Epithermal Cu-Au Deposit Research Articles

Early fluid exsolution suppressed sulfide saturation in Triassic arc volcanic rocks from the Gangdese belt: Implications for Cu depletion in arc magmas and mineralization potential

Early fluid exsolution suppressed sulfide saturation in Triassic arc volcanic rocks from the Gangdese belt: Implications for Cu depletion in arc magmas and mineralization potential

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

• Mantle volatiles and heat contributions in high sulfidation epithermal Zijinshan deposit. • A progressive dilution of a magmatic-sourced hydrothermal fluid by meteoric water in Cu-Au ore-forming processes. • Leaching by meteoric water contributed to the vertical zoning of Au and Cu at Zijinshan. 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 3 He/ 4 He and 40 Ar/ 36 Ar ratios, as well as a sharp drop in 3 He/ 36 Ar ratio, reflects the progressive dilution of a magmatic-sourced hydrothermal fluid by meteoric water. Some pyrites have 3 He/ 4 He ratios nearly identical to those of mantle fluid, indicating that the ore-forming fluids were mantle-derived with insignificant crust assimilation. The 3 He/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 (δ 65 Cu = -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 (δ 65 Cu = -0.05 ± 0.18 ‰), with 9 of 24 samples are likely of supergene origin. Combining with previous study, we confirm that enriched 65 Cu 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 65 Cu-rich fluids produced by leaching may have lost to the groundwater, resulting in little exploration potential for 65 Cu enrichment zone, while the uniform pattern of Cu isotope in the deep indicates a high exploration potential for hypogene Cu mineralization zone at depth.

Evolution and genesis of hydrothermal fluids for the Cretaceous Dongnan Cu deposit, Zijinshan ore district (SE China)

• Two alteration and mineralization types were identified at the Dongnan deposit. • The two types are porphyry-type and high-sulfidation (HS) epithermal-type. • Hydrothermal fluids for porphyry-type came from the Luoboling porphyry deposit. • Hydrothermal fluids for HS type came from the Zijinshan HS epithermal deposit. The Dongnan Cu(-Mo) deposit is a newly discovered porphyry-epithermal system located between the Zijinshan high-sulfidation (HS) epithermal deposit and Luoboling porphyry deposit, within the Zijinshan ore district, a large porphyry-epithermal Cu-Au-Mo-Ag ore system in southeast China. The deposit offers a window to investigate the origins of hydrothermal fluids in a coupled porphyry-HS epithermal magmatic-hydrothermal system. Drill hole logging and alteration mineral mapping has identified four hydrothermal alteration and mineralization stages at the Dongnan deposit, namely: stage I porphyry-type alteration, which can be subdivided into stage IA potassic alteration and stage IB phyllic alteration, stage II HS mineralization and associated alteration which can be subdivided into stage IIA-1 pyrophyllite-dominated, stage IIA-2 illite and illite-montmorillonite and stage IIB dickite-dominated alteration, stage III late veins (i.e., calcite and fluorite) and stage IV supergene alteration. Chalcopyrite and molybdenite mineralization is associated with Stage I, whereas covellite and digenite mineralization formed during Stage II. Stage IB minerals (i.e., muscovite) were largely superimposed by minerals from stage II (i.e., dickite, kaolinite, pyrophyllite and alunite). Stage II epithermal alteration is located mainly in the western part of Zijinshan ore district, whereas the eastern part is dominated by porphyry-type mineralization and alteration. Microthermometry results show the average Th and salinity of each sample suite from stage IB ranging from 341 ± 22 to 442 ± 2 °C and 1.6 ± 1.6 to 19.2 ± 2.6 wt% NaCl equiv. By contrast, stage III fluid inclusions are liquid-dominated, with low temperature of homogenization and low salinity (156 ± 9 to 165 ± 4 °C and < 0.5 wt% NaCl equiv.). Thermodynamic modelling of stage II suggest that the fluid responsible for epithermal mineralization was characterized by high temperature (270 to 320 °C), high water to rock (w/r > 1) and high SO 2 to H 2 S ratios (SO 2 /H 2 S > 1). Because stage IIA pyrophyllite alteration is overprinted by late stage IIB dickite alteration and relatively different forming condition for pyrophyllite (>270 °C) and kaolinite (<270 °C and w/r > 1), stage IIA and stage IIB may have resulted from two different fluids. The Dongnan porphyry-type mineralization formed mainly in response to the cooling and dilution, led by the mixing of acidic magmatic water with meteoric water, whereas stage II alteration was more likely related to volatile gas escaping, resulting in pH decrease and contributing to the formation of pyrophyllite, dickite and alunite. The distribution of alteration minerals and evolution of hydrothermal fluids all indicate that the hydrothermal fluids for the porphyry-type and HS epithermal-type alteration at Dongnan came separately from nearby Luoboling granodiorite porphyry and the Zijinshan HS epithermal Cu-Au deposit, which implies that Luoboling porphyry deposit and Zijinshan HS deposit formed from separate magmatic-hydrothermal events. It suggests that multiple magmatic centers exist in the Zijinshan ore district, a finding which will contribute to both understanding of ore genesis of this overprinted porphyry-epithermal deposit and further mineral exploration in the Zijinshan Ore district.

Fluid inclusions, isotopes and mineralogy of the Kuruer epithermal Cu-Au deposit, Chinese Western Tianshan: Implications for ore genesis and exploration

• The initial ore-forming fluids were magmatic water, mixing with meteoric water . • The metals were derived from the hosing volcanic rocks and hidden causative pluton . • Fluid phase separation caused the formation of liquid bismuth and invisible gold. • The liquid bismuth collector model is responsible for the Au-Bi association. • Kuruer is a subepithermal Cu-Au mineralization related with the hidden porphyries . The Kuruer Cu-Au deposit is located in the Wusun Range of Yili Block, Chinese Western Tianshan, where numerous epithermal Au, skarn Fe-Cu and porphyry Mo-Cu deposits have been recognized. Petrography, fluid inclusions, S-Pb-H-O isotopes, field emission-scanning electron microscopy (FE-SEM) plus energy dispersive spectrometer (EDS) and electron microprobe analysis (EMPA) have been carried out to constrain the genesis of the Kuruer deposit and its implication for further exploration. The minerlization is hosted by volcanic rocks and occur as veins and veinlets structurally controlled by NW-trending faults. Three ore-forming stages were recognized, including quartz-sulfides-bismuth-gold stage (I), quartz-chalcopyrite stage (II) and calcite-chlorite-chalcopyrite stage (III). Six types of fluid inclusions were identified in stage I quartz, including monophase vapor inclusions (type 1), liquid-rich biphase inclusions (type 2), vapor-rich biphase inclusions (type 3), H 2 O-rich CO 2 -H 2 O triphase inclusions (type 4), CO 2 -rich CO 2 -H 2 O triphase inclusions (type 5) and solid halite-bearing triphase inclusions (type 6), whereas only type 2 inclusions were recognized in stage II quartz and stage III calcite. Types 2, 3, 4 and 6 inclusions in stage I have homogenization temperature ( T h ) ranges of 184–359 °C, 209–252 °C, 250–319 °C and 229–263 °C, with salinity ranges of 4.1–8.5 wt% NaCleq, 5.9–6.9 wt% NaCleq, 1.0–6.0 wt% NaCleq and 32.7–33.9 wt% NaCleq, respectively. Type 2 inclusions in stages II and III have T h varying from 144 to 212 °C and 114 to 163 °C, with salinities of 0.2–6.7 wt% NaCleq and 0.1–3.1 wt% NaCleq, respectively. The in-situ δ 34 S values of sulfides in stage I range from −4.66 to 0.34‰. The 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 208 Pb/ 204 Pb ratios of stage I chalcopyrite vary from 18.295 to 18.954, 15.568 to 15.673 and 38.109 to 38.817, respectively, which are consistent with those of Early Carboniferous Dahalajunshan Formation volcanic rocks and granitoids from the Wusun Range. The values of δ 18 O H2O-VSMOW calculated from δ 18 O quartz and δD H2O-VSMOW of stage I quartz range from 0.0 to 2.4‰ and −118.6 to −109.3‰, respectively. These isotopic compositions indicate that both metals and sulfur were sourced from the hosting volcanic rocks and hidden causative pluton, while the initial ore-forming fluids were magmatic in origin, with increasing involvement of meteoric water with time. Evidence from mineralogy, mineral geochemistry and fluid inclusions indicates that the initial fluid phase separation triggered the precipitation of “invisible” gold within pyrite and chalcopyrite during stage I. Subsequently, the decrease of f S2 due to the escape of H 2 S (g) and sulfide precipitation and cooling caused the formation of liquid bismuth from solutions. The bismuth melts have scavenged Au in situ from the residual solutions, resulting in the formation of Bi-Au inclusions within the fractures and intergranular spaces of earlier pyrite. For stages II and III, dilution and cooling due to input of meteoric water facilitated the chalcopyrite precipitation. The Kuruer Cu-Au deposit is classified as a subepithermal mineralization associated with porphyries. Porphyry Cu-Au mineralization could have developed beneath the Kuruer and its vicinity.

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

Abstract 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.

Fluid inclusion and stable isotope study of the Lubin-Zardeh epithermal Cu-Au deposit in Zanjan Province, NW Iran: Implications for ore genesis

Abstract The Lubin-Zardeh deposit is located in the Western Alborz Magmatic belt, 45 km NE of Zanjan, Iran. This deposit contains polymetallic (Cu, Au, Pb, Zn) mineralization which is hosted by the Cenozoic volcanic-intrusive rocks of mainly intermediate and acidic composition. Pyrite, chalcopyrite, galena, sphalerite, bornite and tennantite-tetrahedrite, with native gold and silver are present in the ores. Quartz, adularia and clay minerals (illite-montmorillonite) with minor calcite are the most abundant gangue minerals and generally occur as fine-grained assemblages; some are, however, medium- and coarse-grained assemblages. The ore minerals show disseminated, vein-veinlet, replacement, and brecciated textures while the gangue minerals represent replacement, cockade, crustiform, colloform, comb, vein-veinlet and plumose textures. Alteration haloes along the main vein are silicic, argillic (illite-montmorillonite), sericitic and pyritic. Gold contents of the quartz-chalcopyrite-gold veins range from 0.002 to 10 ppm with an average of 0.52 ppm. The average values for total reserve of 0.5 Mt of Lubin-Zardeh deposit has been determined 1.3%, 0.7% and 0.4% for Cu, Pb and Zn, respectively. Most of fluid inclusions in the quartz-gold-sulfide veins consist of two vapor and liquid phases at room temperature. The primary fluid inclusions have a low to intermediate homogenization temperature between 127 and 327 °C and salinity between 4.07 and 13.98 wt% NaCl equivalent. Stable isotope and fluid inclusion studies indicate that mineralization occurred in two stages at Lubin Zardeh deposit i.e. stage I; along which base metal deposited and stage II which is associated with copper and gold mineralization. The δ18Oquartz values from stage I and stage II range from 9.56 to 12.77‰ and from 7.23 to 9.24‰, respectively while their δ34S values of sulfide minerals range from −0.9‰ to +6.2‰ and form −6.6‰ to −1.9‰. The isotopic and microthermometric data indicate that the hydrothermal solution evolved through mixing of magmatic fluids with meteoric waters. Boiling of magmatic fluid and mixing with meteoric waters were the main mechanisms of ore deposition in the Lubin-Zardeh low sulfidation epithermal deposit.

Alunite 40Ar/39Ar and Zircon U-Pb Constraints on the Magmatic-Hydrothermal History of the Zijinshan High-Sulfidation Epithermal Cu-Au Deposit and the Adjacent Luoboling Porphyry Cu-Mo Deposit, South China: Implications for Their Genetic Association

AbstractThe large Zijinshan high-sulfidation epithermal Cu-Au deposit, together with the adjacent Luoboling porphyry Cu-Mo deposit, constitutes a major porphyry-epithermal ore district in South China. Current debate centers on whether the Zijinshan and the adjacent Luoboling deposits are cogenetic or represent separate ore-forming events, which is a question of importance for exploration in the district. In this contribution, the magmatichydrothermal history of the relationship between Zijinshan and Luoboling is reconstructed based on new alunite 40Ar/39Ar ages from Zijinshan and zircon U-Pb ages of ore-related intrusions from both deposits. This study has been complemented by S isotope analysis on the dated alunite to assess their origin.Three types of coexisting alunite and sulfide assemblages exist at Zijinshan, namely, (1) alunite-quartz-covellite cemented breccias; (2) alunite-digenite veins and (3) banded alunite-pyrite veins. Their field occurrences and S isotope features suggest a magmatic-hydrothermal origin for alunite-quartz-covellite cemented breccias and alunite-digenite veins, whereas the origin of alunite-pyrite veins is likely to be related to magmatic steam. Given the intimate textural coexistence between sulfides and alunite, four undisturbed 40Ar/39Ar plateau ages obtained from alunite-quartz-covellite cemented breccia and alunite-digenite vein-type alunite define the timing of Zijinshan high-sulfidation mineralization from 102.86 ± 0.61 to 101.19 ± 0.60 Ma. These agree with bracketing zircon U-Pb ages of pre-ore dacite porphyry at 104.8 ± 0.9 Ma and 104.7 ± 0.5 Ma and a zircon U-Pb age of a post-ore granite porphyry dike at 99.5 ± 0.7 Ma. Combined with their field occurrences, the four alunite ages may imply episodic hydrothermal pulses and a possible time span of over 500 k.y. for the overall high-sulfidation mineralization. Two alunite samples from alunite-pyrite veins yield a slightly disturbed 40Ar/39Ar plateau age at 101.67 ± 0.61 Ma and an apparently undisturbed age at 99.91 ± 0.59 Ma, probably reflecting partial or complete thermal resetting related to the coeval granite porphyry dikes. At Luoboling, zircon U-Pb analysis yields an age of 133.6 ± 1.1 Ma for a dark, ore vein-bearing quartz-diorite porphyry sample and confirms the petrographic observation that they are xenoliths of early wall rocks for the porphyry mineralization. A granodiorite porphyry sample with abundant A-veins is interpreted as an intermineral porphyry phase, dated at 106.5 ± 1.4 Ma. This age is interpreted as the upper limit for porphyry Cu-Mo mineralization and agrees well with previously reported molybdenite Re-Os and biotite 40Ar/39Ar ages, which collectively suggest porphyry Cu-Mo mineralization and potassic alteration at Luoboling were formed within the interval between ca. 106 and 104 Ma.Taken together, the age of the Zijinshan high-sulfidation mineralization is substantially younger than the porphyry mineralization at Luoboling, and we conclude that there is no direct genetic link between the two deposits. However, the Zijinshan Cu-Au deposit is temporally associated with the deep porphyritic granodiorite, which gives zircon U-Pb ages from 102.1 ± 0.8 to 101.8 ± 0.5 Ma, overlapping with the alunite 40Ar/39Ar ages for the high-sulfidation mineralization. This finding has important implications for the ongoing exploration for the two mineralization types in the ore district and elsewhere.

Sulfur isotope geochemistry of the Chodarchay Cu-Au deposit, Tarom, NW Iran

The Chodarchay porphyry–high-sulfidation epithermal Cu-Au deposit in the Tarom subzone of the western Alborz structural zone of NW Iran is related to quartz-monzonite and alkali-granite intrusions that were emplaced within the volcanic-volcaniclastic rocks of Karaj Formation during Tertiary. The Chodarchay deposit formed as a high-sulfidation epithermal overprint on porphyry type mineralization. The mineralization occurred as stockwork, dissemination, veinlet, open space filling and breccias. Chalcopyrite, pyrite, sphalerite, and galena are the main sulfide minerals in the area. The sulfur isotope composition of sulfide minerals from the Chodarchay deposit is positive, ranging from 0.2 to 6.8 ‰. The sphalerite-galena isotope geothermometer shows 360 °C for the crystallization temperature. Sulfur was sourced from a homogeneous magma, and its isotopic composition decreases with depth and temperature decreasing due to fluid oxidation changes. Therefore, sulfur isotope assemblages show a systematic spatial distribution within the Chodarchay system.

Spatial distribution and variation of ore body, alteration and ore-forming fluid of the giant Zijinshan epithermal Cu-Au deposit, SE China: implication for mineral exploration

The Zijinshan high-sulphidation Cu-Au deposit located in the west Fujian Province is the largest active gold mine in China with total production of gold over 300 tonnes to date. The high-sulphidation ore bodies are characterized by the upper supergene Au and lower hypogene Cu zones bounded roughly by the paleowater table near 600 m elevation. Au-bearing goethite and limonite are the main ore minerals in the supergene zone whereas the hypogene Cu mineralization is dominated by covellite and anilite (or digenite) with minor enargite. The expected porphyry mineralization that coupled with Zijinshan is so far not exposed even to a depth of 1500 m from surface. However, the Luoboling Cu-Mo deposit which occurs only 3 km NE to Zijinshan is identified as a typical porphyry deposit. Current debate centered on whether the Zijinshan high-sulphidation epithermal deposit and the adjacent Luoboling porphyry deposit are genetically linked or discrete hydrothermal systems. Recent deep exploration at Zijinshan revealed an extension trend of Cu ore bodies and quartz-alunite alteration zone toward SE below 0 m elevation. This contradicts previous considered NE trend above 0 m elevation. In this study, fluid inclusion mapping based on rigorous strategy and sample selection was carried out on 20 sample suites scattered over the whole high-sulphidation Cu-Au ore bodies from −450 to 800 m elevation. Aqueous fluid inclusions of unambiguous primary origin in syn-ore miarolitic quartz, coarse-grained alunite crystals and quartz overgrowth zones were measured. Microthermometry results show the average T h and salinity of each sample suite ranging from 205 to 304°C and 2.4 to 5.5 wt% NaCl equiv., respectively. Both fluid temperature and salinity exhibit negative correlation with increasing elevation, indicating convective cooling by mixing and circulating of meteoric water has involved. The good consistence of mineralization distribution pattern and fluid evolution trend implies that the southeastward extending ore bodies probably reflect the fluid pathway which is connected to the deeper porphyry mineralization and their magmatic source. Considering the temperature condition (370–400°C) required for brittle-plastic transition which commonly characterizes porphyry deposits, the potential porphyry mineralization coupled to Zijinshan should have occurred at greater depth under higher temperature. Combined with recent exploration progress and the fluid evolution pattern, we therefore proposed that the Luoboling porphyry Cu-Mo deposit and the Zijinshan high-sulphidation Cu-Au deposit are likely discrete hydrothermal systems, and future porphyry deposit exploration at the deep SE segment of Zijinshan is recommended.

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

Abstract 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 CO 2 -H 2 O (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 10 wt% 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 1.4–2.1 km 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.

Exploration Tools for Linked Porphyry and Epithermal Deposits: Example from the Mankayan Intrusion-Centered Cu-Au District, Luzon, Philippines*

The Mankayan mineral district of northern Luzon, Philippines, hosts several significant ore deposits and prospects of various types within an area of similar to 25 km(2), including the Far Southeast porphyry Cu-Au deposit, the Lepanto high sulfidation epithermal Cu-Au deposit, the Victoria intermediate sulfidation epithermal Au-Ag vein deposit, the Teresa epithermal Au-Ag vein deposit, the Guinaoang porphyry Cu-Au deposit, and the Buaki Old Palidan porphyry Cu-Au prospects, all having formed in a period of about 2 m.y., from similar to 3 Ma. The geologic units include (1) a basement composed of Late Cretaceous to middle Miocene metavolcanic rocks volcaniclastic rocks; (2) the Miocene 12 to 13 Ma tonalitic Bagon intrusive complex; (3) the Pliocene, similar to 2.2 to 1.8 Ma, Imbanguila dacite porphyry and pyroclastic rocks; and (4) postmineralization cover rocks, including die similar to 1.2 to 1.0 Ma Bato dacite porphyry and pyroclastic rocks and the similar to 0.02 Ma Lapangan tuff. Extensive advanced argillic alteration crops out for similar to 7 kin along the inconformity between the basement rocks and the Imbanguila dacite formation consists of quartz-alunite +/- pyrophyllite or diaspore, with local zones of silicic alteration and a halo of dickite +/- kaolinite. The alteration and its subhorizontal geometry indicate that it is a lithocap or coalesced lithocaps. The northwest-striking portion is similar to 4 km long and hosts the Lepanto enargite Au ore deposit, also controlled by the Lepanto fault. The Lepanto epithermal deposit is related to the underlying Far Southeast porphyry; the quartz-alunite alteration halo of Lepanto is contemporaneous with the similar to 1.4 Ma potassic alteration of the porphyry. There are also silicic-advanced argillic alteration patches similar to 600 m above the Far Southeast orebody at the present surface; these are interpreted to be perched alteration. There is no systematic mineralogical or textural zoning in the Lepanto lithocap that indicates direction to the intrusive source. Most surface samples of the lithocap contain less than 50 ppb Au, despite many being less than a few hundred meters from underground Cu-Au ore. This study found that several characteristics of the Lepanto lithocap change systematically with distance from the causative intrusion. The alunite absorption peak at similar to 1,480 nm in the short wavelength infrared (SWIR) spectrum shifts to higher wavelengths where the sample is closer to the intrusive center, due to higher Na and lower K content in the alunite; published experimental studies indicate that high Na/(Na + K) is related to higher formation temperature. High Ca alunite, including huangite, also occurs at locations proximal to the intrusive center. Alunite mineral composition analyzed by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) indicates that the Pb content decreases toward the intrusive center, whereas Sr, La, Sr/Ph, and La/Pb increase markedly. Whole-rock compositions, using only nonmineralized (taken as Cu similar to 350 m above the upper extent of the veins. An airborne geophysics survey indicates that the Far Southeast orebody is associated with a wide zone of demagnetization due to extensive magnetite-destructive phyllic alteration. Such low magnetic anomalies on the margin of a large lithocap elsewhere may, deserve attention. The directional indicators and mineralization signatures found in this study have the potential to indicate direction to the intrusive center during exploration of similar porphyry-epithermal districts.

Evolution of Magmatic Vapor to Gold-Rich Epithermal Liquid: The Porphyry to Epithermal Transition at Nevados de Famatina, Northwest Argentina

Fluid inclusions in the subeconomic porphyry Cu-Mo-Au system at Nevados de Famatina and closely associated high-sulfidation epithermal Cu-Au-(Ag-As-Sb-Te) veins at La Mejicana, northwest Argentina, were studied to reconstruct the evolution of hydrothermal fluids from their deep magmatic source to the shallow epithermal environment. Field geology, vein petrography, fluid inclusion microthermometry, and single-inclusion microanalysis by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) were combined to determine the evolution of pressure, temperature, and ore metal concentrations in the fluids. Cathodoluminescence imaging complements transmitted light petrography to constrain the successive stages of quartz formation and the entrapment sequence of the fluid inclusion populations. Aqueous liquid inclusions of ~5 wt percent NaCl equiv salinity trapped in quartz-sericite-pyrite (QSP) veins between 360° and 325°C contain unusually high concentrations of Cu (400–5,000 ppm), As (~200 ppm), Sb and Te (both up to 100 ppm), and Au (several ppm) along with other ore-forming elements. These veins are paragenetically transitional between subeconomic porphyry copper mineralization exposed in the valley floor, and high-sulfidation epithermal veins with high Au grades, which are preserved along a high ridge adjacent to the porphyry stock. Low-density vapor and hypersaline liquid (i.e., brine) inclusions were trapped in early-formed quartz of the porphyry stockwork veins, between 450° and >600°C. The brine contains lower Cu and Au concentrations than coexisting vapor inclusions and texturally even earlier inclusions of intermediate density that are trapped in phenocrysts and some stockwork veins; the latter may be equivalent to a parental fluid. The low- and intermediate-density fluids compositionally overlap in salinity with the aqueous liquids recorded by the later transitional quartz-sericite-pyrite veins. Fluid inclusions and geologic time relations indicate that the transitional quartz-sericite-pyrite veins were the channelways for metal-rich aqueous liquids that generated the high-sulfidation epithermal Cu-Au deposit. These mineralizing liquids are interpreted to have evolved by continuous density increase (“contraction”) from a low-salinity, S-rich magmatic fluid of low to intermediate density. This vaporlike fluid was produced by exsolution from a magma that existed at greater depth during the late stages of cooling of the magmatic-hydrothermal complex, and probably underwent minor brine separation prior to reaching the present level of exposure. Epithermal mineral precipitation occurred upon dilution of the low-salinity magmatic fluid with meteoric water, which entered the hydrothermal system as it was cooled and successively eroded during continued magmatic fluid ascent.

MINERAL ASSEMBLAGES AND GENESIS OF THE Cu-Au EPITHERMAL DEPOSITS IN THE SOUTHERN PART OF THE PANAGUYRISHTE ORE DISTRICT, BULGARIA

Epithermal Cu-Au deposits hosted within volcanic rocks (Radka, Elshitsa, Krassen) are related to Late Cretaceous andesite-dacite volcanic terrain in the Panagyurishte ore district. The Cu-Au ores are linked by a similar mineralogy and differ by the ratio of tennantite, bornite, enargite and discrete trace minerals of Ga, Ge, In and Bi (e.g., roquesite, germanite, betekhtinite, renierite, vinciennite, aikinite). Bi-Se-Te and Ga-Ge-ln-Sn signature with pronounced Au-enrichment of the bornite rich ores is a characteristic feature underlying the increasing role of the fS2/f02 control during the transition from IS te HS environment. Formation of the epithermal Cu-Au deposits appears to have occurred during a single broad event of contemporaneous formation of epithermal and porphyry systems.The close connection between the volcano-plutonic structures facilitates the multistage and polycyclic character of their hydrothermal systems, the similar character of the epithermal ores and the mineral succession in Elshitsa, Radka and Krassen deposits. The ô^S ratios in the sulphide minerals range from -6.7 to 4.0, suggesting comparable magmatic sources for the epithermal mineralizing fluids and close link with porphyry environment.

Evolution of an intrusion-centered hydrothermal system; Far Southeast-Lepanto porphyry and epithermal Cu-Au deposits, Philippines

Evolution of an intrusion-centered hydrothermal system; Far Southeast-Lepanto porphyry and epithermal Cu-Au deposits, Philippines

Contemporaneous formation of adjacent porphyry and epithermal Cu-Au deposits over 300 ka in northern Luzon, Philippines

Research Article| April 01, 1995 Contemporaneous formation of adjacent porphyry and epithermal Cu-Au deposits over 300 ka in northern Luzon, Philippines Antonio Arribas, Jr; Antonio Arribas, Jr 1Geological Survey of Japan, Higashi 1-1-3, Tsukuba 305, Japan Search for other works by this author on: GSW Google Scholar Jeffrey W. Hedenquist; Jeffrey W. Hedenquist 1Geological Survey of Japan, Higashi 1-1-3, Tsukuba 305, Japan Search for other works by this author on: GSW Google Scholar Tetsumaru Itaya; Tetsumaru Itaya 2Okayama University of Science, Okayama 700, Japan Search for other works by this author on: GSW Google Scholar Toshinori Okada; Toshinori Okada 2Okayama University of Science, Okayama 700, Japan Search for other works by this author on: GSW Google Scholar Rogelio A. Concepción; Rogelio A. Concepción 3Lepanto Consolidated Mining Co., Makati, Manila, Philippines Search for other works by this author on: GSW Google Scholar Jose S. Garcia, Jr. Jose S. Garcia, Jr. 3Lepanto Consolidated Mining Co., Makati, Manila, Philippines Search for other works by this author on: GSW Google Scholar Geology (1995) 23 (4): 337–340. https://doi.org/10.1130/0091-7613(1995)023<0337:CFOAPA>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Antonio Arribas, Jeffrey W. Hedenquist, Tetsumaru Itaya, Toshinori Okada, Rogelio A. Concepción, Jose S. Garcia; Contemporaneous formation of adjacent porphyry and epithermal Cu-Au deposits over 300 ka in northern Luzon, Philippines. Geology 1995;; 23 (4): 337–340. doi: https://doi.org/10.1130/0091-7613(1995)023<0337:CFOAPA>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract There is commonly a close spatial relation between porphyry Cu (± Au) and high-sulfidation epithermal Cu-Au deposits throughout the world, although a genetic association has not been proven. Nowhere is this spatial association better seen than in northern Luzon, Philippines, where the Lepanto epithermal Cu-Au deposit overlies the Far Southeast (FSE) porphyry Cu-Au deposit, both world-class orebodies. Fresh rock and hydrothermal mineral separates yield K/Ar ages indicating that premineralization and postmineralization volcanism occurred at 2.2–1.8 Ma and 1.2–0.9 Ma, respectively, and that the hydrothermal system was active from ∼1.5 to ∼1.2 Ma. K/Ar ages of alunite from Lepanto have the same range as those of hydrothermal biotite and illite from the FSE deposit, indicating that both epithermal and porphyry mineralization formed from an evolving magmatic-hydrothermal system that was active for about 300 ka. This temporal relation strengthens the argument for a genetic link between these two styles of ore deposit, and has implications for exploration. Where one style of mineralization is found, there is potential for the other nearby. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.