Genesis and Evolution of Hydrothermal Fluids in the Formation of the High-Grade Hishikari Gold Deposit: Carbon, Oxygen, and Sulfur Isotopic Evidence

: The Hishikari low-sulﬁdation epithermal gold (Au) deposit in Kyushu, Japan, is world-famous for its premium ore. It has been hypothesized that magmatic contributions to the hydrothermal ﬂuid during early stages of mineralization is possible, even if the hydrothermal ﬂuids for many Au occurrences near the Hishikari deposit are of meteoric origin and are inﬂuenced by basement sedimentary rocks. The purpose of this study is to obtain constraints on the genesis and evolution of hydrothermal ﬂuids in the formation of the high-grade Hishikari Au deposit by carbon and oxygen isotope ratios of calcite-bearing samples. Since the microanalysis of carbon and oxygen isotope ratios in every 12 µ m of the calcite-bearing sample along the growth direction (corresponding to 10 years of the Hishikari mineralization) scatter in a particular range, the ﬂuid evolution might not be a gradual change from a magmatic to a meteoric origin. Alternatively, a rapid turnover of two ﬂuids might be happening locally. The average sulfur isotope ratio of hydrothermal pyrite is similar to that of the adjacent magma. However, according to the secondary ion mass spectrometry (SIMS) microanalysis, local pyrite with extremely low sulfur isotope ratios may interact with basement sedimentary rocks. Unlike other epithermal Au deposits in the vicinity, rapid local mixing of the magmatic-origin deep ﬂuid and meteoric-origin ﬂuid reacted with organic matter containing basement sedimentary rocks might cause gold precipitation at the Hishikari deposit.


Introduction
It is crucial to research the Hishikari gold (Au) deposit in Kyushu, Japan, as an example of vein-type high-grade Au deposits because of its highly regarded high-grade ore.The Sumitomo Metal Mining Co., Ltd. has been mining the Hishikari deposit since 1985.The Hishikari mine has produced 260 metric tons of Au, and the ore reserve amounts to 160 metric tons.The Au production in 2021 is 6 metric tons [1].The average grade of ore is 34 g/t Au, which is significantly higher than those of neighboring and average mines worldwide.An important question to ask is why the Hishikari deposit is of a higher grade among Au deposits in the same district.The early-stage hydrothermal fluid in the Hishikari deposit was enriched in 18 O over local meteoric water, despite its low-sulfidation epithermal deposit [2].Several studies [2][3][4][5][6] have pointed out the possibility of magmatic contribution to the hydrothermal fluid in the earlier stage of mineralization.These previous studies focus on the genesis and evolution of hydrothermal fluids in forming the high-grade Hishikari Au deposit.Fluid-rock reactions play a vital role in the carbon and oxygen isotope budgets of geologic settings of ore-forming hydrothermal systems in the Earth's crust.Although many studies on isotopes in calcites have been undertaken, few researchers have expressed an interest in utilizing the isotope data of hydrothermal calcite.This is partly because calcite often occurs in the last stage of hydrothermal mineralization; therefore, a calcite vein is considered a barren vein in mining districts.However, fertile calcite veins may also exist in the exact location of barren calcite veins.Therefore, this study proposes using calcite's isotope data.Although oxygen isotope ratios of quartz from the Hishikari veins have been reported [2][3][4][5][6], the veins contain silicate minerals such as adularia other than quartz.Therefore, merely analyzing pure quartz is not an easy task.However, calcite isotope data can be obtained using acid from quartz veins containing other silicate minerals.
Furthermore, the calcite isotope measurements still include specific details about the fluid that coexisted with it.Therefore, a set of calcite carbon and oxygen isotope ratios has better information than the oxygen isotope ratio of vein quartz.Consequently, isotope ratio mass spectrometry (IRMS) was used to examine the carbon and oxygen isotope ratios of samples that contained calcite.
On the other hand, pyrite is ubiquitous in the Hishikari veins.Therefore, Morishita et al. [7,8] conducted a microanalysis of Au and As concentrations in pyrite grains to indicate that the Au concentration positively correlates with the As concentration in a small area.Furthermore, sulfur isotope ratios of pyrite help constrain the source of sulfur.Therefore, sulfur isotope ratios of pyrite were measured using secondary ion mass spectrometry (SIMS).
The purpose of this study is to obtain constraints on the genesis and evolution of the hydrothermal fluids in the formation of the high-grade Hishikari Au deposit.Additionally, the isotopic characteristics of the fluid in the Hishikari deposit will be discussed.

Geologic Setting and Au Deposits
Kyushu is located at the eastern margin of the Eurasian plate facing the Philippine Sea plate.Numerous epithermal Au deposits from the Pliocene to Pleistocene are found in Late Cenozoic subaerial andesitic to dacitic volcanic rocks that resulted from the subduction of the Philippine Sea plate beneath the Eurasian plate (Figure 1).The Hokusatsu district of southwestern Kyushu (Figure 1) has the highest Au production in Japan.Most of the ore deposits in this district, such as the Hishikari and Kushikino deposits, sit above a typical basement of the Shimanto Group.
The Hishikari low-sulfidation epithermal Au deposit (Figure 1) is the largest in Japan.Hosono et al. [9] determined the Sr-Nd-Pb isotope compositions of Late Pliocene to Pleistocene volcanic rocks around the Hishikari deposit to elucidate their source characteristics of magma related to gold mineralization.The basement rocks in the Hishikari mining area are sedimentary rocks from the Lower Shimanto Group (Cretaceous accretionary wedge), which are visible underground but do not outcrop close to the deposit.The Hishikari Lower Andesites consist mainly of andesitic pyroclastic rocks.They cover the basement sedimentary rocks unconformably and have been dated by the K-Ar method to be from 1.62 ± 0.09 to 0.98 ± 0.10 Ma for 15 whole-rock samples from within 2 km of the Hishikari mine [10,11].Several studies have previously described the Hishikari deposit's geology (e.g., [9][10][11][12][13][14][15][16]).

Gold-Bearing Veins and Mineral Paragenesis
The Hishikari deposit consists of the Sanjin, Honko, and Yamada ore zones (Figure 2).Each ore zone has multiple vein swarms that extend roughly 1 km from NE to SW.The Hishikari veins strike N50 • E and dip steeply north (70-90 • ).The Sanjin and Honko ore zones comprise high-grade Au-bearing quartz veins in the basement sedimentary rocks of the Cretaceous Shimanto Group and in the andesitic rocks of the Hishikari Lower Andesites that overlie the basement sedimentary rocks.However, relatively low-grade Aubearing quartz veins in the Yamada ore zone occur in the andesitic rocks.K-Ar ages show that the Hishikari deposit's mineralization started at 1. 15 Ma and ended at 0.60 Ma [11].Sanematsu et al. [18] determined the 40 Ar/ 39 Ar ages of the Hishikari adularia-quartz veins.The mineralization ages in the Honko and Sanjin zones range from 1.04 to 0.75 Ma, whereas the majority of results are focused in the range of 1.01-0.88Ma and those in the Yamada zone range from 1.21 to 0.64 Ma [18].Epithermal gold deposits in Kyushu, southwestern Japan (produced from [12,17]).In southern Kyushu, epithermal gold deposits occur in Late Cenozoic subaerial andesitic to dacitic volcanic rocks in the Hokusatsu district.The basement rocks in the district are sedimentary rocks of the Lower Shimanto Group (Cretaceous accretionary wedge), which do not outcrop near the deposits.The location of the Hishikari, Kushikino, and Noya deposits are shown.

Gold-Bearing Veins and Mineral Paragenesis
The Hishikari deposit consists of the Sanjin, Honko, and Yamada ore zones (Figure 2).Each ore zone has multiple vein swarms that extend roughly 1 km from NE to SW.The Hishikari veins strike N50°E and dip steeply north (70-90°).The Sanjin and Honko ore zones comprise high-grade Au-bearing quartz veins in the basement sedimentary rocks of the Cretaceous Shimanto Group and in the andesitic rocks of the Hishikari Lower Andesites that overlie the basement sedimentary rocks.However, relatively low-grade Aubearing quartz veins in the Yamada ore zone occur in the andesitic rocks.K-Ar ages show that the Hishikari deposit's mineralization started at 1.15 Ma and ended at 0.60 Ma [11].Sanematsu et al. [18] determined the 40 Ar/ 39 Ar ages of the Hishikari adularia-quartz veins.The mineralization ages in the Honko and Sanjin zones range from 1.04 to 0.75 Ma, whereas the majority of results are focused in the range of 1.01-0.88Ma and those in the Yamada zone range from 1.21 to 0.64 Ma [18].Epithermal gold deposits in Kyushu, southwestern Japan (produced from [12,17]).In southern Kyushu, epithermal gold deposits occur in Late Cenozoic subaerial andesitic to dacitic volcanic rocks in the Hokusatsu district.The basement rocks in the district are sedimentary rocks of the Lower Shimanto Group (Cretaceous accretionary wedge), which do not outcrop near the deposits.The location of the Hishikari, Kushikino, and Noya deposits are shown.
The Hishikari veins consist mainly of quartz, adularia, and smectite.The metallic minerals in the Hishikari veins are pyrite, marcasite, electrum, naumannite, aguilarite, pyrargyrite, and chalcopyrite [10], of which pyrite is the most abundant.The host rocks also contain hydrothermal pyrite [7,8].Additionally, the veins contain minor amounts of calcite and truscottite [10].The homogenization temperatures for quartz in veins within the basement sedimentary rocks average 213 • C, with most values in the range of 195-230 • C [10].The strontium and carbon isotopic ratios of calcite reveal that the Hishikari ore fluid was affected by the sedimentary basement rocks [19].Bladed quartz (lamellar quartz) is found everywhere in the Hishikari deposit [10,20].When initially produced, calcite reacts with later low-temperature fluids; and it dissolves because calcite's solubility rises as the hydrothermal fluid's temperature falls, leaving cavities for later quartz to precipitate as bladed quartz [10,20].Bladed quartz signifies that bladed calcite was once deposited by boiling fluid and then dissolved during cooling.Boiling occurred during the Hishikari mineralization based on the observations of fluid inclusions [10,14,20].However, other studies [4,21] do not recognize the evidence of boiling in the fluid inclusion observations, suggesting that not all areas of boiling were subject to it.Calcite precipitation from the hydrothermal fluid occurs either with increasing temperature or pH or with decreasing fugacity of CO 2 [22].Among them, loss of CO 2 because of boiling might happen in the Hishikari hydrothermal fluid, and cause calcite precipitation.The Hishikari veins consist mainly of quartz, adularia, and smectite.The metallic minerals in the Hishikari veins are pyrite, marcasite, electrum, naumannite, aguilarite, pyrargyrite, and chalcopyrite [10], of which pyrite is the most abundant.The host rocks also contain hydrothermal pyrite [7,8].Additionally, the veins contain minor amounts of calcite and truscottite [10].The homogenization temperatures for quartz in veins within the basement sedimentary rocks average 213 °C, with most values in the range of 195-230 °C [10].The strontium and carbon isotopic ratios of calcite reveal that the Hishikari ore fluid was affected by the sedimentary basement rocks [19].Bladed quartz (lamellar quartz) is found everywhere in the Hishikari deposit [10,20].When initially produced, calcite reacts with later low-temperature fluids; and it dissolves because calcite's solubility rises as the hydrothermal fluid's temperature falls, leaving cavities for later quartz to precipitate as bladed quartz [10,20].Bladed quartz signifies that bladed calcite was once deposited by boiling fluid and then dissolved during cooling.Boiling occurred during the Hishikari mineralization based on the observations of fluid inclusions [10,14,20].However, other studies [4,21] do not recognize the evidence of boiling in the fluid inclusion observations, suggesting that not all areas of boiling were subject to it.Calcite precipitation from the hydrothermal fluid occurs either with increasing temperature or pH or with decreasing fugacity of CO2 [22].Among them, loss of CO2 because of boiling might happen in the Hishikari hydrothermal fluid, and cause calcite precipitation.
Additionally, mixing fluids might increase temperature or pH, resulting in calcite precipitation.Therefore, calcite might initially form by boiling or mixing fluids.Ore fluids that formed the banding structure of veins, have passed through the veins and they might dissolve most of the calcite precipitated from earlier fluids, because the solubility of calcite increases as the temperature drops.Because of this, calcite is rarely observed in the veins of the Hishikari deposit, and there haven't been many investigations on the carbon and oxygen isotopes of calcite.In this study, we attempted to find as much calcite as possible in the Hishikari deposit and we analyzed the calcite-bearing samples' carbon and oxygen isotope ratios.The presence of ubiquitous pyrite shows that the Hishikari hydrothermal system was under reducing conditions.The mixing of deep fluids with shallow groundwater is thought to have considerably altered the temperature and oxidation conditions of the hydrothermal fluids at the boundary between the basement rocks and the overlying Additionally, mixing fluids might increase temperature or pH, resulting in calcite precipitation.Therefore, calcite might initially form by boiling or mixing fluids.Ore fluids that formed the banding structure of veins, have passed through the veins and they might dissolve most of the calcite precipitated from earlier fluids, because the solubility of calcite increases as the temperature drops.Because of this, calcite is rarely observed in the veins of the Hishikari deposit, and there haven't been many investigations on the carbon and oxygen isotopes of calcite.In this study, we attempted to find as much calcite as possible in the Hishikari deposit and we analyzed the calcite-bearing samples' carbon and oxygen isotope ratios.The presence of ubiquitous pyrite shows that the Hishikari hydrothermal system was under reducing conditions.The mixing of deep fluids with shallow groundwater is thought to have considerably altered the temperature and oxidation conditions of the hydrothermal fluids at the boundary between the basement rocks and the overlying andesites [10].
The Hishikari veins frequently have symmetrical formations, which suggests that vein minerals near the wall rock precipitate earlier than the minerals inside the vein.The outer band close to the wall rock consists mainly of adularia and quartz, and the innermost band in the center consists mainly of quartz [14].However, in the Hishikari veins, asymmetrical formations produced by cutting with later-stage veins are not uncommon.According to the observed crosscutting connections of the veins, Sekine et al. [16] divided the vein system of the Hishikari deposit into early and late veins according to the observed crosscutting relationships of veins.The late veins commonly display symmetrical banding, whereas banding in the early veins is often obscured.

Calcite-Bearing Hand Specimens
Calcite-bearing vein samples obtained were investigated for their mineral compositions using an X-ray diffractometer (XRD) SmartLab (Rigaku, Tokyo, Japan) at Shizuoka University.Figure 2 and Table 1 show calcite-bearing samples' locality and mineral compo-sition.The approximate abundance of calcite was obtained from the XRD calibration curves.Electrum is very fine-grained for microscopic observations.Photos of representative vein samples are shown in Figure 3.   and c (Table 1) are shown.(b) Sample 31002 with the analysis localities a and b (Table 1) are shown.

A Calcite-Dominant Vein Sample for Microanalysis
The Hishikari deposit's high-grade vein sample 20100317 (Figure 4a), taken from a 25 mL E60 Keisen 3-1E, contains continuous calcite in the growth direction.The vein width is about 50 cm.The Keisen No. 3 vein swarms are representative fertile veins in the Sanjin ore zone [8,16].Therefore, vein sample 20100317 is suitable for investigating the fluid evolution in the Hishikari ore-forming hydrothermal system, and no other appropriate sample has been found so far.The vein was expanding from right to left in Figure 4a because  and c (Table 1) are shown.(b) Sample 31002 with the analysis localities a and b (Table 1) are shown.

A Calcite-Dominant Vein Sample for Microanalysis
The Hishikari deposit's high-grade vein sample 20100317 (Figure 4a), taken from a 25 mL E60 Keisen 3-1E, contains continuous calcite in the growth direction.The vein width is about 50 cm.The Keisen No. 3 vein swarms are representative fertile veins in the Sanjin ore zone [8,16].Therefore, vein sample 20100317 is suitable for investigating the fluid evolution in the Hishikari ore-forming hydrothermal system, and no other appropriate sample has been found so far.The vein was expanding from right to left in Figure 4a because its proper end is close to the wall rock, and its left end corresponds to the vein's center.This sample was cut into 10 mm widths and named for each from 1743 to 1749 (10 mm-width sample set), as shown in Figure 4b and Table 2. Then 1761, 1762, and 1763 samples were further cut to a width of 0.9 mm (Figure 4c) with a cutting machine, Minitom (Struers, Denmark) at Shizuoka University and obtained 176-1 to 176-21 sections (0.9 mm-width sample set; Table 3).The 1763 sample corresponds to the same stage as 1743 (Figure 4b).Therefore, compared to the 10 mm-width sample set, the 0.9 mm-width sample set (1761-1763) indicates earlier stages than the 10 mm-width sample set.The blue lines in Figure 4c represent space, which corresponds to the thickness of the blade, 0.3 mm, so the sample interval in the growth direction is 1.2 mm.The quartz-adularia vein's approximate calcite abundance is determined via the XRD calibration curve (Table 3).The 176-1 section consists of 69% of quartz and 31% of adularia (determined by XRD calibration curve) with a minor amount of fine-grained pyrite and clay minerals, which causes the gray color in the early-stage mineral precipitations.Finer samples in the subsequent work were obtained to increase the time resolution.Although cutting the vein sample on a micron scale is impractical, Shizuoka University's biological microtome (FX-801N, Yamato Kohki Industrial Co., Ltd., Saitama, Japan) can    Finer samples in the subsequent work were obtained to increase the time resolution.Although cutting the vein sample on a micron scale is impractical, Shizuoka University's biological microtome (FX-801N, Yamato Kohki Industrial Co., Ltd., Saitama, Japan) can be used to scrape off a small portion of the calcite-rich soft sample.The 176-20 and 176-21 sections (Figure 4c) contain more than 70% of calcite, and they are soft enough to scrape off calcite-dominant powder from the samples with a stainless steel blade of the microtome.The average scraped sample size is roughly 0.4 mg, corresponding to a sample width in the original sample's growth direction of about 12 μm.The continuous samples Quartz (19), Calcite (81) −6.5 Finer samples in the subsequent work were obtained to increase the time resolution.Although cutting the vein sample on a micron scale is impractical, Shizuoka University's biological microtome (FX-801N, Yamato Kohki Industrial Co., Ltd., Saitama, Japan) can be used to scrape off a small portion of the calcite-rich soft sample.The 176-20 and 176-21 sections (Figure 4c) contain more than 70% of calcite, and they are soft enough to scrape off calcite-dominant powder from the samples with a stainless steel blade of the microtome.The average scraped sample size is roughly 0.4 mg, corresponding to a sample width in the original sample's growth direction of about 12 µm.The continuous samples (12 µm-width sample set) in the growth direction obtained from 176-20 and 176-21 sections are listed in Table 4.The scraped thickness is calculated from the weight of the powder scraped, and Table 4 s distance from the microtome cutting's starting point (the 'origin' that is the line separating 176-19 and 176-20) is displayed.The number attached to the original sample number (176-19 and 176-20) indicates the order of crystallization; namely, 176-20-1 is the earliest end of the 176-20 section, and 176-20-12 is the latest grown sample, about 0.14 mm from the origin.176-20 section with a thickness of about 0.76 mm remained unscraped since the sample was broken during the subsequent cutting.176-21 section was divided into 17 samples, from 176-21-1 to 176-21-17.Each scraped size was similar to that for 176-20, and the distance from the same 'origin' is shown in Table 4.The 176-21 section was broken during the 18th cutting after 17 sample powders were obtained.Notably, 29 mineral samples were collected, despite the difficulty of cutting vein samples with a biological microtome.Be aware that the 176-20-12 and 176-21-1 sample differ by approximately 1.06 mm (the blade thickness and the remainder of the 176-20 sample).

Pyrite Samples
Pyrite samples were collected from the main veins of the three ore zones of the Hishikari deposit.The grain size of pyrite is fine, it is mostly between 10 and 30 μm. Figure 2 and Table 5 show the locality of analyzed veins, which are Keisen veins (Sanjin ore zone), Zuisen and Hosen veins (Honko ore zone), and Yusen veins (Yamada ore zone).Additionally, Table 5 includes two chalcopyrite grains for analysis.Figure 5 shows backscattered electron (BSE) images of representative pyrite and chalcopyrite grains.Additionally, pyrite grains in the host rock (shale) adjacent (within 2 cm from the vein boundary) to the Hosen No. 1 vein were also used for analysis.Au and As concentrations were analyzed using SIMS [8,23] on the same pyrite samples used in this study (

Pyrite Samples
Pyrite samples were collected from the main veins of the three ore zones of the Hishikari deposit.The grain size of pyrite is fine, it is mostly between 10 and 30 µm. Figure 2 and Table 5 show the locality of analyzed veins, which are Keisen veins (Sanjin ore zone), Zuisen and Hosen veins (Honko ore zone), and Yusen veins (Yamada ore zone).Additionally, Table 5 includes two chalcopyrite grains for analysis.Figure 5 shows backscattered electron (BSE) images of representative pyrite and chalcopyrite grains.Additionally, pyrite grains in the host rock (shale) adjacent (within 2 cm from the vein boundary) to the Hosen No. 1 vein were also used for analysis.Au and As concentrations were analyzed using SIMS [8,23] on the same pyrite samples used in this study (Table 5).

Carbon and Oxygen Isotope Ratios of Calcite
IRMS determined calcite-bearing samples' carbon and oxygen isotope ratios using the method described in [24].Several aliquots of the powder sample of 0.15 mg each are kept in steel thimbles and dropped down one-by-one into phosphoric acid at 60 • C in an online reaction chamber under vacuum conditions [24].Evolved gas is cryogenically purified to retain CO 2 .The reaction chamber is connected to the inlet system of a Finnigan MAT-250 mass spectrometer (Thermo Finnigan, Bremen, Germany) at Shizuoka University.Isotope ratios are reported in standard δ notation in per mil (‰) relative to the Vienna standard mean ocean water (SMOW) for δ 18 O and relative to the Vienna Pee Dee Belemnite (PDB) for δ 13 C. Reproducibility was approximately ±0.1‰ (2σ) for both the δ 13 C PDB and δ 18 O SMOW values of calcite.Using measurements on a laboratory working standard and the NBS 19, measured isotope ratios were normalized to limestone reference material [25].

Sulfur Isotope Ratios of Pyrite
Sulfur isotope ratios of pyrite were determined using an ims-1270 SIMS (Cameca, France) with a multi-collector at the Geological Survey of Japan (GSJ), National Institute of Advanced Industrial Science and Technology (AIST).Analysis was conducted using positive primary ions and negative secondary ions.A 10 kV defocused Cs+ primary beam (Köhler illumination) was restricted to 20 µm in diameter by a circular aperture to obtain a homogeneous primary beam of about 1 nA.Additionally, an electron flood gun was deployed on the sample surface for charge compensation to achieve better stability of the secondary ions.A 20 µm-diameter circle that served as the primary beam bombardment's target area is the area that was examined on the sample surface.Sputtered negative secondary ions with an accelerating voltage of −10 kV were extracted from the carboncoated sample surface.To guarantee that the same energy band of secondary ions was consistently chosen for experiments, an energy window of 50 eV was adjusted to the energy distribution curve.The secondary 32 S − and 34 S − ions were detected simultaneously without energy filtering using Faraday cups of the multi-collection system.The primary beam intensity was adjusted to around 1 nA to generate a high intensity of secondary ions ( 32 S = 2 × 10 8 cps) for high-accuracy sulfur isotope studies.The measured data were normalized using a working standard sample (Ak pyrite, δ 34 S = +5.1‰)and are reported utilizing the standard δ notation in per mil (‰) relative to Canyon Diablo Troilite for δ 34 S. The accuracy is less than ±0.2‰ (2σ).

Carbon and Oxygen Isotope Ratios of Calcite
IRMS determined calcite-bearing samples' carbon and oxygen isotope ratios using the method described in [24].Several aliquots of the powder sample of 0.15 mg each are kept in steel thimbles and dropped down one-by-one into phosphoric acid at 60°C in an online reaction chamber under vacuum conditions [24].Evolved gas is cryogenically purified to retain CO2.The reaction chamber is connected to the inlet system of a Finnigan MAT-250 mass spectrometer (Thermo Finnigan, Bremen, Germany) at Shizuoka University.Isotope ratios are reported in standard δ notation in per mil (‰) relative to the Vienna standard mean ocean water (SMOW) for δ 18 O and relative to the Vienna Pee Dee Belemnite (PDB) for δ 13 C. Reproducibility was approximately ±0.1‰ (2σ) for both the δ 13

Microanalysis of Calcite from a Calcite-Dominant Vein
Continuous carbon and oxygen isotope analysis of the calcite-dominant vein (20100317 sample) was determined.Samples from 1743 to 1749 (10 mm-width sample set; Figure 4b) were first assessed to understand the isotopic trend through the growing direction.The most central portion of the vein, the 1748 and 1749 samples, have just 100% quartz and no calcite.The δ 13 C and δ 18 O values of calcite range from −7.7‰ to −4.8‰ and from +3.4‰ to +8.2‰, respectively (Table 2).The value of δ 13 C tends to increase in the growth direction, although the value of δ 18 O does not significantly change except for the latest 1747 sample having a higher value.
Every 12 µm of the sample made using a microtome (12 µm-width samples) is microanalyzed for δ 13 C and δ 18 O values in the direction of growth.The δ 13 C and δ 18 O values range from −9.5‰ to −2.5‰ and from +3.6‰ to +10.9‰, respectively (Table 4).Additionally, the distance in µm from the boundary between 176-19 and 176-20 is shown to understand each sample's positional relationship (Table 4).

Sulfur Isotope Ratios of Pyrite
Sulfur isotope ratios of pyrite in quartz veins from three ore zones were determined using SIMS.The δ 34 S values of pyrite from the Sanjin ore zone range from −16.5‰ to +3.5‰ (Table 5).The δ 34 S values of pyrite from veins and sedimentary rocks in the Honko ore zone range from −3.4‰ to +2.1‰ and from +0.7‰ to +3.2‰, respectively (Table 5).The δ 34 S values from the Yamada ore zone range from −2.0‰ to +4.5‰ (Table 5).The δ 34 S values of two chalcopyrite grains from the Zuisen No. 1 vein are −1.4‰ and +1.0‰.The average δ 34 S value of the whole data is −0.7‰.The average δ 34 S values of pyrites in veins and sedimentary rocks are −1.1‰ and +2.0‰, respectively.As the grain size of pyrite is small (mostly between 10 and 30 µm) relative to the analysis area (20 µm), separate analytical values for the rim and core of pyrite are unavailable.

Role of Basement in the Epithermal Au Deposits in Kyushu
Fluid-rock dynamics significantly impact the carbon and oxygen isotope budgets of the geologic contexts of ore-forming hydrothermal systems.First, let's consider the geologic settings of the Kushikino deposit adjacent to the Hishikari deposit (Figure 1).The Kushikino deposit occurs in Pliocene andesitic rocks, and the basement rocks of the deposit are sedimentary rocks of the Lower Shimanto Group (a Cretaceous accretionary wedge).On the other hand, the Noya deposit is found in Pleistocene andesitic rocks in northern Kyushu (Figure 1).The deposit's basement rocks are high-temperature metamorphic and granitic rocks of the Cretaceous period.The influence of basement rocks on the ore-forming fluid is examined in the Kushikino and Noya deposits.The δ 13 C values in the fluid for the Noya and Kushikino gold deposits in Kyushu were estimated to be −6.5‰[26] and −10.8‰ [19,27], respectively.The calculated δ 13 C value of about −7‰ for the Noya deposit is regarded as average crustal carbon (e.g., [28,29]) and as deep-seated sources (e.g., [30,31]).Both deposits have andesitic host rocks, although the basement rocks are mostly granitic for the Noya deposit and sedimentary accretionary rocks for the Kushikino deposit.The difference in basement rocks might cause the difference in δ 13 C value between the two deposits.The δ 13 C value in the Kushikino fluid might be lowered by about 4‰ by reactions with organic carbon in the basement sedimentary rocks [19].
The isotopic equilibrium fractionation lines for calcite from the Kushikino and Noya deposits are shown in Figure 6.The δ 13 C and δ 18 O values of most calcite from the Kushikino deposit lie on the isotopic equilibrium fractionation lines, the Kushikino trend (Figure 6), which suggests that the reaction with the basement sedimentary rocks occurred not locally but in a vast reservoir.There is a discrepancy between the two trends in Figure 6 because the basement rocks for the two deposits are different.Calcites from the Lower Shimanto Group sedimentary basement rocks that are part of the epithermal Au deposits in the Hokusatsu district (Figure 1) are located on the Kushikino trend [19,32].The widely distributed basement rocks of the Shimanto Group may have exerted regional control over the district's relatively low and homogeneous δ 13 C values of ascending ore-forming fluids [32].The Sr isotope ratios ( 87 Sr/ 86 Sr) of the Naya's veins are the same as adjacent andesite (0.704).However, the ratios of the Kushikino and Hishikari veins are both high (higher than 0.706), which is attributed to reactions with basement Cretaceous sedimentary rocks with high Sr isotope ratios [26].So, the δ 13 C depletion and 87 Sr/ 86 Sr enrichment show the basement influence on Kyushu's epithermal ore-forming fluid.2) represent equilibrium fractionation trends for calcite under the assumption that H2CO3 [33] and HCO3 - [34] are the predominant carbon species in the fluid, respectively.The δ 13 C and δ 18 O values of the Noya fluid for both curves are obtained to be -6.5‰ and -7.5‰, respectively [26].The temperatures marked on the upper x-axis are isotopic equilibrium temperatures [35].Curves ( 3) and ( 4) are equilibrium fractionation trends for calcite from the Kushikino deposit.The δ 13 C and δ 18 O values of the Kushikino fluid for both curves are obtained to be -10.8‰and -7.0‰, respectively [19].At about 140°C with decreasing temperature, the predominant carbon species in the Kushikino fluid changed from H2CO3 to HCO3 - [27].Samples of the Kushikino veins are from the Kushikino deposit, and those of the Kammuridake veins are from a peripheral area of the deposit.The oxygen isotopic equilibrium temperatures for the Kushikino hydrothermal fluid are marked on the lower x-axis.1).The average global δ 13 C value of C3 plants is approximately −28.5‰ [36].Local pyrolysis or microbial decomposition of these organic materials in the basement sedimentary rocks can result in the production of CO2.The fluid temperature at the precipitation of the very low δ 13 C calcite is calculated to be around 45°C using the δ 18 O values of the calcites and calibration curve of O'Neil et al. [35], assuming that the δ 18 O value of −7‰ for the fluid, which is similar to that of the Kushikino ore fluid (δ 18 O = −7‰) and regional meteoric water (δ 18 O = −7.1‰)[19,37].Therefore, the calcites with very low δ 13 C values might precipitate after the ore mineralization.1).The average global δ 13 C value of C3 plants is approximately −28.5‰ [36].Local pyrolysis or microbial decomposition of these organic materials in the basement sedimentary rocks can result in the production of CO 2 .The fluid temperature at the precipitation of the very low δ 13 C calcite is calculated to be around 45 • C using the δ 18 O values of the calcites and calibration curve of O'Neil et al. [35], assuming that the δ 18 O value of −7‰ for the fluid, which is similar to that of the Kushikino ore fluid (δ 18 O = −7‰) and regional meteoric water (δ 18 O = −7.1‰)[19,37].Therefore, the calcites with very low δ 13 C values might precipitate after the ore mineralization.1), and open circles are from an author's previous work [19].The equilibrium fractionation trends of calcite for the Noya and Kushikino deposits explained in Figure 6 are also shown.

Hydrothermal Fluids for the Hishikari Deposit
Since the Hishikari and Kushikino deposits both occur in the same Hokusatsu district and share the same basement sedimentary rocks, it is expected that the calcite's δ 13 C and δ 18 O values will follow the Kushikino pattern.Although several isotope data are along the Kushikino trend, the others lie between the Noya and Kushikino trends (Figure 7).These particular characteristics of the Hishikari fluid will be investigated next.
First, the δ 13 C and δ 18 O values of the 10 mm-width sample set of the calcite-dominant vein (Section 3.1.2)are obtained to get a rough idea of the isotope evolution from the early to late stages of vein formation.In Figure 8, the δ 13 C-δ 18 O combination moves slightly from 1743 through 1746 samples.The last sample, 1747, has a high δ 18 O value, probably because the temperature drops at the later stage of calcite mineralization, since the oxygen isotope fractionation between calcite and water increases with decreasing temperature.Next, we take finer samples (0.9 mm-width sample set: from 176-1 to 176-21) from the early mineralization stage than the 10 mm-width sample set (Figure 4b,c).A more precise and definite evolutional isotopic trend of the fluid is expected to appear.However, no such trend is found.The δ 13 C and δ 18 O values of the 0.9 mm-width samples move irregularly over time, but the range is limited (Figure 8).
Finally, maximum efforts to increase the time resolution were made.The δ 13 C and δ 18 O values of calcite from 176-20 and 176-21 sections (12 μm-width sample set; Table 4) are shown in Figures 9a and 9b, respectively.The range of δ 13 C and δ 18 O values for the 176-20 section is slightly bigger than that for the 176-21 section.However, they are similar to the range of 10 mm-width and 0.9 mm-width samples (Figure 9a 1), and open circles are from an author's previous work [19].The equilibrium fractionation trends of calcite for the Noya and Kushikino deposits explained in Figure 6 are also shown.
Since the Hishikari and Kushikino deposits both occur in the same Hokusatsu district and share the same basement sedimentary rocks, it is expected that the calcite's δ 13 C and δ 18 O values will follow the Kushikino pattern.Although several isotope data are along the Kushikino trend, the others lie between the Noya and Kushikino trends (Figure 7).These particular characteristics of the Hishikari fluid will be investigated next.
First, the δ 13 C and δ 18 O values of the 10 mm-width sample set of the calcite-dominant vein (Section 3.1.2)are obtained to get a rough idea of the isotope evolution from the early to late stages of vein formation.In Figure 8, the δ 13 C-δ 18 O combination moves slightly from 1743 through 1746 samples.The last sample, 1747, has a high δ 18 O value, probably because the temperature drops at the later stage of calcite mineralization, since the oxygen isotope fractionation between calcite and water increases with decreasing temperature.Next, we take finer samples (0.9 mm-width sample set: from 176-1 to 176-21) from the early mineralization stage than the 10 mm-width sample set (Figure 4b,c).A more precise and definite evolutional isotopic trend of the fluid is expected to appear.However, no such trend is found.The δ 13 C and δ 18 O values of the 0.9 mm-width samples move irregularly over time, but the range is limited (Figure 8).
Finally, maximum efforts to increase the time resolution were made.The δ 13 C and δ 18 O values of calcite from 176-20 and 176-21 sections (12 µm-width sample set; Table 4) are shown in Figure 9a,b, respectively.The range of δ 13 C and δ 18 O values for the 176-20 section is slightly bigger than that for the 176-21 section.However, they are similar to the range of 10 mm-width and 0.9 mm-width samples (Figure 9a 3).The number with the symbol represents the growth order in the 0.9 mm-width sample set.The equilibrium fractionation trends of calcite for the Kushikino deposits are shown.3).The number with the symbol represents the growth order in the 0.9 mm-width sample set.The equilibrium fractionation trends of calcite for the Kushikino deposits are shown.3).The number with the symbol represents the growth order in the 0.9 mm-width sample set.The equilibrium fractionation trends of calcite for the Kushikino deposits are shown.

Sulfur Isotopes
A histogram of sulfur isotope ratios of pyrite from the Hishikari deposit is shown in Figure 10.The analysis area using the SIMS microanalysis is 20 μm.The whole data's average δ 34 S value is −0.7‰.The δ 34 S values of pyrites in the host rock are similar to those in the adjacent ore vein at the same location of the host rock (E8) and Hosen-1 (E8) in Figure 10, which indicates that the same fluid forms both hydrothermal pyrites.The pyrite grains in the host rock (shale), within 2 cm from the vein, occur near the vein by the ore fluid that flows into the host rock.Late Cenozoic volcanic rocks in the Hokusatsu district are of the magnetite series (similar to I-type granitoids; [38]) that are defined by Ishihara [39].Ishihara et al. [40] measured δ 34 S values of three vein ores and six basement sedimentary rocks from the Hishikari deposit by the conventional method, and the average δ 34 S value is around +0.3‰.The δ 34 S value of stibnite from the Hishikari deposit is −0.2‰ [41], and the δ 34 S values of seven stibnite samples, which are from the latest stage of the Hishikari mineralization, are narrow-ranged (from −0.2‰ to +0.7‰) among several different veins [42].The near-zero values of δ 34 S from the Hishikari hydrothermal system are consistent with that from magnetite series magma [43].

Sulfur Isotopes
A histogram of sulfur isotope ratios of pyrite from the Hishikari deposit is shown in Figure 10.The analysis area using the SIMS microanalysis is 20 µm.The whole data's average δ 34 S value is −0.7‰.The δ 34 S values of pyrites in the host rock are similar to those in the adjacent ore vein at the same location of the host rock (E8) and Hosen-1 (E8) in Figure 10, which indicates that the same fluid forms both hydrothermal pyrites.The pyrite grains in the host rock (shale), within 2 cm from the vein, occur near the vein by the ore fluid that flows into the host rock.Late Cenozoic volcanic rocks in the Hokusatsu district are of the magnetite series (similar to I-type granitoids; [38]) that are defined by Ishihara [39].Ishihara et al. [40] measured δ 34 S values of three vein ores and six basement sedimentary rocks from the Hishikari deposit by the conventional method, and the average δ 34 S value is around +0.3‰.The δ 34 S value of stibnite from the Hishikari deposit is −0.2‰ [41], and the δ 34 S values of seven stibnite samples, which are from the latest stage of the Hishikari mineralization, are narrow-ranged (from −0.2‰ to +0.7‰) among several different veins [42].The near-zero values of δ 34 S from the Hishikari hydrothermal system are consistent with that from magnetite series magma [43].
Very low δ 34 S values from −16.5‰ to −10.1‰ of pyrites are found only in the highgrade Keisen-3 vein of the Sanjin ore zone (Figure 10; Table 5).The very low δ 34 S values, first obtained by the SIMS microanalysis, are apart from the pile of other values (Figure 10).Sanematsu et al. [18] proposed that the fractures corresponding to the Keisen veins were a significant channel for the ascending hot hydrothermal fluids.The δ 34 S values of unaltered Shimanto sedimentary rocks are from −21.5‰ to −1.4‰ [43].Therefore, the pyrite with a very low δ 34 S value might form locally that reacted with the Shimanto sedimentary rocks.The reaction with the sedimentary rocks might occur in the microscopic region because relatively high δ 34 S values are also obtained from the same hand specimen of the Keisen-3 vein (Figure 10).  5.The vertical axis is the number of samples.The Keisen vein is from the Sanjin ore zone, the Zuisen and Hosen veins with the host rocks are from the Honko ore zone, and the Yusen veins are from the Yamada ore zone.The δ 34 S value for each vein is color-coded.The average δ 34 S value of whole data is −0.7‰, and the average δ 34 S value of pyrites in veins is −1.1‰.Pyrite grains in the sedimentary rocks (host rock in Figure 8) have slightly high δ 34 S values than those in quartz veins (Hosen-1) at the same location of E8.Cpy: chalcopyrite.
Very low δ 34 S values from −16.5‰ to −10.1‰ of pyrites are found only in the highgrade Keisen-3 vein of the Sanjin ore zone (Figure 10; Table 5).The very low δ 34 S values, first obtained by the SIMS microanalysis, are apart from the pile of other values (Figure 10).Sanematsu et al. [18] proposed that the fractures corresponding to the Keisen veins were a significant channel for the ascending hot hydrothermal fluids.The δ 34 S values of unaltered Shimanto sedimentary rocks are from −21.5‰ to −1.4‰ [43].Therefore, the pyrite with a very low δ 34 S value might form locally that reacted with the Shimanto sedimentary rocks.The reaction with the sedimentary rocks might occur in the microscopic region because relatively high δ 34 S values are also obtained from the same hand specimen of the Keisen-3 vein (Figure 10).

Genesis and Evolution of Hydrothermal Fluids in the Formation of the Hishikari Deposit
The Hishikari deposit's ore-forming fluids may mix meteoric and magmatic fluids.Particularly along the unconformity between the basement sedimentary rocks and overlying andesites [44].The fluids are formed from meteoric water undergoing isotopic exchange with basement rocks [6].The isotope results in this study also suggest that the oreforming fluid for the Hishikari deposit is a mixture of two fluids.We refer to the two fluids δ 34 S (‰)  5.The vertical axis is the number of samples.The Keisen vein is from the Sanjin ore zone, the Zuisen and Hosen veins with the host rocks are from the Honko ore zone, and the Yusen veins are from the Yamada ore zone.The δ 34 S value for each vein is color-coded.The average δ 34 S value of whole data is −0.7‰, and the average δ 34 S value of pyrites in veins is −1.1‰.Pyrite grains in the sedimentary rocks (Host rock in the legend) have slightly high δ 34 S values than those in quartz veins (Hosen-1) at the same location of E8.Cpy: chalcopyrite.

Genesis and Evolution of Hydrothermal Fluids in the Formation of the Hishikari Deposit
The Hishikari deposit's ore-forming fluids may mix meteoric and magmatic fluids.Particularly along the unconformity between the basement sedimentary rocks and overlying andesites [44].The fluids are formed from meteoric water undergoing isotopic exchange with basement rocks [6].The isotope results in this study also suggest that the ore-forming fluid for the Hishikari deposit is a mixture of two fluids.We refer to the two fluids as Fluid 1 (along the Noya trend), which the basement sedimentary rocks may not affect, and Fluid 2 (along the Kushikino trend), which they may constrain.Fluid 2 is common to the deposits in the Hokusatsu district (Figure 1); that is, the δ 13 C and δ 18 O values of calcite from most Au deposits in the Hokusatsu district are along Fluid 2 [19,32].According to past research [2][3][4][5][6], the Hishikari fluid may have received some magmatic fluid input, particularly during the earliest stages of mineralization.The genesis of the Hishikari hydrothermal fluid is the most of meteoric origin.However, some sporadically input of magmatic origin to the fluid has occurred.The Hishikari deposit also has Fluid 2 [19,21,32], like any other deposit in the district, but it should be emphasized that Fluid 1 is peculiar to the Hishikari deposit.Calcite samples from Fluids 1 and 2 are everywhere in the deposit.
Figure 11 shows the δ 13 C and δ 18 O values of vein calcite with/without electrum [21].Although the δ 13 C values of samples with electrum are relatively high compared to those without electrum, the δ 13 C and δ 18 O values of calcites with electrum lie either near the Noya trend or Kushikino trend.Additionally, since vein calcite samples without electrum in Figure 11 are from Au-rich veins, they are also recognized as fertile.Therefore, at the Hishikari deposit, Fluids 1 and 2 are both created from fluids capable of forming ore (Figure 11).The 20100317 sample is from the Au-rich Keisen 3-1 vein, and the earliest formed calcite in the 20100317 sample (176-5; Table 3) lies on the Noya trend (Fluid 1), which is apart from the Kushikino trend (Fluid 2 in Figure 11).Fluids 1 and 2 are both fertile ore-forming fluids.Fluid 2 is thought to have reacted well with basement sedimentary rocks that contain organic matter, and Fluid 1, on the other hand, is not affected on a large scale by sedimentary rocks.
past research [2][3][4][5][6], the Hishikari fluid may have received some magmatic fluid input, particularly during the earliest stages of mineralization.The genesis of the Hishikari hydrothermal fluid is the most of meteoric origin.However, some sporadically input of magmatic origin to the fluid has occurred.The Hishikari deposit also has Fluid 2 [19,21,32], like any other deposit in the district, but it should be emphasized that Fluid 1 is peculiar to the Hishikari deposit.Calcite samples from Fluids 1 and 2 are everywhere in the deposit.
Figure 11 shows the δ 13 C and δ 18 O values of vein calcite with/without electrum [21].Although the δ 13 C values of samples with electrum are relatively high compared to those without electrum, the δ 13 C and δ 18 O values of calcites with electrum lie either near the Noya trend or Kushikino trend.Additionally, since vein calcite samples without electrum in Figure 11 are from Au-rich veins, they are also recognized as fertile.Therefore, at the Hishikari deposit, Fluids 1 and 2 are both created from fluids capable of forming ore (Figure 11).The 20100317 sample is from the Au-rich Keisen 3-1 vein, and the earliest formed calcite in the 20100317 sample (176-5; Table 3) lies on the Noya trend (Fluid 1), which is apart from the Kushikino trend (Fluid 2 in Figure 11).Fluids 1 and 2 are both fertile oreforming fluids.Fluid 2 is thought to have reacted well with basement sedimentary rocks that contain organic matter, and Fluid 1, on the other hand, is not affected on a large scale by sedimentary rocks.The previous studies [2][3][4][5][6] have suggested that some input from magmatic fluid was found in the Hishikari hydrothermal fluid in the earlier stages of mineralization.In other words, the genesis of the Hishikari fluid is mostly of meteoric origin, but some sporadical input of magmatic fluid to the hydrothermal system has occurred.Additionally, the unusually low δ 34 S readings in the Keisen veins suggest that magmatic fluid only locally and in a small volume interacted with sedimentary rocks.The microanalysis results of δ 13 C and δ 18 O values in every 12 µm of the calcite-bearing sample along the growth direction scatter in a particular range (Figure 9a,b).The duration of 12 µm-thickness mineralization is about 10 years of the Hishikari mineralization according to the 40 Ar/ 39 Ar ages of adularia [45].Since the very high temporal resolution cannot find the isotope evolution of the hydrothermal fluid, the evolution is not a gradual transition from magmatic to meteoric origin.Still, a rapid turnover of two fluids might be locally happening.
The average pyrite δ 34 S value of −0.7‰ from veins and sedimentary rocks is similar to that of the adjacent magma, consistent with previous studies.However, the SIMS microanalysis reveals that very low δ 34 S values from −16.5‰ to −10.1‰ and positive δ 34 S values of pyrites are found in the same hand specimen from the high-grade Keisen-3 vein of the Sanjin ore zone (Figure 10).Therefore, the pyrite having a very low δ 34 S value might form locally that was reacted with the Shimanto sedimentary rocks.The evidence from sulfur isotope data proves that the reaction of the hydrothermal fluid with basement sedimentary rocks occurs locally in the microscopic region.
Fluid 2, the mainstream in the Hokusatsu district, is supposed to flow continuously in the Hishikari deposit during the mineralization.However, Fluid 1, a magmatic-origin deep fluid with little reaction with the basement sedimentary rocks, might inject intermittently into the Fluid 2-filled vein system.Intermittent opening of the top of a vein lowers the pressure in the vein, resulting in the introduction of deep Fluid 1 to the epithermal system and subsequent mixing with Fluid 2 and boiling in some cases.Au was probably transported as Au(HS) 2 − [3] and might be deposited in response to changes in the temperature, pH, log fO 2 , and total sulfur concentrations [46].Boiling would fractionate H 2 S strongly into the vapor, lower HS − activity, and increase pH by losing H 2 S, which causes the deposition of calcite and Au [47].
The characteristics of the high-grade Hishikari deposit, compared to the other Au deposits in the Hokusatsu district, might be caused by Fluid 1. Unlike other epithermal Au deposits in the district, the rapid local mixing of Fluid 1 and 2 might cause the Au-rich ore deposition at the Hishikari deposit.

Concluding Remarks
The Hishikari gold deposit in Kyushu, Japan, is world-famous for its high-grade ore.The Hishikari deposit is one of the numerous epithermal gold occurrences in the Hokusatsu district.It is located in the basement rocks of the Lower Shimanto Group (Cretaceous accretionary wedge).The average pyrite δ 34 S value of −0.7‰ from veins and sedimentary rocks is similar to that of the adjacent magma, consistent with previous studies.However, the SIMS microanalysis reveals that very low δ 34 S values and positive δ 34 S values of pyrites are found in the same hand specimen from the high-grade Keisen-3 vein.Therefore, sulfur isotope measurements demonstrate that the hydrothermal fluid's reaction with the basement sedimentary rocks occurs locally because the pyrite with a very low δ 34 S value might form locally.
Although the basement rocks regulate the feature of the hydrothermal fluids for the deposits, it has been inferred that the incorporation of magmatic-origin deep fluid to the meteoric-origin hydrothermal fluid might cause the gold and calcite precipitation at the Hishikari deposit.Although this scenario applies to the Hishikari deposit generally, the microanalysis of δ 13 C and δ 18 O values of vein calcite reveals that the fluid evolution was not gradually occurring, and a rapid turnover of two fluids might be locally happening.Thus, the δ 13 C and δ 18 O values of hydrothermal calcite can provide insights into the genesis and evolution of the epithermal deposits.

Minerals 2022, 12 , x 3 of 22 Figure 1 .
Figure 1.Epithermal gold deposits in Kyushu, southwestern Japan (produced from[12,17]).In southern Kyushu, epithermal gold deposits occur in Late Cenozoic subaerial andesitic to dacitic volcanic rocks in the Hokusatsu district.The basement rocks in the district are sedimentary rocks of the Lower Shimanto Group (Cretaceous accretionary wedge), which do not outcrop near the deposits.The location of the Hishikari, Kushikino, and Noya deposits are shown.

Figure 1 .
Figure 1.Epithermal gold deposits in Kyushu, southwestern Japan (produced from[12,17]).In southern Kyushu, epithermal gold deposits occur in Late Cenozoic subaerial andesitic to dacitic volcanic rocks in the Hokusatsu district.The basement rocks in the district are sedimentary rocks of the Lower Shimanto Group (Cretaceous accretionary wedge), which do not outcrop near the deposits.The location of the Hishikari, Kushikino, and Noya deposits are shown.

Figure 2 .
Figure 2. Sampling sites are shown on the vein system (red) of the Hishikari deposit.The number and vein name of the sample is attached next to the symbol.Blue symbols are for carbon and oxygen isotope ratios and green symbols are for sulfur isotope ratios.

Figure 2 .
Figure 2. Sampling sites are shown on the vein system (red) of the Hishikari deposit.The number and vein name of the sample is attached next to the symbol.Blue symbols are for carbon and oxygen isotope ratios and green symbols are for sulfur isotope ratios.

22 Figure 3 .
Figure 3. Photos of representative vein samples.(a) Sample 31001 with the analysis localities a, b, and c (Table 1) are shown.(b) Sample 31002 with the analysis localities a and b (Table 1) are shown.

Figure 3 .
Figure 3. Photos of representative vein samples.(a) Sample 31001 with the analysis localities a, b, and c (Table 1) are shown.(b) Sample 31002 with the analysis localities a and b (Table 1) are shown.

Minerals 2022, 12 , x 7 of 22 Figure 4 .
Figure 4. (a) Photo for the 20100317 high-grade vein sample taken from the 25 mL KE-3-1 vein.The vein width is about 50 cm.The right end of the vein is adjacent to the wall rock, and the left is around the center of the vein.In the early stage of mineralization, the gray part contains fine-grained pyrite and clay minerals.The calcite-bearing samples covering early to late mineralization are rare in the Hishikari deposit.(b) The vein sample 20100317 is cut every 10 mm in the growing direction, and every sample is numbered.The rectangle shows the area for Figure 3c.(c) Sections measuring 0.9 mm-width are made from 1761, 1762, and 1763 samples, numbered from 176-1 to 176-21.Blue lines designate areas cut off with a 0.3 mm thick blade.The 12 μm-width powder samples for microanalysis are scraped from 176-20 and 176-21 sections.

Figure 4 .
Figure 4. (a) Photo for the 20100317 high-grade vein sample taken from the 25 mL KE-3-1 vein.The vein width is about 50 cm.The right end of the vein is adjacent to the wall rock, and the left is around the center of the vein.In the early stage of mineralization, the gray part contains fine-grained pyrite and clay minerals.The calcite-bearing samples covering early to late mineralization are rare in the Hishikari deposit.(b) The vein sample 20100317 is cut every 10 mm in the growing direction, and every sample is numbered.The rectangle shows the area for Figure 3c.(c) Sections measuring 0.9 mm-width are made from 1761, 1762, and 1763 samples, numbered from 176-1 to 176-21.Blue lines designate areas cut off with a 0.3 mm thick blade.The 12 µm-width powder samples for microanalysis are scraped from 176-20 and 176-21 sections.

Figure 4 .
Figure 4. (a) Photo for the 20100317 high-grade vein sample taken from the 25 mL KE-3-1 vein.The vein width is about 50 cm.The right end of the vein is adjacent to the wall rock, and the left is around the center of the vein.In the early stage of mineralization, the gray part contains fine-grained pyrite and clay minerals.The calcite-bearing samples covering early to late mineralization are rare in the Hishikari deposit.(b) The vein sample 20100317 is cut every 10 mm in the growing direction, and every sample is numbered.The rectangle shows the area for Figure 3c.(c) Sections measuring 0.9 mm-width are made from 1761, 1762, and 1763 samples, numbered from 176-1 to 176-21.Blue lines designate areas cut off with a 0.3 mm thick blade.The 12 μm-width powder samples for microanalysis are scraped from 176-20 and 176-21 sections.

Minerals 2022 ,
12, x 11 of 22 the slice level for mining.*4: The two grains are chalcopyrite that were confirmed by electron probe microanalysis (EPMA).*5: W1 is a working name.E1 or E8 is the actual location.

Minerals 2022, 12 , x 14 of 22 Figure 6 .
Figure 6.The δ 13 C and δ18 O values of vein calcite for the Noya and Kushikino deposits (Figure1).Calculated as a function of temperature, curves (1) and (2) represent equilibrium fractionation trends for calcite under the assumption that H2CO3[33] and HCO3 -[34] are the predominant carbon species in the fluid, respectively.The δ 13 C and δ 18 O values of the Noya fluid for both curves are obtained to be -6.5‰ and -7.5‰, respectively[26].The temperatures marked on the upper x-axis are isotopic equilibrium temperatures[35].Curves (3) and (4) are equilibrium fractionation trends for calcite from the Kushikino deposit.The δ 13 C and δ 18 O values of the Kushikino fluid for both curves are obtained to be -10.8‰and -7.0‰, respectively[19].At about 140°C with decreasing temperature, the predominant carbon species in the Kushikino fluid changed from H2CO3 to HCO3 -[27].Samples of the Kushikino veins are from the Kushikino deposit, and those of the Kammuridake veins are from a peripheral area of the deposit.The oxygen isotopic equilibrium temperatures for the Kushikino hydrothermal fluid are marked on the lower x-axis.

Figure 7
Figure 7 shows calcite's δ 13 C and δ 18 O values from the Hishikari deposit.The figure excludes two calcite samples with very low δ 13 C values of −23.4‰ and −25.1‰ (Table1).The average global δ 13 C value of C3 plants is approximately −28.5‰[36].Local pyrolysis or microbial decomposition of these organic materials in the basement sedimentary rocks can result in the production of CO2.The fluid temperature at the precipitation of the very low δ 13 C calcite is calculated to be around 45°C using the δ 18 O values of the calcites and calibration curve of O'Neil et al.[35], assuming that the δ 18 O value of −7‰ for the fluid, which is similar to that of the Kushikino ore fluid (δ 18 O = −7‰) and regional meteoric water (δ 18 O = −7.1‰)[19,37].Therefore, the calcites with very low δ 13 C values might precipitate after the ore mineralization.

Figure 6 .
Figure 6.The δ 13 C and δ 18 O values of vein calcite for the Noya and Kushikino deposits (Figure 1).Calculated as a function of temperature, curves (1) and (2) represent equilibrium fractionation trends for calcite under the assumption that H 2 CO 3 [33] and HCO 3 − [34] are the predominant carbon species in the fluid, respectively.The δ 13 C and δ 18 O values of the Noya fluid for both curves are obtained to be −6.5‰ and −7.5‰, respectively [26].The temperatures marked on the upper x-axis are isotopic equilibrium temperatures [35].Curves (3) and (4) are equilibrium fractionation trends for calcite from the Kushikino deposit.The δ 13 C and δ 18 O values of the Kushikino fluid for both curves are obtained to be −10.8‰and −7.0‰, respectively [19].At about 140 • C with decreasing temperature, the predominant carbon species in the Kushikino fluid changed from H 2 CO 3 to HCO 3 − [27].Samples of the Kushikino veins are from the Kushikino deposit, and those of the Kammuridake veins are from a peripheral area of the deposit.The oxygen isotopic equilibrium temperatures for the Kushikino hydrothermal fluid are marked on the lower x-axis.

Figure 7
Figure 7 shows calcite's δ 13 C and δ 18 O values from the Hishikari deposit.The figure excludes two calcite samples with very low δ 13 C values of −23.4‰ and −25.1‰ (Table1).The average global δ 13 C value of C3 plants is approximately −28.5‰[36].Local pyrolysis or microbial decomposition of these organic materials in the basement sedimentary rocks can result in the production of CO 2 .The fluid temperature at the precipitation of the very low δ 13 C calcite is calculated to be around 45 • C using the δ 18 O values of the calcites and

Minerals 2022, 12 , x 15 of 22 Figure 7 .
Figure 7.The δ 13 C and δ 18 O values of calcite from the Hishikari deposit are shown.Solid circles are from hand specimens taken in this study (Table1), and open circles are from an author's previous work[19].The equilibrium fractionation trends of calcite for the Noya and Kushikino deposits explained in Figure6are also shown.
,b).The change in δ 18 O values might reflect temperature changes.However, isotope ratios and growth order do not correlate with one another.The δ 13 C and δ 18 O values of calcite jump around in a particular range (Figure 9a,b), and it is difficult to explain the fluid evolution by a simple change of the fluid in temperature or pH.

( 1 )Figure 7 .
Figure 7.The δ 13 C and δ 18 O values of calcite from the Hishikari deposit are shown.Solid circles are from hand specimens taken in this study (Table1), and open circles are from an author's previous work[19].The equilibrium fractionation trends of calcite for the Noya and Kushikino deposits explained in Figure6are also shown.

22 Figure 8 .
Figure 8.The δ 13 C and δ 18 O values of calcite (10 mm-width sample set and 0.9 mm-width sample set) from the 20100317 sample (Table3).The number with the symbol represents the growth order in the 0.9 mm-width sample set.The equilibrium fractionation trends of calcite for the Kushikino deposits are shown.

Figure 8 .
Figure 8.The δ 13 C and δ 18 O values of calcite (10 mm-width sample set and 0.9 mm-width sample set) from the 20100317 sample (Table3).The number with the symbol represents the growth order in the 0.9 mm-width sample set.The equilibrium fractionation trends of calcite for the Kushikino deposits are shown.

2 , x 16 of 22 Figure 8 .
Figure 8.The δ 13 C and δ 18 O values of calcite (10 mm-width sample set and 0.9 mm-width sample set) from the 20100317 sample (Table3).The number with the symbol represents the growth order in the 0.9 mm-width sample set.The equilibrium fractionation trends of calcite for the Kushikino deposits are shown.

Figure 9 .
Figure 9.The results of microanalysis.The δ 13 C and δ 18 O values of calcite (micro-scale samples obtained by a microtome; Table 4) are superimposed in Figure 8.The number with the symbol represents the growth order.The equilibrium fractionation trends of calcite for the Noya and Kushikino deposits are also shown.(a) The 12 μm-width samples (176-20-1 to 176-20-12) were taken from the 176-20 section.(b) The 12 μm-width samples (176-21-1 to 176-21-17) were taken from the 176-21 section.

Figure 9 .
Figure 9.The results of microanalysis.The δ 13 C and δ 18 O values of calcite (micro-scale samples obtained by a microtome; Table 4) are superimposed in Figure 8.The number with the symbol represents the growth order.The equilibrium fractionation trends of calcite for the Noya and Kushikino deposits are also shown.(a) The 12 µm-width samples (176-20-1 to 176-20-12) were taken from the 176-20 section.(b) The 12 µm-width samples (176-21-1 to 176-21-17) were taken from the 176-21 section.

Minerals 2022, 12 , x 18 of 22 Figure 10 .
Figure 10.A histogram of δ 34 S values of pyrite and chalcopyrite from the Hishikari deposit using the SIMS microanalysis is shown based on Table5.The vertical axis is the number of samples.The Keisen vein is from the Sanjin ore zone, the Zuisen and Hosen veins with the host rocks are from the Honko ore zone, and the Yusen veins are from the Yamada ore zone.The δ 34 S value for each vein is color-coded.The average δ 34 S value of whole data is −0.7‰, and the average δ 34 S value of pyrites in veins is −1.1‰.Pyrite grains in the sedimentary rocks (host rock in Figure8) have slightly high δ 34 S values than those in quartz veins (Hosen-1) at the same location of E8.Cpy: chalcopyrite.

Figure 10 .
Figure 10.A histogram of δ 34 S values of pyrite and chalcopyrite from the Hishikari deposit using the SIMS microanalysis is shown based on Table5.The vertical axis is the number of samples.The Keisen vein is from the Sanjin ore zone, the Zuisen and Hosen veins with the host rocks are from the Honko ore zone, and the Yusen veins are from the Yamada ore zone.The δ 34 S value for each vein is color-coded.The average δ 34 S value of whole data is −0.7‰, and the average δ 34 S value of pyrites in veins is −1.1‰.Pyrite grains in the sedimentary rocks (Host rock in the legend) have slightly high δ 34 S values than those in quartz veins (Hosen-1) at the same location of E8.Cpy: chalcopyrite.

Figure 11 .
Figure 11.The δ 13 C and δ 18 O values of calcite from the Hishikari deposit.Blue solid circles indicate isotope data of calcite from hand specimens.The data from the 10 mm-width, 0.9 mm-width, and 12 μm-width samples are represented by each symbol.Isotope data of calcite with/without electrum (purple star and black cross, respectively) are from [21], and data (open circles) from [19] are shown.The equilibrium fractionation trends of calcite for the Noya and Kushikino deposits are also shown.

Figure 11 .
Figure 11.The δ 13 C and δ 18 O values of calcite from the Hishikari deposit.Blue solid circles indicate isotope data of calcite from hand specimens.The data from the 10 mm-width, 0.9 mm-width, and 12 µm-width samples are represented by each symbol.Isotope data of calcite with/without electrum (purple star and black cross, respectively) are from [21], and data (open circles) from [19] are shown.The equilibrium fractionation trends of calcite for the Noya and Kushikino deposits are also shown.

Table 1 .
Descriptions and isotope data of calcite-bearing vein samples from the Hishikari deposit.
grown sample, about 0.14 mm from the origin.176-20sectionwith a thickness of about 0.76 mm remained unscraped since the sample was broken during the subsequent cutting.176-21section was divided into 17 samples, from 176-21-1 to 176-21-17.Each scraped size was similar to that for 176-20, and the distance from the same 'origin' is shown in Table4.The 176-21 section was broken during the 18 th cutting after 17 sample powders were obtained.Notably, 29 mineral samples were collected, despite the difficulty of cutting vein samples with a biological microtome.Be aware that the 176-20-12 and 176-21-1 sample differ by approximately 1.06 mm (the blade thickness and the remainder of the 76-20 sample).
*: Approximate calcite abundance in quartz-adularia vein was obtained from the XRD calibration curve.

Table 5 .
Locality and the sulfur isotope ratio of pyrite from the Hishikari deposit.
*1: Samples are from quartz veins except for one sample (98121805) from the basement shale.*2: "mL" corresponds to the altitude above sea level.*3: "sl", which corresponds to +3.75 m, stands for the slice level for mining.*4: The two grains are chalcopyrite that were confirmed by electron probe microanalysis (EPMA).*5: W1 is a working name.E1 or E8 is the actual location.

Table 1
lists calcite's δ13C and δ18O values from the Hishikari deposit.The δ 13 C and δ 18 O values of calcite range from −25.1‰ to −2.6‰ and from +3.8‰ to +17.9‰, respectively.The ranges of the δ 13 C and δ 18 O values of calcite, when two samples with extraordinarily low δ 13 C values are excluded, are −10.3‰ to −2.6‰ and +3.8‰ to +14.6‰, respectively.