Zijinshan Orefield Research Articles

Alteration mineralogy, characteristics and shortwave infrared spectroscopy of white mica in the Zijinshan ore field, Fujian Province: Implications for porphyry Cu prospecting

The Zijinshan ore field is situated in the southeastern part of China. in which contains the large Zijinshan high-sulfidation Cu-Au deposit, the Luoboling porphyry Cu-Mo deposit, the Yueyang low-sulfidation Au-Ag deposit, the Longjiangting and the Wuziqilong tansitional Cu deposit, and the Xi’nan porphyry Cu-Mo prospect. Debates on genetic relationship among these deposits, especially the relationship between the Zijinshan Cu-Au deposit and the adjacent Luoboling deposit is a question of importance for further exploration in this ore field. In this contribution, the alteration mineralogy, alteration texture, zonation and mineral chemistry, in combination with shortwave infrared spectroscopy (SWIR) analysis of white mica were used to help focus exploration and assessment of hydrothermal deposits in the Zijinshan ore field.In this study, diaspore-pyrophyllite alteration zone, chlorite-sericite alteration zone and propylitic alteration zone were first identified in the deep drill core of the Zijinshan Cu-Au deposit, which gives way upward to quartz-alunite-kaolinite zone, quartz-alunite zone and the silicic alteration zone. In the Xi’nan Cu-Mo prospect, diaspore-pyrophyllite alteration zone was first recognized in the shallow level with the chlorite-sericite alteration zone and propylitic alteration zone in the deeper level. Andalusite- sericite ± diaspore alteration zone was first recognized in the upper part of the Luoboling Cu-Mo deposit and the deeper part of the Wuziqilong Cu deposit. It indicates that a pervasive occurrence of diaspore -pyrophyllite ± andalusite alteration zones in the Zijinshan ore field, which may potentially represent a transitional environment between the top of porphyry alteration zones and the base of advanced argillic alteration zones. Minerals of the white mica group are extensively distributed in various alteration zones of the Zijinshan ore field. The SWIR analysis of white mica indicated that the wavelength position of the Al-OH (∼2,200 nm; wAlOH) absorption feature increases gradually from the shallow kaolinite-dickite alteration zone to the deep potassic alteration zone. In the advanced argillic alteration zones, the range of wAlOH values of white mica is less than 2205 nm. Conversely, in the porphyry alteration zones, it always exceeds 2205 nm. It is evident that the andalusite-sericite alteration zone with higher wAlOH values (average of 2203 nm) is always proximal to the porphyry mineralization, which may act as indicators for deep porphyry prospecting. The results of electron probe microanalysis (EPMA) reveal that the early enrichment of Mg and depletion of Fe in white mica can be attributed to the preferential incorporation of Fe into iron oxides and iron sulfides in the potassic and propylitic alteration zones. Overall, there is a negative correlation between wAlOH and Al, while wAlOH exhibits a positive correlation with the sum of Fe + Mg + Mn. The distribution characteristics of alteration zones and the variation patterns of the wAlOH of white mica indicate that there are probably several paleo-thermal centers in the deep parts of the Zijinshan ore field, located respectively in the deep parts of the Xi’nan Cu-Mo prospect and the deep part of the Zijinshan Cu-Au deposit and the deep parts of the Wuziqilong Cu deposit, and the latest seems to be more fertile and deserves further exploration.

Ore-forming fluid characteristics and ages of the Xinan Cu-Mo deposit at Zijinshan orefield, SE China: New insights for metallogenic mechanism and exploration

The Xinan deposit, a newly discovered porphyry Cu-Mo deposit in the Zijinshan orefield, Fujian Province, exhibits distinct alteration and porphyry mineralization stages, including the potassic, propylitic, and phyllic alteration stages. The phyllic stage is further divided into molybdenite, chalcopyrite, and pyrite sub-stages. Molybdenite Re-Os model age (108.3 ± 1.1 Ma) and concomitant sericite 40Ar/39Ar plateau age (109.0 ± 6.0 Ma) indicate that the Xinan Cu-Mo deposit was formed at 109 ∼ 108 Ma. Four types of fluid inclusions have been identified at the Xinan deposit, including vapor-rich, liquid-rich, and opaque daughter mineral-bearing subtypes with minor transparent daughter mineral-bearing subtypes. Fluid inclusion microthermometry measurements reveal that the potassic alteration stage exhibits homogenization temperatures of 375–475 °C and salinities range of 4–20 wt% NaCl eqv., suggesting slight fluid boiling. Chlorite geothermometer suggests temperatures of the propylitic alteration stage range from 261 to 336 °C, averaging at 303 °C. The molybdenite, chalcopyrite, and pyrite sub-stages have homogenization temperatures of 325–400 °C, 325–350 °C, and 300–350 °C, respectively, with corresponding salinities of 2–10 wt% NaCl eqv., 4–8 wt% NaCl eqv., and 2–4 wt% NaCl eqv.. The Laser Raman spectroscopy results show that the fluid inclusions in the Xinan deposit consist of H2O with minor CO2, hematite, chalcopyrite, and halite. The evolution of the ore-forming fluids in the Xinan porphyry Cu-Mo deposit is characterized by a transition from high-temperature, low- to moderate-salinity, oxidized, and CO2-bearing conditions during the potassic alteration stage, to moderate- to high-temperature and low-salinity conditions during the propylitic alteration stage. The subsequent phyllic alteration stage, which overprints on the potassic and partial propylitic alteration stages, is marked by moderate- to high-temperature, low-salinity, and low-oxygen fugacity environments. The primary mechanisms driving mineralization in the Xinan porphyry Cu-Mo deposit are thus identified as the reduction in temperature and oxygen fugacity, coupled with CO2 escape. In contrast to the Luoboling-Jintonghu porphyry Cu-Mo deposit, the ore-forming fluid of the Xinan deposit is characterized by lower temperatures, salinity, and CO2 contents, and reduced fluid boiling. This suggests a relatively subdued porphyry-type mineralization. The lack of a distinct potassic alteration zone in the Xinan Cu-Mo deposit suggests the potential existence of a deeper, higher temperature and salinity porphyry mineralization center beneath this deposit.

Volatile-rich and oxidized ore-forming magmas of the Zijinshan porphyry Cu deposit, China: A mineral composition perspective

The Zijinshan orefield (Fujian Province) is a representative Cu-Au-Mo-Ag porphyry-epithermal mineralization system in eastern China. It contains both Cu ore-bearing and ore-barren granitoids, which provide an opportunity to study the unique properties of fertile magmas. This study focuses on chemistry of minerals such as zircon, apatite, amphibole, and plagioclase in ore-related (zircon U–Pb ages of 103–101 Ma) and ore-barren (zircon U–Pb ages of 157–156 Ma and ∼105 Ma) granitoids to constrain the characteristics of mineralized magmas. The results of whole-rock geochemistry and zircon Hf isotopes suggest that both ore-barren and ore-related granitoids were derived from partial melting of the lower crust, with the ore-related magma being influenced by mantle materials. The analysis of mineral chemistry reveals that the Zijinshan Cu ore-bearing porphyry magmas have high oxidation states (ΔFMQ +0.23–+2.25), high water contents (4.4–4.9 wt%), and shallow emplacement depths (1.9–4.0 km). These magmatic conditions are favorable for fluid exsolution and mineralization, similar to the global Cu-fertile porphyry magmas, but distinct from regional pre-mineralization ore-barren igneous rocks. Apatites from the ore-related granitoids have significantly lower Cl contents (0.03–0.83 wt%) and higher F/Cl ratios (1.52–377) compared to coeval ore-barren monzogranites (Cl = 0.14–2.42 wt%; F/Cl = 0.07–2.82). Additionally, the apatites’ volatile budgets, including XOH, XCl and XF values, and their covariation relationship, in the ore-related intrusions are consistent with apatite crystallization in H2O-saturated conditions. This suggests that extensive fluid exsolution from the parent magma in the chamber plays a crucial role in the formation of porphyry Cu deposits from a low-Cl magma. These low-Cl-apatite intrusions have the potential to form porphyry deposits. Together, we propose that the high oxygen fugacity, high water contents, and fluid exsolution of the parent magma may have triggered the Zijinshan porphyry mineralization.

Silver occurrence state and deportment mechanism of Yueyang Ag polymetallic deposit in Zijinshan ore field, Fujian Province, China

Silver occurrence state and deportment mechanism of Yueyang Ag polymetallic deposit in Zijinshan ore field, Fujian Province, China

Genesis and metallogenic characteristic of Dongnan Cu–Mo deposit associated granitoids: LA-ICP-MS zircon U–Pb dating and isotope constraint from Zijinshan ore field in southeastern China

Genesis and metallogenic characteristic of Dongnan Cu–Mo deposit associated granitoids: LA-ICP-MS zircon U–Pb dating and isotope constraint from Zijinshan ore field in southeastern China

Crust–mantle interactions in Zijinshan ore field identified by zircon SIMS U–Pb age and zircon Hf–O isotopes

AbstractThis study presents zircon U–Pb geochronology and Hf and O isotope data for granitic rocks in the Zijinshan ore field, southwestern Fujian Province, China. The intrusive rocks comprise monzogranite, granite and granodiorite. The magmatic zircon U–Pb ages from these granitic rocks can be divided into four episodes: episodes 1 (157.9–159.9 Ma) and 2 (141 Ma) in the Late Jurassic and episodes 3 (108.1–103.2 Ma) and 4 (97.5–99.7 Ma) in the Middle and Late Cretaceous, respectively. Patterns of rare-earth elements (REE) show enrichment in light REE and obvious negative Eu anomalies. These rocks are also enriched in Rb, Th, U, La, Ce, Nd and Hf, and depleted in Ba, Nb, Sr, P and Ti. The increasing La/Yb ratio and decreasing heavy REE content with decreasing age may imply an increasing contribution of mantle-derived materials from the Late Jurassic to Cretaceous. The zircon ϵHf(t) and δ18O values, ranging from −37.7 to −2.8 and 12.0 ‰ to 6.3 ‰, respectively, indicate that the lower crust is an important source of granitic rocks. There was a significant increase in ϵHf(t) values and a decrease in δ18O values in the younger magmatic episodes (3 and 4), which ranged from −11.4 to −0.6 and 10.7 to 6.3 ‰, respectively. This suggests an increasing contribution of mantle-derived magma to the crustal melts from the Late Jurassic to late Early Cretaceous in response to the changing regional tectonic setting from compression to extension and an increasing interaction between the crust and mantle.

Genesis of the giant Zijinshan epithermal Cu-Au deposit, Fujian Province, southeastern China: Cu-He-Ar isotope perspective

The giant Zijinshan high-sulfidation epithermal Cu-Au deposit is located in the Zijinshan ore field of southeastern China. A sharp boundary separates the upper Au orebodies from lower Cu orebodies at roughly 650 m below the original pit surface, below which digenite is the predominant Cu-bearing mineral. The current discussion revolves over whether the shallow Au and deep Cu mineralization are cogenetic or reflect independent ore-forming episodes, as well as whether the digenite formation is hydrothermal or supergene. In this contribution, we investigate the He-Ar isotope compositions of ore-related sulfides to decipher the source and history of ore-bearing fluids, and use the systematic variation of Cu isotope in Cu-bearing minerals to reveal the hydrothermal (hypogene and supergene) process.A gradual decrease in fluid 3He/4He and 40Ar/36Ar ratios, as well as a sharp drop in 3He/36Ar ratio, reflects the progressive dilution of a magmatic-sourced hydrothermal fluid by meteoric water. Some pyrites have 3He/4He ratios nearly identical to those of mantle fluid, indicating that the ore-forming fluids were mantle-derived with insignificant crust assimilation. The 3He/heat ratios that are higher than those of mid-oceanic ridges, indicating that the heat was transported by convection of low-temperature fluids with hydrothermal fluids rather than direct magma volatile injection. The copper isotope composition of the sulfides (δ65Cu = -3.59 to 1.33 ‰) increases with depth, which was likely caused by the release and downward transport of heavier copper isotopes near the surface. More than half (14 of 24) of these sulfides have a hypogene origin (δ65Cu = -0.05 ± 0.18 ‰), with 9 of 24 samples are likely of supergene origin. Combining with previous study, we confirm that enriched 65Cu reservoir is absent at Zijinshan.Based on the mass-balance of Cu isotopes and the spatial orebody relationship, we conclude that the leaching by meteoric water contributed to the conversion of low-grade initial hypogene Au mineralization into supergene, friable high-grade ore, resulting in the vertical zoning of Au and Cu at Zijinshan. Furthermore, the 65Cu-rich fluids produced by leaching may have lost to the groundwater, resulting in little exploration potential for 65Cu enrichment zone, while the uniform pattern of Cu isotope in the deep indicates a high exploration potential for hypogene Cu mineralization zone at depth.

The Early Cretaceous magmatism and geological implication of Shanzhuping deposit in Shanghang region, Zijinshan ore field, Fujian Province, Southeast China

单竹坪矿床位于福建省上杭县紫金山矿田的西南部,形成了Au、Cu和Mo异常,其中Au、Cu富集成矿。选取单竹坪矿床钻孔岩芯中二长花岗岩和花岗闪长岩作为研究对象,开展岩石学、岩相学、全岩地球化学、锆石U-Pb年代学和Lu-Hf同位素研究。研究结果表明,二长花岗岩和花岗闪长岩锆石²⁰⁶Pb/²³⁸U加权平均年龄分别为105.2Ma和113.4Ma。二长花岗岩和花岗闪长岩具有富钠(Na₂O/K₂O>1),过铝质(A/CNK=1.19~1.68),富集轻稀土(LREE)、大离子亲石元素(LIEE,如Ba、K)和Th、U、Pb和Hf等元素,亏损高场强元素(如Nb、Ta和Ti等)的特征,属于高钾钙碱性过铝质岩石系列,具有岛弧岩浆岩特征。同时具有中等的(La/Yb)_N值(13.6~17.4),高Mg^#值(45.89~48.53),以及Eu弱负异常(<i>δ</i>Eu=0.79~0.97)和Ce弱正异常(<i>δ</i>Ce=1.0~1.08)。锆石两阶段Hf模式年龄(<i>t</i>_DM2)峰值分别处于0.95~1.0Ma和1.05~1.10Ma区间;<i>ε</i>_Hf(<i>t</i>)值分别介于-4.47~+2.38和-2.73~+1.47,二长花岗岩以负值为主,花岗闪长岩正负值均有。综合研究认为,二长花岗岩来源于中元古界未受幔源组分影响的古老基底地壳熔融而成,花岗闪长岩来源于新元古界地壳物质并经历了壳-幔混合作用;单竹坪矿床形成于燕山晚期岛弧或活动大陆边缘构造环境,与古太平洋板块的俯冲相关,其西南部或南部是成矿远景区。

Origin of Mesozoic Porphyritic Rocks and Regional Magmatic Evolution in the Zijinshan Ore Field of Fujian Province, China: Hf-O Isotope Characteristics of Magmatic Zircons

Mesozoic porphyritic rocks from the Zijinshan area, southwestern Fujian Province, China, are andesitic to rhyolitic in composition. The whole-rock SiO2 contents of these rocks are between 62.5% and 78.1%. Magmatic zircon from the Mesozoic porphyritic rocks was determined via secondary-ionization mass spectrometry (SIMS) for the U-Pb age and Hf and O isotopes. The zircon U-Pb ages could be mainly divided into three age groups: Group 1: ~138.8 Ma; Group 2: 109.2~107.4 Ma; and Group 3: 99.7~98.2 Ma. The εHf(t) and δ18O values of the porphyritic zircons showed that the porphyritic rocks in Group 2 were more affected by mantle-derived magma. Combined with previous research results, the medium-acidic magmatism in the southwestern Fujian Province can be divided into eight periods: Paleoproterozoic, Mesoproterozoic, Middle Neoproterozoic, Silurian to Lower Devonian, Permian to Triassic, Middle Jurassic to early Lower Cretaceous, late Lower Cretaceous, and late Lower Cretaceous to early Upper Cretaceous. The Paleoproterozoic crust was the predominant magmatic source for the subsequent Mesoproterozoic to Jurassic magmatism, but the only melts that were closely related to mineralization were derived from partial melting of the Mesoproterozoic crust and a more depleted upper mantle.

Evolution of Multistage Hydrothermal Fluids in the Luoboling Porphyry Cu-Mo Deposit, Zijinshan Ore Field, Fujian Province, China: Insights from LA-ICP-MS Analyses of Fluid Inclusions

Abstract The Luoboling Cu-Mo deposit, with 1.4 million tons (Mt) Cu and 0.11 Mt Mo, is the largest porphyry deposit in the Zijinshan district of southeast China. Mineralization at Luoboling is divided into premineralization, synmineralization, and late-mineralization stages. Consistent Cs/(Na + K) ratios in fluid inclusions suggest that the mineralizing fluids originated from a common source—the Luoboling granodiorite porphyry. The absence of initial supercritical fluid inclusions and abundant coexisting vapor and brine fluid inclusions imply that the fluids exsolved at low-pressure two-phase conditions, with temperatures of 250° to 600°C and salinities of 30 to 60 wt % NaCl equiv (brines) and &amp;lt;10 wt % NaCl equiv (vapors). The deposit formed at ~120 to 800 bar, corresponding to the depths of ~1.2 to 3.2 km (assuming a transition from lithostatic to hydrostatic load). Metals such as Mo (up to 77 ppm), Pb (up to 8,800 ppm), Zn (up to 13,000 ppm), and Ag (up to 130 ppm) migrated mainly in brines. Although vapor inclusions have high concentrations of Cu (up to 20,000 ppm), hypersaline fluid was the major medium for Cu transport and precipitation. The successive precipitation of Mo and Cu occurred when fluids cooled to ~500°C and ~350° to 450°C, respectively. The late-stage quartz-pyrite veins with phyllic alteration were formed by Cu-rich magmatic hydrothermal fluids. The Zijinshan epithermal Cu-Au deposit and the Luoboling porphyry Cu-Mo deposit originated from independent hydrothermal systems. Nonetheless, the increasing trends of Pb, Zn, and Ag concentrations in different stage inclusions from Luoboling imply potential for distal Pb-Zn-Ag mineralization.

Molybdenite Re-Os dating and LA-ICP-MS trace element study of sulfide minerals from the Zijinshan high-sulfidation epithermal Cu-Au deposit, Fujian Province, China

The Zijinshan Cu-Au deposit, located in Fujian Province, is the largest high-sulfidation epithermal (HSE) deposit in Southeastern China and is usually regarded as a major part of the porphyry Cu system in the Zijinshan ore field. Molybdenite samples collected from the Cu mineralization zone yield a first weighted mean Re-Os age of 111.31 ± 0.70 Ma, which is explained as the time of dickite-alunite alteration. Combining the newly reported muscovite 40Ar-39Ar and zircon U-Pb ages (~113 Ma), the mineralization of Zijinshan is likely to initiate before ca. 110 Ma. This result is obviously older than the Re-Os age of the adjacent Luoboling porphyry Cu-Mo deposit (~105 Ma).Pyrite, chalcopyrite, bornite, digenite, and covellite collected from the deep potassic, middle phyllic and upper epithermal zones are used to conduct LA-ICP-MS trace element analysis. The spatial zonings of mineralization and alteration and the regular variations of trace elements in sulfides at vertical direction imply a potentially complete transition from porphyry to epithermal mineralization and the deep origin of ore-forming fluids. Mineralogical and trace element characteristics indicate that the chalcopyrite formed in both stages, whereas bornite is the product of epithermal mineralization, rather than a porphyry stage residue. The majority of digenite and covellite has hypogene genesis. Pyrite and digenite in the epithermal zone are major carriers of primary Au. Au in pyrite is Te-Bi related and exists as solid solutions or different-sized telluride and Bi-sulfosalt inclusions. Compared to As, Te and Bi played more important roles to scavenge Au and Ag and achieve the primary Au enrichment. Differently, Au in digenite is independently locked in digenite lattice. Bornite and digenite are good carriers of primary Ag, which mainly exists as solid solutions. The high sulfidation state stage is the major period for concentrations of primary Au and Ag. The upward increase of Au in primary sulfides of HSE Cu zone implies that the distribution pattern of upper Au enrichment and lower Cu enrichment is not only caused by supergene process, but is also controlled by hypogene trend.Based on the mineralization and alteration zonings, the spatial variation of trace elements and the presented Re-Os age, the ore-forming fluids of the Zijinshan Cu-Au deposit most likely originate from deep region, rather than from the adjacent Luoboling porphyry deposit. The Zijinshan and the Luoboling deposits should belong to two independent hydrothermal systems.

Asynchronous formation of the adjacent epithermal Au-Cu and porphyry Cu-Mo deposits in the Zijinshan orefield, southeast China

Adjacent high-sulfidation epithermal (HSE) and porphyry deposits often have similar Cu-Au metal association, suggesting they are cogenetic and formed contemporaneously. The Zijinshan orefield (ZOF) is the largest Au producer in China and contains a series of HSE Au-Cu and porphyry Cu-Mo deposits. This study presents new (1) muscovite 40Ar-39Ar ages for the HSE deposit in this area, new (2) zircon laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb ages for felsic igneous rocks associated with the epithermal and porphyry mineralization, and (3) new zircon Lu-Hf isotopic data for these intrusions, all of which provides insights into why these adjacent epithermal Au-Cu and porphyry Cu-Mo deposits have different metal associations.The age data indicate that the alunite-dickite alteration related to the HSE Au-Cu mineralization formed before ca. 110 Ma and the main HSE Au-Cu mineralizing event occurred at ca. 113 Ma. In comparison, the adjacent porphyry Cu-Mo mineralization formed at ca. 104 Ma, ca. 9 Myr after the HSE event. The volcanic rocks associated with the HSE Au-Cu mineralization yield zircon εHf (t) values from −4.1 to 0.3, whereas the Cu-Mo mineralized porphyry has lower zircon εHf (t) values (−4.5 to −1.2), suggesting that the magmas that formed the latter intrusion were derived from a source containing more crustal material than the magmas associated with the HSE mineralization. The differences in the timing of mineralization and the sources of the magmas indicate that the adjacent HSE and porphyry deposits in the ZOF formed from different magmatic-hydrothermal systems that controlled the different metal associations of the mineralizing systems. This means that future mineral exploration within the ZOF should target porphyry Au-Cu deposit at depths that is genetically related to the HSE Au-Cu deposit. The results also show that not all adjacent porphyry and epithermal deposits, especially those with different metal associations, are cogenetic.

Geology and fluid inclusion geochemistry of the Zijinshan high-sulfidation epithermal Cu-Au deposit, Fujian Province, SE China: Implication for deep exploration targeting

The giant Zijinshan Cu-Au deposit in the Zijinshan orefield, Fujian Province, southeastern China, is the first high-sulfidation epithermal deposit identified in mainland China. The Cu and Au orebodies occur as veins and pods in the NW-trending faults and breccias zones. Intensive and pervasive alteration is characterized by downward and outward zoning from intensively leached silicic alteration (or vuggy quartz, Q), through alunite-quartz-pyrite alteration (advanced aragillic alteration, Q-Alu) and the quartz-alunite alteration overprinting the sericite alteration (Q-Alu-Di-Srt), to sericite (or phyllic) alteration zone. Gold mineralization mainly occurs in the silicic alteration zone, while the copper mineralization is confined in the alunite-quartz alteration zone. On the basis of detailed petrographic study, an early porphyry type mineralization stage, characterized by chalcopyrite-bornite-molybdenite-pyrite-sericite assemblage is recognized at Zijinshan, which is subsequently and strongly overprinted by the sulfate alteration and high-sulfidation Cu-Au mineralization stages. A supergene stage is also identified at shallow depth of the deposit, with gold largely enriched but copper commonly leached. The ore-forming fluids related to the early sericite alteration and possibly porphyry type mineralization are high-temperature, high-salinity magmatic water, characterized by the presence of the halite-bearing inclusions. The CO2-H2O (C-type) inclusions are mostly vapor-rich and abundantly identified in the samples with advance argillic alteration (alunite alteration). They are regarded to be the buoyant vapor phase by fluid boiling of a single-phase, low- to moderate-salinity magmatic fluid at depth, where a separated saline phase and related porphyry mineralization might be expected. A group of secondary inclusions coexisting with enargite grains are recognized in the samples with alunite alteration and suggested to be trapped from the ore-forming fluids of the Cu-Au mineralization stage. The total homogenization temperatures and salinities of the secondary inclusions are below 300°C (peaking at 260–280°C) and under 10wt% NaCl eqv., respectively. Intensive fluid boiling is the major mechanism for the formation of the giant high-sulfidation Cu (covellite-, digenite-dominated) orebodies in the Zijinshan deposit. It is a deep-seated high-sulfidation epithermal deposit according to the estimated depth of 1.4–2.1km from the C-type inclusions in quartz grains from the alunite alteration zone. By fluid inclusion mapping of a nearly NW-trending cross section profile, the isotherms are extrapolated using the average total homogenization temperatures and the possible heat source is suggested. It is indicated that the heat source and possible concealed porphyry mineralization nearly coeval to the high-sulfidation Cu-Au mineralization at Zijinshan might be located at the southeastern Zijinshan deposit or the northern area between the Zijinshan and Wuziqilong deposits, where deep drilling is encouraged.

Mantle volatiles and heat contributions in high sulfidation epithermal deposit from the Zijinshan Cu-Au-Mo-Ag orefield, Fujian Province, China: Evidence from He and Ar isotopes

The source of metal and sulphur in porphyry and related epithermal deposits is a long debated issue. The role of mantle-derived magmas in providing the metals has proved particularly problematic. Here we report new He and Ar isotope determinations from ore fluids from the Zijinshan high sulfidation-epithermal Cu-Au deposit and Wuziqilong transitional Cu deposit from the giant Zijinshan porphyry-epithermal Cu-Au-Mo-Ag ore system (from 105 to 91 Ma), to decipher the contribution of mantle-derived volatiles and heat. Hydrothermal fluids in pyrite and digenite have 3He/4He up to 5.7 Ra, among the highest measured in ancient ore-forming fluids. A linear correlation between He and Ar isotopes indicate that the ore fluids were, to a first order, a mixture between a shallow crustal fluid, with low 3He/4He, and a dominantly mantle-derived fluid with high 3He/4He. The mantle 3He/4He is close to values typical of the upper mantle indicating the initial magmas that provided the heat for hydrothermal systems did not assimilate large volumes of continental crust. The ore-forming fluids have 3He/heat ratios that are 10 to 80 times higher than that of mid-oceanic ridge hydrothermal fluids, indicating that the metal-bearing fluids acquired heat and volatiles in a convective, rather than conductive, hydrothermal regime. It appears that mantle-derived volatiles, heat and probably metals have made a major contribution to the Cu-Au-Mo-Ag mineralization in the Zijinshan orefield.

Geology, fluid inclusion and stable isotope study of the Yueyang Ag-Au-Cu deposit, Zijinshan orefield, Fujian Province, China

The large Yueyang Ag-Au-Cu deposit is commonly regarded as a low-sulfidation epithermal deposit in the Zijinshan orefield, Fujian Province, southeastern China. The Ag-Ag-Cu orebodies hosted in the Zijinshan granitic batholith are mainly stratoid and lens in shape, and controlled by a series of NW-trending listric faults with shallow dip angles. Four mineralization stages are recognized on the basis of mineral assemblage, ore fabrics, and crosscutting relationships of the ore veins, namely: pre-ore (pyrite+sericite+quartz±chlorite), main Cu (chalcopyrite+pyrite+sericite+quartz±bornite), main Ag-Au (Ag and Au minerals+pyrite+quartz+adularia±calcite±apatite±chalcopyrite±galena±sphalerite) and post-ore (quartz±chalcedony±calcite) stages. Fluid inclusions (FIs) in the deposit include aqueous liquid-rich (WL-), aqueous vapor-rich (WV-), and minor carbonic (C-) and daughter mineral-bearing (S-) type ones. WL-subtype is the main inclusion type in the Yueyang deposit, accounting for more than 90% in proportion in each stage. Minor WV-subtype inclusions occur in both the main Cu and Ag stages, while the C-type and S-type ones are only observed in the main Cu stage. Fluid inclusion and H-O isotope study indicated that the ore-forming fluid of the main Cu stage is primarily magmatic vapor, which further underwent fluid boiling and mixing with meteoric water, while the ore-forming fluid of the main Ag stage is meteoric water-dominated, and the precipitation of silver and gold was mainly resulted from fluid boiling and the precipitation of other sulfides. On the basis of the aforementioned geological, fluid inclusion and stable isotope studies, we proposed a two-stage model for the Yueyang deposit, including a magmatic vapor-related porphyry type Cu mineralization and meteoric water-related low-sulfidation epithermal Ag-Au-Cu mineralization, although the porphyry Cu mineralization is very limited in scale. The mineralization and exhumation depths of the Yueyang deposit are estimated to be 448‒527m and 18‒97m, respectively. By comparison with the exhumation depths of other deposits in the Zijinshan orefield, it is suggested that more epithermal deposits could be found in the southwest of the orefield due to less uplift and exhumation therein.

Copper isotopic compositions of the Zijinshan high-sulfidation epithermal Cu–Au deposit, South China: Implications for deposit origin

The Zijinshan high-sulfidation epithermal Cu–Au deposit is located in the Zijinshan ore field of South China, comprising porphyry–epithermal Cu–Au–Mo–Ag ore systems. The Cu ore body is more than 1000m thick and is characterized by an assemblage of digenite–covellite–enargite–alunite. Digenite is the dominant Cu-bearing mineral, which makes this deposit unique, although the mechanisms of digenite formation remain controversial. To elucidate the genesis of digenite, this paper presents the Cu isotopic compositions of Cu-sulfides in the Zijinshan high-sulfidation Cu–Au deposit. The Cu isotopic values (65Cu relative to NIST 976) of all samples range from −2.97‰ to +0.34‰, and most values fall in a narrow range from −0.49‰ to +0.34‰, which is similar to the Cu isotopic signature of typical porphyry systems. Copper isotope ratios of each mineral decrease with increasing depth, a trend that is also typical of porphyry deposits. The variation tendency of δ65Cu values between sulfides is consistent with the sequence of mineral formation. These observations suggest that the Cu-sulfides in the Zijinshan Cu–Au deposit have a hypogene origin.

Mesozoic multiphase magmatism at the Xinan Cu–Mo ore deposit (Zijinshan Orefield): Geodynamic setting and metallogenic implications

The Xinan Cu–Mo deposit, newly-discovered in the Zijinshan Au–Cu–Mo Orefield (the largest porphyry–epithermal system in SE China), is featured by the presence of abundant multi-phase granitoids, which reflects the complex Mesozoic tectono-magmatic evolution in the region.New and published LA-ICP-MS zircon U–Pb age data reveal that the Mesozoic Zijinshan magmatism occurred in two major phases: (1) Middle to Late Jurassic (ca. 169–150Ma), forming the Zijinshan complex granite and the Xinan monzogranite; (2) late Early Cretaceous to earliest Late Cretaceous (ca. 112–98Ma), forming the Shimaoshan volcanic rocks, Sifang granodiorite, and the Xinan (fine-grained) granodiorite porphyry, porphyritic granodiorite and late aplite dykes. Additionally, a possible earliest Cretaceous magmatism (ca. 141Ma) may have occurred based on inherited zircon evidence. Major and trace element geochemistry indicates that all the Zijinshan igneous rocks show subduction-related geochemical affinities. Zircon Ce4+/Ce3+ values of the late Early Cretaceous to earliest Late Cretaceous granitoids (Ce4+/Ce3+=190–1706) are distinctly higher than the Middle to Late Jurassic ones (Ce4+/Ce3+=27–457), suggesting that the former were derived from more oxidized parental magma. The Middle to Late Jurassic Zijinshan complex granite and monzogranite have εHf (t) values of −8.02 to −10.00, with the two-stage Hf model ages (TDM2) of 1.72 to 1.84Ga (similar to the Paleoproterozoic metamorphosed Cathaysia Block basement), suggesting that they were derived from partial melting of the basement. The late Early Cretaceous to earliest Late Cretaceous Sifang granodiorite and Xinan (fine-grained) granodiorite porphyry, porphyritic granodiorite and aplite dykes contain higher and wider range of εHf (t) values (0.66 to −6.05), with TDM2 of 1.12 to 1.56Ga, indicating that they were also partial melting product of the Cathaysia basement but with more mantle and/or juvenile mafic lower crustal input. We propose that the Zijinshan Orefield was in a compressive, Pacific subduction-related tectonic setting during the Middle to Late Jurassic. The regional tectonic regime may have changed to extensional in the late Early Cretaceous to earliest Late Cretaceous, during which the Pacific plate subduction direction change and the accompanying subduction roll-back and slab window-opening occurred. The tectonic regime transition, high oxygen fugacity and mantle/mafic lower crustal materials involvement in the late Early Cretaceous to earliest Late Cretaceous may have generated the Zijinshan porphyry-related Au–Cu–Mo mineralization.

Mineralogy of tin-sulfides in the Zijinshan porphyry–epithermal system, Fujian Province, China

The Zijinshan orefield is a Cu–Au–Mo–Ag porphyry–epithermal mineralization system of Cretaceous age in southeastern China, comprising the Zijinshan high-sulfidation (HS) Au–Cu deposit, Luoboling porphyry Cu–Mo deposits, Yueyang low-sulfidation Au–Ag–Cu deposit, and Wuziqilong and Longjiangting intermediate-sulfidation (IS) Cu deposit. A number of Sn-(W)-sulfides occur in the Zijinshan orefield, including kiddcreekite, hemusite, colusite, vinciennite, stannoidite, mawsonite and kësterite. The occurrence represents the first report of hemusite, colusite and vinciennite in China. The relative abundance and diversity of Sn-(W)-sulfide-bearing assemblages make the Zijinshan orefield possibly unique in the world, and carries implications for the evolution of the mineralizing environment. Detailed electron probe studies of the Sn-minerals reveal that kiddcreekite, hemusite, mawsonite, stannoidite and kësterite have compositions close to ideal formulae. In contrast, colusite displays grain-scale zoning expressed by W, Sn and As. Vinciennite displays compositional variation depending on mineralization style: an average composition of Cu10.74Fe3.88Sn(As0.85,Sb0.08)S15.4 in the Zijinshan HS deposit, Cu10.71Fe3.9SnAs0.85S15.34 in the Wuziqilong Cu deposit and Cu10.76Fe3.7Sn1.02 (As0.5,Sb0.45)S15.54 with higher Sb contents (3.32%) in the adjacent Longjiangting Cu deposit.In the Zijinshan HS Au–Cu deposit, the main Cu-mineral assemblage varies from bornite-rich to digenite- to covellite-rich with increasing depth. Correspondingly, tin mineralogy varies from kësterite at upper levels to stannoidite-dominant at mid-to-upper levels of the copper orebody, to vinciennite- and mawsonite-dominant at depth, implying an increase in sulfidation and oxidation state downwards. Moreover, kiddcreekite is always partially replaced by wolframite and (hypogene) covellite at depth, also indicating overprinting by high-fO2 and -fS2 fluids in the covellite stage of mineralization. Kiddcreekite, along with a primary chalcopyrite–pyrite mineral association, occurs widely in the Zijinshan orefield (Zijinshan, Yueyang, Luoboling, Wuziqilong, Longjiangting and Dayanli), and is likely indicative of the early IS stage of epithermal system. Analogous with published data, kiddcreekite most commonly occurs in porphyry-style mineralization, implying the presence of the mineral has potential as an indicator of porphyry systems. Vinciennite-bearing Cu–Sn–As mineral associations occur in a specific position in the Zijinshan HS Au–Cu, Wuziqilong and Longjiangting Cu deposits, indicative of a transitional zone between porphyry and HS epithermal-style mineralization. The occurrence of the identified Sn-(W)-sulfide-bearing assemblages has considerable potential implications for understanding the architecture of a complex porphyry–epithermal environment and for exploration for underlying porphyry copper deposits. There is potential for discovery of a subjacent porphyry Cu deposit within the Zijinshan orefield.

A subduction-related metasomatically enriched mantle origin for the Luoboling and Zhongliao Cretaceous granitoids from South China: implications for magma evolution and Cu–Mo mineralization

The Luoboling granodiorite porphyry and Zhongliao porphyritic biotite-granodiorite occur within the Zijinshan ore field in Fujian Province, southeast China. LA–ICP–MS zircon U–Pb dating yields ages of 103.1 ± 1.1 Ma (2σ, MSWD = 3.1) and 95.9 ± 0.6 Ma (2σ, MSWD = 1.2) for the Luoboling and Zhongliao intrusions, respectively. All rocks show high SiO2, K2O, and light rare earth element levels, variable CaO and Fe2O3 T, but low heavy rare earth element and high field strength element (Nb, Ta, Ti) concentrations. They also exhibit uniform initial 87Sr/86Sr ratios (0.7064–0.7068) and εNd(t) values (−4.0 to −2.6), falling within the compositional field of Cretaceous basalts and mafic dikes in the Cathaysia Block. Together with their relatively high Hf isotopic ratios (εHf(t) = −5.8 to +0.7), these data suggest that the Luoboling and Zhongliao intrusions were derived from a subduction-enriched mantle source. We infer fractional crystallization processes involving early fractionation of clinopyroxene and olivine, and subsequent fractionation of garnet forming the Luoboling granodiorite porphyry, eventually followed by amphibole- and biotite-dominated crystallization, with minor accessory mineral contribution, producing the (younger) Zhongliao porphyritic biotite-granodiorite. Asthenospheric mantle sources may have also contributed to generating the melts as indicated by initial Pb isotopic compositions and Hf isotopic compositions. The generation of these intrusions was associated with the Pacific subduction in an extensional setting during the Cretaceous.

Geology, geochronology, fluid inclusion and H–O isotope geochemistry of the Luoboling Porphyry Cu–Mo deposit, Zijinshan Orefield, Fujian Province, China

The Luoboling Cu–Mo deposit in the Zijinshan Orefield, Fujian province, southeastern China, is a large porphyry deposit hosted by the Sifang granodiorite and the Luoboling granodiorite porphyry. The largest Cu–Mo orebody is saddle-shaped with various types of hydrothermal veinlets. Intensive hydrothermal alteration in the deposit is characterized by outward zoning from potassic, overprinted by phyllic alteration, to phyllic and alunite–dickite alteration. Based on the mineral assemblages and crosscutting relationships of veins, the ore-forming process can be divided into three stages, namely: an early-stage K-feldspar+quartz±magnetite±molybdenite veins associated with potassic alteration; a middle-stage quartz+molybdenite+chalcopyrite+pyrite veins in phyllic zone; and a late-stage quartz±gypsum veins in the phyllic and alunite–dickite alteration zones. Six molybdenite separates yield a Re−Os isochron age 104.6±1.0Ma, which is identical to the age of emplacement of the Sifang and Luoboling granodiorite porphyries. Three types of fluid inclusions (FIs) were observed at the Luoboling deposit: 1) NaCl–H2O (aqueous), 2) daughter mineral-bearing and 3) CO2–H2O fluid inclusions. FIs of the early and middle stages are predominantly vapor-rich aqueous and daughter mineral-bearing inclusions, together with minor CO2-rich and liquid-rich aqueous inclusions; whereas the late-stage minerals only contain liquid-rich aqueous inclusions. Homogenization temperatures and salinities of FIs trapped in the early-stage minerals range from 420 to 540°C and 0.4 to 62.9wt.% NaCl equiv., respectively. FIs of the middle-stage yield homogenization temperatures of 340 to 480°C and salinities of 0.5 to 56.0wt.% NaCl equiv. CO2 content and the oxygen fugacity (indicated by daughter minerals) of FIs trapped in middle-stage minerals are lower than those in the early stage. The liquid-rich aqueous inclusions of the late-stage homogenize at temperatures of 140 to 280°C, yielding salinities of 0.4 to 8.4wt.% NaCl equiv. The minimum estimated pressures of the three stages are 30–70MPa, 10–40MPa and 1–10MPa, respectively, corresponding to minimum ore-forming depths of 1–2.8km. Fluids trapped in early, middle and late stages yield δD values of −67‰ to −54‰, −54‰ to −70‰, and −62‰, and δ18O values of 5.4‰ to 6.7‰, 2.8‰ to 4.2‰, and −2.1‰, respectively. Fluid boiling, which resulted in the formation of stockworks and the precipitation of sulfides, occurred in the early and middle stages. The fluids subsequently evolved into a low temperature, low salinity system in the late stage, along with an input of meteoric water. The Luoboling porphyry Cu–Mo system was developed in a transition from continental arc to back-arc extension region, which was related to the westward subduction of the paleo-Pacific plate beneath the Huanan Orogen.