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Article

Fluid Inclusions and C–H–O–S–Pb Isotopes of the Huoluotai Porphyry Cu (Mo) Deposit in the Northern Great Xing’an Range, NE China: Implications for Ore Genesis

1
School of Resources and Civil Engineering, Suzhou University, Suzhou 234000, China
2
College of Earth Sciences, Jilin University, Changchun 130061, China
3
Qiqihaer Institute of Geological Exploration, Heilongjiang 161006, China
4
Key Laboratory of Mineral Resources Evaluation in Northeast Asia, Ministry of Land and Resources, Changchun 130061, China
*
Author to whom correspondence should be addressed.
Minerals 2022, 12(9), 1072; https://doi.org/10.3390/min12091072
Submission received: 20 July 2022 / Revised: 18 August 2022 / Accepted: 24 August 2022 / Published: 25 August 2022
(This article belongs to the Special Issue Genesis and Metallogeny of Non-ferrous and Precious Metal Deposits)

Abstract

:
The Huoluotai Cu (Mo) deposit is a recently discovered porphyry Cu deposit in the northern Great Xing’an Range, NE China. Fluid inclusion (FI) micro-thermometry results and the C–H–O–S–Pb isotope compositions of the Huoluotai Cu (Mo) deposit are presented in this study. The ore-forming process consists of the sulfide-barren quartz stage (I), the quartz + chalcopyrite ± pyrite ± molybdenite stage (II), the quartz + polymetallic sulfide stage (III), and the quartz + calcite ± pyrite ± fluorite stage (IV). Cu mineralization occurred mainly in stage II. Four types of FIs were recognized: liquid-rich two-phase FIs (L-type), vapor-rich two-phase FIs (V-type), daughter-mineral-bearing three-phase FIs (S-type), and CO2-bearing FIs (C-type). In stage I, the ore-forming fluids belong to an H2O−NaCl−CO2 system. In stages II, III, and IV, the ore-forming fluids belong to an H2O−NaCl system. The results of the FI micro-thermometry and H–O isotope analysis show that the ore-forming fluids originated from a magmatic origin in stage I and mixed with meteoric water from stages II to IV. The S–Pb isotope results suggest that the source of the ore-forming materials has the characteristics of a crust–mantle-mixing origin. Fluid boiling occurred in stages I and II. The FI micro-thermometric data further show that Cu was mainly deposited below 400 °C in stage II, suggesting that fluid boiling occurring below 400 °C may be the primary factor for Cu precipitation in the Huoluotai Cu (Mo) deposit.

1. Introduction

As one of the largest orogenic collages in the world, the Central Asian Orogenic Belt (CAOB) is located between the East Europe, Siberia, Tarim, and North China cratons (Figure 1A). The northern Great Xing’an Range (NGXR) is tectonically located in the eastern segment of the CAOB (Figure 1A,B) and hosts a number of epithermal and orogenic Au, hydrothermal Ag–Pb–Zn, porphyry, and skarn Pb–Zn deposits (Figure 1C). Over the past decade, many late Mesozoic porphyry deposits in the NGXR have been discovered and raised concern (Figure 1C). Examples include the Daheishan Mo (ca. 147 Ma; [1]), the Chalukou Mo (ca. 148 Ma; [2]), the Fukeshan Cu (Mo) (ca. 149 Ma; [3,4]), and the Xiaokele Cu (Mo) (ca. 150 Ma; [5]) deposits.
The Huoluotai Cu (Mo) deposit, which is located in the NGXR, contains estimated industrial metal resources of >4900 t Cu and >300 t Mo and is currently being explored [8]. Previous studies have focused on the geological characteristics [9], geochronology [9,10], and geochemistry of the igneous rocks in this deposit [11]. According to these studies, the Huoluotai Cu (Mo) deposit is considered to be a porphyry deposit. The magmatic activity of the Huoluotai Cu (Mo) deposit mainly occurred in the Late Jurassic–Early Cretaceous (ca. 150–140 Ma), and Cu (Mo) mineralization was closely related to the Late Jurassic granodiorite porphyry (ca. 149 Ma; [11]). Nevertheless, the lack of comprehensive research on the ore-forming fluids limits our understanding of the ore-forming conditions of the Huoluotai Cu (Mo) deposit. Three important issues have not been resolved: (1) the origin and detailed evolution of the ore-forming fluids are unknown; (2) the source of the ore-forming materials remains uncertain; and (3) the possible mineralization processes have not been determined.
To solve these problems, the present study presents micro-thermometry and laser Raman spectroscopy data of the fluid inclusions (FIs), and C–H–O–S–Pb isotope compositions. The results will provide new clues for further prospecting directions in the Huoluotai Cu (Mo) deposit, as well as the late Mesozoic porphyry Cu deposits in the NGXR.

2. Regional Geology

From west to east, NE China is divided into the Erguna, Xing’an, Songnen, Jiamusi, and Khanka blocks (Figure 1B; [12]). The NGXR is located in the western part of NE China, including the Erguna Block, the northern part of the Xing’an Block, and the northwestern part of the Songnen Block (Figure 1B; [13]). The Huoluotai Cu (Mo) deposit is located in the northern segment of the Erguna Block (Figure 1C). The Erguna Block collided with the Xing’an Block along the Tayuan–Xiguitu suture at ca. 500 Ma (Figure 1C; [14,15]). The main faults in the Erguna Block are NE-striking Erguna and Derbugan River faults (Figure 1C; [16]). The basement of the Erguna Block mainly contains Neoproterozoic granitoids and metamorphic supracrustal rocks [16,17,18,19]. The exposed strata in the Erguna Block mainly consist of Paleozoic marine sediments [20], widely distributed Mesozoic terrigenous clastic rocks, and volcanic rocks [21]. Magmatism in the NGXR can be divided into Paleozoic, Early–Middle Triassic, Late Triassic–Early Jurassic, Middle–Late Jurassic, and Cretaceous (Figure 1C; [12,22,23,24]).

3. Ore Deposit Geology

The Huoluotai porphyry Cu (Mo) deposit is located ~50 km southwest of Mohe City, Heilongjiang Province (Figure 1C). The NNW-striking Huoluotai River Fault is distributed in the northeastern part of the district (Figure 2A). Multiperiod igneous rocks developed in the Huoluotai ore district (Figure 2). The Early Jurassic medium–fine-grained monzogranite (ca. 180 Ma) was intruded by Late Jurassic granodiorite porphyry (ca. 149 Ma), diorite porphyry (ca. 146 Ma), and Early Cretaceous granite porphyry dikes (ca. 142 Ma) (Figure 2; [11]). The quartz diorite porphyry dikes intruded into the granodiorite porphyry (Figure 2B). Mineralization developed around the granodiorite porphyry (Figure 2B), and 66 orebodies have been identified. These orebodies are characterized by disseminations, veinlets, and stockworks and are generally 1–9 m thick, dipping toward the east at angles of 20–35°. In the dipping direction, the explored orebodies usually extend downward for 50–240 m.
Three types of alteration were identified in the Huoluotai Cu (Mo) deposit: potassic, chlorite–epidote, and phyllic alterations from early to late (Figure 3A–D). From center to edge, two alteration zones can be recognized: the potassic alteration zone and the phyllic alteration zone (Figure 2B). Hydrothermal alteration surrounds the granodiorite porphyry and is correlated strongly with the granodiorite porphyry (Figure 2B). Potassic alteration is characterized by secondary K-feldspar and biotite (Figure 3A,B). The ore minerals developed in the potassic alteration zone are mainly magnetite, chalcopyrite, hematite, and small amounts of molybdenite (Figure 3E–H). Magnetite mainly developed as disseminations and/or magnetite ± quartz ± chalcopyrite veinlets. Cu (Mo) orebodies mainly developed in the potassic alteration zone. Chalcopyrite mainly developed as disseminations, masses, or quartz + chalcopyrite veins in the potassic alteration zone (Figure 3G,H). Potassic alteration was locally overprinted by epidote and chlorite alterations. Phyllic alteration can be distinguished by secondary sericite and quartz (Figure 3C,D). The ore minerals present in the phyllic alteration zone are mainly pyrite, chalcopyrite, and molybdenite (Figure 3I). In the phyllic alteration zone, chalcopyrite occurs mainly as disseminations, while molybdenite occurs mainly as disseminations and/or quartz + molybdenite + pyrite ± chalcopyrite veins (Figure 3I).
Based on the mineral assemblages and crosscutting relationships between veins in the Huoluotai Cu (Mo) deposit (Figure 3), four mineralization stages were identified: the sulfide-barren quartz stage (stage I), the quartz + chalcopyrite ± pyrite ± molybdenite stage (stage II), the quartz + polymetallic sulfide stage (stage III), and the quartz + calcite ± pyrite ± fluorite stage (stage IV) (Figure 4). Stage I is characterized by sulfide-barren quartz veins, which are rare and generally discontinuous (Figure 3E). There is no obvious cutting relationship between the veins in stage I and those in other mineralization stages. Stage I veins are mainly concentrated in the potassic alteration zone. Copper is mainly found in stage II. Stage II veins are generally continuous and irregular (Figure 3G) and mainly contain quartz, chalcopyrite, pyrite, and molybdenite. Stage II veins are distributed mainly in the potassic alteration zone. Stage III veins are generally continuous and straight (Figure 3I) and are characterized by quartz, pyrite, and molybdenite. Stage III veins are usually concentrated in the phyllic alteration zone. Stage IV veins are usually irregular and dominated by quartz and calcite (Figure 3J), with small amounts of fluorite. The sulfide observed in stage IV is only pyrite. Supergene mineralization is dominated by molybdite, azurite, and malachite (Figure 3K,L).

4. Analytical Methods

4.1. Fluid Inclusion Measurements

In total, 31 quartz samples were used to perform FI measurements at the Key Laboratory of Mineral Resources Evaluation in Northeast Asia, Ministry of Land and Resources, Changchun, China. Secondary FIs were not analyzed [25]. All types of FIs were selected for laser Raman spectra analyses using an RM-2000 Laser Raman microprobe. Micro-thermometric analyses were performed using a Linkam THMS-600 heating–freezing stage (Linkam Scientific Instruments Ltd., Epsom, UK).

4.2. H–O Isotope Analyses

Six quartz samples were selected for H–O isotope analysis at the Center of Analytical Laboratory in the Beijing Research Institute of Uranium Geology (BRIUG), China National Nuclear Corporation (Beijing, China). The H–O isotope compositions were analyzed by a Finnigan MAT253-EM mass spectrometer. The O and H isotope compositions were analyzed using the conventional BrF5 method and the Zn reduction method, respectively [26,27]. The H–O isotope values were normalized with the Vienna Standard Mean Ocean Water (V-SMOW) standards. The analytical precision was better than 0.2‰ for δ18O and 2‰ for δD.

4.3. C–O Isotope Analyses

Four representative calcite samples were selected for C–O isotope analysis at BRIUG. The C–O isotope analyses of calcite were performed using the 100% phosphoric acid method [28] with a MAT-251EM mass spectrometer. δ13C used the Pee Dee Belemnite (PDB) standard, and δ18O used the SMOW standard. The analytical precision was better than 0.1‰ for δ13C and 0.2‰ for δ18O.

4.4. S–Pb Isotope Analyses

The S isotope compositions of seven representative sulfide samples were analyzed at BRIUG. The values of δ34S for the sulfide samples were determined on SO2 produced by the reaction between the sulfide and cuprous oxide. δ34S used the Vienna Cañon Diablo Troilite (V-CDT) standard. The Pb isotope compositions of four representative sulfide samples were also analyzed at BRIUG. Sulfide samples were dissolved in a mixed solution of HF + HNO3 at 150 °C for seven days. The Pb isotope compositions were measured using a MAT-261 thermal ionization mass spectrometer.

5. Analytical Results

5.1. Fluid Inclusions

5.1.1. Microscopy Investigations of Fluid Inclusions

According to the phases, filling degree, and combination relationship of FIs at a normal temperature (25 °C), four different FI types were identified in the quartz samples from the Huoluotai Cu (Mo) deposit, as described below.
Liquid-rich (L-type) FIs are most common in four mineralization stages, which consist of two phases with VH2O/(VH2O + LH2O) < 50 vol.% at ~25 °C (Figure 5A,C–E,G–I). The vapor phase accounts for 10–20 vol.% of the FI volume. The FIs range from 3 to 20 μm in size and are round or irregular in shape. Commonly, L-type FIs homogenize into liquid during heating.
Vapor-rich (V-type) FIs were identified in stages I, II, and III but absent in stage IV. These FIs consist of two phases with VH2O/(VH2O + LH2O) > 50 vol.% at ~25 °C and have 60–90 vol.% vapor bubbles (Figure 5C,F,G). These FIs are normally round or oval in shape and range in size from 5 to 20 μm. Commonly, V-type FIs homogenize into vapor during heating.
Daughter-mineral-bearing three-phase (S-type) FIs were detected in stages I and II. S-type FIs consist of an aqueous liquid, a vapor bubble, and one or more solid daughter minerals at ~25 °C (Figure 5B,D,E). These FIs are normally oval or irregular in shape and range from 5 to 20 μm in size. Additionally, these FIs may contain one, two, or three daughter minerals, which can be halite or ore minerals (Figure 5B,D,E). The halites are mainly transparent, pale white, and cubic in shape (Figure 5B,D). The ore minerals are opaque (Figure 5B,D,E). Most halites dissolved after the vapor-bubble disappeared during heating.
CO2-bearing (C-type) FIs only occur in stage I. These FIs are normally round, oval, or irregular in shape and range from 8 to 15 μm in size. Most C-type FIs consist of three phases (LH2O + LCO2 + VCO2), and occasionally two phases (LH2O + LCO2) at ~25 °C. The latter changes into three phases with the appearance of CO2 bubbles at ~10 °C. Most C-type FIs have 50–70 vol.% CO2 volumetric proportions [(VCO2 + L CO2)/(VCO2 + L CO2 + L H2O)] at ~25 °C (Figure 5A), and can be homogenized into a liquid CO2 phase.

5.1.2. Micro-Thermometric Results

FI micro-thermometric data in this study are listed in Table 1 and shown in Figure 6. The salinities of L- and V-type FIs were estimated according to the HOKIEFLINCS_H2O–NaCl program [29]. The salinities of S-type FIs were calculated using the equations from [30]. We calculated the salinities of C-type FIs based on the melting temperatures of CO2 clathrate in the H2O–CO2–NaCl system [31].
Stage I (quartz): L-, V-, S-, and C-type FIs were observed in stage I quartz (Figure 5A–C). The L-type FIs homogenized into the aqueous liquid phase at 406–479 °C (peaking at 440–460 °C, n = 32) (Figure 6A) during heating. These FIs yielded final ice-melting temperatures (Tm-ice) of −8.1 to −4.5 °C, with calculated salinities of 7.2–11.8 wt.% NaCl equivalent (peaking at 8–10 wt.% NaCl equivalent, n = 32) (Figure 6B). The V-type FIs homogenized into the vapor phase at 427–471 °C (n = 12; Figure 6A). These V-type FIs yielded final ice-melting temperatures (Tm-ice) of −7.9 to −5.8 °C, corresponding to salinities of 8.9–11.6 wt.% NaCl equivalent (n = 12; Figure 6B). During heating, all S-type FIs commonly homogenized into the aqueous liquid phase, with halite daughter minerals dissolving at temperatures (Th-s) varying from 424 to 485 °C (n = 20; Figure 6A), with calculated salinities of 50.1–57.8 wt.% NaCl equivalent (peaking at 52–56 wt.% NaCl equivalent, n = 20) (Figure 6B). C-type FIs were completely homogenized into liquid H2O at temperatures (Th-total) of 429–470 °C (n = 8) (Figure 6A). These FIs yielded initial melting temperatures (Tm-CO2) of solid CO2 from −57.4 to −56.8 °C and clathrate melting temperatures (Tm–cla) from 3.5 to 5.5 °C, corresponding to salinities of 8.3–11.3 wt.% NaCl equivalent (n = 8) (Figure 6B). The CO2 phase homogenized into the liquid CO2 phase at temperatures (Th-CO2) of 28.2–30.5 °C.
Stage II (quartz): L-, V-, and S-type FIs were observed in stage II quartz (Figure 5D–F). The L-type FIs homogenized into the aqueous liquid phase at 307–398 °C (peaking at 340–380 °C, n = 34) (Figure 6C) during heating. These FIs yielded final ice-melting temperatures (Tm-ice) of −6.6 to −3.1 °C, with calculated salinities of 5.1–10.0 wt.% NaCl equivalent (peaking at 8–10 wt.% NaCl equivalent, n = 34) (Figure 6D). V-type FIs homogenized into the vapor phase at 326–396 °C (n = 14; Figure 6C). These V-type FIs yielded final ice-melting temperatures (Tm-ice) of −6.4 to −3.8 °C, corresponding to salinities of 6.2–9.7 wt.% NaCl equivalent (n = 14) (Figure 6D). During heating, all S-type FIs commonly homogenized into the aqueous liquid phase, with the halite daughter minerals dissolving at temperatures (Th-s) varying from 356 to 414 °C (peaking at 360–400 °C, n = 17) (Figure 6C), with calculated salinities of 43.0–48.9 wt.% NaCl equivalent (n = 17; Figure 6D).
Stage III (quartz): L- and V-type FIs are widespread in stage III quartz (Figure 5G,H). The L-type FIs homogenized into the aqueous liquid phase at 223–336 °C (peaking at 280–320 °C, n = 47) (Figure 6E) and yielded final ice-melting temperatures (Tm-ice) of –4.5 to –0.9 °C, with calculated salinities of 1.6–7.2 wt.% NaCl equivalent (peaking at 4–6 wt.% NaCl equivalent, n = 47) (Figure 6F). The V-type FIs homogenized into the vapor phase at 265–332 °C (n = 16; Figure 6E). These V-type FIs yielded final ice-melting temperatures (Tm-ice) of −3.6 to −1.8 °C, corresponding to salinities of 3.1–5.9 wt.% NaCl equivalent (n = 16) (Figure 6F).
Stage IV (quartz): Only the L-type FIs were recognized in stage IV quartz (Figure 5I). The L-type FIs homogenized into the aqueous liquid phase at 143–249 °C (peaking at 180–220 °C, n = 40) (Figure 6G) and yielded final ice-melting temperatures (Tm-ice) of −2.6 to −0.7 °C, with calculated salinities of 1.2–4.3 wt.% NaCl equivalent (peaking at 2–4 wt.% NaCl equivalent, n = 40) (Figure 6H).

5.1.3. Laser Raman Spectroscopy

The gas phase composition of some representative FIs in the four mineralization stages were selected for laser Raman spectroscopy analysis. Representative laser Raman spectra are shown in Figure 7. C-type FIs in stage I were universally found to be rich in CO2 (Figure 7A). Vapor phases of the V-type FIs in stages I, II, and III only contained H2O (Figure 7B). L-type FIs in the four mineralization stages only contained H2O (Figure 7C,D). These analytical results suggest that the ore-forming fluids of stage I represent an H2O–CO2–NaCl system that transforms into an H2O–NaCl system from stages II to IV.

5.2. H–O Isotopes

The H–O isotope results are listed in Table 2 and illustrated in Figure 8. Here, the δ18OV-SMOW values of the six quartz samples from the four mineralization stages range from 7.5 to 9.6‰. The δ18OH2O values were calculated by the quartz–water equilibrium function [32], with the peak homogenization temperatures of FIs in the same mineralization stage. The calculated δ18OH2O values for stages I, II, III, and IV are 6.5‰, 3.0‰ to 3.5‰, 0.2‰ to 1.9‰, and −2.5‰, respectively (Figure 8). The δD values for stages I, II, III, and IV are −108.1‰, −126.2‰ to −122.5‰, −132.9‰ to −130.9‰, and −139.1‰, respectively (Figure 8).

5.3. C–O Isotopes

The C–O isotope results for the calcites in stage IV are listed in Table 3 and illustrated in Figure 9. Here, the δ13CPDB values of the four calcite samples in stage IV range from −3.1‰ to −0.2‰. The δ18OSMOW values range from 6.6‰ to 8.1‰.
Table 3. C and O isotope data of calcite samples from the Huoluotai Cu (Mo) deposit.
Table 3. C and O isotope data of calcite samples from the Huoluotai Cu (Mo) deposit.
Sample No.MineralMineralized StagesSample Descriptionδ13CPDB (‰)δ18OPDB (‰)δ18OSMOW (‰)
HLT-ZK18-2-CO1CalciteIVQz+Cal+Py vein−0.2−22.18.1
HLT-ZK18-1-CO1CalciteIVQz+Cal+Py vein−2.3−22.87.4
HLT-ZK18-3-CO1CalciteIVQz+Cal+Py vein−3.1−23.56.6
HLT-ZK18-3-CO2CalciteIVQz+Cal+Py vein−0.2−23.36.9
δ18OSMOW = 1.03086 × δ18OV-PDB + 30.86 [34].
Figure 9. Plot of δ13CPDB vs. δ18OSMOW for the calcite from the Huoluotai Cu (Mo) deposit. The three main carbon sources include marine carbonate [35], sedimentary organic matter carbon [36], and magma-mantle carbonate [37].
Figure 9. Plot of δ13CPDB vs. δ18OSMOW for the calcite from the Huoluotai Cu (Mo) deposit. The three main carbon sources include marine carbonate [35], sedimentary organic matter carbon [36], and magma-mantle carbonate [37].
Minerals 12 01072 g009

5.4. S–Pb Isotopes

The S isotope results of the seven sulfide samples from the Huoluotai Cu (Mo) deposit are presented in Table 4 and plotted in Figure 10. The δ34SV–CDT values of the seven sulfides range from 0.2‰ to 3.7‰ (average = 1.9‰) (Table 4; Figure 10).
The Pb isotope compositions of the four sulfide samples from the Huoluotai Cu (Mo) deposit are listed in Table 5 and illustrated in Figure 11. Here, the Pb isotope compositions of sulfides have a limited variation in 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb, varying from 18.352 to 18.435, 15.552 to 15.578, and 38.212 to 38.309, respectively.

6. Discussion

6.1. Source of the Ore-forming Materials

The δ34SV–CDT values (0.2‰ to 3.7‰) of the seven sulfides from the Huoluotai Cu (Mo) deposit overlap those of typical porphyry deposits in the NGXR, such as the Badaguan (–2.4‰ to 3.5‰; [45]), the Chalukou (–1.9‰ to 3.6‰; [43]), the Xiaokele (–1.2‰ to 2.4‰; [5]), and the Fukeshan (–2.3‰ to 3.4‰; [4]) deposits (Figure 10). These values are also consistent with the δ34SV–CDT values of typical porphyry deposits elsewhere in the world (−5‰ to 5‰; [39]). The δ34SV–CDT values of sulfide minerals for all these deposits fall into the magmatic sulfur range and are similar to those of mantle-derived sulfur (Figure 10; [39]). The Pb isotope compositions of sulfide minerals from the Huoluotai Cu (Mo) deposit are similar and homogeneous, indicating that they share a common Pb reservoir. In the 207Pb/204Pb vs. 206Pb/204Pb diagram (Figure 11A), Pb isotope data for the sulfide samples are plotted between the mantle and orogene evolution curves, near the mid-ocean ridge basalt (MORB) region. In the 208Pb/204Pb vs. 206Pb/204Pb diagram (Figure 11B), Pb isotope data are all plotted between the orogene and upper crust evolution curves (near the mantle evolution curve), showing the characteristics of a crust-mantle-mixing origin.

6.2. Estimation of Trapping Pressure

Trapping pressure can be estimated only when the actual trapping temperature is known or if fluid boiling occurred in the hydrothermal system at the time of entrapment [48,49]. During heating, L-type FIs homogenized into the aqueous liquid phase, while the V-type FIs homogenized into the vapor phase. In the Huoluotai Cu (Mo) deposit, the coexistence of L-, V-, and S-type FI assemblages (Figure 5A–F) within the same quartz crystal in stages I and II suggests that fluid boiling occurred in those stages. The trapping pressures in stage I were estimated to range from ~300 to ~500 bar (Figure 12A), assuming a simple NaCl–H2O system using the isobar equations given in [50]. However, the addition of CO2 to an NaCl–H2O system could raise the solvus and increase the entrapment pressure (Figure 12B; [51,52,53,54]). Therefore, in this study, the estimated trapping pressures in stage I represent only the minimum values. The trapping pressures in stage II were estimated to be between ~100 and ~300 bar and were mostly concentrated around ~200 bar (Figure 12A) based on the isobar equations given in [50]. There are clear decreasing trends of pressure from stages I to II (Figure 12A). Fluid boiling did not occur in stages III and IV, so the estimated trapping pressures represent only the minimum values [54]. The minimum trapping pressures in stages III and IV were estimated to range from ~30 to ~150 bar and <50 bar, respectively (Figure 12A).

6.3. Origin of the Ore-forming Fluids

The δ18OH2O values for stage I (6.5‰) were close to those of magmatic water [55], indicating that the ore-forming fluids from stage I were derived from a magmatic source. The δD values for stage I were significantly lower than those for typical magmatic water (Figure 8; [56]). Previous studies have shown that the relatively depleted isotopic values of fluids could have been caused by water–rock interactions or magma degassing [57,58]. The depleted δ18OH2O and δD isotopic characteristics were extensively recorded by fluids from an early stage in porphyry deposits of the NGXR [59], such as the Xiaokele Cu (Mo) (–1.2‰ to 2.4‰; [5]), the Fukeshan Cu (Mo) (–2.3‰ to 3.4‰; [4]), and the Chalukou Mo (–1.9‰ to 3.6‰; [43]) deposits, which were interpreted to be predominantly of magmatic origin. The δD and δ18OH2O values for stages II, III, and IV were relatively lower than those for stage I and plotted in the region between the meteoric water line and the magmatic water field (close to the magmatic water field) (Figure 8), suggesting the involvement of some meteoric water but still dominated by magmatic water. In the δ13CPDB vs. δ18OSMOW diagram (Figure 9), the C–O isotope compositions of calcite in stage IV fell into the field of granite and magmatic carbonate, indicating that a certain amount of magmatic water was still involved in the mineralization process during the late mineralization stage.

6.4. Fluid Evolution and Mineralization Process

The occurrence of L-, V-, S-, and C-type FIs in stage I quartz indicates that the initial fluids belong to an H2O–CO2–NaCl system. These fluids are characterized by high homogenization temperatures and high salinities (Figure 6A,B). High amounts of hematite, magnetite (Figure 3E,F), and hematite-bearing S-type FIs (Figure 5B), but few sulfides, were found in stage I, suggesting that the initial fluids were highly oxidized [60,61]. This result is supported by the detection of oxidized gases (e.g., CO2) in FIs via laser Raman spectroscopy analysis (Figure 7A). Sulfur in the magma was mostly present in the form of sulfate due to high oxygen fugacity and CO2 activity [41,62], but sulfide mineralization would be inevitably constrained. These kinds of initial hydrothermal fluids were observed to be particularly prone to extensive potassic alterations and quartz + K-feldspar ± magnetite ± hematite ± pyrite veins in stage I.
Cu (Mo) mineralization occurred mainly in stage II. L-, V-, and S-type FIs were found in stage II quartz crystals (Figure 5D–F), which suggests that the ore-forming fluids of stage II belong to an H2O–NaCl system. Hematite, magnetite, and C-type FIs were not found in stage II, suggesting that the CO2 content and oxygen fugacity of the fluids were distinctly decreased compared to those in stage I. Such degassing of oxidized gas is considered to be a major process responsible for sulfate reduction [61]. This reduction in oxygen fugacity could be due to the escape of CO2 caused by fluid boiling [63,64,65] and/or magnetite precipitation [66,67,68]. These results suggest that the fluid system only contained minor CO2 in stage I, indicating that it is likely not a CO2-rich system. Therefore, the immiscibility of CO2 and water is not an important process in the Huoluotai Cu (Mo) deposit. The precipitation of magnetite was found to reduce S6+ to S2− (i.e., 12[FeO] + H2SO4 = 4Fe3O4 (Magnetite) + H2S; [62,68]), so the acid in stage II ore-forming fluids became stronger with an increase in S2− and H+ activity [69]. More significantly, the homogenization temperatures of stage II fluids were obviously lower than those of the stage I fluids (Figure 6). H–O isotope data in this study indicate that mixing of hydrothermal fluids and meteoric water occurred in stage II. The addition of cooler and lower-salinity meteoric water inevitably led to a decrease in temperature and salinity of the primary hotter and high-salinity magmatic water, causing the precipitation of sulfides. Furthermore, the micro-thermometric data obtained in this study showed that Cu was mainly deposited below 400 °C in stage II, which is consistent with the temperature at which hydrothermal fluids reached Cu saturation in some micro-thermometric and thermodynamic studies of FIs [70,71,72,73]. Beyond stage I, fluid boiling also occurred in stage II. Generally, fluid boiling can cause widespread hydraulic fracturing and accelerate the influx and circulation of meteoric water, which could lead to rapid deposition of sulfides. In addition, fluid boiling can lead to the exsolution of volatile components from ore-forming fluids [51], which would also promote the enrichment of metals in the ore-forming fluids [74,75]. Thus, we believe that fluid boiling occurring below 400 °C may be the primary factor for Cu precipitation in the Huoluotai Cu (Mo) deposit.
No evidence of fluid boiling was found in stages III and IV. The ore-forming fluids in stages III and IV belong to a homogeneous H2O–NaCl system and became more diluted and cool, as indicated by the H−O isotope data. Magmatic water mixed with meteoric water may have initiated metal sulfide precipitation in stage III [71]. The increasing meteoric water influx may have formed the quartz + calcite ± pyrite ± fluorite veins in stage IV, reflecting waning of the hydrothermal system.

7. Conclusions

(1) The Huoluotai Cu (Mo) deposit is a typical porphyry Cu deposit in the NGXR. The ore-forming process of this deposit consists of the sulfide-barren quartz stage (I), the quartz + chalcopyrite ± pyrite ± molybdenite stage (II), the quartz + polymetallic sulfide stage (III), and the quartz + calcite ± pyrite ± fluorite stage (IV). Cu mineralization occurred mainly in stage II.
(2) The results of FI micro-thermometry and H–O isotope analysis showed that the ore-forming fluids originated from a magmatic origin in stage I and then mixed with meteoric water from stages II to IV. The S–Pb isotope results suggest that the source of the ore-forming materials has the characteristics of a crust–mantle-mixing origin.
(3) Fluid boiling occurring below 400 °C may be the primary factor for Cu precipitation in the Huoluotai Cu (Mo) deposit.

Author Contributions

Conceptualization, Y.S., B.L., X.C. and Q.D.; software, F.M., Y.Q. and L.W.; investigation, Y.S., B.L., X.C. and F.M.; data curation, Y.Q. and L.W.; funding acquisition, B.L.; project administration, B.L.; writing—original draft preparation, Y.S.; and writing—review and editing, Y.S. and B.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (41272093), the National Key R&D Program of China (2017YFC0601304), Natural Science Foundation of Jilin Province (No.20180101089JC), Key Projects of Science and Technology Development Plan of Jilin Province (No.20100445), the Shandong Provincial Natural Science Foundation of China (No. ZR2019PD017), Self-determined Foundation of Key Laboratory of Mineral Resources Evaluation in Northeast Asia, Ministry of Natural Resources (DBY-ZZ-19-04), Basic scientific research project of colleges and universities of Liaoning Provincial Department of education in 2021 (LJKZ0369), and the Heilongjiang Research Project of Land and Resources (201605 and 201704).

Data Availability Statement

Not applicable.

Acknowledgments

We would like to thank staffs of the Qiqihaer Institute of Geological Exploration, Heilongjiang, China for sample collection.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. (A) Location of the CAOB [6]. (B) Geological map of NE China [7]. (C) Geological map of the NGXR (modified from [3]).
Figure 1. (A) Location of the CAOB [6]. (B) Geological map of NE China [7]. (C) Geological map of the NGXR (modified from [3]).
Minerals 12 01072 g001
Figure 2. (A) Geological map of the Huoluotai Cu (Mo) deposit (modified from [8]). (B) Geological sections in the Huoluotai Cu (Mo) deposit (modified from [8]).
Figure 2. (A) Geological map of the Huoluotai Cu (Mo) deposit (modified from [8]). (B) Geological sections in the Huoluotai Cu (Mo) deposit (modified from [8]).
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Figure 3. Photographs and photomicrographs of representative hydrothermal alterations and ore mineralization features in the Huoluotai Cu (Mo) deposit. (A) Potassic alteration observed in the granodiorite porphyry. (B) Potassic alteration overprinted by epidote alteration. (C) Phyllic alteration in the granodiorite porphyry. (D) Phyllic alteration characterized by an alteration assemblage of sericite and quartz. (E) Stage I quartz + hematite vein in potassic-altered granodiorite porphyry. (F) Anhedral hematite and magnetite in stage I. (G) Stage II quartz + chalcopyrite vein in potassic-altered granodiorite porphyry. (H) Dense disseminated chalcopyrite developed in the granodiorite porphyry. (I) Stage III quartz + molybdenite + pyrite vein in phyllic-altered wall rock. (J) Stage IV quartz + calcite vein in potassic-altered granodiorite porphyry. (K) Primary molybdenite oxidized to molybdite. (L) Primary chalcopyrite oxidized to azurite and malachite. Abbreviations: Qz = quartz; Kfs = K-feldspar; Ep = epidote; Ser = sericite; Cal = calcite; Mag = magnetite; Hem = hematite; Py = pyrite; Ccp = chalcopyrite; Mol = molybdenite; Myb = molybdite; Mlc = malachite; Azu = azurite.
Figure 3. Photographs and photomicrographs of representative hydrothermal alterations and ore mineralization features in the Huoluotai Cu (Mo) deposit. (A) Potassic alteration observed in the granodiorite porphyry. (B) Potassic alteration overprinted by epidote alteration. (C) Phyllic alteration in the granodiorite porphyry. (D) Phyllic alteration characterized by an alteration assemblage of sericite and quartz. (E) Stage I quartz + hematite vein in potassic-altered granodiorite porphyry. (F) Anhedral hematite and magnetite in stage I. (G) Stage II quartz + chalcopyrite vein in potassic-altered granodiorite porphyry. (H) Dense disseminated chalcopyrite developed in the granodiorite porphyry. (I) Stage III quartz + molybdenite + pyrite vein in phyllic-altered wall rock. (J) Stage IV quartz + calcite vein in potassic-altered granodiorite porphyry. (K) Primary molybdenite oxidized to molybdite. (L) Primary chalcopyrite oxidized to azurite and malachite. Abbreviations: Qz = quartz; Kfs = K-feldspar; Ep = epidote; Ser = sericite; Cal = calcite; Mag = magnetite; Hem = hematite; Py = pyrite; Ccp = chalcopyrite; Mol = molybdenite; Myb = molybdite; Mlc = malachite; Azu = azurite.
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Figure 4. Paragenetic sequence of the major minerals in the Huoluotai Cu (Mo) deposit.
Figure 4. Paragenetic sequence of the major minerals in the Huoluotai Cu (Mo) deposit.
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Figure 5. Photomicrographs of the representative primary FIs in four mineralization stages from the Huoluotai Cu (Mo) deposit. (A) The coexistence of primary L- and C-type FIs in stage I quartz. (B) S-type FIs with hematite and/or halite daughter minerals in stage I quartz. (C) The coexistence of primary L- and V-type FIs in stage I quartz. (D,E) The coexisting S- and L-type FIs in stage II quartz. (F) Primary V-type FIs in stage II quartz. (G) The coexisting L- and V-type FIs in stage III quartz. (H) Primary L-type FIs in stage III quartz. (I) Primary L-type FIs in stage IV quartz. Abbreviations: LH2O = H2O liquid; VH2O = H2O vapor; LCO2 = CO2 liquid; VCO2 = CO2 vapor; Hal = halite; Hem = hematite; Opa = unidentified opaque mineral.
Figure 5. Photomicrographs of the representative primary FIs in four mineralization stages from the Huoluotai Cu (Mo) deposit. (A) The coexistence of primary L- and C-type FIs in stage I quartz. (B) S-type FIs with hematite and/or halite daughter minerals in stage I quartz. (C) The coexistence of primary L- and V-type FIs in stage I quartz. (D,E) The coexisting S- and L-type FIs in stage II quartz. (F) Primary V-type FIs in stage II quartz. (G) The coexisting L- and V-type FIs in stage III quartz. (H) Primary L-type FIs in stage III quartz. (I) Primary L-type FIs in stage IV quartz. Abbreviations: LH2O = H2O liquid; VH2O = H2O vapor; LCO2 = CO2 liquid; VCO2 = CO2 vapor; Hal = halite; Hem = hematite; Opa = unidentified opaque mineral.
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Figure 6. Frequency histograms of the total homogenization temperatures (Th) and salinities of FIs (wt.% NaCl equivalent) in four mineralization stages from the Huoluotai Cu (Mo) deposit. (A) Homogenization temperatures histogram for L-, V-, S-, and C-type FIs from stage I quartz; (B) Salinities histogram for L-, V-, S-, and C-type FIs from stage I quartz; (C) Homogenization temperatures histogram for L-, V-, and S-type FIs from stage II quartz; (D) Salinities histogram for L-, V-, and S-type FIs from stage II quartz; (E) Homogenization temperatures histogram for L- and V-type FIs from stage III quartz; (F) Salinities histogram for L- and V-type FIs from stage III quartz; (G) Homogenization temperatures histogram for L-type FIs from stage IV quartz; (H) Salinities histogram for L-type FIs from stage IV quartz.
Figure 6. Frequency histograms of the total homogenization temperatures (Th) and salinities of FIs (wt.% NaCl equivalent) in four mineralization stages from the Huoluotai Cu (Mo) deposit. (A) Homogenization temperatures histogram for L-, V-, S-, and C-type FIs from stage I quartz; (B) Salinities histogram for L-, V-, S-, and C-type FIs from stage I quartz; (C) Homogenization temperatures histogram for L-, V-, and S-type FIs from stage II quartz; (D) Salinities histogram for L-, V-, and S-type FIs from stage II quartz; (E) Homogenization temperatures histogram for L- and V-type FIs from stage III quartz; (F) Salinities histogram for L- and V-type FIs from stage III quartz; (G) Homogenization temperatures histogram for L-type FIs from stage IV quartz; (H) Salinities histogram for L-type FIs from stage IV quartz.
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Figure 7. Representative laser Raman spectra for different types of FIs from the Huoluotai Cu (Mo) deposit. (A) The vapor phases of C-type FIs in stage I are rich in CO2; (B) The vapor phases of V-type FIs are almost entirely H2O; (C) The vapor phases of L-type FIs are almost entirely H2O; (D) The liquid phases of L-type FIs are almost entirely H2O.
Figure 7. Representative laser Raman spectra for different types of FIs from the Huoluotai Cu (Mo) deposit. (A) The vapor phases of C-type FIs in stage I are rich in CO2; (B) The vapor phases of V-type FIs are almost entirely H2O; (C) The vapor phases of L-type FIs are almost entirely H2O; (D) The liquid phases of L-type FIs are almost entirely H2O.
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Figure 8. Plot of δD vs. δ18OH2O for the ore-forming fluids in the Huoluotai Cu (Mo) deposit [33]. SMOW = Standard Mean Ocean Water.
Figure 8. Plot of δD vs. δ18OH2O for the ore-forming fluids in the Huoluotai Cu (Mo) deposit [33]. SMOW = Standard Mean Ocean Water.
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Figure 10. S isotope compositions of sulfides from the Huoluotai Cu (Mo) deposit, important S reservoirs [38,39,40], and other typical porphyry deposits elsewhere in the world [4,5,41,42,43,44,45,46].
Figure 10. S isotope compositions of sulfides from the Huoluotai Cu (Mo) deposit, important S reservoirs [38,39,40], and other typical porphyry deposits elsewhere in the world [4,5,41,42,43,44,45,46].
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Figure 11. Pb isotope compositions of sulfides from the Huoluotai Cu (Mo) deposit [47]. (A) 207Pb/204Pb vs. 206Pb/204Pb. (B) 208Pb/204Pb vs. 206Pb/204Pb.
Figure 11. Pb isotope compositions of sulfides from the Huoluotai Cu (Mo) deposit [47]. (A) 207Pb/204Pb vs. 206Pb/204Pb. (B) 208Pb/204Pb vs. 206Pb/204Pb.
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Figure 12. (A) Pressure estimation for FIs from the Huoluotai Cu (Mo) deposit. (B) Isochores for fluid of 4 wt.% NaCl, 5 mol% CO2 (straight lines), and 10 mol% CO2 (dashed lines). Data for the C-type FIs plot in the oval field.
Figure 12. (A) Pressure estimation for FIs from the Huoluotai Cu (Mo) deposit. (B) Isochores for fluid of 4 wt.% NaCl, 5 mol% CO2 (straight lines), and 10 mol% CO2 (dashed lines). Data for the C-type FIs plot in the oval field.
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Table 1. Micro-thermometric data and calculated parameters for FIs from the Huoluotai Cu (Mo) deposit.
Table 1. Micro-thermometric data and calculated parameters for FIs from the Huoluotai Cu (Mo) deposit.
Mineralized
Stages
Host MineralsFI TypesNTm-CO2
(°C)
Tm-cla
(°C)
Th-CO2
(°C)
Th-total
(°C)
Tm-ice
(°C)
Th-s
(°C)
Th-v
(°C)
Salinity
(wt.% NaCl Equivalent)
IQuartzL-type32////−8.1 to −4.5/406–4797.2–11.8
V-type12////−7.9 to −5.8/427–4718.9–11.6
S-type20/////424–485/50.1–57.8
C-type8−57.4 to −56.83.5–5.528.2–30.5429–470///8.3–11.3
IIQuartzL-type34////−6.6 to −3.1/307–3985.1–10.0
V-type14////−6.4 to −3.8/326–3966.2–9.7
S-type17/////356–414/43.0–48.9
IIIQuartzL-type47////−4.5 to −0.9 223–3361.6–7.2
V-type16////−3.6 to −1.8/265–3323.1–5.9
IVQuartzL-type40////−2.6 to −0.7 143–2491.2–4.3
Abbreviations: Th-v = homogenization temperature of vapor-rich or liquid-rich fluid inclusions; Th-s = dissolution temperature of halite; Tm-ice = temperature of final ice melting; Th-total = total homogenization temperature of CO2 fluid inclusions; Th-CO2 = homogenization temperature of the CO2 phases; Tm-cla = final melting temperature of CO2–H2O clathrate; Tm-CO2 = final melting temperature of solid CO2.
Table 2. H and O isotope data of quartz samples from the Huoluotai Cu (Mo) deposit.
Table 2. H and O isotope data of quartz samples from the Huoluotai Cu (Mo) deposit.
Sample No.Mineralized StagesMineralδ18OV-SMOW (‰)T (°C)δ18OH2O (‰)δD (‰)
HLT-ZK18-2-HO1IQuartz9.64506.5−108.1
HLT-ZK18-1-HO1IIQuartz8.33703.5−126.2
HLT-ZK18-1-HO2IIQuartz7.83703.0−122.5
HLT-ZK18-1-HO3IIIQuartz7.52900.2−132.9
HLT-ZK18-2-HO2IIIQuartz9.22901.9−130.9
HLT-ZK18-3-HO1IVQuartz9.2200−2.5−139.1
δ18OH2O of water in equilibrium with quartz were calculated according to the equation of 1000lnαquartz–water = 3.38 × 106/T2 − 3.4 [32], which were defined by the peak homogenization temperatures (T) of FIs for corresponding quartz samples.
Table 4. S isotope data of sulfide samples from the Huoluotai Cu (Mo) deposit.
Table 4. S isotope data of sulfide samples from the Huoluotai Cu (Mo) deposit.
Sample No.MineralMineralized StagesSample Descriptionδ34SV–CDT (‰)
HLT-ZK18-1-S1PyriteIQz+Hem+Py vein2.8
HLT-ZK18-1-S2PyriteIQz+Kfs+Py vein2.3
HLT-ZK18-2-S1ChalcopyriteIIQz+Kfs+Ccp vein1.8
HLT-ZK18-1-S3PyriteIIQz+Kfs+Ccp+Py vein1.4
HLT-ZK18-1-S4ChalcopyriteIIIQz+Ser+Ccp+Py vein0.2
HLT-ZK18-2-S2MolybdeniteIIIQz+Ser+Mol vein3.7
HLT-ZK18-3-S1PyriteIVQz+Cal+Py vein1.4
Abbreviations: Qz = quartz; Kfs = K-feldspar; Ser = sericite; Cal = calcite; Hem = hematite; Ccp = chalcopyrite; Mol = molybdenite; Py = pyrite.
Table 5. Pb isotope data of sulfide samples from the Huoluotai Cu (Mo) deposit.
Table 5. Pb isotope data of sulfide samples from the Huoluotai Cu (Mo) deposit.
Sample No.MineralMineralized StagesSample Description206Pb/204PbError207Pb/204PbError208Pb/204PbError
HLT-ZK18-1-Pb1PyriteIQz+Kfs+Py vein18.4090.00315.5640.00238.2550.005
HLT-ZK18-1-Pb2ChalcopyriteIIQz+Ccp vein18.3520.00215.5520.00238.2120.005
HLT-ZK18-2-Pb1PyriteIIIQz+Mol+Py vein18.4350.00215.5710.00238.2840.005
HLT-ZK18-1-Pb3PyriteIIIQz+Mol+Py vein18.4280.00115.5780.00138.3090.003
Abbreviations: Qz = quartz; Kfs = K-feldspar; Ccp = chalcopyrite; Mol = molybdenite; Py = pyrite.
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Sun, Y.; Li, B.; Chen, X.; Meng, F.; Ding, Q.; Qian, Y.; Wang, L. Fluid Inclusions and C–H–O–S–Pb Isotopes of the Huoluotai Porphyry Cu (Mo) Deposit in the Northern Great Xing’an Range, NE China: Implications for Ore Genesis. Minerals 2022, 12, 1072. https://doi.org/10.3390/min12091072

AMA Style

Sun Y, Li B, Chen X, Meng F, Ding Q, Qian Y, Wang L. Fluid Inclusions and C–H–O–S–Pb Isotopes of the Huoluotai Porphyry Cu (Mo) Deposit in the Northern Great Xing’an Range, NE China: Implications for Ore Genesis. Minerals. 2022; 12(9):1072. https://doi.org/10.3390/min12091072

Chicago/Turabian Style

Sun, Yonggang, Bile Li, Xusheng Chen, Fanbo Meng, Qingfeng Ding, Ye Qian, and Linlin Wang. 2022. "Fluid Inclusions and C–H–O–S–Pb Isotopes of the Huoluotai Porphyry Cu (Mo) Deposit in the Northern Great Xing’an Range, NE China: Implications for Ore Genesis" Minerals 12, no. 9: 1072. https://doi.org/10.3390/min12091072

APA Style

Sun, Y., Li, B., Chen, X., Meng, F., Ding, Q., Qian, Y., & Wang, L. (2022). Fluid Inclusions and C–H–O–S–Pb Isotopes of the Huoluotai Porphyry Cu (Mo) Deposit in the Northern Great Xing’an Range, NE China: Implications for Ore Genesis. Minerals, 12(9), 1072. https://doi.org/10.3390/min12091072

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