Rhyolite Porphyry Research Articles

Origin of Late Jurassichigh‐Kfelsic volcanic rocks and related Au mineralization in the Dongyang deposit, central‐eastern Fujian,SEChina, and its tectonic implications

The newly discovered Dongyang low‐sulphidation epithermal Au deposit is located in central‐eastern Fujian Province, coastal SE China. Ore bodies occur in Late Jurassic rhyolite porphyry, rhyolite, and dacitic crystal tuff lava. In this study, rhyolite and dacitic crystal tuff lava are dated to 151.9 ± 0.4 Ma and 158.3 ± 0.4 Ma, respectively, and belong to the second member of the Nanyuan Formation. They are high in K2O (6.91–3.81 wt%) and Na2O/K2O (0.55–0.02), strongly peraluminous (A/CNK = 2.11–1.67) and high‐K calc‐alkaline or shoshonitic. They contain low ∑REEs (248–125 ppm), are enriched in Rb, K, Au, and depleted in Ba, Sr, P, Zr, Hf, and have slightly negative Eu anomalies (δEu = 0.94–0.56), suggesting that they are weakly fractionated felsic volcanic rocks. The zirconεHf(t) values (−11.2 to −5.4; two‐stage model ages = 2,650–2,128 Ma) suggest that they were mainly derived from Palaeoproterozoic crust. Lead isotope compositions also imply a dominantly lower crustal source. Detailed geological characteristics and elemental and isotopic data suggest that the oxidizing and weakly fractionated nature of the Dongyang high‐K felsic magma may have played a key role in Au mineralization. Integrating new and published data on the tectonic evolution, we suggest that the Late Jurassic Au mineralization and its causative magmatism actually extended to the SE China coastal area. The Dongyang rhyolite and dacitic crystal tuff lava may have been generated from partial melting of the crust caused by underplating of mantle‐derived magmas in an extensional environment. Regional extension may have been related to the NW‐directed roll‐back of the Palaeo‐Pacific Plate beneath the South China Block.

Zircon U-Pb Dating of Magmatism and Mineralizing Hydrothermal Activity in the Variscan Karkonosze Massif and Its Eastern Metamorphic Cover (SW Poland)

SHRIMP (Sensitive high resolution ion microprobe) zircon U-Pb dating of the two main igneous rocks types in the Karkonosze Pluton, porphyritic and equigranular monzogranite, yield 206Pb/238U ages between 312.0 ± 2.9 and 306.9 ± 3.0 Ma. These coincide, within uncertainty, with the majority of previous dates from the pluton, which indicate development of the main magmatic processes between ca. 315 and 303 Ma. They also coincide with molybdenite and sulfide Re-Os ages from ore deposits developed during magmatic and pneumatolitic-hydrothermal (e.g., Szklarska Poręba Huta and Michałowice) or/and metasomatic and hydrothermal (e.g., Kowary, Czarnów and Miedzianka) processes forming Mo-W-Sn-Fe-Cu-As-REE-Y-Nb-Th-U mineralization. The 206Pb/238U zircon age of 300.7 ± 2.4 Ma from a rhyolite porphyry dyke (with disseminated base metal sulfide mineralization) in the Miedzianka Cu-(U) deposit coincides with the development of regional tectonic processes along the Intra-Sudetic Fault. Moreover, at the end-Carboniferous, transition from a collisional to within-plate tectonic setting in the central part of the European Variscides introduced volcanism in the Intra-Sudetic Basin. Together, these processes produced brecciation of older ore mineralization, as well as metal remobilization and deposition of younger medium- and low-temperature hydrothermal mineralization (mainly Cu-Fe-Zn-Pb-Ag-Au-Bi-Se, and Th-U), which became superimposed on earlier high-temperature Mo-W-Sn- Fe-As-Cu-REE mineralization. A few 206Pb/238U ages > 320 Ma remain to be reconciled, but might be due to the high U and Th contents of the zircon and the strong influence of overprinting pneumatolitic-hydrothermal processes.

Tectonic setting and geochronology of the Sarsuk Au polymetallic deposit in Xinjiang, NW China: Constraints from pyrite Re–Os, zircon U–Pb dating and Hf isotopes

The Sarsuk Au polymetallic deposit is located in the Ashele volcano-sedimentary basin of the south Altay Orogenic Belt (AOB), Northwest China. Within the deposit, rhyolite porphyry and diabase are widespread, and emplaced into the strata. The orebodies of the Sarsuk deposit are hosted by the rhyolite porphyry, while diabase cuts through the rhyolite porphyry and part of the orebody. Rhyolite porphyry11Rhyolite porphyry displays two events where only the older (384Ma) one is metallogenically relevant for the sarsuk, the young rhyolite porphyry (302Ma) is not relevant for the formation of the sarsuk deposit. yields a zircon U-Pb age of 384 ± 1.2 Ma (MSWD = 0.69), and the diabases yield a zircon U-Pb age of 380 ± 0.74 Ma (MSWD = 3.1). Four auriferous pyrite samples from vein sulfide ores and one pyrite sample from massive ores display a Re–Os isochron age of 383 ± 11 Ma (MSWD = 1.2). These data show that the bimodal Devonian magmatism and rhyolite porphyry hosted ore bodies emplaced in a narrow interval during 384–380 Ma. Diabases have the geochemical characteristics of tholeiitic basalts, with relatively high Mg# values (49.4–61.4), Cr and Ni, a slight positive Eu anomaly (δEu = 0.98–1.12), and relatively low concentrations of Sr and (La/Yb)N. Rhyolite porphyries have similar characteristics to those of sanukitoide in terms of high Mg# values (47.6–55.7), an obvious negative Eu anomaly (δEu = 0.33–0.35), and enrichments of large ion lithophile elements and light rare earth elements. The aforementioned chemical characteristics indicate that the Sarsuk deposit was located in the arc environment of a subduction zone during the Early to Middle Devonian. Hf isotope analyses of the diabases exhibited εHf(t) values of + 4.86 to + 8.96. The two-stage Hf model age (TDM2) was 805–1064 Ma. Hf isotope analyses of the rhyolite porphyry exhibited a εHf(t) value range of + 1.78 to + 8.49, and the two-stage Hf model age (TDM2) was 449–528 Ma. The original diabase and rhyolite porphyry magmas were derived from a mixing of the depleted mantle and juvenile crust material. The pyrite Re/Os system indicated that crust-derivedand S-rich sediments also contributed to the ore formation. Accordingly, based on the results of this study and a review of the regional magmatic framework, we can conclude that the Sarsuk deposit was formed at 383 Ma in an island arc subduction environment. Furthermore, we establish that the magmatic rocks and ore are co-genetic.

Early Cretaceous bimodal magmatism related epithermal mineralization: A case study of the Gaosongshan gold deposit in the northern Lesser Xing’an Range, NE China

Low-sulfidation (LS) gold mineralization is partially associated with bimodal volcanism in origin. Sources of ore-mineralized fluids and relevant dynamic processes remain poorly understood. To better understand these issues, a study including deposit geology, petrology, zircon U–Pb dating, and element and Sr–Nd–Hf isotope geochemistry of bimodal volcanic rocks at Gaosongshan was conducted. The bimodal volcanic rocks are composed of andesitic rocks (basalt andesite–andesite–trachyandesite–andesitic pyroclastic) of the Meifeng Formation and overlying rhyolite lava of the Fuminhe Formation cut by equivalent porphyry stocks, which contain pyrite-bearing granular-textured quartz cavity with a sugary appearance, with trapped single-phase magmatic fluids. The andesitic suite formed at approximately 106–108 Ma, prior to eruption of the younger rhyolitic magmas (105.6 ± 1.7 Ma; n = 13, MSWD = 1.2). The andesites show calc-alkaline affinities, which is a subduction-related characteristic, and show moderate La/YbN (7.91–11.36) and weakly negative europium anomalies (0.80–1.02), indicating a source in the asthenospheric mantle with varying contamination by both subduction and continental materials. A-type rhyolitic rocks are geochemically comparable to the andesitic suite, and their higher La/YbN (13.01–30.05) and lower Eu/Eu* (0.66–0.73) indicate evolved products of andesitic magmas. The estimated oxygen fugacity of dry (＜1.2% water) rhyolite lava is FMQ −1.87, whereas rhyolite porphyry is more oxidized (FMQ + 0.12) and water rich (2.5–2.8%) with probably being water saturated at 2.0–2.4 km depths. Therefore, it is assumed that the essential constraints of bimodal magmatism on epithermal gold mineralization are sequential processes from ascending and gradual differentiation of crustal-level mantle-derived basaltic magmas to releases of hydrothermal solutions from the silica-rich magma reservoir at shallower levels. Most importantly, the oxygen fugacity of and the fluid fluxes from dry rhyolitic melts are critical restricting parameters for the limited reserves at Gaosongshan; thus, this research contributes objective evidence for investigations of deposit genesis and prospecting targets.

Isotopic (H─O─S─Pb) geochemistry and zircon U─Pb geochronology of the Kaladaban Pb─Zn deposit, in Xinjiang, NW China

The Kaladaban Pb─Zn─Cu volcanogenic massive sulphide deposit (VMS), located within the Altyn region of Xinjiang in NW China, is an economically significant deposit with known reserves of 414,400 t Zn with a grade of 4.14%, 265,200 t Pb with a grade of 2.52%, and 149,200 t Cu with a grade of 1.10%. The mineralization is hosted in basalt, rhyolite, and rhyolite porphyry, with the latter two rock types yielding zircon U─Pb ages of 516 and 505 Ma, respectively, representing the timing of crystallization. Samples of the host volcanic rocks show fractionated rare‐earth element (REE) patterns and enrichment in both large‐ion lithophile elements (e.g., Ba, Rb, U, and light REEs) and high‐field‐strength elements (e.g., Th, Hf, and Zr). These features are similar to those of oceanic island basalt. δ18O values of ore fluids from quartz in orebodies range from +8.1‰ to +13.4‰, and fluid δ18Dwater values vary from −68.5‰ to −99.1‰, indicating a mixture of magmatic hydrothermal and seawater. δ34S values range from +8.5‰ to +14.9‰, suggesting that S that in the Kaladaban ore minerals had a mixed origin of magmatic hydrothermal fluids and sulphate‐reduced seawater. Ratios of 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb from metal minerals in Kaladaban deposit are 18.513–18.740, 15.633–15.727, and 38.236–38.398, respectively, indicating extremely radiogenic characteristics, similar to the host volcanic rocks. We infer that the Kaladaban Pb─Zn deposit formed in an active continental margin setting related to southward subduction of the North Altyn oceanic crust during the early Palaeozoic.

Porphyry Mo and epithermal Au–Ag–Pb–Zn mineralization in the Zhilingtou polymetallic deposit, South China

The Zhilingtou polymetallic deposit, South China, provides an excellent opportunity to investigate the magmatic-hydrothermal evolution of the porphyry Mo to epithermal Au–Ag–Pb–Zn ore spectrum. New zircon U–Pb, sphalerite 40Ar/39Ar, and pyrite Rb–Sr ages, together with previous molybdenite Re–Os ages, indicate that the granitic magmatism and Mo–Au–Ag–Pb–Zn mineralization were coeval and cogenetic in the Early Cretaceous (~ 113 Ma). Fluid inclusions and H–O isotope results have established the evolution from an early high-temperature H2O–NaCl magmatic fluid system (Mo mineralization), to a medium-temperature mixed fluid system of magmatic and meteoric water (Au–Ag mineralization), to a peripheral late-stage low-temperature H2O–NaCl meteoric water fluid system (epithermal Au–Ag–Pb–Zn mineralization). Moreover, the sulfur isotopic compositions (δ34S = 2.1–7.8‰) of the sulfide minerals confirm a genetic link to the granitic magma. Lead isotope data from pyrite and the granite–rhyolite porphyries are similar, indicating that they share a common Pb source. The geochronological, geochemical, and isotopic lines of evidences consistently suggest that the porphyry Mo and epithermal Au–Ag–Pb–Zn mineralization formed in one magmatic–hydrothermal system. The porphyry-epithermal mineralization model for Zhilingtou has significant importance for prospecting work in South China, where Mo and associated Pb–Zn–Ag resources are abundant.

Cu–Mo Differential Mineralization Mechanism of the Dabate Polymetallic Deposit in Western Tianshan, NW China: Evidence from Geology, Fluid Inclusions, and Oxygen Isotope Systematics

AbstractClassic porphyry Cu–Mo deposits are mostly characterized by close temporal and spatial relationships between Cu and Mo mineralization. The northern Dabate Cu–Mo deposit is a newly discovered porphyry Cu–Mo polymetallic deposit in western Tianshan, northwest China. The Cu mineralization postdates the Mo mineralization and is located in shallower levels in the deposit, which is different from most classic porphyry Cu–Mo deposits. Detailed field investigations, together with microthermometry, laser Raman spectroscopy, and O‐isotope studies of fluid inclusions, were conducted to investigate the origin and evolution of ore‐forming fluids from the main Mo to main Cu stage of mineralization in the deposit. The results show that the ore‐forming fluids of the main Mo stage belonged to an NaCl + H2O system of medium to high temperatures (280–310°C) and low salinities (2–4 wt% NaCl equivalent (eq.)), whereas that of the main Cu stage belonged to an F‐rich NaCl + CO2 + H2O system of medium to high temperatures (230–260°C) and medium to low salinities (4–10 wt% NaCl eq.). The δ18O values of the ore‐forming fluids decrease from 3.7–7.8‰ in the main Mo stage to −7.5 to −2.9‰ in the main Cu stage. These data indicate that the separation of Cu and Mo was closely related to a large‐scale vapor–brine separation of the early ore‐forming fluids, which produced the Mo‐bearing and Cu‐bearing fluids. Subsequently, the relatively reducing (CH4‐rich) Mo‐bearing, ore‐forming fluids, dominantly of magmatic origin, caused mineralization in the rhyolite porphyry due to fluid boiling, whereas the relatively oxidizing (CO2‐rich) Cu‐bearing, ore‐forming fluids mixed with meteoric water and precipitated chalcopyrite within the crushed zone at the contact between rhyolite porphyry and wall rock. We suggest that the separation of Cu and Mo in the deposit may be attributed to differences in the chemical properties of Cu and Mo, large‐scale vapor–brine separation of early ore‐forming fluids, and changes in oxygen fugacity.

FORMATION OF THE KHEDOZEROBOLSHOZERSKAYA STRUCTURE OF THE BALTIC SHIELD IN THE LIGHT OF NEW GEOCHEMICAL AND GEOCHRONOLOGICAL DATA

Based on existing and newly obtained geological materials, complemeted by new petrogeochemical, geochronological and isotope-geochemical data, a new interpretation of the history of the geological development of the Khedozero-Bolshozerskaya structure in Central Karelia has been proposed. It is generally believed that the three strata identified within this structure consistently and successively overlap each other. This study established that sedimentation and volcanic activity were disparate both spatially and temporally, and occurred in different tectonic settings. The lower terrigenic and middle volcanogenic strata have tectonic contacts, while the upper volcanogenic stratum is a complex of thin transverse dikes. The accumulation of more ancient terrigenic sediments in the lower strata (of metagraywacke nature) occurred in the south of the structure, began no earlier than 2753 ± 6 Ma and was completed before the start of volcanic activity. The sedimentation conditions were similar to those of primitive oceanic island arcs. Volcanic activity (2712 ± 6 – 2703 ± 7 Ma), which is associated with the formation of the two upper strata, took place in the north of the structure, started with lava outflows of andesibasalts, andesites and dacites from the middle strata, and ended with the intrusion of upper-strata rhyolite porphyry dikes. The volcanism occurred in the settings similar to modern mature volcanic arcs. In the course of further geological development involving complex tectonic deformations and areal granitization, the southern terrigenic and the northern volcanogenic strata spatially converged.

Origin and significance of Early Miocene high‑potassium I-type granite plutonism in the East Anatolian plateau (the Taşlıçay intrusion)

The Early Miocene high-K I-type plutonic rocks constitute the early products of the Neogene to Quaternary magmatism, and the youngest exposed intrusions in the East Anatolian plateau. Here we deal with the petrogenesis of the Early Miocene Taşlıçay intrusion covering an area of ∼62 km2. The intrusion comprises leucogranite, and minor gabbro-monzodiorite and rhyolite porphyry. U-Pb dating of zircons from the leucogranite, monzodiorite and rhyolite porphyry yielded identical igneous crystallization ages of ∼19 Ma (Early Miocene). According to the modified alkali-lime index, the leucogranite and the rhyolite porphyry are alkali-calcic, while the gabbro-monzodiorite is transitional calcic to calc-alkalic. On variation diagrams, the gabbro-monzodiorite and the leucogranite as well as rhyolite porphyry form distinct bimodal groupings, whereby the leucogranite display well-defined linear differentiation trends, in contrast to the gabbro-monzodiorite. The leucogranite has relatively fractionated rate earth element (REE) patterns with concave-upward shapes and significant negative Eu anomalies; middle REEs are hardly fractionated with respect to heavy REEs. The gabbro-monzodiorite is characterized by high abundances of incompatible elements, slightly fractionated chondrite-normalized REE patterns with feebly negative Eu anomaly. The rhyolite porphyry is compositionally similar to the leucogranite. The geochemical features imply a fractionating mineral assemblage of hornblende, plagioclase and biotite for the leucogranite, and hornblende and ± plagioclase for the gabbro-monzodiorite. All the rock types display a narrow Sr and Nd isotopic variation (initial 87Sr/86Sr = 0.7053 to 0.7065; initial εNd = −0.5 to −3.8). The leucogranite and rhyolite porphyry exhibit gradually slightly higher initial 87Sr/86Sr and lower initial 143Nd/ 144Nd ratios relative to the gabbro-monzodiorite. Similarly, δ18O and initial εHf values of zircons suggest slightly increasing amount of crustal component from the leucogranite to the rhyolite porphyry. The gabbro-monzodiorite is probably related to partial melts from the slightly enriched lithospheric mantle. The magmas of the leucogranite and the rhyolite porphyry, on the other hand, probably resulted from the remelting of a middle- to high-K basic to intermediate rocks, compositionally similar to the gabbro-monzodiorite, and assimilated gradually slightly increasing amount of old high-silica crustal material. Several lines of evidence such as (i) presence of the well-developed dike swarm of rhyolite porphyry at the north eastern margin of the intrusion, (ii) exhumation of the intrusion at the earth’s surface by Middle Miocene, (iii) widespread apatite fission tract ages between 22 and 16 Ma from literature, and (iv) the absence of the exposed intrusions younger than the Early Miocene suggest that the Early Miocene represents probably a time of continental extension and exhumation in Eastern Anatolia and NW Iran.

Geochronology, geochemistry, and Pb–Hf isotopes of mineralization-related magmatism in the Dongyang gold deposit, Fujian Province, southeastern China

The recently discovered Dongyang low-sulphidation epithermal Au deposit is located in Fujian Province. The Au mineralization hosted in rhyolite porphyry and the Lower Jurassic Nayuan Formation continental volcanic rocks is considered to be related to intermediate–acidic intrusions (rhyolite porphyry, quartz diorite porphyry, and dacite porphyry). The zircon U–Pb ages of these samples are 160.3 ± 0.8, 156.6 ± 0.8, and 154.1 ± 0.6 Ma, respectively, and the sulphide Rb–Sr isotope isochron age is 152.4 ± 1.7 Ma, indicating a temporal link between porphyry emplacement and Au mineralization. Porphyries are enriched in large-ion lithophile elements and light rare earth elements and slightly depleted in heavy rare earth elements and high field strength elements, belong to the high-potassium calc-alkaline or shoshonitic series, and show characteristics of volcanic arcs or active continental margins. Moreover, the εHf(t) values of the porphyries range from −11.6 to −7.6, −11.2 to −5.4, and −9.8 to −4.6, respectively. The 208Pb/204Pb, 207Pb/204Pb, and 206Pb/204Pb values of the ore minerals are from 38.417 to 38.406, 15.603, and from 18.179 to 18.175, respectively. Pb and Hf isotopes indicate that the intermediate–acidic magma related to mineralization originated from Mesoproterozoic lower crust. Consequently, these data favour an intermediate–acidic magma origin for Au mineralization in the Dongyang deposit. Integrating new and published data on the tectonic evolution, we suggest that the rhyolite porphyry, quartz diorite porphyry, dacite porphyry, and associated Au mineralization in the Dongyang deposit formed at 160–152 Ma in an extensional environment related to subduction of the Palaeo-Pacific Plate beneath the South China block.

Rb–Sr geochronology and geochemistry of the Xiaotongchang basalt-hosted copper deposit in the Jinping area, SW China

The Xiaotongchang basalt-hosted copper deposit in Jinping, southern Yunnan Province, SW China, is located in the southern part of the Emeishan large igneous province. Here, we use Rb–Sr, Re–Os and S–Pb–C–O isotope data to constrain the age and genesis of the deposit. Petrological investigations reveal two main stages of mineralization. The early-stage is characterized by disseminated or massive sulfides in an assemblage of pyrite + chalcopyrite + quartz + albite + calcite. Rb-Sr isotopic dating of early-stage chalcopyrite yields an age of 256 ± 9.4 Ma (MSWD = 5.4), which is slightly younger than the eruption age of the Jinping basalts. The δ34SCDT values of the sulfides range from +5.8‰ to +7.7‰, suggesting that the metals of the early-stage copper mineralization originated from the Emeishan basalts and that the ore-forming fluids were contaminated by crustal rocks. These units may indicate that the early-stage orebodies represents syngenetic hydrothermal mineralization related to the eruption of Emeishan flood basalts. The late-stage mineralization is characterized by a pyrite + chalcopyrite + bornite + chalcocite + quartz + calcite assemblage that is developed in veins or breccia. The Re-Os isotopic dating of late-stage chalcopyrite samples reveals that they formed at 240–231 Ma. The Pb isotopic compositions ((206Pb/204Pb)t = 17.521–19.227, (207Pb/204Pb)t = 15.480–15.760, and (208Pb/204Pb)t = 37.778–38.731; t = 235 Ma) show that the late-stage copper orebodies have a heterogeneous source and originated mainly from the crust. The late-stage sulfides have higher δ34SCDT values (+7.9‰ to +10.7‰) than the early-stage sulfides. The narrow range of sulfur isotopic compositions of the sulfides associated with both stages and the Pb isotopic compositions of late-stage chalcopyrite indicate that some of the metals associated with late-stage mineralization originated from the Jinping basalts. The C–O isotopic compositions of calcite samples show that the magmatic hydrothermal fluids in the late stage flowed through and were contaminated by the Maokou limestone. Therefore, we suggest that the late-stage orebodies represent magmatic hydrothermal mineralization associated with the Late Triassic rhyolite porphyry and that the tectono-magmatic hydrothermal fluid remobilized copper from the basalts. The copper deposits formed at favourable interfaces within the basalt stratigraphy or in favorable structural locations.

Paleoproterozoic volcanic caldera in the Amazonian craton, northern Brazil: Stratigraphy, lithofacies characterization, and lithogeochemical constraints

In the Vila Tancredo Neves locality, Amazonian craton, northern Brazil, occur Paleoproterozoic well-preserved volcano–plutonic centers. The lower 1.88 Ga Sobreiro Formation has overlapped lavas comprising andesite at the base; andesi-basalt and latite at middle; and quartz-latite and rhyolite at the top; besides associated pyroclastic and autoclastic lithofacies. Reveals high-K calc-alkaline and metaluminous signature. This unit shows K, Ba, Sr, and Rb enrichments; and Nb and Ta negative anomalies. Occurs an LREE-enriched pattern relative to HREE. Eu anomaly is absent in the most primitive rocks, whereas the evolved rocks reveal a minor negative Eu anomaly. These chemical characteristics are compatible with arc-related andesites. The upper, fissure-controlled, 1.87 Ga Santa Rosa Formation has peraluminous rhyolites and intrusions of rhyolitic porphyries and granites. These alkali rhyolites erupted in several vents within greater brittle faults, with outflows of ignimbrites and volcaniclastic deposits with variable textures. They reveal HFSE enrichment (Nb and Ta) and strong negative anomalies of LILE (Ba and Sr). Some evolved rhyolitic samples usually attributed to the Santa Rosa Formation are calc-alkaline and have geochemical constraints closer to those of the Sobreiro Formation andesitic rocks. Observations of the volcano–plutonic complex point to a Paleoproterozoic volcanic caldera related to several pulses of felsic and andesitic–rhyodacitic–rhyolitic lavas that comprise a stratovolcano evolution in the pre-caldera stage. Pyroclastic sin-caldera deposits with ignimbrite, ash tuff, crystal-rich tuff, and minor polymictic breccia are less preserved. Later evolved domes, dikes, and volcaniclastic rocks represent the recurrent magmatism in the post-caldera stage. This work supplies new support for more systematic stratigraphic and geochemical studies of these poorly studied, but promising, Proterozoic units.

U–Pb geochronology, Nd–Sm geochemistry, structural setting, and tectonic significance of Late Devonian and Paleogene intrusions in northern Yukon and northeastern Alaska

A suite of six Devonian granites and one syenite were emplaced into the upper crust of northern Yukon between 364.8 ± 2.7 and 371.2 ± 1.4 Ma. The Bear Mountain syenite and related rhyolite porphyry in adjacent Alaska intruded at 52.3 ± 0.4 and 53.5 ± 0.2 Ma, respectively. A felsic volcaniclastic unit and quartz-phyric sill are newly documented adjacent to the Mount Sedgwick granite. The volcaniclastic unit may indicate the presence of a related volcanic edifice. The presence of xenocrystic zircon grains in most of the intrusions suggests initial emplacement of magmas began 10–20 Myr before final emplacement into the upper crust. A Famennian final intrusion age coincides with Late Devonian encroachment of Ellesmerian deformation into the region. Attendant crustal flexure, or evolving foreland structures, may have facilitated upward migration of the magmas. Geochemistry of the intrusions indicates that the Devonian magmatism was largely derived from partial melting of lower and middle crust, implying widespread mafic magmatic underplating in Middle to Late Devonian time. Only Dave Lord syenite retains evidence of an original mantle geochemical signature. Mantle underplating may have played a role in localizing extension, volcanism, and rifting that led to the Late Devonian opening of the Angayucham ocean basin. The Eocene Bear Mountain pluton is inferred to be a northerly example of widespread Cenozoic within-plate magmatism in Alaska.

Details Geological Mapping and Petrological Characteristics of EL Shereik Study Area, River Nile State, North Sudan

The present study focused on details geology of the lithostratigraphy, phenomena and petrogenesis, with full classification of rock units and correlate by the regional geology in the study area. The previous studies, focused on regional geology, which can be divided in Bayuda Terrane, represented by Dem El Tor Shear Zone (DTSZ), its Precambrian to Tertiary ages (isotopic signatures of later cooling 590 to 550 Ma), with dominated by metamorphic and intrusive rocks belonging to the Pre-Nubian basement complex. The study area lies at El Shereik, River Nile State, Sudan. It is characterized by low-lying bed plains, covered with superficial deposits, with an arid climate. The techniques of this work, represented in an official, field works and laboratory test, with used Land Sat Images ETM. And Nubian Arabian Shield, represented by the Keraf Shear Zone (KSZ), its Precambrian to Phanerozoic ages (Neoproterozoic, Pb isotope ages dating, of forms is -730 -710Ma and ended in -565Ma), with dominated by metamorphic, ophiolitic mélange, volcano-sedimentary sequences, and Phanerozoic sediments. But through this detailed surveyed, we discovered different types of rock units; they were found as accumulated and highly deformed, affected by various thrusting faults. collected more than 40 samples, through six traverses, for classification and petrographic studies and classified more than 9 types of rooks units didn’t mentioned before in previous study, all of them well exposed as following: metamorphic rocks, included, migmatites, calc-silicates, wollastonite, talc-schist, carbonaceous (dolomitic marble), amphibolites, graphitic schist, mica schist, quartzo-feldspathic schist, and grey gneiss, While the Igneous rocks, consisted of dykes, as dolerite, trachy-basaltic, Rhyolite porphyry, pegmatites, diorite, and quartz veins, whereas the superficial deposits, included, of aeolian, fluvial, and collovial. These rocks extend and spread to the outside of the limits of the study area and most of them oriented parallel with KSZ SE - NW region and a few of them are oriented E-W, This is maybe due to the collusion of the contact boundary between KSZ and DTSZ Bayuda Tehran. Talc-schist, Wollastonite and graphitic schist, represent a strategic stockpile besides gold mining. Studies conducted with DTSZ, its old age, occurred before Neoproterozoic compared to KSZ. Because it has the first deformation of the folding of pre- KSZ proportion to the presence of folding in the west and east of the Nile zone, according to the border between Bayuda Terrane and Nubian Arabian Shield, as the suggest result. And the previous studies of the ages dating confirm it.

Petrography and geochemistry of tourmaline breccia in the Longtoushan Au deposit, South China: genesis and its exploration significance

The Longtoushan Au deposit, located in the Qin-Hang Metallogenic Belt, South China, is a breccia-hosted epithermal Au deposit. It is characterized by the distinctive occurrence of magmatic-hydrothermal tourmaline-cemented breccia. Tourmaline-group minerals have an extensive range of chemical composition that could reflect their host environments, including some of economic interest. To investigate the potential of tourmaline as a geochemical indicator for ore exploration, chemical and boron isotope compositions of tourmaline from the Longtoushan Au deposit have been determined. Tourmaline mainly occurs as orbicular aggregates, clusters and veinlets in rhyolite porphyries, granite porphyries and in spatially associated hydrothermal breccias (Au-mineralized and Au-barren). Three types of tourmaline (I, II and III) are recognized at Longtoushan, most of which being alkali-deficient schorl-dravites. The pre-ore Tourmaline I in the rhyolite porphyry is Fe-rich schorl, contrasting with the dravitic ore-stage Tourmaline II in the mineralized breccia and Tourmaline III in the granite porphyry. Locally, Tourmaline II shows concentric zoning which correlates with core-rim chemical variations (higher Fe, Al in the rim than in the core). Tourmalines from Longtoushan are characterized by a dominant MgFe -1 exchange vector and have relatively low Na contents (avg. 0.66 apfu; formula normalized on 15 total cations), indicating they possibly crystallized in reduced fluids of low-salinity. The δ 11 B values of tourmalines from this study fall in a narrow range of −14.5 to −10.2‰, indicating dominant magmatic-hydrothermal fluids of continent crust origin. The results suggest that tourmaline from Longtoushan may originate from boron-rich vapor fluids unmixed from felsic magmas. Tourmaline breccia was likely formed by hydraulic fracturing, with open spaces infilled by boron-rich boiling fluids released from the magma. The fluid boiling process during brecciation would be critical for Au-bearing pyrite precipitation, which could compete with coexisting tourmaline for Fe, leaving tourmaline Fe-depleted. We propose that the Fe-poor dravitic tourmaline in the hydrothermal breccia could be used as prospecting guide at the Longtoushan Au deposit. Supplementary material: major element and boron isotope composition analyses of tourmaline are available at https://doi.org/10.6084/m9.figshare.c.4468808

Origin and tectonic significance of the Hoboksar ophiolitic mélange in northern West Junggar (NW China)

Although the Early Paleozoic tectonic framework of northern West Junggar is essential for understanding accretionary processes in the southwestern Central Asian Orogenic Belt, this setting is still not well understood. In order to address this issue, we employed detailed geochronological, geochemical and Sr-Nd-Hf-Os isotope analyses on the Hoboksar ophiolitic mélange in northern West Junggar. The Hoboksar ophiolitic mélange mainly consists of serpentinized peridotites, pyroxenites, gabbros, diabase, cherts, marbles, volcanic and pyroclastic rocks. It is characterized by a “block-in-matrix” structure with serpentinized peridotites as the matrix which is crosscut by later diorite porphyry and rhyolitic porphyry. Olivines and spinels in these serpentinized peridotites show high Fo# and Cr#, respectively. The clinopyroxenes in the pyroxenites exhibit high Mg#, low Al2O3 and Cr2O3. The serpentinized peridotites have extremely low rare-earth element (REE) abundances, U-shaped to flat REE patterns and positive Eu anomalies. Their particularly low Re/Os, initial 187Os/188Os and γOs(t) imply that they could represent residual phases after partial melting of upper mantle. The gabbros and diabases display slight fractionation between light REE and heavy REE, negligible Eu anomalies, depletion in Rb, Nb and Ta, enrichment in Th and U, low initial 87Sr/86Sr and positive εNd(t). The mineral and whole-rock geochemical and isotopic compositions of these ultramafic-mafic rocks demonstrate that the Hoboksar ophiolitic mélange originated from a depleted mantle in a fore-arc supra-subduction zone (SSZ) setting.Zircon UPb dating on diorite porphyry and rhyolitic porphyry yields weighted mean 206Pb/238U ages of 435 ± 4 Ma and 441 ± 2 Ma, respectively, postdating the closure of an ancient ocean represented by the Hoboksar ophiolite. These later intrusions resemble adakitic rocks with high Sr/Y. They exhibit mild depletion in Nb and Ti, low initial 87Sr/86Sr, positive εNd(t) and zircon εHf(t). Therefore the diorite porphyry and rhyolitic porphyry likely derived from juvenile lower crust. Based on our new data and other geologic evidence, we propose that the ancient Hoboksar Ocean resided between two Paleozoic arcs in northern West Junggar during the Early Ordovician, and this ocean was closed before 440 Ma. The emplacement of adakitic stitching intrusions implies a back-arc extensional setting that may be due to (present-day) northward subduction of the Junggar-Balkhash oceanic slab during the Early Silurian.

Geochronology and Geochemistry of the Granites from the Longtoushan Hydrothermal Gold Deposit in the Dayaoshan Area, Guangxi: Implication for Petrogenesis and Mineralization

The gold mineralization in the Longtoushan hydrothermal gold deposit is concentrated within the contact zone of the granitic complex. Whole rock geochemistry and in-situ U-Pb and Hf isotopic data were used to constrain the genesis and age of the granites and related Cu-Au mineralization in the Longtoushan Deposit. The granites mainly consist of the granite porphyry, rhyolite porphyry, porphyritic granite and quartz porphyry. LA-ICP-MS U-Pb dating of zircons from the granite porphyry, rhyolite porphyry and quartz porphyry indicates that they intruded from ca. 94 to 97 Ma. These intrusions exhibit similar trace element characteristics, i.e., right-dipping REE patterns, depletion of Ba, Sr, P and Ti, and enrichment of Th, U, Nd, Zr and Hf. The eHf (t) values of zircons from the granite porphyry, rhyolite porphyry and quartz porphyry range from −26.81 to −8.19, −8.12 to −5.33, and −8.99 to −5.83, respectively, suggesting that they were mainly derived from the partial melting of the Proterozoic crust. The Cu-Au mineralization is mainly related to the rhyolite porphyry and porphyritic granite, respectively. The Longtoushan granites were most likely formed in a post-collisional extensional environment, and the deposit is a part of the Late Yanshanian magmatism related mineralization in the Dayaoshan area and its adjacent areas.

Origin and evolution of ore-forming fluid for the Gaosongshan gold deposit, Lesser Xing'an Range: Evidence from fluid inclusions, H-O-S-Pb isotopes

Epithermal gold deposits are typical precious metal deposits related to volcanic and subvolcanic magmatism. Due to the lack of direct geological and petrographic evidences, the origin of the ore-forming fluid is deduced from the spatial diagenesis-mineralization relationship, chronological data, physicochemical characteristics of mineral fluid inclusions, mineral or rock elements and isotopic geochemical characteristics. By objectively examining this scientific problem via a geological field survey and petrographic analysis of the Gaosongshan epithermal gold deposit, we recently discovered and verified the following points: (1) Pyrite-bearing spherical quartz aggregates (PSQA) occur in the rhyolitic porphyry; (2) the mineralization is structurally dominated by WNW- and ENE-trending systems and occurs mostly in hydrothermal breccias and pyrite-quartz veins, and the ore types are mainly hematite-crusted quartz, hydrothermal breccia, massive pyrite-quartz, etc.; (3) the alteration types consist of prevalent silicification, sericitization, propylitization and carbonation, with local adularization and illitization. The ore minerals are mainly pyrite, primary hematite, native gold, and electrum, with lesser amounts of chalcopyrite, magnetite, sphalerite, and galena, indicating a characteristic epithermal low-sulfidation deposit. The ore-forming fluid may have been primarily derived from magmatic fluid exsolved from a crystallizing rhyolitic porphyry magma. Further zircon U-Pb geochronology, fluid inclusion, physicochemical and isotopic geochemical analyses revealed that (1) rhyolitic porphyry magmatism occurred at 104.6 ± 1.0 Ma, whereas the crystallization of the PSQA occurred at 100.8 ± 2.1 Ma; (2) the hydrothermal fluid of the pre-ore stage was an exsolved CO2-bearing H2O-NaCl magmatic fluid that produced inclusions mainly composed of pure vapor (PV), vapor-rich (WV) and liquid-rich (WL) inclusions with a small number of melt- (M) and solid-bearing (S) inclusions; mineralization-stage quartz contains WL and rare PV, WV and pure liquid (PL) inclusions characterized by the H2O-NaCl system with low formation temperatures and low salinities; (3) the characteristics of hydrogen, oxygen, sulfur, and lead isotopes and those of rare earth elements (REEs) provide insight into the affinity between PSQA and orebodies resulting from juvenile crust or enriched mantle. Combined with previous research on the mineralogenetic epoch (99.32 ± 0.01 Ma), we further confirm that the mineralization of the deposit occurred in the late Early Cretaceous, which coincides with the extension of the continental margin induced by subduction of the Pacific Plate beneath the Eurasian Plate. The formation of the ore deposit was proceeded by a series of magmatic and hydrothermal events, including melting of enriched juvenile crust, upwelling, the eruption and emplacement of the rhyolitic magma, the exsolution and accumulation of magmatic hydrothermal fluid, decompression, the cooling and immiscibility/boiling of the fluid, and mixing of the magmatic fluid with meteoric water, in association with water-rock interaction.

Fluid Inclusion Study on the Moyoulete Sb-Cu Deposit, Xinjiang, China

The Moyoulete Sb-Cu deposit occurs in Devonian Kelan volcanic-sedimentary basin, which strikes NW-SE along the south margin of Altay Mountains, hosted in lower Devonian upper kangbutiebao formation. Sulfide quartz veins could be divided into two stages: early stage (Q1), charactered by white lenticular or veinlet quartz veins of copper mineralization occurring in metamorphic crystal tuff, metamorphic basic volcanic rock, or rhyolite porphyry; late stage (Q2), charactered by copper-bearing grey-white pyrite-quartz veins cutting the metamorphic rocks. The four types of fluid inclusions in the quartz veins can be identified: 1) CO2-rich fluid inclusions; 2) Water-rich fluid inclusions; 3) Carbonic fluid inclusions; 4) Aqueous fluid inclusions. CO2-rich fluid inclusions in Q1 have Tm, CO2 = -61.9∼ -57.9 °C and Th,CO2 = -10.0∼21.6 °C; the Th,totS’ are 358∼388 °C, while in Q2 have Tm,CO2 = -63.2∼ -60.2 °C and Th,CO2 = -20.4∼17.4°C; the Th,totS’ are 270∼325°C in the Moyoulete Sb-Cu deposit. The characteristics of CO2-rich fluid inclusions from the Moyoulete Sb-Cu deposit are similar to those from other Cu-Au mineralization localities. The genesis of vein Sb-Cu mineralization was connected with the orogeny-metamorphism hydrothermal fluid, resulting from the orogeny metamorphism of the Late Permian-Triassic in the south margin of the Altay Mountains.

Application of apatite fission-track analysis and zircon U-Pb geochronology to study the hydrothermal ore deposits in the Lesser Hinggan Range: Exhumation history and implications for mineral exploration

This study uses apatite fission track (AFT) and zircon U-Pb data to reveal the cooling history of bedrocks from the Dong'an, Cuihongshan and Pingdingshan deposits in the Lesser Hinggan Range, which is one of the most important metallogenic districts in NE China. AFT results and modeling of samples identified three cooling phases since late Mesozoic times. Stage one recorded rapid cooling to the low temperature part of the fission track partial annealing zone at circa 100 ± 10 °C during ca. 90–70 Ma with an average exhumation rate of ~29–58 m/Ma. Stage two was a relatively slow cooling period occurring between ~70 and 25 Ma with an average exhumation rate of ~12 m/Ma, suggesting that the Lesser Hinggan Range had been denuded to an area of low relief. Stage three was an increased cooling period took place from the Miocene to Quaternary (<25 Ma) with an average exhumation rate of ~47 m/Ma, which transported the sampled rocks to the present surface at an increased exhumation rate. Zircon U-Pb dating of magmatic rocks from the three deposits yielded Concordia ages of 188.8 ± 0.5 Ma (alkali-feldspar granite) and 115.6 ± 0.4 Ma (rhyolitic porphyry) at the Dong'an deposit, yielded Concordia ages of 195 ± 1 Ma (alkali-feldspar granite) and 200.3 ± 0.5 Ma (monzonitic granite) at the Cuihongshan deposit, and yielded Concordia ages of 259.4 ± 0.82 Ma (Biotite granit) and 225.9 ± 1.1 Ma (dioritic dyke) at the Pingdingshan deposit, which are notably older than their corresponding AFT ages. Our results, combined with other data in and/or around NE Asia (Great Hinggan, Changbai Mts, Yanji, Sikhote Alin Mts, South Korea and SW Japan), suggest micro-continental blocks in NE Asia underwent different uplifting/denudation rates since the Late Cretaceous, which indicates that the Xing'an, Songliao and Nadanhada-Sikhote-Alin accretionary complex blocks may have good potential for mineral exploration to great depths.