Geochronology and Isotope Geochemistry of the Yingfang Pb-Zn-Ag Deposit: Implications for Large-Scale Metallogeny along the Northern Flank of the North China Craton

: The northern ﬂank of the North China Craton (NCC) hosts a linear zone of gold, molybdenum, silver, lead, and zinc polymetallic ore deposits. Among these, the Yingfang Pb-Zn-Ag deposit is located in the central part of the Yanshan–Liaoxi metallogenic belt (YLMB) which extends for approximately 1000 km and forms part of the major mineralized zone. In this study, we characterize the mineralization and trace the ore genesis based on new sulfur and lead isotopic geochemistry and evaluate the timing of mineralization from Rb-Sr isotope dating of sulﬁdes. The pyrite δ 34 S values range from +3.2‰ to +5.8‰ with a mean at +4.07‰, close to the values of mantle and meteorite sulfur. The 206 Pb/ 204 Pb values range from 16.833 to 18.956, 207 Pb/ 204 Pb from 15.374 to 15.522, and 208 Pb/ 204 Pb from 37.448 to 37.928. Five samples of sulﬁde, from the Yingfang deposit, yield a Rb-Sr isochron age of 135.7 ± 4.1 Ma. This age is close to the age of the adjacent Niujuan Ag-Au deposit and the associated Er’daogou granite, suggesting a close relationship between magmatism and metallogeny in this region. The S and Pb isotopes of the regional silver polymetallic deposits show similar sources of ore-forming materials. According to a compilation of the available age data on the Mesozoic ore deposits in the northern ﬂank of the NCC, we divide the mineralization into the following four periods: 240–205 Ma, 190–160 Ma, 155–135 Ma, and 135–100 Ma. Mesozoic magmatism and mineralization in the Yingfang deposit mainly took place at 245 Ma and 145–135 Ma. We correlate the Pb-Zn-Ag mineralization to metallogeny associated with large-scale inhomogeneous lithosphere thinning beneath the NCC.

Several new Au, Mo, Ag, Pb, and Zn polymetallic deposits were recently discovered in the Yanshan-Liaoxi metallogenic belt (YLMB), the central segment along the northern flank of the NCC (Figure 1c) [9][10][11][12][13]. The YLMB comprises a series of porphyry-, skarn-, quartz vein-, altered rock-and epithermal-ore deposits. Located in the central part of the YLMB, the Yingfang Pb-Zn-Ag deposit is spatially associated with Mesozoic intrusions and occurs along the contact between the intrusions and Paleoproterozoic metamorphic rocks (Figure 2a [14]); (b) Geological map of the Niujuan Ag (Au) deposit and the Yingfang Pb-Zn-Ag deposit (A-B: exploration line; modified after [13,15]). This region exposes voluminous igneous rocks [16], most of which were emplaced during Jurassic to Early Cretaceous (185- 80 Ma), and a minor volume during Paleozoic [11,16,17]. The complex tectonic processes associated with cratonization, the later destruction of the NCC, and the related multiple magmatic activities provided favorable conditions for metallogeny in this region [2,3,18,19]. Previous studies on Ag, Pb, and Zn polymetallic deposits generally have focused on their geological characteristics [10,11,16], ore-controlling factors [1,20], fluid inclusions, associated magmatism [15,21,22], and timing of ore formation [13,23,24]. However, the relationship between magma emplacement and polymetallic mineralization, as well as the corresponding geodynamic settings of Mesozoic magmatism and mineralization in this region, remain debated. The source of ore-forming materials of Au-Ag polymetallic deposits of the YLMB remains controversial both with respect to theoretical models and exploration strategies. A systematic compilation of previous geochemical data is helpful to understand the origin of the deposits in a broad perspective. Although an important deposit in the YLMB, few studies have been carried out on the Yingfang deposit. These studies were focused mainly on dating the intrusions or gangue minerals associated with the Pb-Zn-Ag mineralization to determine the formation age of the Yingfang deposit [2,15]. On the basis of the geological relationship and the zircon U-Pb ages, the Pb-Zn-Ag mineralization was inferred to be later than the emplacement of the Er'daogou fine-grained granite (145 Ma) [2]. The timing of Pb-Zn mineralization has not been constrained. In this study, we used sulfides Rb-Sr methods to date the sulfides in the ores in order to constrain the mineralization time, and we documented stable isotopic data on the ore sulfides in order to gain better insights on the ore-forming materials in the Yingfang deposit. According to our new data and those from previous work, we evaluate the relationship between magmatism and Ag, Pb, and Zn polymetallic mineralization with a view to understanding the link between regional geodynamics and Ag, Pb, and Zn mineralization.

Geological Setting
The Yanshan-Liaoxi metallogenic belt (YLMB, 39 is located in the northern flank of the NCC (Figure 1a), covering the northern Hebei and western Liaoning provinces [6]. The Archean-Paleoproterozoic crystalline basement in this region comprises migmatite, amphibolite-greenschist, and granulite facies rocks. The Neoproterozoic sedimentary cover, up to 10 km in thickness, is related to the intra-cratonic aulacogen rifting processes in this region, consisting of bathyal to shallow sea clastic and carbonate rocks including fine-grained sandstone, shale, dolomite, and limestone. The Phanerozoic strata can be divided into four sequences as follows: (1) [9,16,25]. In addition to volcanosedimentary rocks, the Mesozoic plutonic rocks are also widely distributed in the YLMB, including granitoids, diorite, syenite porphyrite, lamprophyre, gabbro, and dolerite [26,27]. From Early Jurassic to Late Cretaceous, the mafic magmatism evolved into more felsic composition [9]. Most granitoid plutons occur mainly as stocks or dykes, with outcrops covering more than 10 km 2 [16,26,28,29]. Fault structures are well developed in the YLMB, showing mainly EW-, NE-and NNE-trends ( Figure 1c).
In Mesozoic, the northern margin of the North China experienced the "Yanshan Movement" [30,31] that resulted in uplift and erosion, volcanic eruptions, and magmatic intrusion, as well as large-scale fold, nappe thrust structures. Zhao et al. (2004) [32] proposed the following three tectonic episodes in the YLMB in the Yanshanian: (1) Episode A (175-160 Ma) marked by angular unconformity below the andesites of the Tiaojishan (or Lanqi) Formation volcanic rocks; (2) The intermediate Episode (165-156 Ma) represented by intensive volcanic activity (e.g., the Tiaojishan and Lanqi Formations); (3) Episode B (156-139 Ma) marked by strong fold and nappe thrust structures. From the Early Cretaceous, the tectonic deformation was dominated by extension, with successive volcanic eruptions and associated weak tectonic deformation.

Orefield Geology
The Yingfang Pb-Zn-Ag deposit is located in the contact region of the Baiyingou granite and the Paleoproterozoic Hongqiyingzi Group metamorphic rocks, and about 0.5 km south of the Niujuan silver deposit. The basement rocks exposed in the southern of Fengning orefield is mainly the Paleoproterozoic Hongqiyingzi Group metamorphic rocks, which comprise biotite plagioclase gneiss and biotite-bearing plagioclase amphibolite. The Baiyingou coarse-grained granite in this orefield occupies most part of the exposed Mesozoic granitoids and is the largest outcrop in this area. The Er'daogou fine-grained granite is distributed in both eastern part and western part of the orefield and is not far from the orebodies. Some felsic dykes, mainly quartz diorite and quartz veins, are also distributed in the region (Figure 2a). The Kangbao-Weichang EW-trending deep fault, Fengning-Longhua NE-trending deep fault, and Shanghuangqi-Wulonggou NNE-trending deep fault are located in the north, west, and east of the Fengning area, respectively. The Niuquan-Laohuba fault (F 1 ), a secondary structure produced parallel to the Shanghuangqi-Wulonggou deep fault, is the main fault in the Fengning area to control rocks and ores and has a close spatial relationship with the Yingfang Pb-Zn-Ag deposit.
Four orebodies are hosted in the Baiyingou coarse-grained granite in the Yingfang Pb-Zn-Ag deposit and are mostly controlled by NNE-trending faults. Among these orebodies, the largest one (No. 1, Figure 2b) is about 425 m in length, 263 m in depth, and around 5.41 m in width, with average grades of 124 g/t Ag, 6.5% Pb, and 3.5% Zn.
The ore minerals are mainly galena, sphalerite, pyrite, chalcopyrite, pyrrhotite, arsenopyrite, and magnetite ( Figure 3). The main silver-bearing minerals are argentite, native silver, and freibergite. The main gangue minerals are quartz, calcite, muscovite, biotite, chlorite, and garnet. In addition, sericite, fluorite, and ankerite are also identified in the Yingfang deposit. The ores show xenomorphic granular, euhedral-subhedral granular, exsolution, poikilitic, and intergrowth textures (Figure 3a-f). The xenomorphic granular galena and sphalerite are replaced by the later formed chalcopyrite (Figure 3a). The sphalerite metasomatized galena and the pyroxene distributed in galena along the fracture (Figure 3b). The euhedral-subhedral pyrite and sphalerite grains are intergrown, and chalcopyrite occurs as exsolved blebs in sphalerite crystals (Figure 3c). Pyroxene metasomatism sphalerite, metasomatism edge formed in sphalerite, galena metasomatism natural silver ( Figure 3d). Pyrite is cataclastic due to dynamic metamorphism ( Figure 3e). The cut surface of pyrite is striped, and pyrite is interbedded with pyrite ( Figure 3f). Hydrothermal alteration in the Yingfang Pb-Zn-Ag deposit consists of silicification, sericitization, kaolinization, chloritization, and carbonatization, with a variety of alteration minerals such as sericite, kaolinite, chlorite, and calcite. Silicification and sericitization are the predominant alteration and show a close relationship with Pb-Zn-Ag mineralization in the Yingfang deposit. Silicic and sericitic alteration are usually overprinted by argillic alteration characterized by the formation of chlorite and kaolinite.
According to the characteristics of the mineral paragenesis, vein crosscutting and the symbiotic relationship among minerals (Figure 4), the dominant ore-forming process in the Yingfang deposit can be divided into the following three stages: early mineralization stage (Stage I), main mineralization stage (Stage II), and late mineralization stage (Stage III). The mineral paragenetic sequences of the three stages in the Yingfang deposit are shown in Figure 5. The three stages are characterized as follows:

Early mineralization stage (Stage I)
The main minerals are quartz, sericite, pyrite, arsenopyrite, galena, sphalerite, etc. Pyrite has a coarse particle size, a high degree of idiomorphism, and is distributed in the disseminated form ( Figure 4a).
Sampling was undertaken according the following criteria: (1) to minimize the effect of weathering, (2) to ensure that materials were available from both hanging wall and footwall of Niujuan-Laohuba fault (Figure 2b), and (3) to include representative samples of all the ore types. After crushing and sieving of the representative samples, the separated mineral grains of 40-60 mesh size were handpicked under a binocular stereo microscope to ensure >99% purity.

Rubidium-Strontium Isotopes
The Rb and Sr isotope analyses were carried out using a VG-354 ionization mass spectrometer at the Modern Analysis Center, Nanjing University. The chemical separation and mass spectrometric procedures followed those in [33]. In this study, the measurement of the American Standard Reference Material NBS987 Sr gives 87 Sr/ 86 Sr value of 0.710233 ± 0.000006 (2σ). 87 Sr/ 86 Sr is normalized to 86 Sr/ 88 Sr of 0.1194 to correct for instrumental fractionation.

Sulfur and Lead Isotopic Analyses
Sulfur isotopes were determined using a Finnigan MAT-251 mass spectrometer, at the Beijing Research Institute of Uranium Geology, following the procedures outlined by [34]. The precision for δ 34 S is better than ±0.2‰ and the data are reported relative to Vienna Canon Diablo Troilite (V-CDT) sulfide. Pb isotopic ratios were analyzed using the same mass spectrometer with an analytical precision better than ±0.2‰.

Rb-Sr Isochron Age
The Rb and Sr isotopic data of Stage II sulfides are listed in Table 1. The Rb contents of the samples are relatively low, ranging from 0.1269 to 0.3927 ppm and the Sr contents are also relatively low, ranging from 0.2256 to 1.698 ppm. The 87 Rb/ 86 Sr ratios vary from 0.2374 to 5.137 and the 87 Sr/ 86 Sr ratios from 0.711364 to 0.720768. Regression and age calculations of isochrons were performed using Isoplot/Ex Version 3.00 software (Berkeley Geochronology Center, Berkeley, CA, USA, [35]), and with λ = 1.42 × 10 −11 , using 1% errors for 87 Rb/ 86 Sr ratios and 0.005% errors for 87 Sr/ 86 Sr ratios at a confidence level of 95%. The sulfides yield a Rb-Sr isochron age of 135.7 ± 4.1 Ma (MSWD = 2) with an initial 87 Sr/ 86 Sr ratio of 0.71086 ± 0.00014 ( Figure 6).

S and Pb Isotope Systematics
Sulfur isotope analyses are listed in Table 2. The δ 34 S values of 27 samples (seven samples from this study and the rest compiled from previous studies) range from 3.2‰ to 5.8‰ with a mean value of 4.07‰. The narrow range of δ 34 S values suggests that the sulfur in the Yingfang deposit was derived from a common source.

Timing of Ore Mineralization
The precise dating of mineralization has important implications for understanding the duration of ore-forming systems and their temporal relationship to various geological events. Shepherd and Darbyshire (1981) [36] first demonstrated the feasibility of obtaining Rb-Sr fluid inclusion isochrons by analyzing the Rb and Sr isotopic compositions in inclusions within quartz from a tungsten vein-type deposit, which confirmed the significance of fluid inclusions as precise Rb-Sr geochronometers. In recent years, important breakthroughs have been made in constraining the timing of mineralization by the Rb-Sr isochron ages of ore minerals or gangue minerals related to mineralization [37][38][39][40][41][42][43][44][45]. To get precise Rb-Sr isochron date, all samples are expected to be homologous and formed in the same stage, and the isotopic systems should be closed [46]. Most of the samples in this study are collected from the main mineralization stage (Stage II) and are well crystallized without any fractures, and therefore the Rb-Sr isochron age, in this study (135.7 ± 4.1 Ma), can be used to constrain the mineralization age of the Yingfang deposit.

Origin of the Ore-Forming Constituents
The stable isotopic composition of sulfide minerals is a useful tool to constrain the origin of hydrothermal fluids [47]. Sulfur isotopic composition of the hydrothermal system is determined by the following physicochemical conditions: (1) isotopic composition of the hydrothermal fluid from which the mineral was deposited, (2) temperature of deposition, (3) chemical composition of the dissolved element species including pH and ƒ(O 2 ) during mineralization, and (4) relative amount of the minerals deposited from fluids [48][49][50]. Sulfur isotopic composition of hydrothermal sulfides depends not only on the δ 34 S value of source materials, but also on the physicochemical condition of the ore-forming fluid [51]. Therefore, determining the total S isotopic composition (δΣS) of the hydrothermal fluids during sulfide precipitation is essential for tracing the sulfur source. However, under equilibrium hydrothermal conditions where H 2 S is the dominant sulfur species in the fluid, the average δ 34 S (H 2 S) values will approximate the δΣS value of hydrothermal fluid [49,52].
In the Yingfang Pb-Zn-Ag deposit, the dominant S-bearing minerals formed during Stage II are all sulfides, including galena, sphalerite, and pyrite, which indicate a relatively simple paragenesis. The δ 34 S values obtained from the three sulfides show a general evolution of δ 34 S pyrite > δ 34 S sphalerite > δ 34 S galena ( Table 2), suggesting the equilibrium fractionation of sulfur isotope among these sulfide minerals and the ore-forming fluid [53,54]. The δ 34 S (H 2 S) values, therefore, can directly represent the δ 34 S value of total sulfur (δΣ 34 S) of the fluids. According to the study of [55], the δ 34 S(H 2 S) values involved in hydrothermal system can be calculated as follows: where i refers to different sulfides; Ai value is 0.4 for pyrite, 0.1 for sphalerite, and −0.63 for galena, respectively; T (in degrees kelvin) refers to the equilibrium temperature at which the sulfide minerals are deposited. It is calculated by the following formula [56]: △ 34 δ Sp-Gn = δ 34 S Sp − δ 34 S Gn = 1000lna Sp-Gn = 0.87 × 10 6 t −2 − 0.57, where "t" is the temperature in degrees celsius (T = t + 273.15). Mineral twin samples 9-45-3(g), 9-45-3(s) and 9-45-2(g), 9-45-2(s) ( Table 2) were adopted for the calculation of the equilibrium temperature. The equilibrium temperature values range from 267 • C to approximately 278 • C, with an average of 272.5 • C for Equation (1). The δ 34 S(H 2 S) values range from 2.8‰ to 8.3‰ (Table 2) and are close to those of meteorite and mantle, suggesting a homogeneous source with the involvement of mantle-derived components during the ore-forming processes [51,57]. The δ 34 S values of samples from the Mesozoic intrusions (Er'daogou fine-grained granite and Baiyingou coarse-grained granite) that formed during the main magmatic activity are from −0.5‰ to 7.7‰ [13], suggesting a genetic relationship between the ore-forming fluid of the Yingfang Pb-Zn-Ag deposit and the Mesozoic intrusions (Figure 7).
where Y is the age of the earth; a 0 and b 0 are the initial lead isotopic compositions of the earth; λ8 and λ5 are the decay constants of 238 U and 235 U, respectively [58]. The single-stage lead model ages obtained range from 1038 to 1119 Ma, which are significantly younger than the ages of the Hongqiyingzi Group metamorphic rocks (2.6-1.7 Ga) [59] but older than the emplacement ages of the Baiyingou coarse-grained granite (245 Ma) [10] and the Er'daogou fine-grained granite (145 Ma) [13] and the mineralization age of the Yingfang Pb-Zn-Ag deposit (135 Ma) (this study). In addition, the lead isotopic values do not plot along the growth curve of single-stage lead in the diagram of 207 Pb/ 204 Pb versus 206 Pb/ 204 Pb, and the µ and ω values of ore lead (9.25-9.55 and 39.44-42.95, respectively) are obviously higher than the values of normal lead (8.686-9.238 and 35.55 ± 0.59) [58]. On the basis of the above features, it is obvious that the ore lead of the Yingfang Pb-Zn-Ag deposit is radiogenic with complex evolution rather than single-stage normal lead.
The lead isotopic values of sulfides are distributed along a straight line with good linear relation in the diagram of 207 Pb/ 204 Pb versus 206 Pb/ 204 Pb (Figure 8a). The reference line regressed through the data has a slope of 0.1359 which corresponds to an unrealistic secondary Pb-Pb isochron model age of 2175 Ma [60]. It appears that lead was mobilized from a dominantly single Pb source during discrete hydrothermal events in the Paleoproterozoic. This suggest that the radiogenic ore lead signature might have been contributed by the isotopically evolved Paleoproterozoic basement.
The Pb isotopic compositions of the sulfides from the Yingfang Pb-Zn-Ag deposit show a restricted range in the lead isotope evolution diagrams [61]. As shown in the plot of 207 Pb/ 204 Pb versus 206 Pb/ 204 Pb (Figure 8a), the Pb isotopic data for sulfides plot in the region between the curves of orogenic belt and mantle evolution. However, in the 208 Pb/ 204 Pb versus 206 Pb/ 204 Pb diagram (Figure 8b), the sulfide data show a linear trend near the lower crust evolution curve. The µ values of metal sulfides from the Yingfang deposit are between 9.35 and 9.58, which are obviously higher than the mantle value (8.92) and slightly lower than crustal value (9.58) [62], implying that Pb was mainly derived from the crust with a mantle contribution.  (Table 1), which are lower than the continental crust average 87 Sr/ 86 Sr ratio of 0.719 [64] and higher than the mantle initial value of 0.704 [58], indicating that the Sr originated from lower crust with limited input of mantle materials.

Comparison with Other Deposits in the YLMB along the Northern Flank of the North China Craton (NCC)
Sulfur isotopic data on 332 samples from 20 silver polymetallic deposits in the YLMB show that the Mesozoic ore deposits have values from −14.40‰ to +11.80‰ (Figure 9a and Table 3), with most of the values clustering between 0‰ and 6‰ (Figure 9b). The sulfur isotope compositions of the sulfide minerals from most of these deposits show the characteristics of equilibrium fractionation [2,65,66]. As illustrated in Figure 8a, the sulfur isotope characteristics of the Yingfang deposit are similar to those of other silver polymetallic deposits in the YLMB and are close to meteorite and mantle.  Table 3 for data) and histogram; (b) Sulfur isotopic composition of sulfides from the silver polymetallic deposits on the YLMB.  (Table 3 and Figure 8). In the lead isotopic evolution diagrams (Figure 8), most data plot between the lower crust and mantle evolution curves, suggesting that the Pb was derived from multiple sources including mantle and the lower crust. The S and Pb isotopic compositions of the sulfides from the Yingfang deposit and other silver polymetallic deposits in this region show marked similarity (Figure 8), suggesting the same or similar lower crustal source with additional mantle input.
Studies of the S and Pb characteristics of silver polymetallic deposits in the northern flank of the NCC suggest similar sources of ore-forming materials implying common geodynamic setting.

The Tectonic Setting and Metallogenic Model
The temporal distribution of the complex Mesozoic mineralization events along the northern flank of the NCC is poorly understood. On the basis of previous studies and the results presented in this study (Table 4) 100 Ma). In contrast to the northern flank of the NCC, the timing of mineralization in the YLMB is relatively within a narrow interval.  The tectonic setting evolution of the mineralization in the YLMB is primarily from the closure of the Paleo-Asian Ocean and the formation of the Xing'an-Mongolia Orogenic Belt (XMOB) [108]. The North China-Mongolia plate and the southern margin of the Siberian plate are separated by the Mongolian-Okhotsk Ocean [109]. During Triassic (240-205 Ma), the northern flank of the NCC was in a post-orogenic extensional tectonic setting following the closure of the Paleo-Asian Ocean, which resulted in the lithospheric delamination and asthenosphere upwelling (Figure 11a). This caused extensive volcanism and the emplacement of subvolcanic rocks. Under the influence of the far-field stresses during the extension, the gold and molybdenite mineralization occurred across the XMOB and the NCC coevally with the emplacement of the Triassic felsic or mafic intrusions (Figure 11a) [110].  Table 4 for data) formed during the Mesozoic. The collision between the Siberian Plate and the North China-Mongolia Block might have been ongoing until the closure of the Mongolia-Okhotsk Ocean in the Late Jurassic [25,[112][113][114][115][116][117]. Thus, the effect of the collision between the Siberian Plate and the North China-Mongolia Block on the Early-Mid Jurassic magmatic activity and mineralization episode cannot be excluded in this region [25,66,114]. During Early-Middle Jurassic , the geodynamic setting of the northern flank of the NCC was related to the subduction of the Paleo-Pacific plate and the collision between the Siberian Plate and the North China-Mongolia Block (Figure 11b) [96,111]. Widespread volcanism and magmatic activity occurred in the Yanshan-Liaoning area, with associated gold and molybdenite mineralization [118].
During Late Jurassic, influenced by the northwestward subduction of the Paleo-Pacific plate, the regional E-W trending tectonic systems were resurrected and further superposed by NE trending or NNE trending tectonic systems [55,119]. During this period, the adjustment of the lithosphere tectonic regime not only caused volcanic eruption, but also enhanced the mantle-crust interaction, and granitic magmas derived from crustal melting were emplaced at the intersection of the NNE and E-W trending faults, forming syntectonic granodiorite, granite porphyry, adamellite, and syenite [96,117]. Along with the emplacement of the granitic magma, lead, zinc, molybdenum, and copper mineralization formed in association with the I-type or mixed crust-mantle derived granitic magmas, mainly during the end of Late Jurassic (140 ± 5 Ma) [96,111,120] and produced deposits such as Yingfang deposit in this study. These marked a transformation in the tectonic regime (Figure 11c).
The extensive ore-forming events are considered to be a direct geodynamic consequence of the inhomogeneous lithosphere thinning beneath the NCC. Since the magmatism and mineralization mostly took place in early Cretaceous, large-scale inhomogeneous delamination would also be a feasible model for the thinning of the NCC [2,3]. Following asthenosphere upwelling and lithospheric thinning resulted by the post-collisional extensional environment, the mantle-derived magmas penetrated into the crust, resulting in extensive crustal-reworking and strong interaction between crust and mantle [110,121]. During the lithosphere extension and thinning, magma emplacement and volcanic eruptions were associated with large-scale Mesozoic mineralization in this region [2,3,17,118,[122][123][124][125]. Different types of ore deposits are widely distributed in the northern flank of the NCC, including skarn copper deposit, quartz vein gold deposit, and volcanic-type silver polymetallic deposits (Figure 11d).

1.
The Rb-Sr isochron age of sulfides from the Yingfang deposit obtained in this study mark the timing of mineralization as 135.7 ± 4.1 Ma, and the ore-forming materials were primarily derived from crust, with minor input of mantle materials.

2.
Mesozoic magmatism and mineralization in the Yingfang deposit mainly took place at 245 and 145-135 Ma. The Pb-Zn-Ag mineralization is related to large-scale inhomogeneous lithosphere thinning beneath the NCC. 3.
The silver polymetallic deposits in the YLMB possess similar sources of ore-forming materials. Data Availability Statement: Data available in a publicly accessible repository.

Conflicts of Interest:
The authors declare no conflict of interest.