Geology and Isotope Systematics of the Jianchaling Au Deposit , Shaanxi Province , China : Implications for Mineral Genesis

The giant Jianchaling Au (52 t Au) deposit is located in the Mian-Lue-Yang Terrane in the southern part of the Qinling Orogen of central China and is hosted by metamorphosed carbonate rocks of the Late Neoproterozoic Duantouya Formation. The deposit consists of multiple generations of mineralised quartz(-carbonate) veins in WNW-trending extensional ductile-brittle shear zones. Based on the mineral assemblages and cross-cutting relationships between the quartz(-carbonate) veins, the paragenesis is characterised by an early coarse-grained pyrite-pyrrhotite-pentlandite-dolomite-quartz assemblage (I), followed by pyrite-sphalerite-galena-carbonate-arsenopyrite-fuchsite-carbonate-quartz containing gold (II), and fine-grained pyrite-dolomite-calcite-quartz-realgar (As2S2)-orpiment (As2S3) (III). The H-O-C isotope systematics for the three vein sets indicate that the mineralising fluid is probably sourced from the metamorphic dehydration of carbonate rocks in the Duantouya Formation, and gradually mixed with meteoric water during the emplacement of the third vein set. The δ34S values for sulfides (6.3–16.6h) from the second auriferous vein set are greater than zero, indicating sulfates reduction from the Neoproterozoic metamorphic rocks (Duantouya Fm). The (Pb/Pb)i ratios from pyrite (17.521–18.477) from each of the vein sets overlap those of the ultramafic rocks (18.324–18.717) and the Bikou Group (17.399–18.417), indicating that the units are possible sources for the sulfides in the mineralisation. Both εNd(t) and Isr(t) of sulfide overlap with the meta-ultramafic field and Duantouya formation and dominated with mature Sr-Nd character, which indicated that the Duantouya may play an important role during the ore formation and there may exist a minor ultramafic source that is involved in the ore fluid. The S-Pb-Sr-Nd isotopic ratios are closely related to those of the Bikou Group and Duantouya Formation, which indicates that the mineralised fluid has interacted with both units. Combining the previously published data with data from this study on the mineralised area, we surmise that Jianchaling is characteristic of an orogenic-type gold deposit related to the Triassic Qinling Orogeny associated with continental collision.

The Jianchaling Au deposit is located in the triangular area marked by Mianxian, Lueyang, and Yangpingguan towns (MLY), in the South Qinling Terrane of the Qinling Orogen (Figure 1c).The deposit has a measured resource of 52 t Au with an average grade of 5 g/t hosted by quartz-veins in a ductile-brittle shear zone [21,[39][40][41][42][43].Even though the genesis of the mineralisation at the deposit has been studied, the source of the metals and nature of the mineralising fluids have remained unclear.
This contribution summarises the geology, mineralisation, and H-O-C-S stable and Pb-Sr-Nd isotopic systematics for the giant Jianchaling deposit with the aim to clarify the source of the metals and nature of the mineralising fluid.This, in turn, provides a better understanding of the tectonic and mineralising processes in MLY.

Geological Setting
The Qinling Orogen is located south of the North China Block (NCB) and has experienced a complex tectonic history [44][45][46].It is located in the central portion of the east-trending Central China Orogen, and developed during the Mesozoic collision between the North China and Yangtze blocks (Figure 1a,b) [1,[47][48][49].The Luanchuan Fault is the northern boundary of the orogen, and the southern boundary is the Longmenshan Fault.Deformation associated with the orogen extends into the Huaxiong Domain that is also included in the southern part of the Precambrian North China Block.The subdivisions of the orogen are shown in Figure 1b.
The Jianchaling deposit is a fault-controlled lode-gold deposit hosted by the Neoproterozoic Duantouya Fm in the eastern part of the MLY (Figure 1).The group unconformably underlies Late Paleozoic turbiditic successions in the Songpan-Ganzi Basin situated between the Mian-lue Suture to the north and Han Jiang Suture to the south (Figure 1c).The area is an important part of the Qinling Orogen and hosts many mineral deposits (e.g., Au, Cu, Ni, Zn, Pb, Mn) in various lithological and structural settings (Figure 1c), and is commonly known as the Golden Triangle [42].
The rock-types in the MLY area include metamorphosed Neoarchean granite-greenstones in the Yudongzi Complex, Neoproterozoic volcanic sequences in the Bikou Group, Late Neoproterozoic calcareous units in the Duantouya and Jiudaoguai formations, and Paleozoic carbonate in the Lueyang Formation (Figure 2).The Bikou Group is widespread in the area and consists of greenschist to amphibolite facies felsic and mafic volcanic protoliths.Various generations of metamorphism and ductile to brittle NE-and NW-trending faults (including thrusts and basin-forming extensional faults) have developed in the area, which control the location of felsic, mafic and ultramafic intrusive rocks and mineralisation (Figure 2).

Geology and Mineralization of the Jianchaling Area
Rocks outcropping in the Jianchaling area Neoarchean Yudongzi Complex, Neoproterozoic Bikou Group, Late Neoproterozoic Duantouya and Jiudaoguai formations, and Paleozoic Lueyang Group (Figure 2).The deposit can be subdivided into northern and southern zones containing five lenticular mineralisation in the WNW-trending Hejiayan and NW-trending Xiqugou faults and their splays.The richest mineralisation is the "No.1 Au orebody" that is 1950 m long, up to 23 m wide, and dips >43 • N.
The Hejiayan and Xiqugou faults are brittle-ductile shear zones [50], and host mineralised lenticular quartz veins at the contact between ultramafic rocks and calcareous beds in the Late Neoproterozoic Duantouya and Jiudaoguai formations (Figures 2 and 3).The quartz veins shallowly dip between 20 • and 40 • WSW is places in steeply dipping sections of the fault.The mineralisation includes native gold and lesser amounts of electrum and native silver associated with pyrite and minor amounts of hematite, magnetite, limonite, chromite, marcasite, realgar, and orpiment.The gangue minerals are dolomite, calcite and quartz, with minor amounts of serpentine, fuchsite, and albite (Figure 4a-c) [39].
Yue [21,39] recognized early deformed and recrystallised quartz-pyrite-carbonate vein crosscut by the quartz-gold-fuchsite-arsenopyrite-pyrite-magnetite second generation vein set, and the third generation of dolomite-calcite-quartz-fine-grained pyrite-realgar-orpiment veins (Figure 4c).The pyrite associated with each of the vein sets are also distinct from each other.The first vein set contains pyrite that is >2 mm across, variably fractured, anhedral to subhedral in shape, and intergrown with euhedral fuchsite and serpentine (Figure 4d,e).The second pyrite generation is not deformed, subhedral, 1-2 mm across, and commonly has cores or inclusions of the first generation pyrite, chalcopyrite, and sphalerite (Figure 4f,g).This pyrite is also commonly altered to hematite with martite pseudomorphing magnetite (Figure 4h).The third generation of pyrite is <10 µm across, subhedral to euhedral, and present in alteration zones containing the third vein (Figure 4i).The paragenesis is illustrated in Figure 5.

Sampling and Analytical Methods
Fresh samples were collected from each of the vein sets at depth in the Jianchaling mine.The samples were examined in thin section to confirm their paragenetic relationship.The sample characteristics are listed in Table 1.
Six samples of pyrite from the second (mineralised) vein set and five samples of the Duantouya Formation and meta-ultramafic from the wall-rock were collected for lead, strontium, and neodymium isotopic studies.The samples were crushed into power.
The samples were then crushed to a minus 10 mesh size (420 microns, and sulfide and carbonate fragments were handpicked under a binocular microscope.Between 10 and 50 mg of the powder was leached in acetone and washed in distilled and deionised water to remove contamination, then dried in an oven at 60 • C. The samples were then dissolved in a solution of HF + HNO 3 + HClO 4 , dried, and redissolved in 6 N HCl, redried, and redissolved in 0.5 N HCl (for Sr and Nd separation) or 0.5 N HBr (for Pb separation).The Sr and Nd fractions were separated following standard chromatographic techniques using AG50 × 8 and PTFE-HDEHP resins with HCl as eluent.The Pb fraction was separated using a strong alkali anion exchange resin with HBr and HCl as eluents.
The lead isotopes were analysed using a MAT-261 thermal ionization mass spectrometer with the standard NBS 981 in the Analytical Laboratory at the Beijing Research Institute of Uranium Geology, China.Measurements of the common-Pb standard NBS 981 gave average 208 Pb/ 206 Pb values of 2.1681 ± 0.0008, 207 Pb/ 206 Pb of 0.91464 ± 0.00033, and 204 Pb/ 206 Pb values of 0.059042 ± 0.000037; the uncertainty is of <0.1% at the 95% confidence level.Some of the U, Th and Pb values were used to estimate the Pb isotope ratios assuming an age of 198 Ma, which is the 40 Ar/ 39 Ar date determined on fuchsite from the Jianchaling deposit [39].These Pb isotopic ratios are presented as ( 208 Pb/ 204 Pb) i , ( 207 Pb/ 204 Pb) i and ( 206 Pb/ 204 Pb) i .
A TRITON thermal ionization mass spectrometer was used to measure the Sr and Nd isotopes in the Analytical Laboratory at the Tianjin Institute of Geology and Mineral Resources, China.The 87 Sr/ 86 Sr isotope ratios were normalized against the 86 Sr/ 88 Sr = 0.1194 and 143 Nd/ 144 Nd isotope ratios to 146 Nd/ 144 Nd = 0.7219.The JNdi Nd-Standard yielded 143 Nd/ 144 Nd ratios of 0.512118 ± 0.3 against a reference value of 0.512115 ± 0.7 [52], and the NBS 987 Sr standard with a reference level of 0.710248 was used yielding 87 Sr/ 86 Sr ratios of 0.710250 ± 0.7.The Sr and Nd isotopic compositions were measured with a thermal ionization ISOPROBE-T mass spectrometer.

Isotope Results
The following are isotopic values determined from samples from the Jianchaling deposit.

Carbon, Oxygen and Hydrogen Isotopes
The δ 13 C, δ 18 O and δD values from quartz and carbonate from each of the three vein sets and the surroundings rocks are listed in Table 2.These results are published on [21].The δ 13 C values for first vein set ranges from −4.4 to 0.6 , the δ 13 C values for the second (mineralised) vein set ranges from −2.9 to −0.4 , and the δ 13 C value for the third vein set is between −4.4 to 2.2 (Table 2).
The δ 18 O values from carbonate and quartz for the first vein set forms two groups of 18.9-23.4and 14.0-17.3 .The δ 18 O values from the second vein set are between 13.8 and 19.0 (averaging 16.4 ), and for the third vein set are between 11.9 and 16.3 (Table 2).

Sulfur Isotopes
The δ 34 S isotopic values for the sulfides samples are listed in Table 3 and cited from [21].The Jianchaling deposit is characterized by highly δ 34 S positive values with a narrow range.The first vein set has a δ 34 S value of 14.3 (Table 3).The second vein set has δ 34 S values between 8.2 and 14.3 .One shale rock sample of the Duantouya Formation have δ 34 S values of 16.6 .Two samples of the metamorphosed ultramafic rocks (listwanite and serpentinite) have δ 34 S values of 6.1 to 8.6 .

Lead Isotopes of Sulfides and Wall Rocks
The Pb isotopic analyses completed for this study and previous data are listed in Table 4.In order to compare the contribution of the wall rocks, we also put the lead isotopes of the wall rocks including Yudongzi Fm, Porphyritic granite, Duantouya Fm and Bikou Group in Table 3 4).

Strontium and Neodymium Isotopes of Sulfides and Wall Rocks
Four pyrite samples from the gold-bearing second generation vein set have I Sr values in the range 0.706709-0.715929(average of 0.711973, Table 5), which is similar to that of the meta-ultramafic rocks.The ( 143 Nd/ 144 Nd) i values of the samples are between 0.511376 and 0.512453 (average of 0.511823, Table 6), and the ε Nd values are between −19.6 and 1.4.
Samples from the Duantouya Formation have ( 143 Nd/ 144 Nd) i values of 0.511865-0.512114(average of 0.511953, Table 6), and ε Nd values of −10.1 to −5.3.The meta-ultramafic samples have ( 143 Nd/ 144 Nd) i values of 0.512137-0.512152(average of 0.512144, Table 6), and ε Nd values between −4.8 and −4.5.Notation: # the peak of homogenization temperatures (the range of homogenization temperatures) are from [39].The δ 18 O wtaer values were calculated using equations for quartz-water and carbonate-water [54,55].The δ 13 C in CO 2 equilibrated with dolomite and calcite were calculated using the equations of [56,57].The oxygen and hydrogen stable isotopes are often used to indicate the source of mineralised hydrothermal fluids [62].However, the overlap in the metamorphic and magmatic fields in δD versus δ 18 O diagrams creates uncertainty in deciphering the genesis of mineralisation [63].This is the case for the mineralising fluid at Jianchaling, which has been interpreted as being magmatic [64,65], meteoric [53], mixed metamorphic and magmatic [42,43,51], and primarily metamorphic [39].This places a significant doubt on the usefulness of the δD and δ 18 O values in directly pinpointing the origin of the mineralising fluid at Jianchaling.
Using fluid-inclusion homogenisation temperatures and detailed paragenetic studies by Yue [39] (Table 2), the δ 18 O water values were calculated using the quartz-water equation by [54] and carbonate-water equation by [55].The calculated quartz-carbonate δ 18 O values for the hydrothermal fluid associated with the first vein set range from 7.5 to 17.7 , the mineralised second vein set have δ 18 O values between 5.7 and 11.1 , and the third vein set range from 1.3 to 4.3 (Table 2).Using this data, the δ 18 O and δD values for first vein set plot in the magmatic field and close to the metamorphic field (Figure 6).However, assuming that magmatic fluids are generated above the lowest eutectic point at temperatures above 573 • C [66], continuous cooling and water-rock reactions result in reduction of δ 18 O water values during the crystallisation of hydrothermal minerals such as quartz and alkali feldspar [66].Furthermore, magmatic fluids have average δ 18 O water values of 18.8 at temperatures of 355 • C [39], which is the average homogenization temperature of fluid inclusions from first vein generation (Table 2).This means that the initial δ 18 O water value must have been higher than 18.8 at temperatures above 355 • C, which is higher than the 5.7-11.1 range for the mineralised second vein set.In addition, the Late Triassic to Early Jurassic plutons in the southern part of the Qinling Orogen commonly have δ 18 O values of <18.8 .The high δ 18 O values for the early hydrothermal fluids are consistent with a major contribution from metamorphic sources (rather than a minor contribution as suggested by Figure 6).This interpretation is supported by the low salinity and high CO 2 content of fluid inclusions in the first vein set [7,39].Furthermore, the δ 18 O values for quartz in granite porphyry and aplite in the area range between 11.3 and 14.5 [67].This indicates that the δ 18 O water value of 10.0 calculated at a temperature of ~573 • C for the first vein set cannot exceed the δ 18 O water value of 13.2 for the second vein set that crystallised at ~300 • C (as determined from the fluid inclusion homogenisation temperatures).In addition, the regional metamorphism in the Jianchaling area is at the greenschist facies [68], further supporting a ~300 • C temperature for the crystallisation of the mineralised second vein set.
The 3rd vein δ 18 O water values are between 1.3 and 4.3 , with a δD value of −81 , they are plot in the meteoric field in Figures 6 and 7.The δ18Owater values of carbonate-quartz from the mineralised vein set vary between 5.7 and 11.1 , which are values between those for the first and third vein sets.Exactly, on the base of the δ 18 O water values (5.7-11.1 ), we think the 2nd vein set is similar to lode gold deposits and add the possible range of the 2nd vein set in Figure 6 that based on the feature of many lode gold deposits worldwide.This is indicative of the mixing of metamorphic and meteoric fluids during mineralisation (Figure 6).
The δ 18 O values for quartz from lode-gold deposits around the world are higher than 10 with the values for the mineralising fluids ranging between 5 and 25 [6].The δ 18 O water values of the gold deposits on the Jiaodong Peninsula of eastern China range from 4.9 to 10.9 , with corresponding δ D values of −78 to −101 (Figure 6) [69,70].The δ 18 O and δD values for mineralising fluids at Jianchaling plot in the lode-gold deposit field (Figure 6; Table 2; [6]).Figure 6 also shows that the first vein set containing higher δ 18 O and δD values are sourced from metamorphic fluids.In contrast, the mineralised second vein set are similar lode gold deposits, and the fluids related to the third vein set have (again) a composition close to that of meteoric fluid.[71].Included are the fields for the Xiaoqinling and Jiaodong gold deposits [69]; Juneau gold belt, Mother Lode, Victorian Goldfields and Meguma Terrace Au deposits [6].

Carbon and Oxygen Isotopes
The δ 13 C CO2 values determined for quartz-carbonate from each of the vein sets are essentially the same, hovering around approximated zero (Figure 7).The corresponding δ 18 O SMOW values show a significant trend with the first vein set being approximately 15 , the mineralised second vein measuring around 9 , and the third being around 3 (Figure 7).The implication for this trend is that all of the vein sets have similar sources for carbon with a gradual decrease in available oxygen in the hydrothermal fluid with time.Another implication is that there was only one hydrothermal fluid that has changed in composition with time.
The δ 13 C CO2 values for the hydrothermal fluids related to the three vein sets are significantly higher than the values for organic matter (averaging −27 ) [62], the content of CO 2 in the atmosphere (−11 to −7 [62]), freshwater carbonate (−20 to −9 [72]), magmatic rocks (−30 to −3 [72]), the continental crustal (−7 [73]), and the mantle (−7 to −5 [72]).However, marine carbonate (i.e., −3 to 2 δ 13 C CO2 [72]) and carbonate in the wall rock (i.e., −0.4 to 2.3 δ 13 C CO2 ; Table 2), are similar in δ 13 C CO2 composition.This indicates a local source for the hydrothermal fluids related to each of the vein sets.In addition, the close relationship between the ultramafic rocks and the vein sets shown in Figure 7 indicates that the ultramafic rocks are also local sources for the carbon and oxygen in the hydrothermal fluids.[21].Data sources: greenschist facies carbonate rocks after [74]; reduced C in sedimentary and metamorphic rocks after [75]; carbonates in most orogenic Au deposits after [76].
On the other hand, the δ 13 C CO2 and δ 18 O SMOW of the mineralised fluids overlap with those of the forming fluid of Archean Au deposits (Figure 7).δ 18 O SMOW value of the third vein sets are similar with the meteoric water, indicating meteoric water mixed into the fluid system in late stage.

Sulfur Isotopes
The δ 34 S signatures for various in the MLY and others from throughout the world are presented in Figure 8.The figure shows that most of the sulfides in the MLY have δ 34 S signatures greater than zero, are predominantly higher than those for orogenic Au deposits throughout the world, and higher than those for basaltic magmatic rocks, overlap the sulfide values in ultramafic rocks, and are coincide with the high end of sulfides in metamorphic rocks.In fact, the δ 34 S signatures for the metamorphic rocks are the best fit, which includes the wallrocks at Jianchaling (Table 3).Such heavy δ 34 S values for the sulfides at Jianchaling is consistent with derivation from sulfates that are characterised by heavy δ 34 S values [77,78].It is envisages that organic material derived by the metasedimentary rocks in the study area would have reacted with sulfate resulting in the crystallisation of sulfides [78,79].Examples of such reducing agents are CH 4 , C 2 H 6 , H 2 S and graphite, which have been detected in fluid inclusions using Laser Raman [39].The conversion of sulfate to sulfide will proceed in the following chemical reaction: CH 4 + SO Therefore, the Neoproterozoic metamorphic rocks in the MLY are likely sources for sulfur in the Jianchaling area.[62,72,80]; Juneau gold belt, Bendigo Au, Kumtor Au and Major orogenic Au deposits in the world after [12,81]; Shanggong Au and Tieluping Ag after [44]; Yindongpo Au after [66]; Poshan Ag after [82]; Major Au deposits in the Qinling Orogen [24].

Lead Isotopes
The country rocks in the Jianchaling area have a wider range in Pb isotopic ( 206 Pb/ 204 Pb, 207 Pb/ 204 Pb and 208 Pb/ 204 Pb) ratios than the sulfides in the Jianchaling mineralisation (Table 4).
The range of the Pb-isotopes is shown in Figure 9 that includes trends defining tectonic settings [83].The range of Pb-isotopes shown in Figure 9 correlates with defined tectonic setting of orogenic and upper crustal fields, even though there is a limited number of 10 data points.This is in agreement with the observations made in the discussion section above.
Furthermore, these Pb signatures of the sulfides from the mineralisation overlap those of the ultramafic rocks and the Bikou Group, indicating that the units are possible sources for the sulfides in the mineralisation.In contrast, the distinct incongruence of the sulfides from the mineralisation and the granitic rocks indicates that the granitic rocks are not the source for the sulfides in the mineralisation (Figure 9).

Strontium and Neodymium Isotopes
The I Sr (t) values of sulfide samples from the Jianchaling deposit range from 0.706709 to 0.715929 (Table 5; Figure 10a).These values are higher than the mean values (0.703 to 0.705) established for mantle-derived oceanic basalt (MORB, OIB, IAB) and continental basalt, and are suggestive of a crustal source [84,85].
The I Sr (t) values for the sulfide samples from the deposit are also lower than those for the Duantouya Formation (Table 5), and the ( 143 Nd/ 144 Nd)i sulfide ratios for the mineralised second vein set overlap with those of the Duantouya Formation and the meta-ultramafic rocks (Table 6; Figure 10a,b).The εNd (t) and Isr (t) of sulfide are indicative of a crustal source and dominated with mature Sr-Nd character (Tables 5 and 6; Figure 10a), and εNd (t) overlaps with meta-ultramafic field, indicated that the Duantouya may play an important role during the ore formation and there may exist minor ultramafic source been involved in the ore fluid.The Bikou Group has I Sr (t) values that overlap with those from the Mian-Lue ophiolite, meta-ultramafic rocks, partly with the second vein set, and are lower than those from the Duantouya Formation (Figure 10a; Tables 5 and 6) [60,61,86].Although the pyrite in audiferous rocks has I Sr (t) values that overlap with porphyritic granite partly (Figure 10c), it is unlikely to come from porphyritic granite, the evidence is mainly from lead isotopes, as mentioned above.
These relationships can be explained with a mixing model where the mineralised sulfide-bearing fluids interacted with lithological units (Figure 10).This interpretation is supported by the conclusion drawn from the Pb isotope data collected from the Huachanggou gold deposit in the northwestern part of MLY [25,59] (Figure 1c).
Fuchsite separated from the mineralised second vein set yield a well-defined 40 Ar/ 39 Ar isotopic age of 198 ± 2 Ma, which suggests that the mineralisation took place during the Triassic Indosinian Orogeny [39].Implications of this are that the Neoproterozoic (ca.927 Ma) magma-hydrothermal event associated with the emplacement of ultramafic intrusions.Triassic (ca.216 Ma) porphyritic granites in the area are ~18 Ma older than the Jianchaling mineralisation, again indicating that the granites are not related to the gold mineralisation.
The C, H and O stable isotopes indicate that the ore-forming fluids are predominantly metamorphosed in origin and contaminated with meteoric fluid during the deposition of the gold at Jianchaling.On the other words, the mineralising fluid is probably sourced from the metamorphic dehydration of carbonate rocks in the Duantouya Formation, and gradually mixed with meteoric water.The 87 Sr/ 86 Sr, I Sr (t), ε Nd , Pb and S isotopic data (Figure 10) confirm that the sulfides in the mineralised are sourced from the metamorphosed Duantouya Formation, Bikou Group and minor ultramafic rocks.
From the discussion above, combining the comparison of the geological characteristics between Jianchaling and Orogenic gold deposit (Table 7), the Jianchaling deposit is here interpreted as an orogenic-type deposit and summarised in Figure 11.

Conclusions
Hydrogen, oxygen and carbon isotopic systematics indicate that the ore-forming fluids at the Jianchaling Au deposit progressively evolved from an early stage represented by the first vein set associated with deformation and metamorphism of the country rocks.This was succeeded by a late tectonic stage represented by the mineralised second vein set sourced from a mixed metamorphic and meteoric fluid, and progressed to a late stage represented by the third vein set.The S-Pb-Sr-Nd isotopic data indicate that the mineralising fluids were sourced locally around Jianchaling.From these observations, the Jianchaling Au deposit is interpreted as an orogenic Au deposit formed during the Mesozoic Indosinian Orogeny.

Figure 1 .
Figure 1.Geological maps showing: (a) the tectonic setting of China; (b) tectonic subdivision of Qinling Orogen and location of the Mianxian, Lueyang, and Yangpingguan (MLY) area[18]; and (c) regional geology and location of gold deposits in the MLY[39].

Figure 3 .
Figure 3. Cross-section of the of the Jianchaling Au deposit at a 870 m elevation showing the relationship of the mineralisation and fault [21,51].

Figure 4 .
Figure 4. Photomicrographs of samples from the Jianchaling Au eposit showing: (a) intergrown pyrite and fuchsite in the mineralised second vein set; (b) a second vein set with quartz containing pyrite; (c) third vein set with comb-like quartz, calcite and dolomite vein orpiment and realgar; (d) pyrite in the first vein set intergrowth; (e) fine-grained cataclastic pyrite following schistosity developed during brittle-ductile deformation before emplacement of the mineralised second vein set; (f) pyrite wrapping sphalerite and chalcopyrite in the mineralised second vein set; (g) pyrite in the first vein set overgrown by pyrite related to the mineralised second vein set; (h) hematite formed from pyrite, and martite; (i) euhedral fine-grained pyrite in the third vein set.Abbreviations: Cal = calcite; Car = carbonates; Cpy = chalcopyrite; Dol = dolomite; Fuc = fuchsite; Hm = hematite; Orp = orpiment; Py = pyrite; Q = quartz; Rea = realgar; Sph = sphalerite.
. Sulfides from gold deposits have 206 Pb/ 204 Pb values between 17.257 and 18.477, 207 Pb/ 204 Pb values between 15.530 and 15.704, and 208 Pb/ 204 Pb values of 36.927 to 38.757 (Table 4).Their calculated ( 206 Pb/ 204 Pb) i , ( 207 Pb/ 204 Pb) i and ( 208 Pb/ 204 Pb) i values are the same as the measured values due to their very low U and Th contents.Therefore, the analytical data is interpreted as being reliable and representative of the source for metals in the mineralising fluid.The ultramafic rocks have 206 Pb/ 204 Pb values of 17.952-19.193, 207Pb/ 204 Pb values of 15.520-15.785,and 208 Pb/ 204 Pb ratios of 36.029-38.920(Table

Table 4 .
Lead isotope composition of ore sulfide and wallrocks at the Jianchaling deposit and in the Bikou Group.

Table 5 .
The Sr isotope ratios of sulfides and wallrocks at the Jianchaling Au deposit and in the Bikou Group.

Table 6 .
The Nd isotope ratios of sulfides and wallrocks at the Jianchaling deposit.

Table 7 .
Geological characteristics comparison between the Jianchaling and Orogenic gold deposit.

Table 7 .
Cont. ± CH 4 ± N 2 ± H 2 S. The fluids inclusion type has H 2 O-CO 2 , rich CO 2 (with an unquantifiable CH 4 and a small amount of H 2 O) and gas-liquid two-phase H 2 O inclusions Aqueous solution with low salinity and low density, containing CO 2 ± CH 4 ± H 2 S. The fluids inclusion type has NaCl-H 2 O, CO 2 -H 2 O-NaCl ± CH 4 and pure CO 2 -CH 4