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Article

Genesis and Formation of the Tuwaishan Gold Deposit in Hainan Island, South China: Implications from H-O-S Isotopes

by
Yuheng Liu
1,2,
Jingwen Mao
3,4,*,
Jun Hu
5,6,
Lei Wang
7 and
Deming Xu
7
1
MNR Key Laboratory of Geochemical Exploration, Institute of Geophysical and Geochemical Exploration, Chinese Academy of Geological Sciences, Langfang 065000, China
2
UNESCO International Centre on Global-Scale Geochemistry, Langfang 065000, China
3
MNR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China
4
Key Laboratory for Exploration Theory & Technology of Critical Mineral Resources, China University of Geosciences, Beijing 100083, China
5
Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Lab of Submarine Geosciences and Prospecting Techniques, MOE and College of Marine Geosciences, Ocean University of China, Qingdao 266100, China
6
Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China
7
Wuhan Center, China Geological Survey (Geosciences Innovation Center of Central South China), Wuhan 430205, China
*
Author to whom correspondence should be addressed.
Minerals 2023, 13(8), 1082; https://doi.org/10.3390/min13081082
Submission received: 2 June 2023 / Revised: 24 July 2023 / Accepted: 28 July 2023 / Published: 14 August 2023
(This article belongs to the Special Issue Understanding Hydrothermal Ore Deposits)
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Abstract

:
The Tuwaishan gold deposit is located at the northeastern end of the Gezhen shear zone in the western part of Hainan Island, South China. It is one of a series of similar gold deposits hosted in the Mesoproterozoic basement rocks and structurally controlled by the Gezhen shear zone. The hydrothermal ore-forming period can be divided into quartz-pyrite-arsenopyrite stage, quartz-pyrite-base metal sulfides stage and quartz-carbonate stage. Eleven gold-bearing quartz vein samples yield δDV-SMOW and δ18OV-SMOW values of −75.9‰ to −54.4‰ and +8.1‰ to +13.7‰, respectively, and the corresponding δ18Owater values range from +3.1‰ to +8.7‰. In addition, the pyrite separates from 14 ore samples yield δ34S values of +4.5‰ to +7.9‰. The H-O-S isotopic data, along with fluid properties of the Tuwaishan and other gold deposits along the Gezhen shear zone, suggest that the ore-forming fluid and materials are of metamorphic rather than magmatic origin. Hence, we propose that the Tuwaishan gold deposit is best classified as orogenic gold deposit that resulted from regional metamorphism. Considering that the Mesoproterozoic basement rocks have experienced amphibolite facies metamorphism prior to the gold mineralization, the metamorphic devolatilization of the Ordovician-Silurian rocks at depth would provide a realistic source of fluid, gold and sulfur for the Tuwaishan and other gold deposits of the Gezhen gold belt.

1. Introduction

Hainan Island is located in the southern margin of the South China Block, and is adjacent to the northern part of the Indochina Block [1,2] (Figure 1a). More than 50 gold deposits and occurrences have been discovered on this island, making Hainan Island a prospective region for gold exploration in South China [3,4,5,6,7]. The Gezhen gold belt, which consists of a series of similar gold deposits along the NE-trending Gezhen shear zone in the western Hainan Island, has become the most prospective gold exploration target within the island [4,5,8].
Studies on ore deposit geology, ore-forming fluid characteristics and isotope compositions have been conducted to constrain the source and to further identify the genesis of the Gezhen gold deposits, but debates persist on whether those deposits are sedimentary-reworked, magmatic-hydrothermal or orogenic in genesis [5,8,10,11,12,13]. The metamorphic rocks in the Mesoproterozoic Baoban Group have long been accepted as the source of Au for the Gezhen gold belt because (1) they are the host rocks of those gold deposits and (2) they possess a relatively high content of Au [5,11,12,14,15,16,17]. However, the rocks in the Baoban Group were deposited at 1460–1430 Ma and have experienced amphibolite facies metamorphism at 1.3–1.0 Ga, whereas the Gezhen gold deposits were formed at ~243 Ma [8,18,19,20,21,22]. On account of the metamorphic devolatilization model, Au and sulfur would be released into the fluid phase during the prograde metamorphic transition of greenschist to amphibolite facies [23,24,25,26,27,28]. Therefore, if the Gezhen gold deposits are orogenic in genesis, then reevaluation is required for whether the regional metamorphism of the Baoban Group rocks led to the formation of the Tuwaishan and other gold deposits along the Gezhen shear zone.
In this study, we present new H-O-S isotopic compositions of ore samples from the Tuwaishan gold deposit and summarize the previously published H-O-S isotopic data for the Gezhen gold deposits to identify the source characteristics of ore-forming fluid and materials of the Tuwaishan and other gold deposits along the Gezhen shear zone. In addition, we carried out integrated analyses of source characteristics, deposit geology, regional geology of the Gezhen gold belt, as well as tectonic settings of Hainan Island to further identify the potential source for gold mineralization along the Gezhen shear zone.

2. Regional Geology

Hainan Island is separated from the mainland of South China by the Qiongzhou Strait in the north and is regarded as the southernmost extension of the Cathaysia Block [1,2,24] (Figure 1a). It is tectonically located at the junction of the Eurasian plate, the Indian–Australian plate and the Pacific plate [29,30,31,32,33].
The Gezhen shear zone lies between the Changjiang–Qionghai and Jianfeng–Diaoluo E-W trending faults in the western part of the Hainan Island [9] (Figure 1b). It extends for more than 55 km with a width of 0.5–3 km [34,35,36]. The Gezhen shear zone trends 35–40°, dips to the northwest with dip angles gradually varying from 60–80° on the surface to 15–30° with increasing depth and is characterized by both sinistral and reverse movement [9,36,37] (Figure 2). It is a multi-phase superimposed brittle-ductile shear zone and is disrupted by later NW- and E–W-trending faults [5,38] (Figure 2). The youngest shear deformation age was 227.4 ± 0.2 Ma from 40Ar/39Ar dating of synkinematic muscovite along the shear zone [9].
The hanging wall rocks of the Gezhen shear zone include the Mesoproterozoic Baoban Group and contemporaneous granitic and mafic rocks while the footwall rocks comprise the Ordovician Nanbigou Formation and the lower Silurian Tuolie Formation [20,21,39,40] (Figure 2). The Baoban Group comprising the lower Gezhencun Formation and upper Ewenling Formation was deposited at 1460–1430 Ma and suffered amphibolite facies metamorphism at 1.3–0.9 Ga [18,19,20,21,22]. It represents the oldest crystalline basement of the Hainan Island [37,41]. The Gezhencun Formation rocks consist of gneiss and migmatitic gneiss and have experienced migmatization and upper amphibolite facies metamorphism, while the Ewenling Formation rocks consist of quartz-mica schist, mica-quartz schist, quartzite and thin graphite layers and have experienced lower amphibolite facies metamorphism [8,19,22,37,41]. The protoliths of the Gezhencun Formation rocks are inferred to be intermediate-felsic volcanic and volcaniclastic rocks based on their whole rock geological composition while the rhythmic layering as well as relict clastic texture suggest that the protoliths of the Ewenling Formation rocks were mainly siliciclastic rocks [19,22,37,41]. The Nanbigou Formation rocks are mainly composed of quartz-mica schist, quartz-sericite phyllite and metamorphic siltstone, interspersed with metamorphic basic volcanic rocks. The overall metamorphism of the Nanbigou Formation is greenschist facies while some areas have reached upper greenschist facies metamorphism [4,42]. The low-grade metamorphic successions in the Tuolie Formation consist of phyllite, slate and metamorphic sandstone, with limestone and tuff, and the overall metamorphism is lower greenschist facies [4,42].
Magmatic rocks outcropped along the Gezhen shear zone include the Mesoproterozoic granitic and mafic rocks, as well as Middle Permian Changjiang and Datian plutons [20,21,43]. The Mesoproterozoic granitoids intruded the Baoban Group at 1450–1430 Ma, and were generally subjected to metamorphism and deformation, resulting in the formation of granitic gneiss and granitic mylonite [18,21,39,40]. The Mesoproterozoic mafic rocks were formed at 1440–1420 Ma and were metamorphosed to plagioclase amphibolite, metabasic gabbro and metabasic diabase, which are mainly lenticular, dyke and stratified in the Baoban Group [20,44]. The Datian pluton intruded the Baoban Group, Nanbitou Formation and Tuolie Formation at 263 ± 1.2 Ma [43]. It is composed of biotite monzogranite and shows gneissic schistosity within the Gezhen shear zone [43]. The Changjiang pluton consists of biotite monzogranite with a formation age of 262 ± 2.2 Ma [43].
Along the Gezhen shear zone, from NE to SW, the Tuwaishan, Baoban, Erjia and Bumo gold deposits as well as other gold deposits and occurrences have been discovered, making up the Gezhen gold belt [5,8,45,46,47]. Confirmed a total measured metal Au reserve of ~275 t, the Gezhen gold belt has become the most economically significant gold belt in the Hainan Island [4,5,8].

3. Deposit Geology

The Tuwaishan gold deposit is located at the northeastern end of the Gezhen shear zone, approximately 15 km southwest of the Changjiang City (Figure 2). This gold deposit was discovered during the gold rush in the Hainan Island during 1988–1991 and has been mined underground since 1997 [48]. The combined proven gold reserves and historical gold production are about 22 t at 3.5 g/t [48].
Rocks in the deposit area include quartz-mica schist of the Ewenling Formation and mylonitized Mesoproterozoic granitoids on the hanging wall, as well as schist and phyllite of the Ordovician-Silurian metamorphic successions on the footwall of the Gezhen shear zone (Figure 2 and Figure 3). The dominant structure in the deposit area is the Gezhen shear zone. It is approximately 1.5 km in width, trends 35–40°, dips to the northwest with dip angles ranging from 60° to 80° in the mining area (Figure 3). Plagioclase amphibolites are locally observed as dykes or lenses in the Baoban Group rocks, and the dioritic porphyrites have also been found as dykes in the Mesoproterozoic metamorphic and magmatic rocks in the mining shafts [5,8,10,11]. More than 60 orebodies have been discovered in the granitic mylonites and are divided into 4 ore zones [48]. The orebodies are 150–300 m long, 5–25 m wide, strike 35–40° and dip NW from 75° on the surface to 55° with increasing depth [48]. All lenticular orebodies and gold-bearing veins are controlled by the Gezhen shear zone and its secondary fractures [5,8,47].
Two types of gold mineralization have been identified in the Tuwaishan gold deposit—disseminated ores hosted in the granitic mylonite and less common auriferous sulfide-bearing quartz veins (e.g., the smoky quartz veins; Figure 4). The granitic mylonites are the main wallrocks in the gold deposit while the mineralized quartz-mica schists and plagioclase amphibolites have also been observed. Silicification, sulfidization and sericitization have close relationships with gold mineralization while chloritization and carbonatization are also related to orebodies. Ore minerals include pyrite, arsenopyrite with lesser pyrrhotite, galena, sphalerite and chalcopyrite (Figure 5). The occurrence of gold is predominantly native gold, and electrum grains occur adjacent to or in fractures of sulfide grains and gangue minerals as free gold (Figure 5). Major gangue minerals include quartz, albite, sericite, chlorite and calcite (Figure 4 and Figure 5).
Based on crosscutting relationships and mineral assemblages, the hydrothermal ore-forming period of the Tuwaishan gold deposit can be divided into three stages. The early stage gray and milky quartz veins contain pyrite, arsenopyrite, gold and local pyrrhotite (Figure 4 and Figure 5). The middle stage is characterized by smoky quartz veins crosscutting early stage quartz veins or superimposed on the early stage silicification, containing base metal sulfides and native gold, and is the main stage for gold mineralization (Figure 4 and Figure 5). The late stage is represented by quartz–calcite veins commonly crosscutting the earlier two stages of quartz veins with trace sulfides and almost no gold, reflecting the end of this period of ore-forming hydrothermal activity (Figure 4).

4. Sample Description and Analytical Methods

In this study, 11 and 14 ore samples have been collected at different sections from shaft 2, 3 and 4 of the Tuwaishan gold deposit to carry out H-O and S isotope analyses, respectively. Descriptions of the samples are presented in Table 1.
The H and O isotope analyses were completed at the Beijing Research Institute of Uranium Geology, China (BRIUG). Quartz grains were crushed into 40–60 mesh and further handpicked under a binocular microscope, followed by fine grinding and sieving before treatment with dehydrated ethanol to ensure a purity of better than 99% [49,50]. The H and O isotopic compositions of the purified quartz were measured using a MAT-253 gas isotope ratio mass spectrometer (Thermo Fisher Scientific, Waltham, MA, USA). Hydrogen isotope was measured on water released from fluid inclusions of the quartz via thermal decrepitating. The purified quartz samples were first degassed through heating under a vacuum at 90 °C for 12 h. Then, the water was released from fluid inclusions by heating the samples to 400–500 °C [51]. The released water was trapped and reduced to H2 by zinc powder before analyses with gas isotope ratio mass spectrometer. Oxygen isotope analyses were based on the BrF5 extraction technique, with O being extracted by reacting with BrF5 [52]. The resulting O2 was reacted with graphite rods to produce CO2 before analyses with gas isotope ratio mass spectrometer. The isotopic results were standardized with Vienna-Standard Mean Ocean Water (V-SMOW) for H and O isotopes, while the analytical precisions were better than ±2% for δD values and ±0.2% for δ18O values. The isotopic fractionation of oxygen between quartz and water was calculated using the equation of 1000lnα = 3.38 × 106/T2 − 3.4 [52].

5. Results

The H and O isotopic compositions of gold ores from the Tuwaishan gold deposit, alone with those of the Baoban, Bumo, Erjia gold deposits as well as the wallrock granitic mylonites from previous studies are presented in Table 2 and plotted in Figure 6. The 11 ore samples of the Tuwaishan gold deposit yield δDV-SMOW and δ18OV-SMOW values from −75.9‰ to −54.4‰ and from +8.1‰ to 13.7‰, respectively. Given 360 °C as the trapping temperature for the main stage of gold mineralization of the Tuwaishan gold deposit [47], the corresponding δ18Owater values range from +3.1‰ to +8.7‰.
The S isotope data of pyrites from the Gezhen gold deposits as well wallrocks and dykes are listed in Table 3 and plotted in Figure 7. The 14 ore samples of the Tuwaishan gold deposit show δ34S values of +4.5‰ to +7.9‰ with a narrow variation of 3.4‰ and an average of +6.3‰.

6. Discussion

6.1. Ore-Forming Fluid Source

Many workers have carried out H-O isotope analyses to constrain the fluid source of the Gezhen shear zone gold deposits, and it has been proposed that a mixture of magmatic water and metamorphic water with variable contents of meteoric water are most likely the source for the Gezhen gold deposits [5,10,11,12,14]. The δDV-SMOW and calculated δ18Owater values are from −87.0‰ to −55.0‰ and from −0.1‰ to +8.1‰ for the Tuwaishan gold deposit [13,16,55,56], indicating a hybrid source for ore-forming fluid [53]. Some researchers proposed that the ore-forming fluid of the Tuwaishan gold deposit originated from a mixture of magmatic water and meteoric water [10,13], while some other researchers argued that a mixture of metamorphic and meteoric water with lesser contribution of magmatic water could be the source fluid for this deposit [17].
Our new H-O isotopic data for quartz grains separated from 11 ore samples of the Tuwaishan gold deposit predominantly fall into either the metamorphic water field or the magmatic water field or the overlap zone between them in the δDH2O vs. δ18OH2O plot (Figure 6), indicating a mixture of metamorphic and magmatic water for the ore-forming fluid source [53,58,59,60]. Meanwhile, half of our new data fall into the typical orogenic gold fluid field in the δDH2O vs. δ18OH2O plot [54], suggesting the involvement of metamorphic water in the formation of the Tuwaishan gold deposit [24,54,61,62]. The ore-forming fluid of the Gezhen gold deposits is characterized as medium temperature (200–380 °C), low salinity (predominantly 3.0%–7.0%NaCleqv), reducing (H2S exists in the gas phase composition) and CO2 rich [12,13,15,47,63]. It is compatible with metamorphic fluid but is significantly different from the magmatic fluid [64,65,66,67]. Thus, combined with ore-forming fluid properties and H-O isotopic compositions, it is proposed that the ore-forming fluid of the Tuwaishan gold deposit is most likely sourced from metamorphic water.

6.2. Sulfur Source

Although there are plenty of available sulfur isotopic data for the Gezhen gold deposits as well as the wallrocks, intrusions and dykes (Table 3, Figure 7), debates still exist for the sulfur source of the Gezhen gold deposits. This is partly because the similarity among δ34S values of the gold deposits, the Baoban Group metamorphic rocks, the granitic mylonites and the diorite porphyrite dykes (Table 3, Figure 7). Some researchers suggest that the sulfur was sourced from the magmatic fluid which has interacted with wallrocks of the Baoban Group metamorphic rocks or the granitic mylonites during its ascending, as the positive δ34S values of the Gezhen gold deposits are slightly higher than those of the magmatic fluid, and are close to those of the wallrocks [10,16] (Table 3; Figure 7). However, some other workers believe that the sulfur was originated from the metamorphism of the Baoban Group rocks [12,17,68]. The indistinctive positive δ34S values are not fully consistent with either magmatic fluid or sedimentary fluid [12]. In addition, the narrow variation of δ34S values for the Gezhen gold deposits indicates a sulfur isotope homogenization during regional metamorphism [10,17,69,70,71]. Considering the high gold content of the Baoban Group rocks as well as their close spatial relationship with the Gezhen gold deposits, many researchers believe that the metamorphism of the Baoban Group rocks played a key role in the formation of those gold deposits [12,16,17,68].
Field and microscopic observations suggest that ore minerals of the Gezhen gold deposits are predominantly sulfides including pyrite, arsenopyrite, sphalerite, galena and chalcopyrite whereas sulfates are absent [16,47]. Thus, the sulfur isotope compositions of sulfides should be approximately the same as those of the ore-forming fluid [69,72]. Our new δ34S values of pyrite separates from 14 ore samples from the Tuwaishan gold deposit show positive values (from +4.5‰ to +7.9‰) with a narrow variation (3.4‰), which strongly imply a sulfur isotope homogenization caused by regional metamorphism during the formation of the gold deposit [27,54,70]. Furthermore, the same δ34S values among the Tuwaishan, Baoban, Erjia and Bumo gold deposits request a common source for all gold deposits along the Gezhen shear zone (Table 3; Figure 7). Thus, the plagioclase amphibolites as well as the diorite porphyrite dykes are not likely the sources of sulfur for the Gezhen gold deposits due to their scattered distribution and limited scales [5,16]. It is concluded that the sulfur of the Tuwaishan gold deposit, as well as other gold deposits along the Gezhen shear zone, is originated from regional metamorphism of sources rocks.

6.3. Genesis and Formation of the Tuwaishan Gold Deposit

The Gezhen gold deposits have been traditionally classified as sedimentary-reworked [10,11,12] or magmatic-hydrothermal origin [13]. Xu et al. [5] summarized previous studies on deposit geology, ore-forming fluid characteristics and isotope compositions of the Gezhen gold deposits and concluded that these gold deposits were best classified as orogenic in genesis. Our new data on H-O-S isotopic compositions of the Tuwaishan gold deposit further support the orogenic gold classification not only because the H-O-S isotopic compositions of the Tuwaishan gold deposit are consistent with those of typical orogenic gold deposits worldwide [6,54,73,74] (Figure 6 and Figure 7) but also because the comprehensive interpretations of our new H-O-S isotopic data with ore-forming fluid properties favor a metamorphic rather than a magmatic origin.
As discussed above, the Tuwaishan gold deposit belongs to orogenic gold deposit and is most likely sourced from metamorphism. Therefore, the host rocks of the Baoban Group metamorphic rocks are seemingly the potential sources of both ore-forming fluid and materials for the Tuwaishan gold deposit as well as other gold deposits along the Gezhen shear zone. In fact, it has been widely accepted by early researchers on Hainan gold deposits that the Baoban Group rocks are the source rocks for the Gezhen gold deposits [5,11,12,14,15,16,17]. Accordingly, it has been proposed that the metamorphic fluid released from regional metamorphism of the Baoban Group rocks mixed with magmatic fluid or the magmatic fluid that extracted Au from the Baoban Group rocks during its ascending, which deposited Au and sulfides in appropriate spaces in the Gezhen shear zone, is the major mechanism of gold mineralization along the shear zone [11,16,17].
However, despite the fact that the Gezhen gold deposits were sourced from metamorphism, and the Baoban Group metamorphic rocks are the host rocks, those Mesoproterozoic basement rocks are not necessarily the source for the Gezhen gold deposits [8]. Based on the metamorphic devolatilization model for orogenic gold deposits, most of sulfur and Au would have been released from the source rocks into the metamorphic fluid during the prograde metamorphic transition from the greenschist to the amphibolite facies [23,24,75,76,77]. This is when the source rocks were first heated through a temperature-pressure window that broke chlorite, pyrite, organic matter and various other minerals and contributed to the fluid phase [24]. The Baoban Group rocks together with the Mesoproterozoic mafic rocks have experienced amphibolite facies regional metamorphism at 1.3–0.9 Ga [18,19,22], during which time those Mesoproterozoic basement rocks have lost most of their Au and sulfur [8,24,54,77]. Therefore, the Baoban Group rocks could not be a source for the fluid and gold for the gold mineralization at ca. 243 Ma along the Gezhen shear zone [8]. Instead, The Ordovician Nanbigou Formation rocks and the Silurian Tuolie Formation rocks on the footwall of the Gezhen shear zone have experienced greenschist facies and lower greenschist facies regional metamorphism, respectively [4,42]. Even through the timing and duration for this metamorphism have not been well constrained, the continuous amalgamation process from back-arc consumption (272–252 Ma) to orogenic assembly (251–243 Ma) between the South China and Indochina Blocks represents an important tectono-thermal event that would promote regional metamorphism in Hainan Island [2,8,78]. Considering the fact that the Ordovician–Silurian rocks are on the footwall of the reverse Gezhen shear zone (Figure 2), and the dip angle gradually decreases with increasing depth [9,36], metamorphic devolatilization of these rocks at depth would provide a realistic source of fluid, gold and sulfur for the gold mineralization along the shear zone. Therefore, we propose that the Ordovician–Silurian rocks on the footwall of the Gezhen shear zone are most likely the sources of ore-forming fluid and materials for the Tuwaishan gold deposit and other gold deposits along the Gezhen shear zone.

7. Conclusions

New H-O-S isotopic data of the Tuwaishan gold deposit in Hainan Island are reported here. In combination with H-O-S isotopic compositions and ore-forming fluid properties of the Gezhen gold deposits from previous works, this study identified the ore-forming fluid and material source characteristics of the Tuwaishan and other gold deposits along the Gezhen shear zone. Furthermore, with integrated studies on source characteristics, deposit geology and regional geology of the Gezhen gold deposits, as well as tectonic settings of Hainan Island, a realistic source has been proposed for the Tuwaishan and other gold deposits along the Gezhen shear zone. The main conclusions are as follows:
(1)
The δD and δ18O values for ore-forming fluid of the Tuwaishan gold deposit are from −75.9‰ to −54.4‰ and from +3.1‰ to +8.7‰, indicating a source of metamorphic fluid.
(2)
The δ34S values for the ore-related pyrites of the Tuwaishan gold deposit are from +4.5‰ to +7.9‰, reflecting a source of metamorphism for the ore-forming materials.
(3)
The Tuwaishan and other gold deposits along the Gezhen shear zone are orogenic gold deposit that were formed as a result of regional metamorphism.
(4)
The Mesoproterozoic basement rocks could not be the source of the Gezhen gold deposits. Instead, the Ordovician–Silurian rocks on the footwall of the Gezhen shear zone are most likely the source for the Tuwaishan and other gold deposits along the shear zone, even though more work is required to confirm such a source.

Author Contributions

Formal analysis, Y.L.; funding acquisition, D.X. and Y.L.; investigation, Y.L., L.W. and J.H.; writing—original draft, Y.L.; writing—review and editing, J.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research was jointly funded by the National Natural Science Foundation of China (Grant No. U2244219), the National Nonprofit Institute Research Grant of IGGE (AS2022P03), and the Chinese Geological Survey Program (Grant Nos. DD20190047, DD20221807, DD20230013).

Data Availability Statement

All data generated or used during the current study are available in full within this article.

Acknowledgments

We sincerely thank Lingku Meng for the permission of sampling in the Tuwaishan gold mining area. We are grateful to three anonymous reviewers for their constructive comments.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. (a) Structural outline of Southeast Asia. (b) Simplified geological map of Hainan Island. (Revised from [9]).
Figure 1. (a) Structural outline of Southeast Asia. (b) Simplified geological map of Hainan Island. (Revised from [9]).
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Figure 2. Geological map of the Gezhen shear zone and the Gezhen gold belt (Revised from [5]).
Figure 2. Geological map of the Gezhen shear zone and the Gezhen gold belt (Revised from [5]).
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Figure 3. Mining geology of the Tuwaishan gold deposit (Revised from [47]).
Figure 3. Mining geology of the Tuwaishan gold deposit (Revised from [47]).
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Figure 4. Wallrocks and orebodies of the Tuwaishan gold deposit. (a) The early stage milky quartz veins with pyrite and chlorite in alteration zones. (b) Disseminated ore with lots of pyrite grains. (c,d) The middle stage smoky quartz veins crosscut or superimposed on the early stage quartz veins or silicification. (e) The late stage barren quartz vein crosscut the earlier quartz veins. (f) The late stage pink calcite vein. Qtz = Quartz, Py = Pyrite, Chl = Chlorite, Cal = Calcite.
Figure 4. Wallrocks and orebodies of the Tuwaishan gold deposit. (a) The early stage milky quartz veins with pyrite and chlorite in alteration zones. (b) Disseminated ore with lots of pyrite grains. (c,d) The middle stage smoky quartz veins crosscut or superimposed on the early stage quartz veins or silicification. (e) The late stage barren quartz vein crosscut the earlier quartz veins. (f) The late stage pink calcite vein. Qtz = Quartz, Py = Pyrite, Chl = Chlorite, Cal = Calcite.
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Figure 5. Alteration stages and mineral assemblages of the Tuwaishan gold deposit. (a,b) Euhedral pyrite and arsenopyrite grains with later hydrothermal alteration and deformation. (c) Gold grains formed in the fractures or adjacent to pyrite and arsenopyrite grains. (d) Pyrite, sphalerite and galena assemblage, euhedral pyrite grains altered by later sphalerite and galena. (e). Pyrite, arsenopyrite and galena assemblage with gold grains. (f). Gold grains formed in quartz grains near pyrrhotite grains. Py = Pyrite, Apy = Arsenopyrite, Po = Pyrrhotite, Gn = Galena, Sph = Sphalerite, Au = Gold.
Figure 5. Alteration stages and mineral assemblages of the Tuwaishan gold deposit. (a,b) Euhedral pyrite and arsenopyrite grains with later hydrothermal alteration and deformation. (c) Gold grains formed in the fractures or adjacent to pyrite and arsenopyrite grains. (d) Pyrite, sphalerite and galena assemblage, euhedral pyrite grains altered by later sphalerite and galena. (e). Pyrite, arsenopyrite and galena assemblage with gold grains. (f). Gold grains formed in quartz grains near pyrrhotite grains. Py = Pyrite, Apy = Arsenopyrite, Po = Pyrrhotite, Gn = Galena, Sph = Sphalerite, Au = Gold.
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Figure 6. Plot of δD versus calculated δ18Owater for quartz veins of the Gezhen gold deposits. Base map modified after [43]. Magmatic water, metamorphic water and meteoric water line are from [53]. Hydrogen and oxygen isotopic compositions of typical orogenic gold deposits are from [54].
Figure 6. Plot of δD versus calculated δ18Owater for quartz veins of the Gezhen gold deposits. Base map modified after [43]. Magmatic water, metamorphic water and meteoric water line are from [53]. Hydrogen and oxygen isotopic compositions of typical orogenic gold deposits are from [54].
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Figure 7. Comparison of sulfur isotopic compositions of the Gezhen gold deposits with wallrocks, intrusions and dykes.
Figure 7. Comparison of sulfur isotopic compositions of the Gezhen gold deposits with wallrocks, intrusions and dykes.
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Table 1. Sample location and description of the Tuwaishan gold deposit.
Table 1. Sample location and description of the Tuwaishan gold deposit.
NumberLocationLithologyCharacteristicsAnalyses
NW-7Section 5, shaft 2Quartz vein oreQuartz vein with sulfidesS
JC-20Section 5, shaft 2Quartz vein oreQuartz vein with sulfidesH-O
13JC-11Section 6, shaft 3Disseminated oreGranitic mylonites with quartz, pyrite and chloriteH-O-S
13JC-12Section 6, shaft 3Disseminated oreGranitic mylonites with quartz, pyrite and chloriteS
13JC-13Section 6, shaft 3Disseminated oreGranitic mylonites with sulfidesS
13JC-16Section 5, shaft 2Disseminated oreGranitic mylonites with sulfidesH-O-S
13JC-18Section 5, shaft 2Disseminated oreGranitic mylonites with pyriteS
13JC-19Section 5, shaft 2Quartz vein oreQuartz vein with sulfides and chlorite along each sides H-O-S
13JC-20Section 5, shaft 2Quartz vein oreQuartz vein with sulfidesH-O
13JC-21Section 5, shaft 2Quartz vein oreQuartz vein with sulfidesH-O
13JC-27Section 5, shaft 3Quartz vein oreQuartz vein with sulfidesS
16JC-16Section 7, shaft 3Quartz vein oreQuartz breccia with granitic mylonitesH-O-S
16JC-19Section 7, shaft 3Quartz vein oreSmoky quartz veins with fine-grained sulfidesH-O-S
16JC-25Section +25 m, shaft 4Quartz vein oreSmoky quartz veins with fine-grained sulfidesS
16JC-26Section +25 m, shaft 4Quartz vein oreSmoky quartz veins with fine-grained sulfidesH-O-S
16JC-27Section +25 m, shaft 4Quartz vein oreSmoky quartz veins with fine-grained sulfidesH-O-S
16JC-29Section +25 m, shaft 4Quartz vein oreSmoky quartz veins with fine-grained sulfidesH-O
16JC-30Section +25 m, shaft 4Disseminated oreGranitic mylonites with pyrite and chloriteS
Table 2. Hydrogen and oxygen isotopic data of quartz veins from the Gezhen gold deposits.
Table 2. Hydrogen and oxygen isotopic data of quartz veins from the Gezhen gold deposits.
Gold DepositSample NumberLithologyMineralδ18OSMOW (‰)δ18OH2O (‰)δDSMOW (‰)Equilibrium Temperature (°C)Data Source
Tuwaishan16JC-16Gold oreQuartz8.5 3.5 −63.6 360This study
Tuwaishan16JC-19Gold oreQuartz12.6 7.6 −75.9 360This study
Tuwaishan16JC-26Gold oreQuartz13.7 8.7 −64.2 360This study
Tuwaishan16JC-27Gold oreQuartz12.9 7.9 −65.9 360This study
Tuwaishan16JC-29Gold oreQuartz10.8 5.8 −64.0 360This study
Tuwaishan13JC-11Gold oreQuartz8.4 3.4 −75.9 360This study
Tuwaishan13JC-16Gold oreQuartz8.1 3.1 −65.8 360This study
TuwaishanJC-20Gold oreQuartz12.4 7.4 −62.6 360This study
Tuwaishan13JC-19Gold oreQuartz9.7 4.7 −58.2 360This study
Tuwaishan13JC-20Gold oreQuartz9.7 4.7 −54.4 360This study
Tuwaishan13JC-21Gold oreQuartz12.3 7.3 −56.2 360This study
Tuwaishan2-4-B1Gold oreQuartz13.0 3.7 −74.0 252Yang, 2008 [13]
Tuwaishan2-4-B2Gold oreQuartz14.8 6.0 −80.0 253Yang, 2008 [13]
Tuwaishan2-4-B3Gold oreQuartz15.0 7.6 −85.0 287Yang, 2008 [13]
Tuwaishan2-4-A3Gold oreQuartz15.3 4.7 −87.0 238Yang, 2008 [13]
Tuwaishan3-A1Gold oreQuartz14.3 3.2 −81.0 211Yang, 2008 [13]
Tuwaishan3-A3Gold oreQuartz14.4 2.4 −74.0 195Yang, 2008 [13]
Tuwaishan3-A5Gold oreQuartz15.0 3.6 −73.0 224Yang, 2008 [13]
Tuwaishan3-A4Gold oreQuartz14.9 3.8 −76.0 209Yang, 2008 [13]
Tuwaishan2-4-C1Gold oreQuartz12.1 1.3 −75.0 214Yang, 2008 [13]
Tuwaishan2-4-C2Gold oreQuartz12.5 1.3 −68.0 208Yang, 2008 [13]
TuwaishanTIV-2Gold oreQuartz12.1 3.1 −67.8 252Hou et al., 1996 [16]
TuwaishanTIV-3Gold oreQuartz9.6 0.6 −61.7 252Hou et al., 1996 [16]
TuwaishanT-02Gold oreQuartz14.2 8.1 −68.0 323Xiao, 1989 [55]
TuwaishanT-179Gold oreQuartz10.9 4.7 −85.0 320Xiao, 1989 [55]
TuwaishanT-09Gold oreQuartz11.5 4.4 −61.9 293Xiao, 1989 [55]
TuwaishanT-05Gold oreQuartz13.1 2.1 −61.9 212Xiao, 1989 [55]
TuwaishanT-021Gold oreQuartz15.1 3.1 −66.8 196Xiao, 1989 [55]
TuwaishanT-35Gold oreQuartz12.8 1.2 −73.0 200Xiao, 1989 [55]
TuwaishanT-56Gold oreQuartz10.2 −0.1 −87.0 220Xiao, 1989 [55]
TuwaishanV2-3Gold oreQuartz13.7 −0.1 −73.0 171Feng, 1989 [56]
TuwaishanV5-161Gold oreQuartz10.7 2.1 −55.0 259Feng, 1989 [56]
TuwaishanV102-05Gold oreQuartz13.1 2.1 −62.0 212Feng, 1989 [56]
BaobanPV1-1Gold oreQuartz10.0 2.7 −61.0 290Chen et al., 1993 [11]
BaobanPV1-2Gold oreQuartz9.8 2.5 −54.0 290Chen et al., 1993 [11]
BaobanB249Gold oreQuartz7.5 −3.5 −76.0 210Xiao, 1989 [55]
BaobanB279Gold oreQuartz10.3 −2.7 −59.0 180Xiao, 1989 [55]
BaobanV1-9-3Gold oreQuartz10.2 1.9 −66.0 265Feng, 1989 [56]
BaobanV1-8-8Gold oreQuartz11.1 1.3 −78.0 234Feng, 1989 [56]
BaobanV1-8-1Gold oreQuartz11.3 −0.6 −71.0 197Feng, 1989 [56]
BaobanV101-021Gold oreQuartz16.1 3.4 −67.0 200Feng, 1989 [56]
BaobanV101-09Gold oreQuartz11.5 4.4 −62.0 292Feng, 1989 [56]
Baoban021Gold oreQuartz15.1 7.0 −67.0 280Feng, 1989 [56]
Baoban09Gold oreQuartz11.5 3.4 −62.0 280Feng, 1989 [56]
Baoban05Gold oreQuartz13.1 5.0 −62.0 280Feng, 1989 [56]
ErjiaJ107-1Gold oreQuartz13.1 4.2 −64.2 250Chen, 1996 [57]
ErjiaJ107-3Gold oreQuartz13.5 4.5 −55.0 250Chen, 1996 [57]
ErjiaJ107-6Gold oreQuartz12.7 3.7 −70.2 250Chen, 1996 [57]
ErjiaJ107-8Gold oreQuartz12.5 3.6 −59.3 250Chen, 1996 [57]
ErjiaJ107-10Gold oreQuartz11.3 2.4 −61.4 250Chen, 1996 [57]
ErjiaJ107-11Gold oreQuartz12.1 3.2 −61.2 250Chen, 1996 [57]
ErjiaA58Gold oreQuartz10.4 1.8 −59.0 270Tu and Gao, 1993 [12]
ErjiaA66Gold oreQuartz13.2 4.6 −60.0 270Tu and Gao, 1993 [12]
BumoBM4-1Gold oreQuartz12.2 4.3 −66.3 280Hou et al., 1996 [16]
BumoB3-7Gold oreQuartz8.8 0.3 −62.0 270Tu and Gao, 1993 [12]
BumoB4Gold oreQuartz11.6 3.1 −62.0 270Tu and Gao, 1993 [12]
BumoB10Gold oreQuartz8.1 −5.4 −64.0 180Tu and Gao, 1993 [12]
BumoB11Gold oreQuartz11.9 −1.7 −65.0 180Tu and Gao, 1993 [12]
BumoB20Gold oreQuartz9.4 −2.2 −80.0 210Tu and Gao, 1993 [12]
BumoB25Gold oreQuartz9.8 1.3 −56.0 270Tu and Gao, 1993 [12]
BumoB26Gold oreQuartz8.8 0.3 −66.0 270Tu and Gao, 1993 [12]
Table 3. Sulfur isotopic data of pyrites from the Gezhen gold deposits, wallrocks, intrusions and dykes.
Table 3. Sulfur isotopic data of pyrites from the Gezhen gold deposits, wallrocks, intrusions and dykes.
Gold DepositSample NumberLithologyMineralδ34S‰Sample SizeData Source
TuwaishanNW-7Gold orePyrite5.0 This study
Tuwaishan13JC-11Gold orePyrite4.5 This study
Tuwaishan13JC-12Gold orePyrite7.1 This study
Tuwaishan13JC-13Gold orePyrite6.9 This study
Tuwaishan13JC-16Gold orePyrite7.0 This study
Tuwaishan13JC-18Gold orePyrite6.8 This study
Tuwaishan13JC-19Gold orePyrite7.5 This study
Tuwaishan13JC-27Gold orePyrite4.5 This study
Tuwaishan16JC-16Gold orePyrite7.1 This study
Tuwaishan16JC-19Gold orePyrite6.1 This study
Tuwaishan16JC-25Gold orePyrite7.9 This study
Tuwaishan16JC-26Gold orePyrite6.5 This study
Tuwaishan16JC-27Gold orePyrite6.8 This study
Tuwaishan16JC-30Gold orePyrite5.0 This study
TuwaishanNo.1Gold orePyrite6.3 Hou et al., 1996 [16]
TuwaishanNo.6Gold orePyrite6.4 Hou et al., 1996 [16]
TuwaishanTV-IVGold orePyrite6.8 Hou et al., 1996 [16]
TuwaishanTj-2lGold orePyrite6.4 Hou et al., 1996 [16]
TuwaishanT-55Gold orePyrite5.2 Hou et al., 1996 [16]
TuwaishanT-90-2Gold orePyrite6.5 Hou et al., 1996 [16]
TuwaishanT-35Gold orePyrite6.1 Hou et al., 1996 [16]
TuwaishanT-90-1Gold orePyrite6.1 Hou et al., 1996 [16]
TuwaishanT-54Gold orePyrite7.1 Hou et al., 1996 [16]
TuwaishanT-56Gold orePyrite5.6 Hou et al., 1996 [16]
TuwaishanT-27Gold orePyrite6.7 Hou et al., 1996 [16]
TuwaishanB-249Gold orePyrite8.2 Hou et al., 1996 [16]
Tuwaishan Gold orePyrite5.0–8.2UnknownLiang, 1992 [10]
Tuwaishan Gold orePyrite4.0–8.210 Xia, 2002 [17]
BaobanP202Gold orePyrite6.7 Tu and Gao, 1993 [12]
BaobanBV30-1Gold orePyrite6.7 Hou et al., 1996 [16]
BaobanB-470Gold orePyrite4.0 Hou et al., 1996 [16]
ErjiaJ107-3Gold orePyrite6.4 Chen, 1996 [57]
ErjiaR5-1Gold orePyrite6.5 Chen, 1996 [57]
ErjiaR5-2Gold orePyrite6.0 Chen, 1996 [57]
ErjiaR1-1Gold orePyrite5.1 Chen, 1996 [57]
ErjiaR1-2Gold orePyrite5.1 Chen, 1996 [57]
ErjiaR2-1Gold orePyrite3.2 Chen, 1996 [57]
ErjiaR2-2Gold orePyrite3.6 Chen, 1996 [57]
ErjiaA16Gold orePyrite6.8 Tu and Gao, 1993 [12]
ErjiaA19Gold orePyrite6.5 Tu and Gao, 1993 [12]
ErjiaA22Gold orePyrite7.4 Tu and Gao, 1993 [12]
ErjiaA24Gold orePyrite7.2 Tu and Gao, 1993 [12]
ErjiaA25Gold orePyrite6.7 Tu and Gao, 1993 [12]
ErjiaA32Gold orePyrite6.9 Tu and Gao, 1993 [12]
ErjiaA34Gold orePyrite7.5 Tu and Gao, 1993 [12]
ErjiaA62Gold orePyrite7.6 Tu and Gao, 1993 [12]
ErjiaHR34Gold orePyrite6.8 Tu and Gao, 1993 [12]
ErjiaHR35Gold orePyrite6.6 Tu and Gao, 1993 [12]
ErjiaEJV-23Gold orePyrite4.1 Hou et al., 1996 [16]
Erjia Gold orePyrite3.4–7.713 Xia, 2002 [17]
BumoB4Gold orePyrite4.4 Tu and Gao, 1993 [12]
BumoB4-1Gold orePyrite4.2 Tu and Gao, 1993 [12]
Bumo Gold orePyrite4.3–6.47 Xia, 2002 [17]
Erjia Baoban Group rocksPyrite3.7–6.85 Huang and Ding, 1992 [14]
TuwaishanTyD3-5Granitic mylonitesPyrite7.8 Hou et al., 1996 [16]
TuwaishanTyD3-6Granitic mylonitesPyrite6.2 Hou et al., 1996 [16]
TuwaishanNo.21Granitic mylonitesPyrite8.5 Hou et al., 1996 [16]
ErjiaEj-13Granitic mylonitesPyrite8.2 Hou et al., 1996 [16]
Tuwaishan Granitic mylonitesPyrite4.1–7.8UnknownLiang, 1992 [10]
Erjia Granitic mylonitesPyrite2.4–8.210 Huang and Ding, 1992 [14]
Erjia Metamorphic basic rocksPyrite7.9 Chen et al., 1993 [11]
Tuwaishan Metamorphic basic rocksPyrite7.4–7.9UnknownLiang, 1992 [10]
Erjia Diorite porphyrite dykesPyrite6.9 Chen et al., 1993 [11]
BaobanP103Diorite porphyrite dykesPyrite6.9 Hou et al., 1996 [16]
Tuwaishan Diorite porphyrite dykesPyrite2.6–3.73Liang, 1992 [10]
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Liu, Y.; Mao, J.; Hu, J.; Wang, L.; Xu, D. Genesis and Formation of the Tuwaishan Gold Deposit in Hainan Island, South China: Implications from H-O-S Isotopes. Minerals 2023, 13, 1082. https://doi.org/10.3390/min13081082

AMA Style

Liu Y, Mao J, Hu J, Wang L, Xu D. Genesis and Formation of the Tuwaishan Gold Deposit in Hainan Island, South China: Implications from H-O-S Isotopes. Minerals. 2023; 13(8):1082. https://doi.org/10.3390/min13081082

Chicago/Turabian Style

Liu, Yuheng, Jingwen Mao, Jun Hu, Lei Wang, and Deming Xu. 2023. "Genesis and Formation of the Tuwaishan Gold Deposit in Hainan Island, South China: Implications from H-O-S Isotopes" Minerals 13, no. 8: 1082. https://doi.org/10.3390/min13081082

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