Sulﬁde S and Pb Isotopic Constraint on the Genesis of Diyanqinamu Mo-Pb-Zn Polymetallic Deposit, Inner Mongolia, China

: The Great Hinggan Range (GHR) hosts many large Mo deposits and vein-type Pb-Zn deposits and is one of the most important polymetallic metallogenic belts in China. Although Mo and Pb-Zn deposits are locally closely related in space in the GHR, it is disputed whether the Mo and Pb-Zn deposits have a genetic relationship. The Diyanqinamu Mo deposit located at the middle part of the northern GHR is a Late Jurassic large porphyry Mo deposit and closely adjacent by vein-type Pb-Zn deposit. In this work, we discussed the relationship between Mo and Pb-Zn deposits in Diyanqinamu mine based on the data of S and Pb isotopic geochemistry and geological information. In this mine, the Mo deposit is concentrated in the southern area faces of the same porphyry system. This Mo-Pb-Zn metallogenic system would provide important clues on further prospecting of Mo and Pb-Zn resources in the GHR.


Introduction
The Great Hinggan Range (GHR) in the easternmost Central Asian Orogenic Belt (CAOB) is one of the most important polymetallic metallogenic belts in China (Figure 1), which hosts a great many of Mo,  [2]). (B) Simplified geologic map of the GHR and its adjacent areas (modified after [9,23,24]).
Isotope geochemistry is a powerful tool to determine the sources of ore-forming fluids and melts in hydrothermal deposits. Sulfur isotope has been widely applied to constrain the genesis of hydrothermal deposits [25,26]; lead isotope is a significant monitor for tracing sources of hydrothermal fluids and their migration paths [26][27][28].
The Diyanqinamu Mo deposit in the middle part of northern GHR contains a proven reserve of 0.79 Mt Mo metal with an average grade of 0.099% ( Figure 1B) [23]. The vein-type Pb-Zn deposit  [2]). (B) Simplified geologic map of the GHR and its adjacent areas (modified after [9,23,24]).
Isotope geochemistry is a powerful tool to determine the sources of ore-forming fluids and melts in hydrothermal deposits. Sulfur isotope has been widely applied to constrain the genesis of hydrothermal deposits [25,26]; lead isotope is a significant monitor for tracing sources of hydrothermal fluids and their migration paths [26][27][28]. The Diyanqinamu Mo deposit in the middle part of northern GHR contains a proven reserve of 0.79 Mt Mo metal with an average grade of 0.099% ( Figure 1B) [23]. The vein-type Pb-Zn deposit adjacent to the Mo deposit contains 50,100 t Pb + Zn ore reserves with mean grades of 2.61 wt% Pb, 3.04 wt% Zn, and Ag resource 0.94 t at 106 g/t ( Figure 2) [29]. Previous studies mostly focused on the Mo deposit in alteration [30], metal sources [31], the ore genesis and tectonic setting [2,24,32], however, the genetic relationship between porphyry Mo and vein Pb-Zn deposits is poorly studied. In order to probe their genetic relationship, detailed geological and geochemical studies have been carried out on the vein-type Pb-Zn and porphyry Mo deposits in the Diyanqinamu mine.
Minerals 2020, 10, x FOR PEER REVIEW 3 of 15 adjacent to the Mo deposit contains 50,100 t Pb + Zn ore reserves with mean grades of 2.61 wt% Pb, 3.04 wt% Zn, and Ag resource 0.94 t at 106 g/t ( Figure 2) [29]. Previous studies mostly focused on the Mo deposit in alteration [30], metal sources [31], the ore genesis and tectonic setting [2,24,32], however, the genetic relationship between porphyry Mo and vein Pb-Zn deposits is poorly studied.
In order to probe their genetic relationship, detailed geological and geochemical studies have been carried out on the vein-type Pb-Zn and porphyry Mo deposits in the Diyanqinamu mine.
In this paper, we present new S-Pb isotopic compositions of sulfide minerals from both deposits. Combined with previous results, we propose that the vein-type Pb-Zn deposit is a distal face of the porphyry Mo deposit in Diyanqinamu mine. This Mo-Pb-Zn metallogenic system would provide important clues on further prospecting of Mo and Pb-Zn resources in the GHR.  [24,32]).

Regional Geology
The GHR is one part of the eastern CAOB between the Siberian Craton and the North China Craton ( Figure 1) [33,34], and a NE-SW-trending tectonic domain that is bordered by the Xar-Moron Fault to the south, the Mongol-Okhotsk suture zone to the north, and the Songliao Basin to the east [6]. The GHR experienced a long and complex tectonic evolution from the Paleozoic to Mesozoic [5,6]. During the Paleozoic, the GHR experienced multiple collision and suture between Siberia and North China Cratons which is mainly controlled by tectonic evolution of the Paleo Asian Ocean [34]. During the Mesozoic, the GHR successively overprinted by a prolonged complicated tectonic of Mongolia-Okhotsk Ocean tectonic domain in the north [35][36][37][38], and circle Paleo-Pacific Ocean tectonic domain in the east [39,40] and/or lithosphere thinning process [41]. Accordingly, this area exposed widespread Mesozoic igneous rocks with positive εNd(t) and young Nd model ages, which mostly formed during the Late Jurassic to the Early Cretaceous and constitutes one of the largest plutonic provinces in the world [34,39,42,43]. Many of these plutons are fertile and constitute the GHR metallogenic province [44].   [24,32]).
In this paper, we present new S-Pb isotopic compositions of sulfide minerals from both deposits. Combined with previous results, we propose that the vein-type Pb-Zn deposit is a distal face of the porphyry Mo deposit in Diyanqinamu mine. This Mo-Pb-Zn metallogenic system would provide important clues on further prospecting of Mo and Pb-Zn resources in the GHR.

Regional Geology
The GHR is one part of the eastern CAOB between the Siberian Craton and the North China Craton ( Figure 1) [33,34], and a NE-SW-trending tectonic domain that is bordered by the Xar-Moron Fault to the south, the Mongol-Okhotsk suture zone to the north, and the Songliao Basin to the east [6]. The GHR experienced a long and complex tectonic evolution from the Paleozoic to Mesozoic [5,6]. During the Paleozoic, the GHR experienced multiple collision and suture between Siberia and North China Cratons which is mainly controlled by tectonic evolution of the Paleo Asian Ocean [34]. During the Mesozoic, the GHR successively overprinted by a prolonged complicated tectonic of Mongolia-Okhotsk Ocean tectonic domain in the north [35][36][37][38], and circle Paleo-Pacific Ocean tectonic domain in the east [39,40] and/or lithosphere thinning process [41]. Accordingly, this area exposed widespread Mesozoic igneous rocks with positive εNd(t) and young Nd model ages, which mostly formed during the Late Jurassic to the Early Cretaceous and constitutes one of the largest plutonic provinces in the world [34,39,42,43]. Many of these plutons are fertile and constitute the GHR metallogenic province [44]. Four pulses of Mo metallogenic events of 250-200 Ma, 200-160 Ma, 160-130 Ma, and <130 Ma (130-100 Ma) have been identified in the GHR [9].
The middle part of northern GHR within Chinese territory is bordered by the Erlian-Hegenshan fault in the south ( Figure 1B). Paleozoic and Mesozoic rocks are discontinuously exposed and the Precambrian rocks are largely absent [45]. The Paleozoic strata are composed mainly of the Ordovician intermediate-acid volcanics interbedded with clastic rocks, the Devonian and Carboniferous clastic rocks, and Permian intermediate-acid volcanics with interlayers of bioclastic limestone [23,46]. The Mesozoic strata overlying uncomfortably on the Paleozoic strata are composed mainly of Jurassic volcaniclastic rocks intercalated with mafic volcanic and sedimentary rocks, and Cretaceous sandstone, mudstone, and conglomerate with interlayers of lignite, without the Triassic rocks [23,46]. Many of the Paleozoic and Mesozoic granites are fertile and are considered to be closely related to various mineral resources [7,9,[47][48][49].

Ore Deposit Geology
The strata in the Diyanqinamu mine consist mainly of Duobaoshan Formation and Chagannuoer Formation ( Figure 2). The Duobaoshan Formation emplaced at Middle Ordovician and consists of weak metamorphic rocks, such as tuffaceous slab and tuffaceous sandstone. The Chagannuoer Formation is composed of tuff, andesite, basalt, dacite, and pyroclastic rock [23,24]. Recently, LA-ICPMS zircon U-Pb chronological results indicated that the basalt of Chagannuoer Formation emplaced at 260 ± 4.0 Ma [50]. This age is earlier than Late Jurassic as previously considered [30,31,51]. The Diyanqinamu area was subjected to intensive tectonic and magmatic activities [49]. NE-(F2, F3 and F4) and NW-trending faults (F1, F2) controlled the morphology of the Mo ore-bodies. The intrusive bodies are porphyritic granites, discovered in the drill holes ZK9701 and ZK8502, and aplitic granites penetrated in drill holes ZK4522 and ZKp2104 [32]. These granites are located in the southeast quadrant of the Diyanqinamu mine, intruded the andesite, basalt, and volcaniclastic ( Figure 3). Both porphyritic granites and aplitic granites are high-K calc-alkaline and highly fractionated I-type granites [32]. Petrography shows that the granites experienced fluid exsolution, as demonstrated by the corroded quartz in the porphyritic granites, skeletal quartz in the aplitic granites, and the unidirectional solidification texture (UST) in the apex of the aplitic granites [23]. The middle part of northern GHR within Chinese territory is bordered by the Erlian-Hegenshan fault in the south ( Figure 1B). Paleozoic and Mesozoic rocks are discontinuously exposed and the Precambrian rocks are largely absent [45]. The Paleozoic strata are composed mainly of the Ordovician intermediate-acid volcanics interbedded with clastic rocks, the Devonian and Carboniferous clastic rocks, and Permian intermediate-acid volcanics with interlayers of bioclastic limestone [23,46]. The Mesozoic strata overlying uncomfortably on the Paleozoic strata are composed mainly of Jurassic volcaniclastic rocks intercalated with mafic volcanic and sedimentary rocks, and Cretaceous sandstone, mudstone, and conglomerate with interlayers of lignite, without the Triassic rocks [23,46]. Many of the Paleozoic and Mesozoic granites are fertile and are considered to be closely related to various mineral resources [7,9,[47][48][49].

Ore Deposit Geology
The strata in the Diyanqinamu mine consist mainly of Duobaoshan Formation and Chagannuoer Formation ( Figure 2). The Duobaoshan Formation emplaced at Middle Ordovician and consists of weak metamorphic rocks, such as tuffaceous slab and tuffaceous sandstone. The Chagannuoer Formation is composed of tuff, andesite, basalt, dacite, and pyroclastic rock [23,24]. Recently, LA-ICPMS zircon U-Pb chronological results indicated that the basalt of Chagannuoer Formation emplaced at 260 ± 4.0 Ma [50]. This age is earlier than Late Jurassic as previously considered [30,31,51]. The Diyanqinamu area was subjected to intensive tectonic and magmatic activities [49]. NE-(F2, F3 and F4) and NWtrending faults (F1, F2) controlled the morphology of the Mo ore-bodies. The intrusive bodies are porphyritic granites, discovered in the drill holes ZK9701 and ZK8502, and aplitic granites penetrated in drill holes ZK4522 and ZKp2104 [32]. These granites are located in the southeast quadrant of the Diyanqinamu mine, intruded the andesite, basalt, and volcaniclastic ( Figure 3). Both porphyritic granites and aplitic granites are high-K calc-alkaline and highly fractionated I-type granites [32]. Petrography shows that the granites experienced fluid exsolution, as demonstrated by the corroded quartz in the porphyritic granites, skeletal quartz in the aplitic granites, and the unidirectional solidification texture (UST) in the apex of the aplitic granites [23].   In the Diyanqinamu mine, vein-type Pb-Zn deposit occurs in close proximity of the porphyry Mo deposit, displaying a Mo-Pb-Zn mineralization distribution pattern ( Figure 2). The Pb-Zn deposit is about 500 m to the porphyry Mo deposit in this mine ( Figure 2).

Mo Sulfide Deposit
The Mo deposit mainly consists of three Mo ore-bodies, and most of them are concentrated in the andesite and volcaniclastic rocks. Overall, ore-bodies are barrel-and diamond-shaped at depth and plan, respectively, with most of them located at above 400 m elevation, whereas individual ore-body in some places may reach −250 m elevation at depth such as drill holes ZK4111 and ZK4522 ( Figure 3) [23].
Molybdenum mineralization is dominated by veins, disseminated grains, banded and fracture infills (Figure 4a-f) [24]. The main ore minerals are molybdenite and pyrite, with minor chalcopyrite, galena, sphalerite, bismuthinite, and arsenopyrite. In addition, magnetite presenting in the early barren and fertile stage indicate that the hydrothermal fluids are relatively oxidized at the early stage ( Figure 4f) [23]. As subordinate sulfide phase, sphalerite presents during and after Mo mineralization. According to their mineral association, three generations of sphalerite could be primarily discerned (

Mo Sulfide Deposit
The Mo deposit mainly consists of three Mo ore-bodies, and most of them are concentrated in the andesite and volcaniclastic rocks. Overall, ore-bodies are barrel-and diamond-shaped at depth and plan, respectively, with most of them located at above 400 m elevation, whereas individual orebody in some places may reach −250 m elevation at depth such as drill holes ZK4111 and ZK4522 ( Figure 3) [23].
Molybdenum mineralization is dominated by veins, disseminated grains, banded and fracture infills (Figure 4a-f) [24]. The main ore minerals are molybdenite and pyrite, with minor chalcopyrite, galena, sphalerite, bismuthinite, and arsenopyrite. In addition, magnetite presenting in the early barren and fertile stage indicate that the hydrothermal fluids are relatively oxidized at the early stage ( Figure 4f) [23]. As subordinate sulfide phase, sphalerite presents during and after Mo mineralization. According to their mineral association, three generations of sphalerite could be primarily discerned   mine is exposed by a small amount of borehole data with the extension in depth poorly constraint currently. The Pb-Zn ore-bodies occur chiefly as lenses and veins, and are concentrated mainly in the NW-trending fractures with a dip angle of 60°-70° in the weak metamorphic rocks of Duobaoshan Formation ( Figure 5). The Pb-Zn deposit mainly contains of five ore-bodies containing 50,100 t Pb + Zn ore reserves with mean grades of 2.61 wt% Pb, 3.04 wt% Zn; No. I-1 ore-body is one of the largest ore-bodies, displaying 50-100 m in length and 0.8-19 m in width [29].  Hydrothermal alteration is well developed in both the concealed porphyry and the volcanic rocks. The dominated alteration types are potassic alteration, silification, phyllic, and propylitic alteration [23,24,52]. Based on field and microscopic observations on the crosscutting relationships of various veins and paragenetic relationships of hydrothermal minerals, four stages of hydrothermal veins have been identified. Stage I is composed of quartz and K-feldspar, and minor molybdenite, magnetite, pyrite, epidote, and chlorite; Stage II contains predominantly quartz, fluorite, and molybdenite, and minor pyrite; Stage III is mainly composed of quartz, fluorite, pyrite, chalcopyrite, galena, sphalerite, and molybdenite; Stage IV is composed of quartz, fluorite, calcite, dolomite, galena and sphalerite, and absence of molybdenite [23,24,52]. Similar to some Mo deposits in China [11,14], fluorite alteration with diverse colors including purple, green, and white is found to be one of the most important alterations. Interestingly, the fluorites intergrowth with molybdenite are mostly purple. Combined evidence of widespread fluorite alteration, similar Sr and Nd isotopic compositions between the purple fluorite and the concealed granites, and high fluorine content of the apatite from the concealed granites, Sun et al. [23] proposed that the metallogenic granite is F-enriched, and the Mo ore-forming fluids may have been derived from this granitic magma.

Pb-Zn Sulfide Deposit
The morphology of Pb-Zn deposit adjacent to the Mo deposit in the northwest of Diyanqinamu mine is exposed by a small amount of borehole data with the extension in depth poorly constraint currently. The Pb-Zn ore-bodies occur chiefly as lenses and veins, and are concentrated mainly in the NW-trending fractures with a dip angle of 60 • -70 • in the weak metamorphic rocks of Duobaoshan Formation ( Figure 5). The Pb-Zn deposit mainly contains of five ore-bodies containing 50,100 t Pb + Zn ore reserves with mean grades of 2.61 wt% Pb, 3.04 wt% Zn; No. I-1 ore-body is one of the largest ore-bodies, displaying 50-100 m in length and 0.8-19 m in width [29].
The ore minerals include sphalerite, galena, pyrite, argentiferous tetrahedrite, and argentite. Sphalerite and galena display granular textures and coexist with pyrite (Figure 6a-f). It is worth noting that chalcopyrite disease structure in sphalerite is common in both the Mo and Pb-Zn ores (Figure 4g, Figure 6d-f), which may be related to the exsolution of chalcopyrite from sphalerite during cooling or replacement of original Fe-bearing sphalerite by an aggregate of chalcopyrite [53]. Gangue minerals include quartz and minor pyrolusite. Alteration assemblage are mainly kaolinization, sericitization, silification at depth, and ferritization at the surface. The ore minerals include sphalerite, galena, pyrite, argentiferous tetrahedrite, and argentite. Sphalerite and galena display granular textures and coexist with pyrite (Figure 6a-f). It is worth noting that chalcopyrite disease structure in sphalerite is common in both the Mo and Pb-Zn ores (Figure 4g, Figure 6d-f), which may be related to the exsolution of chalcopyrite from sphalerite during cooling or replacement of original Fe-bearing sphalerite by an aggregate of chalcopyrite [53]. Gangue minerals include quartz and minor pyrolusite. Alteration assemblage are mainly kaolinization, sericitization, silification at depth, and ferritization at the surface.

Analytical Methods and Samples
All the samples in this study were collected from different drill holes in the Diyanqinamu mine. Twenty-six samples were chosen for S isotopic analyses, fourteen of them from the Pb-Zn deposit and twelve from the Mo deposit. Besides, ten samples from the Pb-Zn deposit and four samples from the Mo deposit in this mine were chosen for Pb isotopic analyses. All of these minerals were separated by hand picking under a binocular microscope. Separated grains were rinsed with distilled water. After drying at 25~30 °C, the concentrations were grounded to powder for S-Pb isotope analyses.
Sulfur isotope analyses of these sulfide minerals were carried out at the State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, by using Continuous Flow Mass Spectrometer. GBW 04415 and GBW 04414 Ag2S were used as the external standards, and the relative errors (2σ) were better than 0.1‰ from the replication of standard materials. Sulfur isotopic compositions are reported relative to Canyon Diablo Troilite (CDT).
Lead isotope compositions were determined using ~100 mg sulfide powder that was dissolved in concentrated HF + HNO3 for 48 h. Lead was separated and purified using diluted HBr before isotopic compositions were determined using MAT 261 mass spectrometer at the Geological Analysis

Analytical Methods and Samples
All the samples in this study were collected from different drill holes in the Diyanqinamu mine. Twenty-six samples were chosen for S isotopic analyses, fourteen of them from the Pb-Zn deposit and twelve from the Mo deposit. Besides, ten samples from the Pb-Zn deposit and four samples from the Mo deposit in this mine were chosen for Pb isotopic analyses. All of these minerals were separated by hand picking under a binocular microscope. Separated grains were rinsed with distilled water. After drying at 25-30 • C, the concentrations were grounded to powder for S-Pb isotope analyses.
Sulfur isotope analyses of these sulfide minerals were carried out at the State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, by using Continuous Flow Mass Spectrometer. GBW 04415 and GBW 04414 Ag 2 S were used as the external standards, and the relative errors (2σ) were better than 0.1% from the replication of standard materials. Sulfur isotopic compositions are reported relative to Canyon Diablo Troilite (CDT).
Lead isotope compositions were determined using~100 mg sulfide powder that was dissolved in concentrated HF + HNO 3 for 48 h. Lead was separated and purified using diluted HBr before isotopic compositions were determined using MAT 261 mass spectrometer at the Geological Analysis Laboratory under the Ministry of Nuclear Industry, China. The precision of the 208 Pb/ 206 Pb measurements (1 µg of Pb) is ents (1 µgositions were determined using MAT 261 mass spectrometer at the Geologic 208 Pb/ 206 Pb = 36.611 ± 0.004, 207 Pb/ 206 Pb = 15.457 ± 0.002, and 204 Pb/ 206 Pb = 16.937 ± 0.002, in agreement with the reference value [54].
The Pb isotopic results of the sulfide samples from both of Pb-Zn and Mo deposit are listed in the    [56]. Lead isotopic data of the molybdenite separates in Mo ores from Leng et al. [24]. Mineral abbreviations are the same as those in Figure 5.    Figure 7. Sulfur isotope histogram of galena and sphalerite sampled from Mo and adjacent vein-type Pb-Zn deposits in the Diyanqinamu mine. Sulfur isotopic data of the molybdenite separates from Mo ores are quoted from [24]. Mineral abbreviations are the same as those in Figure 6.   6. Discussion

Possible Source of Sulfur
The vein-type Pb-Zn deposit is located about 500 m northwest of the porphyry Mo deposit in Diyanqinamu mine (Figure 2). Both deposits in this mine have simple sulfide mineral assembly, mainly composed of molybdenite, pyrite, galena, and sphalerite with molybdenite absent in the Pb-Zn deposit. The lack of sulfate minerals suggests that the sulfide δ 34 S values can trace the δ 34 S values of the ore-forming fluids [55,57,58]. All galena and sphalerite samples from Pb-Zn deposit have homogenous δ 34 S CDT values ranging from +2.38% to +5.21% and +4.46% to +5.46% , respectively (Table 1 and Figure 7). Galena and sphalerite samples from the Mo deposit have a wide range of δ 34 S CDT values, ranging from +1.08% to +1.73% and +4.13% to +7.29% , respectively (Table 1 and Figure 7). Overall, the δ 34 S values of galena and sphalerite samples from both deposits are broadly similar to those of molybdenite from the Diyanqinamu mine (ranging from +3.3% to +10.2% with average of +8.2% [24]) ( Figure 7B). Because no marine evaporites or carbonates are in this region, these relatively high δ 34 S values of the sulfides from the Mo deposit in the Diyanqinamu mine have been suggested could be inherited from a magmatic source [24], which is also supported by the evidence that the fluorite coexisting with molybdenite presents similar Sr and Nd isotopic composition to the concealed high-F granite [23]. Therefore, in the Diyanqinamu mine, the δ 34 S values of the sulfide samples from the Pb-Zn deposit present overlap with those of the Mo deposit (Figure 7), suggesting that the two deposits have a common S source.
In addition, all δ 34 S values of galena and sphalerite samples from Pb-Zn deposit are characterized by δ 34 S sphalerite > δ 34 S galena . Under microscope, these galena and sphalerite coexisted with each other ( Figure 5). These lines of evidence suggest that the S isotope fractionation has reached equilibrium in hydrothermal fluids. The formation temperatures calculated based on the sulfur isotope balance fractionation between sphalerite and coexisted galena range from 220 • C to 315 • C with average temperature of 247 • C (Table 1) which is lower than the formation temperature of Mo mineralization (292-510 • C, [52]). Therefore, the S isotopic data and other evidence imply that the Mo and Pb-Zn deposits in the Diyanqinamu mine share a common S source and present the descending temperature of the hydrothermal fluid.

Origin of Ore-forming Metals
Sulfides generally have very low U and Th contents, and hence their radiogenic Pb are negligible and age correction is not needed. Therefore, the lead isotopic compositions of sulfide samples in the Diyanqinamu could inherit source signals of ore-forming metals. The lead isotopic data of galena, sphalerite, and molybdenite from Mo and Pb-Zn deposits in the Diyanqinamu are distributed between the orogenic belt and mantle average evolution curves in the 207 Pb/ 204 Pb vs. 206 Pb/ 204 Pb diagram, and form an elongate narrow trend (Figure 8, [56]). These sulfide samples from the Mo deposit are characterized by overlapping with each other in 206 Pb/ 204 Pb and 207 Pb/ 204 Pb ratios, with the molybdenite showing much lower values than those of galena and sphalerite ( Figure 8B). Previous works on the Pb isotope proved that the ore-forming metals of Mo mineralization were predominantly derived from granitic magma [23,24]. In contrast, the sphalerite and galena samples from the Pb-Zn deposit in this mine display much higher 206 Pb/ 204 Pb and 207 Pb/ 204 Pb ratios, and well overlap with those of the sphalerite and galena samples from the Mo deposit. The variation in Pb isotope may be resulted from a mixing of two or more isotopically distinct sources in the ore-forming process. This prediction is broadly confirmed by the fluid inclusion analyses and H-O isotope variation, which indicates that fluid mixing existed during the late stage of the Mo mineralization [52]. In addition, S isotopic data above suggest that the galena and sphalerite from the Mo and the Pb-Zn deposits in the Diyanqinamu mine are most likely of magmatic hydrothermal origin [23,24]. Therefore, mixing of a magmatic fluid possessing low 206 Pb/ 204 Pb and 207 Pb/ 204 Pb ratios with isotopically evolved crustal materials of high corresponding ratios would be a plausible explanation. The sulfides from the Pb-Zn deposit exhibiting higher 208 Pb/ 204 Pb and 207 Pb/ 204 Pb ratios represent a mixed source with more external material. This speculation is also consistent with the geology fact that the fresh rocks of Duobaoshan Formation, as the host rocks of Pb-Zn ore-bodies, are characterized by high abundance of Pb, Zn, and Ag [59]. The strong kaolinization, sericitization, and silification alteration of these rocks could promote the leaching of Pb, Zn, and Ag from the host rocks, leading to the enhancement of the metallogenic potential for Pb-Zn deposit subsequently.

Genesis of Diyanqinamu Mo-Pb-Zn Polymetallic Deposit
Many porphyry districts in the world exhibit close association in space between the porphyry Mo deposit and vein-type Pb-Zn deposit [12,17]. At Climax Mo deposit in USA, East Qinling molybdenum belt in China, and MAX Mo deposit in Canada, vein-type Pb-Zn deposits have been suggested to be a distal member of the porphyry system [12,14,15]. A continuum hydrothermal evolution model was proposed by Silitoe [60] to explain this close spatial relationship between vein-type Pb-Zn and porphyry Mo deposits. Lawley et al. [12] suggested that porphyry deposit is genetically related to a wide range of deposit types, including skarn, base, and precious metal veins, and epithermal precious-metal deposits.
In the Diyanqinamu mine, the vein-type Pb-Zn deposit are close to the porphyry Mo deposit in space with a short distance of about 500 m. In mineral assemblage, many galena and sphalerite were present during and after the Mo mineralization. S and Pb isotope data of galena and sphalerite in both the Pb-Zn and Mo deposits show that they share similar S and metal sources. Although the formation temperature of Pb-Zn mineralization is lower than the fluid inclusion homogenization temperature of molybdenite-bearing quartz vein [52], this evolution trend of temperature is consistent with metal zonation typically observed in a porphyry-related hydrothermal system [17]. Therefore, it is reasonable to infer that the temperature discrepancy between Mo and Pb-Zn mineralization reflects the evolution of the hydrothermal fluids. That is, during the late evolution stage of granitic magma, there existed exsolution of a high-temperature, F-rich, and high-f O 2 ore-bearing hydrothermal fluids. According to the results of microscopic temperature measurement of inclusions and H-O isotope, this hydrothermal fluid experienced at least three stages of fluid boiling during the evolution of hydrothermal veins from Stage I to Stage III and was diluted by meteoric water, leading to the deposition of molybdenite as veins or infills along the fractures adjacent to the concealed granite [23,52]. As the migration of this hydrothermal fluid, the fluid could extract some metals from the host rocks, such as the Duobaoshan Formation, through convective circulation, meanwhile, lead to the strong hydrothermal alterations and the enhanced capability of the Pb-Zn mineralization subsequently. Thus, the Mo and Pb-Zn deposits in the Diyanqinamu mine represent different faces of the same porphyry system. As more and more Mo and Pb-Zn deposits are discovered in the north of GHR (e.g. [1,61]), in this case, the view of Mo-Pb-Zn metallogenic system has significant implication for Mo and Pb-Zn mineral exploration in this area.

Conclusions
In the Diyanqinamu mine, the vein-type Pb-Zn deposit is closely adjacent to the porphyry Mo deposit in space. Sulfides from both Mo and Pb-Zn deposits in this mine have similar δ 34 S values and show magmatic origin. The formation temperature of the coexisted galena and sphalerite based on S isotopic data of galena-sphalerite pairs for Pb-Zn deposits is lower than the fluid inclusion homogenization temperature of the molybdenite-bearing quartz vein. Lead isotopic data from both of Mo and Pb-Zn deposits are characterized by an evolution trend, with the molybdenite showing lower values, and the galena and sphalerite showing higher ratios. This kind of Pb isotopic signature suggests that both deposits share a mixed metal source, with more material from the host rocks for the Pb-Zn deposits. Combined with the previous research results and our work this time, we suggest that the Mo and Pb-Zn deposits in the Diyanqinamu mine consist of a zoned magmatic hydrothermal system. The association of Mo and Pb-Zn deposits, in this case, could provide an important exploration indicator for each other, and would discharge important information for the regional mineral exploration.