divided into several lenses. Copper mineralization is intensive in the local ductile deformation area, forming a copper-rich ore body.

3.3. Intrusive Rocks

The mining area records five magmatic intrusive phases, characterized by the emplacement of Early Ordovician granodiorite, Middle Ordovician granodiorite porphyry, Late Triassic oligoclase granite and hornblendite pegmatite, Middle Jurassic andesitic porphyrite, and Early Cretaceous diorite. The contacts between these intrusive masses are distinct (Figure 4).

3.3.1. Syn-Metallogenic Intrusive Rocks

The Early Ordovician granodiorite and the Middle Ordovician granodiorite porphyry are the two dominant ore-bearing rocks in the mining area, followed by the Late Triassic and oligoclase granite.

Granodiorite is stock-like, occurring as NW- and SE-trending apophyses. It shows a southwest trend, with a dip angle of 60° and an area of about 8 km². It expands downwards and intrudes into the andesite of Lower Ordovician Duobaoshan Formation (Figure 5). Granodiorite is grayish white and light gray, showing dominantly hypautomorphic granular texture, followed by porphyritic granitic texture and massive structure. The minerals are dominated by plagioclase, quartz, striped plagioclase and biotite, followed by zircon, apatite, arpidelite and magnetite. The rocks have undergone intense chalcopyrite mineralization, molybdenite mineralization, pyritization, silicification, sericitization, potassic mineralization, epidotization and carbonation.

Two lenticular granodiorite porphyry rock masses with respective areas of 0.08 km² and 0.09 km² intruded into granodiorite [11]. They show a dip angle of 65–75° with northwest strike. These rocks are grayish white in color, with porphyritic texture and porphyry content of 25–30%. The matrix shows microscopic granitic structure while the microcrystals are dominated by quartz, followed by perthite and biotite. The rock is composed of plagioclase, quartz, potash feldspar, biotite mineral and a small amount of secondary minerals, such as magnetite and apatite. Phenocryst quartz consists of hexagonal cone-shaped particles with sizes of 0.5–0.8 cm. Quartz, feldspar and dark minerals exhibit shear (elongated) deformation. The rock has undergone chalcopyrite mineralization, pyrite mineralization, silicification, sericitization, epidotization and carbonation. The distribution of orebodies is closely related to the distribution of granodiorite and granodiorite porphyry.

The oligoclase granite rock with an area of about 0.05 km², tendency of northeast and dip angle of 70–80° intrudes into the Duobaoshan andesite. In this rock, weakly disseminated pyritization, sericitization, silicification and epidotization are common. Particularly, minor molybdenum mineralization and chalcopyrite mineralization can be observed in deep strata, with minor vein type pyrite mineralization and chalcopyrite mineralization. The rock is light yellow in color and mainly composed of quartz, oligoclase, plagioclase and dark minerals, such as hornblende and biotite.

3.3.2. Post-Metallogenic Intrusive Rocks

The intrusive rocks of post-metallogenic epoch include the Late Triassic hornblenolite pegmatite, Middle Jurassic andesite porphyrite and Early Cretaceous diorite. These rock masses cut and destroy orebodies and are the products of tectonic–magmatic activities of post-metallogenic epoch.

Hornblende pegmatite occurs as apophyse, with a width of 2–5 m and intrudes into oligoclase granite. The contact boundary is steep, with a dip angle of 80–85° northwest. The rock is composed of plagioclase (20%) and hornblende (80%), and hornblende is long columnar, with a width of 1–1.5 cm. Sericitization, epidotization and chloritization are common.

The andesite porphyrite also occurs as apophyse and intrudes as a vein into the andesite of Duobaoshan Formation. The vein is steep, with a width of 1.5 m. Epidotization and carbonation are observed as common alteration phenomena, with minor sericitization.

The diorite veins with a widths of about 2 m intrudes into oligoclase granites. This rock is fresh and fine-grained. The contact interface is steep, with a inclining of northwest and a dip angle of 55–65.

3.4. Mineralization and Alternation Characteristics

The Duobaoshan deposit consists of four ore bodies with different sizes and forms [11]. The lenticular, plate and banded orebodies are mainly distributed in the granodiorite and granodiorite porphyry. Some orebodies are distributed in the andesite of Duobaoshan Formation. Mineralized bodies can be identified in oligoclase granite. The mineralization degree gradually increases along a certain direction.

Orebodies mainly occur in sericitization zone. The ores have three types, namely dotted disseminated type, fine vein disseminated type and fine vein type. The flat and annular ore body surrounds granodiorite porphyry body, within a distance of 0~500 m. Copper mineralization is the most intensive and uniform within the distance of 50–150 m away from porphyry body [11]. Ore minerals are dominated by chalcopyrite, pyrite, bornite and molybdenite (Figure 6), showing a certain zonation. Bornite, chalcopyrite and pyrite occur from the center to the margin [39]. Gangue minerals include quartz, plagioclase and potassium feldspar.

The surrounding rocks of the mining area show multiple-phased alteration, and the rocks in the mining area are also intensively altered and show various alternation. The alteration minerals are dominated by potassium feldspar, sericite, epidote, chlorite and calcite. Alteration minerals shows some homogeneous distribution characteristics and mainly occur in granodiorite, granodiorite porphyry and surrounding fissures and micro-fissures. From the inner side to the outer side, the silica-potassic zone, sericitization zone and propylitization zone can be observed, among which, the sericitization zone is the most common [1].

4. Sampling and Analytical Technique

4.1. Sampling and Petrography

In order to accurately determine the crystallization age of the rocks in the mining area, the zircon samples from the rocks related to the mineralization and the intrusive deposits of late stage from the mining area were collected in order to conduct LA-ICP-MS zircon U-Pb dating. The samples for zircon dating were all collected from No. III pit, and the specific sampling location is shown in Figure 4. Before choosing the samples, the intrusive relationships among different geological bodies was clarified.

Sample No. DBS02 (granodiorite) is mainly composed of plagioclase, quartz, biotite and potassium feldspar. Plagioclase crystals are mostly automorphic–hypautomorphic columnar, with a size of 0.5~4 mm. Some plagioclase shows polycrystalline twin crystals with a content of 65%. Potassium feldspar is xenomorphic granular, with a particle size of 0.2–1 mm and a content of 15%; quartz is xenomorphic granular, with a particle size of 0.1–0.5 mm and a content of 15%. Biotite is flaky, with a diameter of 0.1–0.4 mm and a content of 5% (Figure 7a).

Sample No. DBS07 and DBS08 (granodiorite porphyries) show porphyritic texture and massive structure. The rock is mainly composed of plagioclase and quartz. Phenocryst consists of automorphic columnar plagioclase with particle size of 1–4 mm and a content of 55%. Xenomorphic granular quartz shows a particle size of 3–10 mm, with 25% content. Matrix consists of plagioclase, potassic feldspar and quartz, with a content of 20% (Figure 7b).

Sample No. DBS01 (oligoclase granite) displays granitic texture and massive structure. The rock is composed of plagioclase, quartz, potassium feldspar and a small amount of muscovite. Plagioclase is mostly hypautomorphic columnar, with a particle size of 0.5–3 mm and a content of 50%. Potassium feldspar is xenomorphic granular and is distributed in the interstitial spaces of plagioclase, with a particle size of 0.5–1.5 mm and a content of 20%. Quartz is mostly xenomorphic granular, with a particle size of 0.3–1.5 mm and a content of 25%. The muscovite is flaky and well crystallized, with a diameter of 0.3–2 mm and mostly found as secondary mineral altered from biotite (Figure 7c), but minor primary muscovite is also witnessed.

Sample No. DBS04 (hornblende pegmatite) shows granular texture and massive structure. Hornblende is mostly hypautomorphic columnar and granular, with particle size of 1–4 mm and a content of 80%. Xenomorphic granular plagioclase is distributed in the interstitial spaces of hornblende, with a particle size of 1~3 mm and a content of 20% (Figure 7d).

Sample No. DBS39 is composed of andesitic porphyrite which intrudes into the andesite of Duobaoshan Formation in a form of vein. It has porphyry texture and massive structure. Phenocryst is dominated by columnar plagioclase, with a content of 15%. Matrix is cryptocrystalline (Figure 7e).

Sample No. DBS05 is composed of diorite. It is dominated by plagioclase and hornblende, with granular texture and massive structure. Plagioclase is mostly automorphic–hypautomorphic granular, with a particle size of 0.1~0.6 mm and a content of 85%. Hornblende is mostly hypautomorphic–automorphic granular, with a particle size of 0.05–0.1 mm and a content of 15% (Figure 7f).

4.2. Analytical Technique

Zircon U-Pb isotope dating was performed using LA-ICP-MS technique in Shangpu Analyse Science and Technology Co., Ltd., Wuhan, China. The laser ablation system was GeoLas 2005 (Coherent, Germany) with an ICP-MS Agilent 7700e (Agilent Technologies, Santa Clara, CA, USA). In laser ablation process, helium was used as a carrier gas while argon was used as a compensation gas to adjust the sensitivity. The two were mixed by a T-joint before entering into the ICP. The laser ablation system was equipped with a signal smoothing device. The laser pulse frequency was kept as low as 1 Hz to achieve an analytical signal [40]. The resolved and analyzed data at each time interval include a blank signal of approximately 20–30 s, and a sample signal of 50 s. The off-line processing of analytical data (including selection of the samples and blank signals, instrument sensitivity drift correction, elemental content and U-Th-Pb isotope ratio and age calculation) was performed using the ICPMS DataCal software (V11.8, Developed by the research group of Liu Yongsheng, China University of Geosciences (Wuhan, China)) [41,42].

Zircon standard 91500 was used as the external standard for isotope fractionation calibration during U-Pb isotope dating. When each five sample points were analyzed, zircon standard 91500 was analyzed twice. The U-Th-Pb isotope ratio drift associated with the analysis time was corrected by linear interpolation using the variation in zircon standard 91500 [42]. The recommendation value of U-Th-Pb isotope ratio for zircon standard 91500 was referred to in the results of [43]. The U-Pb age concordia plots and average weighted mean age calculations for the zircon samples were performed using Isoplot/Ex_ver 3.6 [44].

5. Results

Granite diorite (DBS02): Zircon crystals are mostly automorphic–hypautomorphic short columnar with minor columnar and rounded morphologies having a particle size of 60–160 μm and an aspect ratio of 1:1 to 3: 1, with obvious oscillatory zoning (Figure 8a). The narrow annular shaped zircons are of magmatic origin with Th/U ratio ranging from 0.30 to 0.50 (

Table 2. LA-ICP-MS zircon U-Pb analytical data of the Duobaoshan Cu deposit.

Analysis Point	Composition (10−6)		Th/U	Isotopic Ratios						Age (Ma)
	Th	U		207Pb/206Pb	1σ	207Pb/235U	1σ	206Pb/238U	1σ	206Pb/238U	1σ	207Pb/206Pb	1σ
Granodiorite
DBS02-01	47.5	138	0.3	0.0572	0.0019	0.6237	0.0209	0.0791	0.0008	490.5	4.7	501.9	69.4
DBS02-02	90.6	217	0.4	0.0562	0.0015	0.5842	0.0160	0.0753	0.0007	467.8	4.0	457.5	59.3
DBS02-03	168	271	0.6	0.0554	0.0015	0.5806	0.0151	0.0760	0.0006	472.3	3.6	427.8	61.1
DBS02-04	51.2	154	0.3	0.0563	0.0019	0.5988	0.0189	0.0774	0.0008	480.8	4.7	461.2	106.5
DBS02-05	71.0	184	0.4	0.0577	0.0017	0.6043	0.0167	0.0763	0.0008	474.2	5.0	520.4	65.6
DBS02-06	86.0	177	0.5	0.0573	0.0015	0.6215	0.0161	0.0788	0.0009	489.1	5.6	501.9	55.6
DBS02-07	87.2	194	0.5	0.0602	0.0020	0.6453	0.0200	0.0781	0.0007	484.6	4.1	609.3	70.4
DBS02-08	44.2	133	0.3	0.0598	0.0020	0.6310	0.0209	0.0765	0.0006	475.5	3.8	598.2	104.6
DBS02-09	47.1	136	0.3	0.0597	0.0019	0.6356	0.0201	0.0773	0.0008	479.8	4.6	590.8	69.3
DBS02-10	106	199	0.5	0.0607	0.0018	0.6257	0.0184	0.0748	0.0008	465.0	4.7	627.8	63.7
DBS02-11	72.4	175	0.4	0.0584	0.0021	0.6023	0.0215	0.0748	0.0008	465.0	4.8	546.3	77.8
DBS02-12	31.2	105	0.3	0.0563	0.0021	0.6065	0.0235	0.0785	0.0010	487.2	6.1	461.2	85.2
DBS02-13	27.0	90.5	0.3	0.0528	0.0020	0.5642	0.0212	0.0774	0.0009	480.5	5.1	320.4	85.2
DBS02-14	58.3	135	0.4	0.0565	0.0020	0.5982	0.0205	0.0770	0.0007	478.4	4.4	472.3	77.8
DBS02-15	74.4	144	0.5	0.0574	0.0019	0.5970	0.0191	0.0755	0.0007	469.3	4.2	505.6	78.7
DBS02-16	78.0	153	0.5	0.0562	0.0018	0.5979	0.0199	0.0770	0.0007	478.4	4.3	457.5	70.4
DBS02-17	58.9	159	0.4	0.0570	0.0016	0.6097	0.0166	0.0776	0.0007	481.8	4.3	500.0	63.0
DBS02-18	123	235	0.5	0.0566	0.0015	0.5867	0.0154	0.0752	0.0007	467.2	4.3	476.0	91.7
DBS02-19	58.9	158	0.4	0.0590	0.0019	0.6235	0.0192	0.0766	0.0008	475.9	4.5	568.6	68.5
DBS02-20	39.5	118	0.3	0.0567	0.0022	0.6096	0.0219	0.0786	0.0008	487.5	5.1	479.7	85.2
DBS02-21	37.6	115	0.3	0.0600	0.0024	0.6379	0.0229	0.0777	0.0008	482.3	5.0	611.1	85.2
DBS02-22	51.8	139	0.4	0.0585	0.0020	0.6284	0.0209	0.0782	0.0008	485.2	4.5	550.0	77.8
DBS02-23	34.7	105	0.3	0.0581	0.0024	0.6155	0.0247	0.0772	0.0008	479.3	4.9	600.0	97.2
DBS02-24	52.6	152	0.3	0.0567	0.0019	0.6141	0.0214	0.0783	0.0008	485.8	4.8	479.7	41.7
DBS02-25	41.1	122	0.3	0.0585	0.0021	0.6366	0.0220	0.0790	0.0008	490.2	4.7	550.0	80.5
Granodiorite porphyry
DBS07-01	86.1	219	0.4	0.0571	0.0015	0.5850	0.0155	0.0744	0.0007	462.4	4.0	498.2	57.4
DBS07-02	58.0	157	0.4	0.0571	0.0020	0.5804	0.0196	0.0739	0.0007	459.9	4.1	494.5	77.8
DBS07-03	94.9	237	0.4	0.0576	0.0016	0.5779	0.0155	0.0731	0.0006	454.6	3.9	516.7	63.0
DBS07-04	68.5	171	0.4	0.0598	0.0019	0.6179	0.0192	0.0752	0.0008	467.3	4.9	594.5	70.4
DBS07-05	63.3	169	0.4	0.0538	0.0018	0.5438	0.0173	0.0737	0.0007	458.6	4.2	361.2	74.1
DBS07-06	85.3	198	0.4	0.0568	0.0018	0.5855	0.0181	0.0752	0.0008	467.7	4.8	483.4	72.2
DBS07-07	113	224	0.5	0.0558	0.0015	0.5622	0.0155	0.0732	0.0008	455.5	4.9	455.6	61.1
DBS07-08	60.7	166	0.4	0.0557	0.0017	0.5666	0.0165	0.0740	0.0007	460.1	4.4	442.6	64.8
DBS07-09	76.2	185	0.4	0.0561	0.0017	0.5604	0.0160	0.0726	0.0006	451.6	3.8	457.5	64.8
DBS07-10	40.2	132	0.3	0.0586	0.0021	0.5885	0.0201	0.0731	0.0006	454.6	3.8	553.7	79.6
DBS07-11	110	223	0.5	0.0562	0.0015	0.5790	0.0147	0.0747	0.0007	464.1	4.2	461.2	26.9
DBS07-12	70.4	184	0.4	0.0556	0.0017	0.5717	0.0167	0.0745	0.0006	462.9	3.7	438.9	68.5
DBS07-13	56.5	133	0.4	0.0569	0.0019	0.5813	0.0193	0.0741	0.0007	460.9	4.0	487.1	76.8
DBS07-14	114	218	0.5	0.0555	0.0016	0.5617	0.0167	0.0733	0.0006	456.0	3.8	431.5	64.8
DBS07-15	68.8	161	0.4	0.0562	0.0019	0.5809	0.0193	0.0752	0.0007	467.3	4.4	461.2	108.3
DBS07-16	115	220	0.5	0.0553	0.0016	0.5544	0.0164	0.0726	0.0007	451.7	4.0	433.4	60.2
DBS07-17	91.7	219	0.4	0.0584	0.0017	0.5910	0.0164	0.0736	0.0007	457.9	4.2	542.6	63.0
DBS07-18	90.2	177	0.5	0.0579	0.0017	0.6002	0.0180	0.0749	0.0006	465.5	3.8	527.8	63.0
DBS07-19	60.1	159	0.4	0.0583	0.0020	0.5892	0.0192	0.0735	0.0006	457.3	3.6	538.9	74.1
DBS07-20	77.4	222	0.3	0.0572	0.0017	0.5841	0.0164	0.0743	0.0008	461.7	4.6	498.2	63.0
DBS08-01	87.7	200	0.4	0.0579	0.0017	0.5985	0.0162	0.0752	0.0007	467.3	4.5	527.8	64.8
DBS08-02	53.7	157	0.3	0.0599	0.0016	0.6393	0.0178	0.0771	0.0007	478.9	4.4	611.1	57.4
DBS08-03	122	240	0.5	0.0574	0.0016	0.5847	0.0165	0.0736	0.0006	457.6	3.4	509.3	56.5
DBS08-04	57.6	168	0.3	0.0627	0.0021	0.6396	0.0196	0.0743	0.0007	461.7	4.4	698.2	70.4
DBS08-05	121	237	0.5	0.0589	0.0019	0.5906	0.0192	0.0725	0.0007	451.4	4.0	564.9	65.7
DBS08-06	71.4	174	0.4	0.0551	0.0017	0.5497	0.0170	0.0722	0.0006	449.2	3.8	416.7	70.4
DBS08-07	46.8	124	0.4	0.0560	0.0022	0.5850	0.0230	0.0758	0.0008	470.7	4.8	450.0	119.4
DBS08-08	70.3	165	0.4	0.0569	0.0018	0.5869	0.0183	0.0746	0.0007	463.9	4.3	487.1	75.0
DBS08-09	32.8	102	0.3	0.0582	0.0022	0.5883	0.0223	0.0733	0.0008	455.7	4.8	538.9	83.3
DBS08-10	67.7	186	0.4	0.0595	0.0018	0.6186	0.0183	0.0753	0.0008	468.1	4.9	587.1	64.8
DBS08-11	32.4	101	0.3	0.0594	0.0021	0.6272	0.0210	0.0769	0.0008	477.5	5.0	588.9	75.9
DBS08-12	117	242	0.5	0.0564	0.0015	0.5715	0.0154	0.0734	0.0006	456.3	3.9	477.8	59.3
DBS08-13	49.3	147	0.3	0.0610	0.0021	0.6108	0.0198	0.0728	0.0007	452.9	4.1	640.5	78.7
DBS08-14	92.8	198	0.5	0.0574	0.0017	0.5809	0.0170	0.0733	0.0006	456.3	3.6	505.6	64.8
DBS08-15	55.7	129	0.4	0.0578	0.0020	0.6125	0.0214	0.0768	0.0008	477.0	4.6	524.1	71.3
DBS08-16	60.6	179	0.3	0.0545	0.0015	0.5643	0.0150	0.0749	0.0007	465.9	4.0	394.5	61.1
DBS08-17	136	256	0.5	0.0553	0.0014	0.5619	0.0141	0.0736	0.0005	458.1	3.2	433.4	59.3
DBS08-18	144	228	0.6	0.0554	0.0014	0.5577	0.0139	0.0730	0.0006	453.9	3.5	427.8	59.3
DBS08-19	63.1	157	0.4	0.0551	0.0019	0.5835	0.0203	0.0766	0.0008	475.5	4.7	416.7	80.5
DBS08-20	93.3	196	0.5	0.0560	0.0019	0.6011	0.0188	0.0780	0.0008	483.9	4.6	453.8	69.4
DBS08-21	141	258	0.5	0.0541	0.0015	0.5418	0.0148	0.0724	0.0006	450.9	3.8	376.0	58.3
DBS08-22	179	287	0.6	0.0569	0.0014	0.5917	0.0145	0.0753	0.0006	467.9	3.8	487.1	53.7
DBS08-23	118	188	0.6	0.0518	0.0018	0.5354	0.0185	0.0751	0.0007	466.9	4.2	276.0	81.5
DBS08-24	199	267	0.7	0.0561	0.0015	0.6045	0.0164	0.0781	0.0010	484.8	5.7	457.5	59.3
DBS08-25	72.7	176	0.4	0.0564	0.0016	0.5613	0.0162	0.0721	0.0007	448.9	4.0	464.9	32.4
Oligoclase granite
DBS01-01	67.7	98.5	0.7	0.0555	0.0035	0.2608	0.0157	0.0342	0.0005	217.1	2.9	431.5	140.7
DBS01-02	112	142	0.8	0.0526	0.0028	0.2536	0.0132	0.0355	0.0005	224.7	2.8	309.3	122.2
DBS01-03	55.4	78.5	0.7	0.0525	0.0034	0.2656	0.0161	0.0371	0.0006	235.0	3.6	309.3	148.1
DBS01-04	65.6	110	0.6	0.0557	0.0027	0.2674	0.0130	0.0349	0.0004	221.1	2.8	442.6	109.2
DBS01-05	118	145	0.8	0.0560	0.0028	0.2704	0.0130	0.0353	0.0004	223.4	2.4	450.0	111.1
DBS01-06	125	152	0.8	0.0533	0.0025	0.2647	0.0128	0.0362	0.0005	229.1	2.9	342.7	112.0
DBS01-07	109	156	0.7	0.0504	0.0026	0.2478	0.0120	0.0362	0.0005	229.4	3.0	213.0	120.4
DBS01-08	94.2	136	0.7	0.0560	0.0027	0.2737	0.0135	0.0356	0.0005	225.4	2.9	453.8	113.9
DBS01-09	75.0	122	0.6	0.0527	0.0025	0.2595	0.0118	0.0359	0.0004	227.1	2.7	322.3	102.8
DBS01-10	77.5	122	0.6	0.0508	0.0028	0.2449	0.0124	0.0350	0.0004	222.0	2.4	235.3	134.2
DBS01-11	239	248	1.0	0.0512	0.0019	0.2596	0.0098	0.0367	0.0004	232.2	2.5	250.1	83.3
DBS01-12	80.6	117	0.7	0.0559	0.0035	0.2627	0.0168	0.0344	0.0005	218.0	2.9	450.0	138.9
DBS01-13	107	139	0.8	0.0503	0.0025	0.2461	0.0121	0.0356	0.0004	225.6	2.7	209.3	110.2
DBS01-14	93.2	121	0.8	0.0515	0.0026	0.2495	0.0134	0.0349	0.0004	221.1	2.5	264.9	116.7
DBS01-15	100.0	147	0.7	0.0524	0.0024	0.2606	0.0119	0.0361	0.0004	228.4	2.8	301.9	137.9
DBS01-16	64.5	106	0.6	0.0535	0.0026	0.2729	0.0128	0.0371	0.0005	235.0	3.1	350.1	109.2
DBS01-17	80.0	119	0.7	0.0531	0.0028	0.2629	0.0125	0.0363	0.0005	230.0	2.9	344.5	118.5
DBS01-18	96.6	135	0.7	0.0546	0.0026	0.2695	0.0121	0.0361	0.0004	228.7	2.7	394.5	105.5
DBS01-19	89.6	116	0.8	0.0503	0.0034	0.2430	0.0162	0.0353	0.0004	223.7	2.8	209.3	155.5
DBS01-20	88.3	145	0.6	0.0509	0.0026	0.2611	0.0131	0.0373	0.0004	235.8	2.5	235.3	113.9
DBS01-21	107	153	0.7	0.0554	0.0023	0.2833	0.0113	0.0373	0.0004	236.2	2.7	427.8	94.4
DBS01-22	266	242	1.1	0.0521	0.0022	0.2494	0.0100	0.0349	0.0003	220.9	2.1	287.1	99.1
DBS01-23	128	149	0.9	0.0550	0.0024	0.2639	0.0118	0.0349	0.0004	221.2	2.6	409.3	98.1
DBS01-24	50.1	89.3	0.6	0.0513	0.0033	0.2526	0.0155	0.0357	0.0005	226.1	3.0	253.8	151.8
DBS01-25	74.5	139	0.5	0.0503	0.0026	0.2494	0.0125	0.0364	0.0005	230.5	3.1	209.3	122.2
Amphibole pegmatite
DBS04-01	311	259	1.2	0.0529	0.0020	0.2507	0.0092	0.0345	0.0003	218.4	2.1	324.1	85.2
DBS04-02	143	185	0.8	0.0538	0.0022	0.2617	0.0107	0.0354	0.0004	224.4	2.8	361.2	94.4
DBS04-03	355	357	1.0	0.0553	0.0020	0.2700	0.0088	0.0356	0.0004	225.5	2.4	433.4	79.6
DBS04-04	407	336	1.2	0.0534	0.0019	0.2564	0.0091	0.0348	0.0003	220.4	1.9	346.4	84.3
DBS04-05	600	372	1.6	0.0520	0.0018	0.2515	0.0083	0.0352	0.0004	222.7	2.4	287.1	79.6
DBS04-06	227	235	1.0	0.0508	0.0021	0.2493	0.0107	0.0355	0.0004	224.7	2.4	227.8	96.3
DBS04-07	558	484	1.2	0.0495	0.0014	0.2459	0.0067	0.0361	0.0003	228.6	1.9	172.3	68.5
DBS04-08	341	293	1.2	0.0510	0.0017	0.2479	0.0081	0.0353	0.0004	223.5	2.2	239.0	77.8
DBS04-09	213	230	0.9	0.0531	0.0020	0.2512	0.0092	0.0345	0.0004	218.7	2.4	331.5	87.0
DBS04-10	401	265	1.5	0.0500	0.0018	0.2454	0.0081	0.0358	0.0004	226.5	2.3	194.5	81.5
DBS04-11	469	431	1.1	0.0502	0.0015	0.2491	0.0071	0.0359	0.0003	227.6	1.9	205.6	36.1
DBS04-12	314	252	1.2	0.0525	0.0018	0.2554	0.0085	0.0353	0.0003	223.8	2.0	305.6	75.0
DBS04-13	468	302	1.6	0.0501	0.0018	0.2413	0.0085	0.0350	0.0003	221.8	1.8	198.2	78.7
DBS04-14	829	650	1.3	0.0495	0.0014	0.2429	0.0069	0.0355	0.0003	225.0	1.8	172.3	64.8
DBS04-15	1014	647	1.6	0.0502	0.0013	0.2402	0.0060	0.0347	0.0003	220.0	1.7	211.2	61.1
DBS04-16	499	455	1.1	0.0537	0.0017	0.2540	0.0076	0.0344	0.0003	217.9	1.9	366.7	73.1
DBS04-17	312	305	1.0	0.0504	0.0017	0.2390	0.0078	0.0344	0.0004	218.1	2.3	213.0	43.5
DBS04-18	184	243	0.8	0.0530	0.0021	0.2614	0.0097	0.0359	0.0004	227.6	2.3	327.8	88.9
DBS04-19	425	358	1.2	0.0510	0.0016	0.2525	0.0079	0.0358	0.0003	227.0	2.0	239.0	72.2
DBS04-20	159	192	0.8	0.0503	0.0021	0.2531	0.0106	0.0366	0.0004	231.7	2.5	209.3	98.1
DBS04-21	336	289	1.2	0.0476	0.0017	0.2300	0.0081	0.0352	0.0004	223.1	2.5	79.7	85.2
DBS04-22	222	268	0.8	0.0461	0.0015	0.2273	0.0073	0.0358	0.0003	226.6	2.1	400.1	−320
DBS04-23	425	342	1.2	0.0497	0.0015	0.2502	0.0077	0.0365	0.0003	231.0	2.1	189.0	70.4
DBS04-24	178	194	0.9	0.0481	0.0020	0.2357	0.0101	0.0355	0.0004	224.9	2.7	105.6	−94.4
DBS04-25	307	263	1.2	0.0495	0.0019	0.2482	0.0088	0.0366	0.0003	231.6	2.2	168.6	87.0
Andesitic porphyrite
DBS39-03	82.4	93.5	0.9	0.0588	0.0061	0.1985	0.0160	0.0265	0.0007	168.7	4.3	566.7	225.0
DBS39-06	454	431	1.1	0.0540	0.0029	0.1937	0.0101	0.0259	0.0004	165.0	2.2	368.6	115.7
DBS39-07	156	152	1.0	0.0533	0.0043	0.1930	0.0128	0.0266	0.0005	169.4	3.3	342.7	186.1
DBS39-08	4378	1616	2.7	0.0476	0.0032	0.1653	0.0111	0.0254	0.0003	161.5	2.0	79.7	151.8
DBS39-09	291	318	0.9	0.0543	0.0047	0.1903	0.0136	0.0260	0.0004	165.5	2.7	383.4	194.4
DBS39-10	415	474	0.9	0.0470	0.0024	0.1847	0.0095	0.0282	0.0004	179.5	2.3	50.1	118.5
DBS39-11	427	360	1.2	0.0527	0.0031	0.2293	0.0140	0.0314	0.0008	199.6	5.2	316.7	126.8
DBS39-12	254	248	1.0	0.0478	0.0034	0.1897	0.0137	0.0287	0.0006	182.4	3.7	100.1	153.7
DBS39-13	116	368	0.3	0.0521	0.0022	0.4706	0.0201	0.0651	0.0009	406.3	5.2	300.1	96.3
DBS39-14	114	141	0.8	0.0526	0.0044	0.2017	0.0146	0.0284	0.0005	180.3	3.3	309.3	195.3
DBS39-15	166	192	0.9	0.0517	0.0045	0.1966	0.0150	0.0279	0.0006	177.4	3.5	272.3	198.1
DBS39-16	203	204	1.0	0.0551	0.0041	0.2004	0.0148	0.0266	0.0004	169.0	2.7	416.7	168.5
DBS39-17	58.3	106	0.5	0.0575	0.0036	0.5765	0.0340	0.0733	0.0013	455.9	7.6	509.3	135.2
DBS39-18	430	175	2.5	0.0540	0.0038	0.2436	0.0157	0.0335	0.0006	212.6	3.8	372.3	159.2
DBS39-19	132	252	0.5	0.0511	0.0033	0.2144	0.0131	0.0306	0.0004	194.3	2.7	255.6	143.5
DBS39-20	1221	670	1.8	0.0535	0.0022	0.2447	0.0102	0.0331	0.0004	209.7	2.8	350.1	90.7
DBS39-21	168	384	0.4	0.0772	0.0020	1.9348	0.0506	0.1807	0.0017	1070	9.1	1127	56.5
DBS39-22	5.48	31.6	0.2	0.0799	0.0050	1.7331	0.1038	0.1599	0.0028	956.2	15	2062	118.5
Diorite
DBS05-01	25.2	75.0	0.3	0.0563	0.0040	0.5533	0.0354	0.0722	0.0012	449.6	7.3	464.9	159.2
DBS05-02	437	776	0.6	0.0534	0.0017	0.2330	0.0076	0.0314	0.0003	199.4	2.0	342.7	39.8
DBS05-03	48.8	141	0.3	0.0534	0.0026	0.5599	0.0271	0.0765	0.0012	475.3	7.1	346.4	109.3
DBS05-04	61.2	103	0.6	0.0481	0.0041	0.2209	0.0160	0.0340	0.0006	215.7	3.7	101.9	198.1
DBS05-05	94.7	169	0.6	0.0560	0.0032	0.4214	0.0236	0.0546	0.0006	343.0	3.8	450.0	125.9
DBS05-06	53.2	111	0.5	0.0588	0.0030	0.6030	0.0298	0.0757	0.0011	470.6	6.4	566.7	111.1
DBS05-07	193	356	0.5	0.0546	0.0019	0.5753	0.0192	0.0768	0.0010	477.2	5.9	398.2	75.9
DBS05-08	97.2	106	0.9	0.0511	0.0056	0.1342	0.0117	0.0203	0.0006	129.2	3.5	255.6	224.1
DBS05-09	190	528	0.4	0.0693	0.0016	1.4804	0.0358	0.1574	0.0015	927.4	8.2	909.3	47.1
DBS05-10	26.1	88.0	0.3	0.0535	0.0030	0.5522	0.0295	0.0753	0.0011	468.0	6.8	350.1	125.9
DBS05-11	78.1	179	0.4	0.0568	0.0023	0.5556	0.0231	0.0710	0.0009	442.1	5.5	483.4	90.7
DBS05-12	48.2	130	0.4	0.0599	0.0033	0.6228	0.0333	0.0763	0.0010	473.9	6.2	611.1	117.4
DBS05-13	198	350	0.6	0.0537	0.0019	0.5222	0.0181	0.0703	0.0007	437.8	4.2	361.2	77.8
DBS05-14	348	272	1.3	0.0479	0.0039	0.1143	0.0085	0.0176	0.0003	112.7	1.9	100.1	172.2
DBS05-15	78.3	176	0.4	0.0554	0.0024	0.5846	0.0258	0.0761	0.0009	472.9	5.6	427.8	94.4
DBS05-17	154	232	0.7	0.0582	0.0026	0.4315	0.0190	0.0541	0.0007	339.6	4.5	538.9	96.3
DBS05-18	174	147	1.2	0.0507	0.0053	0.1254	0.0110	0.0190	0.0004	121.5	2.7	233.4	216.6
DBS05-19	311	211	1.5	0.0539	0.0047	0.1363	0.0094	0.0184	0.0004	117.7	2.2	368.6	191.6
DBS05-20	28.6	92.5	0.3	0.0559	0.0035	0.5695	0.0332	0.0747	0.0012	464.2	7.3	455.6	143.5
DBS05-21	87.5	166	0.5	0.0592	0.0028	0.6065	0.0286	0.0742	0.0009	461.5	5.4	576.0	97.2
DBS05-22	95.8	130	0.7	0.0499	0.0045	0.1825	0.0141	0.0268	0.0005	170.4	3.2	190.8	196.3
DBS05-25	129	160	0.8	0.0551	0.0048	0.1375	0.0102	0.0186	0.0004	118.7	2.4	416.7	202.8
DBS05-26	63.9	571	0.1	0.0769	0.0020	1.4727	0.0382	0.1379	0.0012	832.5	7.0	1116	51.4

) [45]. A total of 25 spots were analyzed. The calculated ages are in a narrow range with high degree of concordance. The ²⁰⁶Pb/²³⁸U age varies between 465 and 491 Ma, with a weighted mean of 478.1 ± 3.2 Ma and MSWD of 2.9 (Figure 9a), which represent the formation age of the granodiorite crystals.

Granodiorite porphyry (DBS07): Zircon crystals are mostly automorphic–hypautomorphic short and long columnar, with a particle size of 50–150 μm and an aspect ratio of 2:1–3:1. Oscillating zoning is observed in CL images of the zircon derived from the sample (Figure 8b). The Th/U ratio is from 0.30 to 0.50 (Table 2), showing the characteristics of magmatic zircon. A total of 20 spots were tested which gave concentrated ages with high degree of concordance. The ²⁰⁶Pb/²³⁸U age varies between 452 and 468 Ma, with a weighted mean age of 459.5 ± 2.3 Ma and MSWD of 1.5 (Figure 9b), which reliably represents the crystallization time of the granodiorite porphyry.

Granodiorite porphyry (DBS08): Zircon crystals of this rock are mostly automorphic–hypautomorphic short and long columnar, with particle size of 100~200 μm and an aspect ratio of 2:1 to 3:1. Oscillatory zoning can be observed in CL images (Figure 8c). The Th/U ratio is 0.30~0.50 (Table 2), showing the characteristics of magmatic zircon. A total of 25 spots were tested, which are highly concordant. The ²⁰⁶Pb/²³⁸U ages are concentrated showing a narrow range between 449 and 485 Ma, with a weighted mean age of 462.1 ± 4.3 Ma and MSWD of 6.2 (Figure 9c), which represents the formation age of the granodiorite porphyry.

Oligoclase granite (DBS01): Zircon crystals are observed mostly as automorphic–hypautomorphic long columnar, with a particle size of 40–140 μm and an aspect ratio of 2:1–3:1. Oscillatory zoning can be seen in CL images of the zircon (Figure 8d). The Th/U ratio is 0.50–1.10 (Table 2), showing the characteristics of magmatic zircon. A total of 25 spots were analyzed which yielded concentrated and highly concordant ages. The ²⁰⁶Pb/²³⁸U age varied between 217 and 236 Ma, with a weighted mean age of 226.3 ± 2.3 Ma and MSWD of 4.0 (Figure 9d), which represents the formation age of oligoclase granite.

Hornblende pegmatite (DBS04): Zircons of the Hornblende pegmatite are mostly automorphic long columnar, with a particle size of 60~300 μm and an aspect ratio of 2:1 to 4:1 with very weak or no oscillatory zoning (Figure 8e). The Th/U ratio is 0.80~1.60 (Table 2), indicating that these zircons are magmatic in origin. A total of 25 spots were tested which yielded highly concordant ages. The ²⁰⁶Pb/²³⁸U age varied between 218 and 232 Ma, with a weighted mean age of 224.3 ± 1.7 Ma and MSWD of 3.8 (Figure 9e), which represents the crystallization age of the hornblende pegmatite.

Andesite porphyrite (DBS39): Zircon crystals from this rock are mostly automorphic, short columnar and rounded, with a particle size of 30~70 μm and aspect ratio of 1:1 to 2:1. There is very weak or no oscillatory zoning (Figure 8f). The Th/U ratios are from 0.20 to 2.70 (Table 2), showing the characteristics of magmatic zircon. A total of 18 zircon spots were tested and yielded four population of ages, among which, the highly concordant age suit which varied between 161 and 182 Ma (10 spots), with a weighted mean age of 170.1 ± 5.5 Ma and MSWD of 7.7 (Figure 9f), is considered as the formation age of the andesite porphyrite (Figure 9f). Four zircon grains yielded a population age between 194.3 and 212.6 Ma which might be the captured zircons from the Late Triassic–Early Jurassic granites and their peripheries in the mining area. The third age population which varies between 406.3 and 455.9 Ma represents the sedimentary age of the Ordovician and Devonian sandstone and slate; the fourth age population which varies between 956.2 and 1070.7 Ma indicates the residual zircons, and might represent the crystalline basement.

Diorite (DBS05): The zircon separated from this rock are mostly automorphic–hypautomorphic and short columnar, with minor rounded morphologies. The particle size is 40–90 μm, with an aspect ratio of 1:1–2:1. There is very weak to no oscillatory zoning observed in CL images (Figure 8g). The Th/U ratio ranges from 0.10 to 1.50 (Table 2), showing the characteristics of magmatic zircon. A total of 23 spots were analyzed which yielded five population ages. The age suit ranging between 113 and 129 Ma, with a weighted mean age of 118.1 ± 6.6 Ma and MSWD of 4.8, represents the formation age of diorite rock mass. Five zircon data points show high degree of concordance (Figure 9g,h). The second suit of ages ranging between 170.4~215.7 Ma, which might be the formation age of Late Triassic–Middle Jurassic granite mass in the mining area. The ages of the zoned magmatic zircon grains (third group) range between 339.6 and 343.0 Ma, which might show the formation age of Early Carboniferous granite in the mining area. The age of the fourth group (11 zircon grains) ranges between 437.8 and 477.2 Ma, which likely represents the age of Ordovician–Silurian sedimentary formation in the Duobaoshan ore-concentration area. The age of the fifth group are in between 832.5 and 927.4 Ma, which are considered to reveal the age of the crystalline basement termed as Xinkailing Group.

6. Discussion

6.1. The Crystallization Age and Mineralization Ages of the Duobaoshan Deposit

The Duobaoshan deposit has a large span of diagenetic and metallogenic age, that is, ranging from Paleozoic to Mesozoic time (Table 3), so it is very important to accurately determine the formation time of the deposit.

The dating results of this paper is consistent with the successive intrusive relationship between the observed rock masses. Since the zircon U-Pb system does not reset below the temperature of 800 °C [46], the analytical data accurately reflect the diagenetic age of rock mass. Granodiorite (DBS02) is an ore-bearing rock mass with a diagenetic age of 478.1 ± 3.2 Ma, which is consistent with the results of zircon LA-ICP U–Pb dating (478.1 ± 4.1 Ma) [13] and LA-ICP U–Pb dating (479 ± 2 Ma) [20], and it is also consistent with the molybdenum Re-Os dating results by (475.1 ± 5.1 Ma) [17] and (475.9 ± 7.9 Ma) [47]. The diagenetic and metallogenic age of the Duobaoshan porphyry copper–molybdenum deposit is 475~479 Ma. The metallogenic age is the same or later than the diagenetic age, which is the Early Ordovician.

Table 3. Geochronological ages from the Duobaoshan Cu deposit.

Names of Intrusive Rocks	Test Object	Isotopic Age (Ma)	Test Method	Sources
Paleozoic
Biotite syenite granite	Zircon	483.9 ± 4.5	U-Pb	[17]
Granodiorite		478.1 ± 4.1
Granodiorite porphyry		474.8 ± 4.7
Altered ore-bearing granite		474.4 ± 1.3		[30]
Altered andesite		460.5 ± 3.2
Granodiorite porphyry	Zircon	479.5 ± 4.6		[48]
Granodiorite porphyry		474.9 ± 1.8		[24]
Granodiorite porphyry		485 ± 8		[48]
Granodiorite		479.2 ± 5.2		[36]
Mineral	Molybdenite	475.9 ± 7.9	Re-Os	[19]
		475.1 ± 5.1		[17]
		506 ± 14		[10]
		521 ± 20
		509 ± 5
		507 ± 3
	Chalcopyrite	477.2 ± 3.1, 488.9 ± 4.2		[18]
	Pyrite	482.6 ± 4.3, 487.1 ± 10.3
Andesite	Zircon	493.1 ± 6	U-Pb	Unpublished data
Granodiorite		478.1 ± 3.2		This study
Granodiorite porphyry		462.1 ± 3.3
		459.5 ± 2.3
Mesozoic
Sericitized granodiorite	Sericite	224.69 ± 4.08	K-Ar	[10]
		209.03 ± 3.34
		251.8
		217
		252.5	40Ar/39Ar
		175.4
Altered granite	Sericite	175.4 ± 2.0	40Ar/39Ar	[12]
		172.5 ± 1.8
		183.6 ± 1.9
	Potash feldspar (Sericite)	236.9 ± 2.5
	Sericite	224.5 ± 2.1
	Potash feldspar (Sericite)	178.1 ± 2.5
	Sericite	252.5 ± 1.6
	Biotite (Sericite)	161.7 ± 2.1
	Potash feldspar (Sericite)	222.6 ± 1.6
	Iolite	226.6 ± 1.7
Quartz diorite	Zircon	230.9 ± 2.3	U-Pb	[31]
Oligoclase granite		226.3 ± 0.4		This study
Amphibole pegmatite		224.3 ± 1.7
Andesitic porphyrite		170.1 ± 5.6
Diorite		118.1 ± 6.6

Table 3. Geochronological ages from the Duobaoshan Cu deposit.

Names of Intrusive Rocks	Test Object	Isotopic Age (Ma)	Test Method	Sources
Paleozoic
Biotite syenite granite	Zircon	483.9 ± 4.5	U-Pb	[17]
Granodiorite		478.1 ± 4.1
Granodiorite porphyry		474.8 ± 4.7
Altered ore-bearing granite		474.4 ± 1.3		[30]
Altered andesite		460.5 ± 3.2
Granodiorite porphyry	Zircon	479.5 ± 4.6		[48]
Granodiorite porphyry		474.9 ± 1.8		[24]
Granodiorite porphyry		485 ± 8		[48]
Granodiorite		479.2 ± 5.2		[36]
Mineral	Molybdenite	475.9 ± 7.9	Re-Os	[19]
		475.1 ± 5.1		[17]
		506 ± 14		[10]
		521 ± 20
		509 ± 5
		507 ± 3
	Chalcopyrite	477.2 ± 3.1, 488.9 ± 4.2		[18]
	Pyrite	482.6 ± 4.3, 487.1 ± 10.3
Andesite	Zircon	493.1 ± 6	U-Pb	Unpublished data
Granodiorite		478.1 ± 3.2		This study
Granodiorite porphyry		462.1 ± 3.3
		459.5 ± 2.3
Mesozoic
Sericitized granodiorite	Sericite	224.69 ± 4.08	K-Ar	[10]
		209.03 ± 3.34
		251.8
		217
		252.5	40Ar/39Ar
		175.4
Altered granite	Sericite	175.4 ± 2.0	40Ar/39Ar	[12]
		172.5 ± 1.8
		183.6 ± 1.9
	Potash feldspar (Sericite)	236.9 ± 2.5
	Sericite	224.5 ± 2.1
	Potash feldspar (Sericite)	178.1 ± 2.5
	Sericite	252.5 ± 1.6
	Biotite (Sericite)	161.7 ± 2.1
	Potash feldspar (Sericite)	222.6 ± 1.6
	Iolite	226.6 ± 1.7
Quartz diorite	Zircon	230.9 ± 2.3	U-Pb	[31]
Oligoclase granite		226.3 ± 0.4		This study
Amphibole pegmatite		224.3 ± 1.7
Andesitic porphyrite		170.1 ± 5.6
Diorite		118.1 ± 6.6

Granodiorite porphyry (DBS07, DBS08) intrudes into the granodiorite and is another ore-bearing rock mass in the mining area. The zircon U-Pb age of the two samples DBS07 and DBS08 is 462.1 ± 4.3 Ma and 459.5 ± 2.3 Ma, respectively. The two ages are statistically indistinguishable within analytical error., but they are distinctively different from the zircon U-Pb age obtained by previous studies [17,24,47] (Table 3). Since the contact boundary between granodiorite porphyry and granodiorite is clear, the diagenetic and metallogenic age of granodiorite porphyry should be considered as ~460 Ma. The disseminated and vein hosted types of pyrite and chalcopyrite in the 460 Ma granodiorite porphyry, combined with the absence of captured Early Ordovician granodiorite, reflect that there was a second phase of copper mineralization that occurred in the mining area during the Middle Ordovician.

The zircon U-Pb age of oligoclase granite (DBS01) is 226.3 ± 0.4 Ma (Late Triassic), which is consistent with that of tonalite obtained by [19]. Chalcopyrite was observed in the 225 Ma oligoclase granite (Cu contents ranging from 0.041 to 0.071% in the drill No. ZK6201), indicating another Cu mineralization event in the Duobaoshan area, which was evidenced by the molybdenite Re-Os age (229.4 ± 3.5 Ma) from the Late Triassic porphyritic granite in the Duobaoshan area [19].

The zircon U-Pb age of hornblende pegmatite (DBS04) is 224.3 ± 1.7 Ma, slightly later than the diagenetic age of the oligoclase granite. The andesite porphyrite (DBS39) with zircon U-Pb age of 170.1 ± 5.6 Ma intrudes into the andesite of Duobaoshan Formation. The diorite (DBS05) with zircon U-Pb age of 118.1 ± 6.6 Ma intrudes into oligoclase granite. The rock mass represented by the three samples DBS04, DBS39 and DBS05 does not contain copper–molybdenum mineralization.

The diagenetic ages of the intrusive rocks in the mining area reveal that there are three main metallogenic ages, including the main metallogenic age of Early Ordovician granodiorite copper–molybdenum, the main metallogenic age of Middle Ordovician granodiorite porphyry copper–molybdenum and the main metallogenic age of the Late Triassic oligoclase granite weak copper–molybdenum. The intrusion of Late Triassic hornblenolite pegmatite, Middle Jurassic andesite porphyrite and Early Cretaceous diorite has a destructive effect on the porphyry deposit.

The above-mentioned isotopic age data reflect that the Duobaoshan copper–molybdenum deposit is the product of multi-phased tectonic–magmatic activities. The mineralization began in the Caledonian Early Ordovician time and was superimposed by the magmatism of Middle Ordovician and Late Triassic granite.

Based on the statistics of previous diagenetic and metallogenetic ages, a frequency spectrum map was developed. As shown in Table 3 and Figure 10a, there are three main diagenetic and metallogenic ages, i.e., 485–460 Ma, 236–217 Ma and 183–162 Ma, indicating that the mining area have undergone multi-phased magmatic activities. The time between 183 and 162 Ma was the superposition period of the magmatic–hydrothermal activities [12].

6.2. Metallogenic Epochs of the Porphyry Copper and Molybdenum Deposit in the Northern Greater Khingan Range

The metallogenic epoch of the porphyry copper and molybdenum deposits in the northern Greater Khingan Range lasted from the Early Paleozoic to the Late Yanshanian. The metallogenic epoch and the main metallogenetic element are closely related with metallogenetic tectonic setting.

6.2.1. Ordovician Mineralization

In the northern Greater Khingan Range, only the Duobaoshan and Tongshan copper–molybdenum deposits formed during the Paleozoic. The Duobaoshan deposit is always treated as a representative since it is only 4 km away from the Tongshan deposit, and the two deposits share similar geological background. The zircon U-Pb ages in this study and previously reported isotopic dating listed in Table 3 indicate that the main Cu-Mo mineralization stage in the Duobaoshan area happened during the Early–Middle Ordovician.

6.2.2. Late Triassic Mineralization

The Re-Os isotope weighted mean model age of the molybdenite from the Badaguan porphyry copper–molybdenum deposit in the Erguna Block is 226.7 ± 2.4 Ma [48], while the zircon U-Pb age of granodiorite porphyry is 230.6 ± 2.8 Ma and the Re-Os model age of molybdenite is 228.7 ± 3.1 Ma [28]. The two Re-Os isochron ages of the molybdenite in the Taipingchuan porphyry copper–molybdenum deposit are 202.1 ± 9.4 Ma and 187.8 ± 9.5 Ma [49]. The zircon U-Pb age of ore-forming granodiorite porphyry is 202 ± 5.7 Ma [27]. These data indicate that the crystallization age and mineralization of the Badaguan and Taipingchuan porphyry copper–molybdenum deposit occurred in the Indosinian Late Triassic. In the Duobaoshan mining area, the zircon U-Pb age of the granodiorite related with Xiaoduobaoshan copper deposit is 232.8 ± 1.7 Ma [36], indicating that the Xiaoduobaoshan skarn copper deposit formed in the Indosinian Late Triassic. In recent years, a Late Triassic large-size Au deposit named as Erdaokan was newly discovered with pyrite Rb-Sr age of 232 Ma [35]. The zircon U-Pb age of the Tongshan porphyry granite, which intruded into the Tongshan ore bodies, is 235.4 ± 2.7 Ma and the Re-Os model age of disseminated molybdenite is 229.4 ± 3.5 Ma [36]. Copper–molybdenum mineralization occurs in the Duobaoshan oligoclase granite (225.8 ± 0.4 Ma) and the Tongshan porphyry granite, indicating the Late Triassic copper–molybdenum mineralization is superimposed on the Duobaoshan and Tongshan formed during the Ordovician.

The discovery of the copper–molybdenum deposit in the Erguna and the Xing’an Blocks confirms that mineralization occurred in the northern Greater Khingan Range during the Indosinian Late Triassic.

6.2.3. Early and Late Jurassic Mineralization

The crystallization age of the granodiorite associated with the Sanjiaogou skarn-type copper mineralization in the Duobaoshan deposit is 175.9 ± 1.1 Ma [37]. The crystallization age of the granodiorite associated with the Yubaoshan skarn-type copper deposit is 174.22 ± 1.7 Ma [36], indicating that the diagenetic and metallogenetic age of the Sanjiaogou and Yubaoshan skarn-type copper deposit is the Early Jurassic.

The work of [50] shows that the Re-Os isochron age is 178 ± 10 Ma. The results of [29] show that the Rb-Sr isochron age of the monzonitic granite porphyry is 178.2 ± 9.2 Ma and the Re-Os isochron age of molybdenite is 177.6 ± 1.2 Ma. All the above data indicate that the diagenetic and metallogenetic age of the Wunugetushan deposit is about ~178 Ma. This time is consistent with the metallogenetic epoch (Early Jurassic) of the Sannougou and Yubaoshan copper deposits in the Duobaoshan mining area.

The Chalukou porphyry molybdenum deposit is currently the largest molybdenum deposit in the Northeast China with molybdenite Re-Os ages of 148 ± 1–146.96 ± 0.79 Ma. The Heishan molybdenum deposit that is about 1.7 km away from the Chalukou deposit formed in 147 ± 1 Ma [22]. The Xiaokele porphyry copper deposit that is located near the new Forestry Bureau in the northern Greater Khingan Range was a newly discovered copper deposit in recent years. The zircon LA-ICP-MS age of ore-bearing granodiorite porphyry from the Xiaokele Cu-Mo deposit is 149.6 ± 1.0 Ma, indicating that the metallogenic age of the Xiaokele porphyry copper deposit was the same as that of the Chalukou porphyry molybdenum deposit, which is the Late Jurassic age.

The metallogenetic epochs of the above-mentioned deposits indicate that the Yanshanian Jurassic period was an important metallogenetic period for the porphyry copper–molybdenum deposits in the northern segment of the Greater Khingan Range, where mineralization occurred in the Early and Late Jurassic time.

6.2.4. Cretaceous Mineralization

Wang et al. [34] obtained the isochron age of molybdenum ore in the Taipinggou Mo deposit as 129.4 ± 3.9 Ma. Wu et al. [20] and Zhang et al. [35] yielded the mineralization age of Xing’an as 131~124 Ma. Huang et al. [43] obtained the molybdenite Re-Os age of 131.8 ± 1.5 Ma of the Yuyili Mo deposit, indicating that the metallogenic epoch of the three porphyry deposits were the Early Cretaceous.

In summary, there should be at least five magmatic events (i.e., Early Ordovician, Late Triassic, Early Jurassic, Late Jurassic, Early Cretaceous) in the porphyry copper–molybdenum and molybdenum deposits in the Greater Khingan Range (Figure 10b,c), among which at least three magmatic events contributed to the metallogeny in the Duobaoshan copper–molybdenum deposits, namely the Early Paleozoic Ordovician (480–460 Ma), the Late Triassic (~230 Ma) and the Jurassic (~175 Ma).

6.3. Metallogenic Geodynamic Background

6.3.1. Early Paleozoic Porphyry Copper–Molybdenum Deposits

The metallogenetic rock mass is granodiorite and granodiorite porphyry. The surrounding rocks of Duobaoshan Formation are mainly composed of shore–shallow marine volcanic lava, pyroclastic rocks and clastic volcanic sedimentary rocks, which developed Paleozoic island arc volcanic rocks [10,11,51]. Li (1998) [52] studied the structure of the northeastern region and concluded that the geotectonic location of the rock association is a typical island arc. Based on the work of Ge et al. [19], the Duobaoshan granodiorite is type I granite and belongs to the calc-alkaline series, with w(SiO₂) of about 66%, Na₂O < K₂O and aluminum index (ASI) of 1.04–1.17. It is characterized by high Sr (241 × 10⁻⁶), low Y (10.6 × 10⁻⁶) and Yb (1.07 × 10⁻⁶) contents, high Sr/Y (22.9) and high (La/Yb)_N (8.1) ratios, similar to the characteristics of the host granodiorite of porphyry copper deposit [53,54]. The geochemical data of the calc-alkaline Duobaoshan porphyry [19] is consistent with that of the arc super-large porphyry deposit summarized by Cooke et al. [55].

Summarily, the Duobaoshan porphyry copper–molybdenum deposit was formed in island arc environment during the subduction of the Paleo-Asian Oceanic Plate during the Early Paleozoic (Figure 11a).

6.3.2. Late Triassic Porphyry Copper–Molybdenum Deposits

The Upper Triassic igneous rocks of the Erguna and Xing’an Blocks are dominated by intrusive rocks, while volcanic rocks only occur in the Heihe area of the Xing’an Block. The igneous rocks of this phase consist of basic or intermediate acidic rocks which are dominated by granitic rocks, including syenogranite, monzonitic granite, granodiorite, quartz diorite, with minor gabbro diorite, diorite, trachybasalt and andesite. This rock association is similar to that occurs in active continental marginal environment [56]. The major element data show that the Upper Triassic igneous rocks of the Erguna and Xing’an Blocks belong to the high-K calc-alkaline series. The existence of calc-alkaline rock association can be used as an effective marker to determine the occurrence of paleo-subduction [57]. The granitic rocks of this phase have the characteristics of type I granite, since they do not contain aluminum-rich secondary minerals nor alkaline dark minerals.

The Late Triassic tonalite (oligoclase granite) rock mass in the Duobaoshan mining area is characterized by high calcium and sodium contents, with aluminum saturation index of less than 1.1. It does not contain garnet, cordierite or other aluminum minerals, suggesting that it is weakly peraluminous and high-k calc-alkaline type I granite. The rocks are enriched in light rare earth elements, large ion lithophile elements (Rb, Ba, K) and incompatible elements (U, Th), but depleted in high-field-strength elements (Nb, Ta and Ti), showing that they have the geochemical characteristics of island arc magma. In terms of trace element content and ratio, they have adakite properties [36]. The Badaguan porphyry copper–molybdenum deposit on the Erguna Block formed in the active continental marginal environment when Okhotsk Plate subducted southward [19,28]. The Duobaoshan tonalite and the granodiorite of the Badaguan porphyry copper–molybdenum deposit have similar geochemical characteristics [19]. Moreover, they have consistent formation ages, indicating that they were formed in the same tectonic setting which was the subduction environment of the Mongolian–Okhotsk Ocean [58,59,60,61] (Figure 11b).

6.3.3. Early Jurassic Porphyry Copper–Molybdenum Deposits

The Mongolian–Okhotsk Ocean closed like a scissor from the west to east [58,62,63]. The closure of the east part might have lasted from the Late Jurassic to Early Cretaceous [64,65]. In the Early Jurassic, Mongolia–Okhotsk Ocean Plate continued its southward subduction to the Erguna–Xing’an Blocks [57]. The Early Jurassic igneous rocks are dominated by intermediate-acid intrusive rocks, including diorite, monzonitic, syenogranite, quartz porphyry and granite porphyry. They are enriched in light rare earth elements and large ion lithophile elements (such as Ba, Rb, K, etc.), but depleted in heavy rare earths and high-field-strength elements, such as Nb, Ta, P and Ti. They have similar geochemical characteristics with the igneous rocks formed in active continental marginal environments [66,67,68,69,70]. The geochemical data of the Sankuanggou Early Jurassic granodiorite show that the major elements show the characteristics of sodium-rich, quasi-aluminum and high-potassium–calcium–alkaline rock series, indicating that they have the geochemical characteristics of type I granite formed in the active continental marginal setting [36].

In summary, the Early Jurassic porphyry deposit and skarn deposit in the Erguna–Xing’an Blocks formed in an active continental marginal setting in response to the orogenetic mineralization of Mongolia–Okhotsk (Figure 11c).

6.3.4. Late Jurassic Porphyry Copper–Molybdenum Deposits

The Late Jurassic magmatism in the northeastern region only occurred in the Erguna and Xing’an Blocks. The northeastern continental margin (including the eastern part of the Northeast, the Russian Far East, and Japan and the Korean peninsula) lacks a magmatic event, indicating that the formation of Late Jurassic igneous rocks in the Erguna and Xing’an Block is not related to the Pacific Rim tectonic system [71,72,73]. The northern Greater Khingan Range has been in a post-collision and extensional environment during the Middle Jurassic–Late Jurassic [59,74]. The post-collisional environment usually forms in the background of regional extensional tectonic setting after collisional orogeny, accompanied with the formation of strike-slip and extensional structures, so large-scale magmatism and mineralization tend to occur [75,76]. The Late Jurassic igneous rock assemblage in the Greater Khingan Range includes A-type granite and alkaline intermediate-basic volcanic rocks that formed in extensional environment [48,77]. In response to the closure of the Mongolian–Okhotsk Ocean in the Middle Jurassic, the northern Greater Khingan Range is in extensional environment after collisional orogeny in the Late Jurassic [72,78,79]. The Late Jurassic magmatism should occur in the lithospheric extensional environment caused by the collapse and detachment of thickened continental crust after the closure of Mongolian–Okhotsk Ocean [80]. Therefore, the extensional environment of the Greater Khingan Range formed due to the magmatism during the Late Jurassic should be consistent with that formed after the closure of the Mongolian–Okhotsk Ocean.

The zircon U-Pb age of granite associated with the Binnan molybdenum deposit is 155 ± 1.5 Ma, the zircon U-Pb age of the granodiorite porphyry of the Xiaokele copper deposit is 149.6 ± 1.0 Ma, and the Re-Os age of the molybdenite of the Lulukou porphyry molybdenum deposit is 146.9 ± 0.8 Ma. These deposits were formed in the Late Jurassic, while the Late Jurassic granitic rocks associated with mineralization were formed in the post-collisional extensional environment of the Mongolia–Okhotsk orogenic belt [23,32,81].

In summary, the crystallization age and mineralization of the northern Greater Khingan Range occurred in extensional orogenic setting after the closure of the Mongolia–Okhotsk Plate in the Late Jurassic (Figure 11d).

6.3.5. Early Cretaceous Porphyry Molybdenum Deposits

During the Middle-Late Jurassic, Mongolia–Okhotsk Ocean was closed [78,82,83,84]. During the Early Cretaceous, the Greater Khingan Range was in extensional setting after the closure of the Mongolia–Okhotsk Ocean [57]. The thickened crust of the Mongolia–Okhotsk tectonic belt began to detach after collisional orogeny. Intensive extensional activities occurred in the Northeast Asia, forming a large amount of the Cretaceous magmatic rocks [85]. Shao et al. [86] believed that the Early Cretaceous granite-volcanic activities evolved in extensional setting in the Greater Khingan Range. Zhang et al. [87] considered the Early Cretaceous volcanic rocks of calc-alkaline formed at extensional stage after the westward subduction of the East Pacific after studying the geochemical characteristics and Sr−Nd−Pb−Hf isotope. Sun (2016) [88] believed that the magmatism of the Greater Khingan Range magmatic belt mainly occurred between 162 and 125 Ma. The continental margin had continental arcs and occurred post-arc extension during the Early Cretaceous. The spatial distribution characteristics were related to the subduction of the Paleo-Pacific Plate. Hou et al. [89] studied the seismic reflection profile and concluded that the tectonic evolution of the Greater Khingan Range was obviously affected by the subduction of the Mongolia–Okhotsk Ocean and the Paleo-Pacific Plate.

The Late Jurassic-Early Cretaceous was an important peak period for molybdenum mineralization in the middle and northern segment of the Greater Khingan Range [81,90,91]. Jiang et al. [92] believed that the mineralization related to the evolution of the Mongolian–Okhotsk Ocean occurred from 240 Ma to 110 Ma. The main peak period was from 180 to 120 Ma, with the minor peak of 150–130 Ma. For example, the mineralization age of the Guzhonggonglu molybdenum deposit (142.3 ± 2.0 Ma), Taipinggou molybdenum deposit (129.4 ± 3.9 Ma), Xinzhangfang molybdenum deposit (134 ± 2.0 Ma), Xing’an molybdenum deposit (129 Ma), Yili molybdenum deposit (131.8 ± 1.5 Ma) was between 143 and 129 Ma, which was the Early Cretaceous. In response to the detachment of the thickened continental crust, the Guzhonggonglu molybdenum deposit formed under the extensional tectonic setting of the Mongolia–Okhotsk orogenic belt [24]. The Taipinggou molybdenum deposit was related to the post-arc extension caused by the subduction of the Pacific Plate [24]. The Xing’an molybdenum deposit formed in the transitional tectonic regime from the crustal shortening–thickening to extension-thinning during the process of continental collision caused by the closure of the Mongolian–Okhotsk Ocean. While the crustal extension in post-collision regime strengthen as a result of the post-arc extension caused by the subduction of the Pacific Plate during the Early Craterous [35].

Tang et al. [81] believed that the magmatism and deformation of the Early Cretaceous occurred in the extensional setting formed by the collapse of thickened continental crust or detachment after the closure of the Mongolian–Okhotsk Ocean, but had no relation to the subduction of the Paleo-Pacific Plate. The magmatism and deformation in the late Early Cretaceous could be linked to the post-arc extensional setting formed due to the subduction of Paleo-Pacific Plate to the Eurasian continent and to the detachment of the thickened continental crust after the closure of the Mongolia–Okhotsk Suture Zone.

Based on the above information, it is difficult to judge which point of view is correct under current research level, but in general, the study area was in extensional tectonic setting. Combined with previous research results, we argue that the study area was under extensional tectonic setting due to the two events of extension of the Mongolian–Okhotsk Ocean after closure and the westward subduction of the Paleo-Pacific Ocean during the Early Cretaceous time (Figure 11e).

7. Conclusions

(1)

There are five phases of magmatism and three metallogenic epochs in the Duobaoshan porphyry copper–molybdenum deposit, namely the metallogenic epoch of Early Ordovician granodiorite (−475 Ma), the metallogenic epoch of Middle Ordovician granodiorite porphyry (~460 Ma), and the weak copper–molybdenum metallogenic epoch of Late Triassic oligoclase granite (225.8 Ma).

(2)

There are five copper and molybdenum metallogenic epochs in the Greater Khingan Range, including the Caledonian Ordovician metallogenic epoch which resulted in the formation of the Duobaoshan porphyry copper–molybdenum deposit, the Indosinian Late Triassic epoch during which the Badaguan porphyry copper–molybdenum deposit was formed, the Yanshanian Early Jurassic epoch when the Wunugetushan porphyry copper–molybdenum deposit formed, the Late Jurassic epoch when the Xiaokele copper deposit and Chalukou molybdenum deposit were formed, and the Early Cretaceous epoch during which the Taipinggou molybdenum deposit was formed. In addition to the Sankuanggou iron–copper deposit, the Duobaoshan ore-concentration area contains four mineralization stages.

(3)

The formation of the Early Paleozoic Duobaoshan porphyry copper–molybdenum deposit in the northern segment of the Greater Khingan Range is related to the island arc environment formed by the subduction of the Paleo-Asian Ocean. The Triassic and Jurassic crystallization age and mineralization of the Duobaoshan area were affected by the subduction of the Mongolian–Okhotsk Ocean. The formation of the Early Cretaceous porphyry molybdenum deposit is affected by the extension after the closure of Mongolian–Okhotsk Ocean and the westward subduction of the Paleo-Pacific Ocean.

(4)

By studying the tectonic setting for the formation of Cu-Mo deposits in the northern Great Xing’an Range, we conclude that the magmatism in the Duobaoshan area was controlled by the Paleo-Asian Ocean, the Okhotsk Ocean and the Paleo-Pacific Ocean tectonic regimes.