Phyllic Alteration Research Articles

Magma evolution leading to veinlet-disseminated tungsten mineralization at the Muguayuan deposit: In-situ analysis of igneous minerals

Whole rock geochemistry combined with spatially resolved geochemistry of zircon, apatite, biotite and plagioclase allows us to uncover the magmatic processes leading to ore formation at the Muguayuan deposit. The Sanxianba granite, associated with the Muguayuan veinlet-disseminated scheelite deposit, is located in the middle of the Jiangnan Orogen. Whole rock Sr and Nd isotopes, and zircon Lu-Hf isotopes suggest it might originate from the Neoproterozoic Banxi group strata. The Rb element modeling shows that, after ~35% of partial melting, the Banxi group metasandstone can generate the primary Sanxianba melt with 164 ppm Rb and 21 ppm W. The intra-/intercrystal texture and compositions of zircon and plagioclase indicate that W and other elements such as HREE, Th, U, Nb, Ta, and P increase in the melt during fractional crystallization. The water content in the early Sanxianba magma, calculated through the plagioclase-hydrometer, is ~4.4 wt%, and its enrichment in the melt is reflected by the increasing water content in biotite with fractionation. F content in the early apatite is relatively high and invariable but further elevated in the late apatite. Chlorine, LREE and Na contents in the early apatite also present an enrichment trend. When H2O and Cl start to be saturated with the magma fractionation in the deep magma chamber, Cl-, Na-, and LREE-rich but W-poor fluid exsolves from the melt, resulting in the albitization and chloritization of feldspar and biotite phenocrysts, respectively. The subsequent decrease of Cl, Na2O and La2O3 in the late apatite record this first fluid exsolution. Fluorine, P, H2O and W continue to enrich in the evolved melt with fractionation after the Cl-rich fluid exsolution. These fluxing components reach oversaturation during the shallow-ward emplacement of the magma, forming the F-, P- and W-rich fluids. The apex of the intrusion cools and forms a solid barrier, which prevents the escape of fluids. The exsolved fluids from the underlying magma continuously supply upward and react with the apex along fractures, resulting in greisenization and phyllic alteration. During alteration, Ca is released from calcium-rich plagioclase and combines with tungsten in the fluids to form scheelite mineralization. Magma evolution leading to the tungsten mineralization may be also the general scenarios in the other granite-related veinlet-disseminated scheelite deposits.

Potential for Volcanogenic Massive Sulfide Mineralization at the A6 Anomaly, North-West British Columbia, Canada: Stratigraphy, Lithogeochemistry, and Alteration Mineralogy and Chemistry

The Middle Jurassic A6 Anomaly is located 30 km southeast of Eskay Creek, north-central British Columbia and consists of thick, altered felsic igneous rocks overlain by a mafic volcano-sedimentary package. Lithogeochemistry on igneous rocks, X-ray diffraction on altered felsic units, and electron probe microanalysis and secondary ion mass spectrometry on illite and quartz were applied to explore the volcanogenic massive sulfide (VMS) potential, characterize alteration, and determine fluid conditions at the A6 Anomaly. Lithogeochemistry revealed calc-alkaline rhyodacite to trachyte of predominantly FII type, tholeiitic basalts with Nb/Yb < 1.6 (i.e., Group A), and transitional to calc-alkaline basalts and andesites with Nb/Yb > 2.2 (i.e., Group B). The felsic units showed weakly to moderately phyllic alteration (quartz–illite with minor orthoclase and trace chlorite–pyrite–calcite–barite–rutile). Illite ranged in composition from illite/smectite (K = 0.5–0.69 apfu) to almost endmember illite (K = 0.69–0.8 apfu), and formed from feldspar destruction by mildly acidic, relatively low temperature, oxidized hydrothermal fluids. The average δ18O composition was 10.7 ± 3.0‰ and 13.4 ± 1.3‰ relative to Vienna Standard Mean Ocean Water for illite and quartz, respectively. Geothermometry involving illite composition and oxygen isotope composition on illite and quartz yielded average fluid temperatures of predominantly 200–250 °C. Lithogeochemical results showed that the A6 Anomaly occurred in a late-Early to Middle Jurassic evolving back-arc basin, further east then previously recognized and in which transitional to calc-alkaline units formed by crustal assimilation to enriched Mid-Ocean Ridge Basalt (EMORB) (i.e., felsic units, Group B), followed by thinning of the crust resulting in tholeiitic normalized MORB basalts (i.e., Group A) with a minor crustal component. The alteration assemblage is representative of distal footwall alteration, and metal transport in this zone was limited despite favorable temperature, pH, and redox state, indicating a metal depleted source (i.e., felsic units).

Geochemistry of Rhenium and Other Trace Elements in Molybdenite, Sar Cheshmeh Porphyry Cu‐Mo Deposit, Iran

AbstractLA‐ICP‐MS analysis of molybdenite from the Sar Cheshmeh porphyry Cu‐Mo deposit (PCD), Iran, shows moderate concentration of Re (average ∼207 ppm) and low concentration of chalcogenides (average of Pb + Te + Bi, ∼31 ppm) as well as metalloids (average of As + Sb + Ge, ∼4.5 ppm). The early‐formed quartz–molybdenites associated with potassic alteration are characterized by moderately low concentration of Re (21–215 ppm with an average of 83 ppm), whereas the transitional quartz–molybdenite veins related to the sericitic stage of mineralization contain more Re (62–465 ppm, with an average of 207 ppm). In contrast, the late‐formed quartz–molybdenite veins associated with phyllic alteration show the highest concentration of Re (up to 1273 ppm with an average of 395 ppm). Gradual increase in Re content of molybdenites deposited throughout the evolution of the porphyry system is probably related to elevated ƒO2 and acidic conditions of the ore fluids governing the transitional and late stage of mineralization, when compared to the moderately low ƒO2 and basic conditions of the ore fluids precipitating the low‐Re molybdenites associated with potassic alteration. The mixed mantle/crustal source of the ore‐related magma and its fractionated composition in Sar Cheshmeh are consistent with magmatic conditions for the formation of Mo‐rich and Re‐poor PCDs in the world.

The superlarge Tyrnyauz skarn W-Mo and stockwork Mo(-W) to Au(-Mo, W, Bi, Te) deposit in the Northern Caucasus, Russia: Geology, geochemistry, mineralization, and fluid inclusion characteristics

The Tyrnyauz deposit (>850 Kt WO3, >220 Kt Mo, ~60 t Au, with additional ~140 t Au at a satellite deposit) is the largest W skarn deposit in Russia and the FSU. It comprises large mineralized (molydoscheelite) skarn zones of the intermediate-redox type, followed by overprinting and much wider systems of post-skarn quartz-garnet-pyroxene, quartz-garnet, quartz-wollastonite, quartz-feldspar and quartz veins with molybdenite and minor scheelite. Younger quartz-molybdenite (±scheelite) stockworks in zones of propylitic (quartz-amphibole-chlorite) alteration are typically more distal, and so are the complex W-Au-Bi-As-Te-Sb quartz-sulfide stockworks occurring in zones of phyllic (carbonate-phyllic) alteration. The mineralization appears to be associated with at least two separate igneous suites, possibly a Late Paleozoic low-K “trondhjemite” plutonic suite (quartz diorite, tonalite-granodiorite, and plagiogranite) followed by the formation of mineralized skarns, and a Neogene moderate- to high-K, plutonic to subvolcanic suite (leucocratic granite, biotite granite, rhyolite to rhyolite-dacite, vitroandesite, to trachyandesite-trachybasalt). The Neogene intrusions exhibit a reverse (toward less silicic rocks) overall differentiation trend, cut skarns, and alternate with the post-skarn hydrothermal stages.Prograde calcic skarn was formed from a carbonic-free aqueous, low-salinity (~3 wt% NaCleq.), high-pressure (~1.3 kbar), hot fluid, which could be sourced from crystallizing magma. As the magma degassing progressed, a Na-K-Ca-chloride, high salinity (~50 wt% NaCleq.), but still high-pressure (~1.4 kbar) fluid formed mineralized (with molybdoscheelite) retrograde skarn. After the Neogene leucocratic granite emplacement, the molybdenite (±scheelite) stockworks were formed from a boiling aqueous-carbonic fluid at decreasing (from 420 to 390 °C to 370–350 °C) temperatures and much lower (~0.5 kbar) pressures. A short (?) episode of the late quartz-pyroxene-fluorite-calcite veins with scheelite occurred after the rhyolite emplacement, and a corresponding influx of boiling high-temperature (600–650 °C), Na-K-Ca-chloride, high-salinity (>50 wt% NaCleq.), methane-rich fluid interrupted the generally low- to moderate-salinity carbonic-aqueous fluid supply. A moderate- to low-salinity (22 to 4–9 wt% NaCleq.), aqueous Na-K-chloride fluids formed the late Cu-Zn sulfide to W-Au-Bi-As-Te-Sb mineralization. The superposition of different fertile igneous suites and related mineralization styles may have been the key reason for the giant metal endowment.

The Glafirinskoe and related skarn Cu-Au-W-Mo deposits in the Northern Altai, SW Siberia, Russia: Geology, igneous geochemistry, zircon U-Pb geochronology, mineralization, and fluid inclusion characteristics

The Glafirinskoe and related skarn Cu-Au (+Mo, W) deposits represent an Early Paleozoic (Late Cambrian to very early Ordovician) mineralization in the Altaid Belt, also known as the Central Asian Orogenic Belt. They are associated with multiphase plutons of high-K calc-alkaline to shoshonitic rocks that are related to a low-degree partial melting of metasomatically-enriched upper mantle, followed by amphibole fractionation in a deep (lower crustal ?) magma chamber and then by magma fractionation and emplacement at shallower crustal levels. Isotopic U-Pb zircon dating of the igneous rocks yields early Ordovician (ca. 480–478 Ma and 483 Ma) age. These rocks were emplaced in a continental magmatic arc after the Late Cambrian collision, in a post-collisional setting involving the stall and break-off of the subducting slab during the Late Cambrian to Early Ordovician.The deposits comprise prograde and retrograde skarns that are characterized by abundant andradite-rich garnet, which defines their oxidized type. Wider zones of potassic (quartz-K-feldspar) and calc-potassic (quartz-K-feldspar-calcite-garnet) alteration occur in the igneous rocks, with their further overprint by propylitic (with abundant scapolite) and phyllic (carbonate-phyllic) alteration. All these alteration assemblages bear abundant chalcopyrite and minor bornite. Phyllic alteration assemblages also contain various As, Sb, Pb, Zn, Co, Ni sulfides and sulfosalts, tellurides, Bi minerals, and native Au. Scheelite and/or molybdenite are locally present in some mineralized zones. The Cu-Au-Mo(-W) mineralization occurs as skarn orebodies that are spatially associated with porphyry-style alteration assemblages reflecting the high exploration potential for additional, but concealed, skarn-porphyry Cu-Au-Mo deposits in the vicinity.The retrograde skarn and potassic (calc-potassic) alteration assemblages were formed from high temperature (570–580 °C), high salinity, aqueous chloride magmatic-hydrothermal fluid, with its boiling and phase separation indicating hydrostatic conditions at a relatively deep (~6 km) skarn-porphyry environment. Propylitic alteration assemblages were formed at lower temperatures (~380–420 °C) from a Ca-Na-chloride, low salinity (~8 wt% NaCl-eq.) magmatic-hydrothermal fluid. Fluid inclusions in minerals from phyllic alteration assemblages indicate the influx of a CO2-rich fluid at about 270–290 °C and 1400 ± 50 bars and subsequent mixing with more saline (20 wt% NaCl-eq.) and cooler (~240 °C) hydrothermal fluids.

Porphyry Cu mineralization processes of Xinqiao deposit, Tongling ore district: Constraints from the geochronology and geochemistry of zircon, apatite, and rutile

Xinqiao is a large ore deposit that is well known for its stratabound massive sulfide and skarn ores. Recently, deep drilling has shown that Xinqiao also has typical porphyry mineralization and alteration features. The Cu grade is 0.3–0.6% and occurs as quartz-pyrite-chalcopyrite in potassic and phyllic alteration zones. The characteristics and genetic processes of the porphyry mineralization at Xinqiao have not previously been reported.Three intrusion types are recognized; pyroxene diorite, quartz diorite and quartz monzodiorite porphyry; Cu mineralization is associated with the quartz diorite and quartz monzodiorite porphyry. Zircon U-Pb dating shows that the three intrusions were all emplaced at about 140 Ma. Zircons from the quartz diorite and quartz monzodiorite porphyry show higher Ce4+/Ce3+ and Eu/Eu* (>0.5), 10,000(Eu/Eu*)/Y (>5), and (Ce/Nd)/Y (>0.01), than the pyroxene diorite, and apatites from the mineralized intrusions have slightly higher SO3 (average 0.40) contents than ones from the pyroxene diorite (average 0.33). These results indicate that the fertile magmas were more oxidized, hydrous, and S-rich than the barren pyroxene diorite, consistent with their association with porphyry Cu mineralization. U-Pb dating of hydrothermal rutile from the porphyry mineralization and garnet from the skarn ore both yield ages of about 140 Ma, suggesting that the porphyry and skarn mineralization belong to same system. The geochemistry of hydrothermal rutile and apatite in the porphyry mineralization zone also indicates that Xinqiao ores were produced from a S-rich magmatic-hydrothermal fluid system. Our results highlight huge porphyry Cu mineralization potential beneath stratabound and skarn deposits in the Middle-Lower Yangtze River metallogenic belt.

Genesis and fluid evolution of the Yuku porphyry Mo deposit, East Qinling orogen, China

The Yuku is a large porphyry Mo deposit (1.5 Mt at 0.12% Mo) in the Luanchuan ore district of the East Qinling orogen, central China. The economic Mo ore bodies occur as veins, veinlets, and disseminated ore and are developed mainly within the late Mesozoic Yuku porphyritic granite. Molybdenum mineralization is generally associated with potassic and phyllic alteration. Hydrothermal processes in the Yuku deposit are divided into four stages: (I) a quartz–K‐feldspar–biotite ± pyrite stage, (II) a quartz–molybdenite ± pyrite ± K‐feldspar ± sericite stage, (III) a quartz–polymetallic sulphide stage, and (IV) a calcite ± quartz ± fluorite ± pyrite stage. The fluid evolution during these hydrothermal stages was constrained through systematic investigation of fluid inclusions (FIs) and H−O isotopes. Four types of primary or pseudosecondary FIs were recognized in hydrothermal quartz and calcite: two‐phase liquid‐rich inclusions (L‐type), two‐phase vapour‐rich inclusions (V‐type), halite‐bearing (hypersaline) inclusions (H‐type), and three‐phase CO2‐bearing inclusions (C‐type). FIs within Stages I–IV have homogenization temperatures of 375 to >550, 297–400, 198–298, and 149–188°C, with salinities of 0.53–13.18, 0.35–40.23, 5.11–11.81, and 5.71–9.73 wt% NaCl equiv., respectively. In Stage I, coexisting vapour‐rich (V‐type) and liquid‐rich (L‐type) FIs have similar homogenization temperatures (488 to >550°C) and distinct salinities, indicating fluid boiling during the formation of quartz–K‐feldspar–biotite veins at a pressure of 550–700 bar and a lithostatic depth of 2.3–2.8 km. In Stage II, FIs in quartz were also trapped under boiling conditions, as evidenced by coexisting hypersaline H‐type (34.13–40.23 wt% NaCl equiv.) and low‐salinity V‐type (0.35–2.24 wt% NaCl equiv.) inclusions, which formed at temperatures of 309–361°C and hydrostatic depths of 1.0–2.0 km, equivalent to pressures of 100–200 bar. During Stage III, the ore‐forming fluids were cooler (198–298°C) and more dilute (5.11–11.81 wt% NaCl equiv.) due to the involvement of meteoric water, with minimum trapping pressures estimated at <100–150 bar, corresponding to a hydrostatic depth of <1.0 km. In Stage IV, temperatures decreased further to 149–188°C, with lower salinities (5.71–9.73 wt% NaCl equiv.), indicating a post‐ore fluid stage. These data suggest that the mineralizing fluids forming the Yuku Mo deposit changed from early moderate‐ to low‐salinity CO2‐rich fluids in the H2O–NaCl–CO2 system that formed at high temperature and pressure, to late H2O–NaCl low‐salinity fluids that formed at low temperature and pressure. H−O isotopic compositions indicate that the mineralizing fluids had a dominantly magmatic signature but were diluted by meteoric waters. Combining our integrated analysis of the fluid evolution and deposit geology, we propose that fluid boiling and fluid–rock interaction, including intensive potassic alteration, changed the salinity and triggered CO2 escape, leading to a decrease in fO2 and an increase in the acidity of the ore‐forming fluids, which ultimately controlled the deposition of molybdenite in the Yuku Mo deposit.

Sulphide geochemistry of the superlarge Tiegelongnan Cu (Au) deposit in Tibet, China: Implication for the mineralization process

The Tiegelongnan deposit in central Tibet presents a typical high‐sulfidation porphyry Cu (Au) mineralization system. Optical microscopy, scanning electron microscopy–energy dispersive spectrometry (SEM–EDS), and laser ablation inductively coupled plasma mass spectrometry (LA–ICPMS) were used to understand the mineralization processes. The advanced argillic alteration zone directly contacts the phyllic alteration zone, which is linked to the Early Cretaceous porphyritic intrusions. In this study, the spatial distributions of chief copper sulphides with variable gangue minerals are illustrated. The deep inner phyllic zone typically produced an end‐member assemblage of chalcopyrite–sericite (±dolomite), which trended upwards to produce more bornite–sericite (±siderite ± magnesite), and subsequently, the advanced argillic alteration yielded the representative end‐member assemblage of tennantite–alunite ± (aluminium‐phosphate‐sulphate, namely, APS, ±kaolinite). In the phyllic–advanced argillic transition zone, intensive covellite precipitation with the widespread occurrence of sericite–kaolinite (±APS) assemblage is proposed as an important feature in this study, which is mainly produced on the southwest side of the ore‐body centre. The typical co‐occurrence of chalcopyrite with dolomite at great depths indicates that it was related to a gently acidic fluid containing CO2; however, the pervasive tennantite–alunite association present at shallower levels suggests that fluids with SO2 were mainly involved and produced stronger acidic conditions. Acidic fluids are demonstrated to highly accelerate water‐rock alteration. Trace element analyses of the copper sulphides reflect that Au concentrations of bornite and tennantite are higher than chalcopyrite and covellite and present small signal variations. Moreover, comparing the presence of micron‐sized Au‐telluride in tennantite under advanced argillic alteration with the nano‐sized native gold in bornite resulting from phyllic alteration suggests that to a certain extent, Au enrichment is affected by the shift of more Te contents in fluid towards shallower levels, which could promote Au precipitation. Additionally, the Se contents of the selected samples were typically concentrated in chalcopyrite, bornite, and covellite, which yielded contents an order of magnitude greater than those in tennantite, indicating the intimate hydrothermal origin of the first three sulphides. Overall, the sulphide–gangue mineral associations and their copper sulphide geochemistry indicate that the hypogene–chalcopyrite of low Au contents from the phyllic zone closely corresponds to the action of gentle acidic fluids with CO2, while more acidic fluids with SO2 are involved in the formation of supergene tennantite with relatively high values of Au and Te in the advanced argillic alteration.

Evolution of the gold (copper) mineralization in the porphyry stock and the related skarn zones and epithermal veins in the Astarghan area, NW Iran: Evidence from fluid inclusion, mineral chemistry and sulfur isotope analyses

The Astarghan area in northwest Iran (~50 km north of Tabriz) represents an excellent example of coexisting and associated skarn, porphyry and epithermal mineralizations of copper and gold. This contribution aims to study the geology, alteration and mineralization in these deposits, as well as the occurrence of gold and its host minerals, and present the physico-chemical characteristics of ore-forming fluids and the sulfur origin, in order to get a better understanding of development and evolution of these mineralizations. The Astarghan porphyry stock (Oligo–Miocene) intruded the upper Cretaceous flysch-type sedimentary sequence (calcareous sandstone and limestone with intercalations of siltstone, shale and marl) and brought about metamorphism and metasomatism along the contact. The Cu–Au mineralization in the Astarghan area occurred mainly in three forms: (1) skarn patches along the contact (Zone A), (2) stockwork-type and disseminated porphyry mineralization within the potassic (at Kaghdara and Boiokwari areas) and phyllic (at Sildirimdara area) alteration zones (Zone B), and (3) native gold-bearing low-sulfidation epithermal veins within the argillic alteration zone at Nowrozkala area (Zone C). The micro-thermometric studies on the porphyry-type Kaghdara potassic alteration zone showed that homogenization temperatures for liquid-rich and vapor-rich 2-phase, as well as halite-bearing multiphase inclusions range about 160–420 °C, 220–460 °C, and 320–580 °C, respectively. Salinities of the 2-phase and multiphase inclusions have ranges of 5–25 and 40–70 wt% NaCleq., respectively. However, fluid inclusions present in the epithermal veins of Nowrozkala are mainly liquid-rich 2-phase, and their homogenization temperature and salinity values lie within the ranges of 118–325 °C and 0.6–7.4 wt% NaCleq., respectively. The approximate estimated depth of the sulfide and gold mineralization in the porphyry system ranges from 1.6 to 2.5 km, and in the epithermal system is < 0.9 km. The sulfur isotopic analysis of pyrite from the porphyry and epithermal mineralizations in the potassic alteration zone at Kaghdara and argillic alteration zone at Nowrozkala indicate that the δ34S values (–0.1 to –0.3 and –0.5 to –1.1‰, respectively) are close to the range of magmatic sources. Finally, electron probe micro-analyses indicate that besides independent particles of 50–200 μm in the epithermal veins, gold is mainly hosted by tetrahedrite within the porphyry-related phyllic alteration zone, but especially stibnite within the epithermal veins; these minerals, as well as epithermal polyhedral pyrites contain native gold inclusions.

Integration of concentration-area fractal model and relative absorption band depth method for mapping hydrothermal alterations using ASTER data

Those image processing methods which use both spatial and spectral properties of remotely sensed images often increase accuracy of image classification. In this study, the concentration-area (C-A) fractal model and Relative absorption Band Depth (RBD) were applied to map hydrothermal alteration zones using ASTER data covering the northern part of Rabor area, Iran. Based on the field observations and spectral analysis of rock samples, three types of RBD were calculated and applied to map hydrothermal altered rocks (RBD6 for phyllic, RBD8 for propylitic, and RBD5 for argillic). A log-log plot of area-digital number value for RBD images showed that there are three populations in each image. Representation of these populations revealed that the third population of each RBD has enhanced separation of alteration zones. To verify the results, a spectral library of ground rock samples was built and used to compare with 10 spectra derived from each image. Spectral Angle Mapping, Spectral Feature Fitting, and Binary Encoding were applied to assess the matching of image spectra with the spectral library spectra. Results confirmed that third population of RBD6 and RBD8 contain pure pixels of phyllic and propylitic alterations, respectively whereas there are some interference between argillic and phyllic alterations in RBD5.

Genesis of the Gongpoquan porphyry Cu deposit in Beishan Orogen, NW China: Evidence from geochronology, fluid inclusions, H–O–S isotopes, and sulfides trace element

• The Gongpoquan porphyry Cu deposit is located in the Beishan Orogen, NW China. • Muscovite 40 Ar/ 39 Ar dating yielded Early Devonian (404.0 ± 2.2 Ma) mineralization age. • Ore fluid was magmatic-sourced with more meteoric water input toward late stage. • Fluid mixing and boiling were likely effective mechanism for Cu ore precipitation. • The Devonian mineralization was likely related to Paleo-Tianshan Ocean sbuduction. The Gongpoquan is a representative porphyry Cu deposit in the Beishan Orogen, which is located between the Tarim–North China Craton and South Mongolia. The mineralization is associated with dacite porphyry and granodiorite porphyry, and occurs as veins/veinlets, and disseminations. The mineralization can be divided into three stages: (I) quartz–sericite/muscovite–K-feldspar ± chalcopyrite/bornite veins associated with phyllic alteration, (II) quartz–K-feldspar–chalcopyrite/bornite/pyrite veins/veinlets associated with propylitic alteration, and (III) quartz–calcite ± pyrite ± epidote veins. The mineralizing fluids are characterized by intermediate-low temperatures (peak at 210 to 220 °C), intermediate-low salinities (peak at 1.5 to 5.5 wt% NaCl eqv.), and belong to a H 2 O–NaCl–CO 2 ± CH 4 ± N 2 system. Oxygen and hydrogen isotope data indicate that stage I and II fluids were dominantly magmatic-sourced, with increasing meteoric water input toward stage III. Stage I and IIa-b chalcopyrite, bornite, and sphalerite have in situ δ 34 S values of −9.0 to −2.4‰, indicating a magmatic sulfur origin. The chalcopyrite has largely similar contents of Ti, Ge, As, Sn, Sb, and Se across stage I to III, and the contents are higher than those of bornite and sphalerite. This indicates that sulfide formation are controlled by intermediate-low temperatures with no mineral textural modification or chemical remobilization throughout the mineralization. Muscovite 40 Ar/ 39 Ar dating of stage I vein in the granodiorite porphyry ore host yielded an Early Devonian age of 404.0 ± 2.2 Ma (MSWD = 0.40), indicative of the close temporal with the Gongpoquan arc granitoids formed during the Paleo-Tianshan Ocean subduction.

Characterization of hydrothermal events associated with the occurrence of copper-molybdenum minerals in the El Chucho creek at Cerrito, Valle del Cauca-Colombia

At El Chucho creek, located to the west of the Valle del Cauca department in Colombia, some hydrothermal alterations affecting the Buga Batholith rocks and dykes of porphyritic quartz-dioritic and tonalitic composition were identified. These lithological units host mineral occurrences of pyrite, chalcopyrite, and molybdenite that occur disseminated in the rocks or associated with quartz veinlets. The hydrothermal alterations identified were phyllic, propylitic, and, in minor quantity, potassic. The two firsts alterations’ distribution is related to structures and pervasive, whereas the last one seems restricted to contact zones of porphyritic dykes on tonalite. Microthermometric data were acquired i) on quartz veinlets of 1 cm thick over a phyllic alteration zone, and ii) on quartz veinlet of 1 cm thick with chalcopyrite ± molybdenite and copper silicates, both veinlets cutting the phaneritic tonalite. Those data suggest that the mineralizing fluids have an aqueous-saline chemical system and were trapped under low volatile content. The microthermal data allowed authors to identify two mineralizing events. One of them of higher temperature, with homogenization temperatures between 275°C-480°C; as the second event is characterized by lower homogenization temperatures that range from 100°C to 139°C.

Significance of chlorite hyperspectral and geochemical characteristics in exploration: A case study of the giant Qulong porphyry Cu-Mo deposit in collisional orogen, Southern Tibet

Abstract The genetic mechanism and exploration model for porphyry deposits in subduction zones has been comprehensively and systematically investigated; in contrast, our understanding for porphyry mineralization in collisional orogeny is limited. Qulong porphyry Cu-Mo deposit, a typical porphyry Cu deposit (PCD) developed in the collisional setting, was chosen as the subject of this study. The study is mainly focused on interpretation of short-wave infrared (SWIR) spectroscopy combined with mineral geochemistry of chlorite from Qulong deposit to guide exploration in future. Hydrothermal alteration in Qulong mineralization system can be divided into three zones, which are the inner potassic alteration zone, the outside propylitic alteration zone and phyllic alteration. Phyllic alteration can be intensively superimposed on the early potassic and prophylitic alteration zones. Chlorite is widely distributed in both of the propylitic and phyllic zones. Four types of chlorite were observed in Qulong deposit, including three stages of vein-related chlorite (Chl-I, Chl-II, Chl-III) and one type of disseminated chlorite (Chl-D). Mineral assemblage of Chl-I stage includes chlorite–anhydrite–pyrite. Minerals in Chl-II stage consist of chlorite–epidote–pyrite–chalcopyrite. Mineral assemblage of Chl-III stage is composed of chlorite–sericite–quartz–chalcopyrite, which is later than both Chl-I and Chl-II. Chl-D was developed mainly by alteration of primary biotite phenocryst. Chl-I, Chl-II and Chl-D were formed along with the propylitic alteration; however, Chl-III is from the phyllic alteration. Chl-II and Chl-III are both closely related with Cu mineralization. The major element compositions of chlorite show a regular variation of Mg# with fluid evolution. Transition from shorter wavelength chlorite (Fe feature around 2250 nm) to longer wavelength goes with the decrease of Mg#, except for Chl-D. In summary, chlorite associated with Cu mineralization in Qulong is mainly occurred in veins and has low Mg# ratios and longer wavelength. Such chlorite is the indicator for Cu mineralization and should be the target in future exploration. In addition to chlorite, sericite in Qulong also shows systematic change from early-stage phengite to late-stage muscovite. In combination of mineral geochemistry and thermodynamic modelling, we suggest that ore-forming fluid gradually evolved to be more acidic with higher silica activity over time.

Fluid-rock reactions of the Triassic Taiyangshan porphyry Cu-Mo deposit (West Qinling, China) constrained by QEMSCAN and iron isotope

The multiphase hydrothermal superposition phenomena on porphyry deposits, the mineral complexity and characteristics of the alteration-associated assemblages limit a further determination for the magmatic-hydrothermal evolution in porphyry deposits. The Taiyangshan porphyry Cu-Mo deposit in the northern margin of the Triassic West Qinling Orogenic Belt exhibits a multi-stage, alteration-related quartz sulfide veins that recorded element migration processes during fluid-rock reactions. In this study, we investigated hydrothermal veins in the Taiyangshan deposit focusing on vein compositions and structures as well as the evolution of ore formation, using quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN) and iron isotope analyses. The formation of the early K-feldspar-biotite-quartz-magnetite-apatite veins is closely associated with the early potassic alteration, and during the fluid-rock reactions, Si, S, Fe, and K migrated in, while Mg, Ca and Na migrated out. K-feldspar-chlorite-pyrite-chalcopyrite-quartz veins correlated to the propylitic alteration, dominantly caused the migration of Si, Fe, S, Ca Mg, Al and K. Quartz-sericite-pyrite veins corresponding to the phyllic alteration processes that occurred in a relatively late stage, during the fluid-rock reactions of which, Si, Fe, S, and K migrated into the system. The δ56Fe whole-rock values of altered porphyries range from 0.08‰ to 0.31‰, and δ56Fe values of pyrite from quartz veins range from 0.30‰ to 0.57‰. Iron isotope compositions of both pyrites of the ore-bearing wall rocks and the quartz-sulfide veins of the Taiyangshan Cu-Mo deposit are generally uniform, which indicate the same source origin between the ore-bearing porphyry and the iron isotope compositions of the metal sulfide in the quartz veins, and additionally highlight that the ore-forming source is closely related to the ore-bearing porphyry. Magnetite precipitated in the early stage of potassic alteration, resulting in the enrichment of the light Fe isotope in the early fluids. Crystallization and precipitation of pyrite mainly occurred during processes of propylitic and phyllic alteration, leading to an absorption of the light Fe isotope, and elsewhere, an enrichment of the heavy Fe isotope in the fluids. During the fluid-rock reactions of propylitic and phyllic alteration, a large amount of S migrated into the veins, thereby promoting the fractionation of Fe isotope. Moreover, the development of the ore-forming fluids enriched with heavy Fe isotope from early potassic- to late phyllic alteration, are indicative of isotopic progressions from the early lithostatic pressure to the late hydrostatic pressure. Our research on the Taiyangshan Cu-Mo porphyry deposit helps to explain the evolutionary processes of the magmatic–hydrothermal system, and improves our understanding of the porphyry metallogenic evolution model.

Petrology, Geochemistry, and Sr-Nd-S Isotopic Compositions of the Ore-Hosting Biotite Monzodiorite in the Luanjiahe Gold Deposit, Jiaodong Peninsula, China

The Jiaodong Peninsula is one of the most important Au ore provinces in China. There is an ongoing debate on the correlation between ore formation and magmatism in this province, because few intrusive rocks exhibit a clear association with ore deposits. A mineralized biotite monzodiorite (BM) stock, with disseminated ore, pervasive phyllic alteration, and no deformation, was found in a borehole in the footwall of the Zhaoping fault within the Luanjiahe Au deposit, which may shed light on this debate. The biotite monzodiorite contains explosion breccias, miarolitic cavities, skeletal and dendritic quartz, and late-stage evolved aplite dikes, and the in-situ δ34S values of the disseminated pyrite which is associated with Au mineralization are -1.7‰ to 7.3‰ (mean=3.5‰), indicative of a magmatic-hydrothermal system. These findings, combined with the reported age of 123 Ma, show that the intrusion has close spatial, temporal, and geochemical relationships with Au mineralization in the area. The biotite monzodiorite is metaluminous, high-K calc-alkaline and shoshonitic, with enrichment in light rare earth elements (REEs) and large-ion lithophile elements (LILEs), depletion in high-field-strength elements (HFSEs), and enriched Sr-Nd isotopic compositions. The intrusion may be the product of partial melting of enriched lithospheric mantle with a small lower crustal component. The hydrous, Au-bearing, enriched mantle source, and the strongly oxidized magma that was generated, created favorable conditions for Au mineralization.

Hydrothermal evolution and ore genesis of the Jiamante Au deposit in Western Tianshan, Xinjiang, China: Evidence from the geology, fluid inclusions, and C–H–O–S–Pb isotopes

The Jiamante Au deposit is one of the important deposits in the Axi ore cluster of the Western Tianshan, Xinjiang. The orebodies occurring mainly as quartz‐sulphide veins are hosted in Late Devonian volcanoclastic rocks and granitic porphyries, and structurally controlled by a group of NNW‐ and NNE‐ trending extensional faults and volcanic breccias. Primary metallic minerals are chalcopyrite, galena, pyrite, sphalerite, and native gold, with minor amounts of bismuthinite and bismuth. Nonmetallic minerals are dominated by quartz, sericite, chlorite, and calcite. Medium to low temperature hydrothermal alterations are well developed and characterized by silicification, beresitization, phyllic alteration, and chloritization. Two hydrothermal stages were identified: (a) the main‐ore quartz‐sulphide stage; and (b) the post‐ore quartz‐calcite stage. Microthermometric measurements indicate that the primary biphase liquid‐rich aqueous fluid inclusions within quartz of the main‐ore stage homogenize at temperatures (Th) of 176 to 251°C and have salinities of 2.1 to 7.4 wt% NaCleqv. A lower range of homogenization temperatures (169 to 212°C) and salinities (1.6 to 5.2 wt% NaCleqv) were obtained in calcite of the post‐ore stage. The fluid characteristics of moderate to low temperatures and salinities imply that the ore‐forming process occurred in an epithermal environment. In addition, there is a positive relationship between Th and salinities consistent with the fluid mixing trend. Together with H–O isotopic data (δDH2O = −118 to −97‰ and δ18OH2O = −5.5 to −1.6‰) and fluid characteristics, it is suggested that the ore‐forming fluids were a mixture of magmatic and meteoric waters. The δ13C values for CO2 in the hydrothermal fluids range from −3.2 to −2.7‰, and the sulphides have δ34S values of −5.2 to 2.9‰ with relatively uniform Pb isotopic compositions (206Pb/204Pb = 18.228 to 18.287, 207Pb/204Pb = 15.574 to 15.617, and 208Pb/204Pb = 38.151 to 38.251), indicating that the ore‐forming materials were magmatic sources that were derived directly from magmatic fluids and/or leached from volcanic‐subvolcanic rocks by hydrothermal fluids. Combined with the evidence from the mineralization and alteration, fluid inclusions, and C–H–O–S–Pb isotopes suggest that the Jiamante deposit is an intermediate‐sulphidation epithermal Au deposit. A combination of fluid mixing and fluid–rock interactions is inferred as the important factors causing ore deposition. According to the close spatial and temporal relationship between intermediate‐epithermal deposits and porphyry deposits, it is further suggested that porphyry‐type mineralization should have a good potential at the deep sites of the Jiamante deposit and its vicinity.

Hydrothermal alteration in Eshtehard volcanoes, Iran: Constraints from trace elements redistribution and stable isotope geochemistry

We use the mineralogy, trace element compositions and elemental mass balance of volcanic materials collected from propylitic, potassic and phyllic alteration facies in the Eshtehard area of Iran to document the nature and effects of hydrothermal alteration. Incompatible element abundances in hydrothermally–altered samples show transformations that include: (i) depletion of alkalis and alkaline earth elements (i.e., Ba, Sr), (ii) variable behavior of first series transition elements (depletion in Cr, Co and Ni; enrichment in Zn and Cu), and (iii) depletion of HREE, Hf and Th relative to U and LREE. In detail, potassic (associated with a major addition of Cu) and phyllic zones are characterized by enrichment of SiO2 and MgO whereas propylitization depleted SiO2 and MnO, enriched MgO and Fe2O3, and increased LOI. Whole rock geochemistry along hydrothermal facies revealed consistent negative Ce and Eu anomalies, indicating that reducing conditions persisted during hydrothermal processes. Substantial changes in isovalent elements ratios (i.e., K/Ba, K/Rb, Y/Ho, Sr/Eu, Zr/Hf and Eu/Eu*) along the facies illustrate non–charge and radius control behavior are construed as lanthanide tetrad–effect phenomena. The co–occurrence of zigzag patterns (i.e., M and W–shapes) is evidence for partial or incomplete tetrad effect reaction between REE3+ and F-and Cl-rich fluids in hydrothermal systems. Low T4 tetrad–effect values overall suggest rock–fluid interaction involving rather low temperature hydrothermal solutions. Mass (ΔM) and volume (ΔV) were slightly depleted in the propylitic (−3.80% and −5.66%) potassic (−3.48% and −5.66%), and phyllic (−2.52% and −2.91%) zones with isocon slopes of 1.06, 1.06 and 1.03, respectively. We envisage a secondary phenomenon in open system conditions which accompanied fluid–rock interaction as the plausible cause of slight REE tetrad effect observed in the hydrothermally altered samples. Fluid inclusions studies yield homogenization temperatures of 275–596 °C and salinity ranging from 34 to 39 wt% NaCl equivalent suggesting boiling during mineralization in the Eshtehard area. The calculated δ18O and δD of the fluids range between 5.3 and 7.1 and −75 to −62 per mil, respectively. On this basis, we suggest that the ore-forming fluids had a magmatic source and underwent boiling and/or exchange with hydrous minerals.

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.

Genesis of the Xiaoyuzan epithermal Au deposit in the Yelimodun volcanic basin, Western Tianshan, China: Constraints from geology, geochronology, isotopes and mineralogical compositions

The Tulasu and Yelimodun volcanic basins are two important Au districts in the northwestern Chinese Western Tianshan. Two large Au deposits have been discovered in the Tulasu basin, whereas only small-sized Au deposits and prospects, including the Xiaoyuzan deposit, were found in the Yelimodun basin. The purpose of this study is to examine the genesis of the Xiaoyuzan deposit and its implications for further exploration through geological, geochronological, geochemical and mineralogical studies of the host rocks and ores. The orebodies are mineralized veins and veinlets and are structurally controlled by NW- and NNW-trending faults within the Lower Carboniferous Dahalajunshan Formation volcanic rocks (DF). Sulfides are abundant (10–20 vol%) in the ores and consist of pyrite, sphalerite, galena, chalcopyrite and minor tetrahedrite. Electron microprobe analysis (EMPA) indicates that pyrite and sphalerite are both auriferous. Three ore-forming and alteration stages were distinguished: (I) quartz-pyrite stage with silicification and propylitization, (II) quartz-polysulfide stage with silicification and phyllic alteration, and (III) quartz-carbonate stage with carbonatization.The mineralization age is constrained to 357–331 Ma by a LA-ICP-MS U-Pb age of 357.3 ± 4.0 Ma for zircon from the ore-hosting tuff and the unconformably overlying Lower Carboniferous Aqialehe Formation containing fossils of the Visean period. The zircons from the tuff have highly positive εHf(t) values ranging from 5.9 to 10.1, indicating a magma source of depleted mantle with limited crustal contribution. The values of δ18OH2O-VSMOW calculated from δ18Oquartz and δDH2O-VSMOW measured from fluid inclusions of stage II quartz range from −4.0‰ to −2.9‰ and −117‰ to −109‰, respectively. The values of δ13CCO2 calculated from δ13Ccal and δ18OH2O calculated from δ18Ocal range from −1.6‰ to −1.4‰ and −9.8‰ to −2.7‰, respectively. The in-situ δ34S values range from 2.6‰ to 3.7‰ for pyrite and 2.7‰ to 4.1‰ for sphalerite, respectively. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of pyrite vary from 18.196 to 18.253, 15.564 to 15.642, and 38.063 to 38.300, respectively, similar to those of ore-hosting DF and granites from the Tulasu-Yelimodun volcanic belt. The above geochemical characteristics suggest that the ore-forming fluids were mixtures of magmatic and meteoric waters, and the metals and sulfur may have been derived partly from magmatic fluids generated from the hidden causative intrusions and partly from the hosting volcanic rocks. These, together with high sulfide abundance and development of sulfide assemblages representing intermediate-sulfidation state, suggest that Xiaoyuzan is an intermediate-sulfidation epithermal Au deposit. Considering the limited erosion for the Au mineralization within the interior of Yelimodun basin and close spatio-temporal relationship between intermediate-sulfidation and porphyry mineralization, it is inferred that there may be concealed porphyry Cu-Au mineralization underneath the Xiaoyuzan deposit and its vicinity.

Mineralogy and geochemistry of rare earth elements in the Moyil Valley alteration zones, Meshkinshahr (northwest Iran)

Abstract Sabalan Mountain (northwest Iran) witnessed intense volcanic activity during the Cenozoic (Plio-Pleistocene). The result of this manifests itself in the conical geometry of the Sabalan stratovolcano and ahigh hydrothermal gradient around it, which can be detected by geological phenomena such as hot springs, smoke gases and steam outlet pores. The high hydrothermal slope and upward migration of hot water in this area have caused extensive alteration zones in the host rocks. A mineralogical study of alteration zones in thewells drilled in the Moyil Valley to the northwest of Sabalan Mountain has revealed the presence of phyllic, argillic, calcitic and propylitic alterations in volcanic rocks (trachyandesite) and alteration phyllic and propylitic ones in monzonite rocks. In chondrite-normalised rare-earth-element diagrams, trachyandesite rocks exhibit an HREEs enrichment when compared to MREEs and LREEs in propylitic and calcitic alteration zones. This result can be explained by the acidic nature of hydrothermal fluids containing complex ions such as (SO-2, Cl-). The (La/Yb)cn, (La/Sm)cn and (Tb/Yb)cn ratios for argillic, phyllic, propylitic and calcitic alteration zones have revealed that they are higher in fresh rocks compared to altered rocks, suggesting the enrichment of HREEs in comparison to LREEs and MREEs. The anomalies of Eu do not change remarkably in the argillic and propylitic alteration zones of trachyandesite rocks; apparently, alteration hadno effect on them. Such behaviour reflects the presence of gold cations in Eu+3 formed at temperatures below 250°C. Eu anomalies increased in propylitic alteration zones in monzonite rocks and calciticand phyllic alteration zones in trachyandesiterocks.