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The Mines Gaspé area hosts multiple Cu–Mo skarn and porphyry orebodies near the town of Murdochville in the northeastern part of the Gaspé Peninsula, Québec. The orebodies occur within overlapping alteration aureoles in calcareous Lower Devonian sedimentary rocks. The strata are intruded by numerous multiphase porphyry sills, dykes, and plugs of Devonian age. The Porphyry Mountain intrusion and a sill in the Copper Mountain pit have been dated at 378.80 ± 0.37 and 377.60 ± 0.45 Ma, respectively, refining the results of previous studies, and demonstrating Porphyry Mountain intrusion emplacement at least 0.38 m.y. before Copper Mountain. Circa 392 Ma inherited zircon grains at Mines Gaspé suggest an early phase of magmatism that produced the extensive skarn alteration aureoles throughout the Gaspé Peninsula at sites such as Mines Gaspé and the nearby McGerrigle Complex, followed by significantly later (>10 m.y.) porphyritic intrusions and associated mineralization that added to existing skarn resources. Epidote at both Mines Gaspé and Sullipek occur as disseminated/granular crystals within the host groundmass and as larger crystals within veinlets or veinlet halos in metasomatised sedimentary rocks. Epidote ages suggest that there are several different propylitic hydrothermal events within the region at Mines Gaspé and Sullipek, which combined with new zircon U–Pb ages implies a prolonged and complex history of propylitic alteration within Gaspésie. [ABSTRACT FROM AUTHOR]

The Laird Lake property, southwest Red Lake greenstone belt, straddles the contact between the Balmer (2.99–2.96 Ga) and the Confederation (2.74–2.73 Ga) assemblages. The property is 10 km along strike from the Madsen and Starrat–Olsen Au mines that are hosted near the contact. The Balmer assemblage consists of fine-grained, aphyric, locally pillowed mafic volcanic rocks, ultramafic intrusive and volcanic rocks with flow breccia textures hosting local spinifex-bearing clasts, and banded-iron formations. In contrast, the Confederation assemblage comprises porphyritic mafic volcanic rocks intercalated with intermediate to felsic volcanic rocks that include crystal lapilli tuffs, crystal tuffs, and tuffs. The Balmer assemblage is composed of tholeiitic mafic volcanic rocks with minor Al-undepleted komatiites, whereas the Confederation assemblage is calc–alkalic. Neodymium isotopes, in conjunction with trace element geochemistry, suggests that parts of the Balmer assemblage were weakly contaminated by an older intermediate basement. Both arc and back-arc volcanism occurs in the Confederation assemblage, with the arc rocks showing a stronger crustal component than the back-arc rocks. A maximum U–Pb age of 2741 ± 19 Ma for a crystal tuff and an age of 2737.68 ± 0.79 Ma for a diorite are consistent with a Confederation assemblage affinity for the intermediate calc–alkaline rocks south of the Au-bearing horizon. The Balmer assemblage represents an oceanic plateau formed by plume magmatism on the margins of the North Caribou Terrane, whereas the Confederation assemblage at Laird Lake formed in an oceanic arc setting where both arc and back-arc volcanism occurred simultaneously. [ABSTRACT FROM AUTHOR]

The St. Ignace Island complex in Northern Ontario is a package of dominantly felsic rocks emplaced within the upper portions of the Osler Volcanic rocks of the ~1.1 Ga Midcontinent Rift System. The Osler volcanic rocks are predominantly tholeiitic basalts intercalated with rare interflow sediments and rhyolites. The St. Ignace Island complex is an ~26-km2 stock with a felsic core of quartz–feldspar–phyric rhyolites and dacites and an outer ring of anorthosite and gabbro. Textures at a variety of scales within the rocks of the complex show clear evidence of the mingling and mixing of partially crystallized mafic and felsic liquids. Two multigrain (zircon/baddeleyite) fractions from a sample of the gabbro define a Discordia line with an upper intercept date of 1107 ± 8.9 Ma. The core of the complex consists of dacites and rhyolites with similar REE abundances with negative Nb anomalies, whereas the surrounding mafic rocks are gabbros to monzogabbros that are less LREE-enriched than the felsic rocks but with similar HREE. Felsic units have a narrow range of 87Sr/86Sri (0.7032–0.7045) and 143Nd/144Ndi (0.51051–0.51057), whereas the mafic end members have similar 87Sr/86Sri (0.7040–0.7061) but more radiogenic 143Nd/144Ndi (0.51067–0.51085). Very well-preserved silicate melt inclusions (MI), many completely glassy, were observed in quartz, clinopyroxene, and some plagioclase phenocrysts from the complex. These represent some of the oldest unrecrystallized silicate melt inclusions described to date. Melt inclusions within quartz from the felsic volcanics are broadly rhyolitic in composition, whereas MI from plagioclase in the mafic volcanics range from basalt to basaltic andesite; these felsic and mafic melt compositions are interpreted to represent the end-member liquids in the system and bulk rock analyses affirm mixtures of the two. Concentrations of Cu and Ag (in both mafic and felsic MI), and Mo (in felsic MI), are up to an order of magnitude higher in the mafic and felsic MI than in continental crust. Bulk rock metal concentrations are also significantly lower than in the MI, suggesting that the melt inclusions may preserve pre-eruptive metal tenors that were subsequently modified by sulfide saturation, degassing, or post-solidus hydrothermal alteration. The whole rock and MI geochemistry of the St. Ignace complex are broadly similar to the Central Osler Group and, given the broad similar ages, suggests they may have been derived from a similar mantle source, but distinct from the source of rhyolites in the Black Bay Peninsula. The negative Nb anomalies and negative εNd values for the St. Ignace complex are consistent with mixing with older continental crust during ascent and emplacement. The rocks of the St. Ignace Island complex likely formed as the result of emplacement of a large mafic magma chamber at the base of the Osler volcanic pile that triggered partial melting to generate the rhyolite end members. The felsic melts ascended to shallower levels in the crust where they mixed with mafic magmas derived directly from the deeper chamber. Generally, melt inclusions in the complex have very high Cu and Ag contents, similar to those observed in arc-related and extremely oxidized early rift-related rocks and may account for the world-class volcano-sediment-hosted Cu–(Ag) deposits within the rift and the presence of small porphyry-style deposits. [ABSTRACT FROM AUTHOR]

The Midcontinent Rift System of North America is a ∼1.1 Ga large igneous province comprising mainly flood basalts and intrusive rocks. We present new data for the Pillar Lake Volcanics and Inspiration Sill from the northern edge of the Midcontinent Rift in the northwestern Nipigon Embayment. The Pillar Lake Volcanics comprise a ∼20–40 m thick, flat-lying sequence of mafic pillowed and massive flows, pillowed flow breccia, and hyaloclastite breccia. They are characterized by SiO2 of 52–54 wt%, TiO2 of 1.2–1.3 wt%, and K2O of 0.9–1.1 wt%. They are light rare earth element (LREE) enriched, with La/Smn of 3.0–4.4 with fractionated heavy rare earth elements (HREE) (Gd/Ybn = 1.4–1.7). The Inspiration diabase sill is ≤ 50 m thick and is in direct contact with the underlying Pillar Lake Volcanics. Baddeleyite and zircon data from the Inspiration Sill yield a combined U–Pb upper intercept age of 1105.6 ± 1.6 Ma. The Inspiration Sill is characterized by uniform SiO2 of 52–53 wt%, TiO2 of 1.1–1.2 wt%, and K2O of 0.9–1.2 wt%. Inspiration Sill samples are LREE enriched with La/Smn of 3.2–3.3 and fractionated HREE (Gd/Ybn = 1.6). The Pillar Lake Volcanics are at least 1120 Ma, and perhaps as old as 1130 Ma, and represent an early, thin, and restricted mafic volcanic sequence, largely preserved below the younger Inspiration Sill. The Pillar Lake Volcanics and Inspiration Sill display a marked geochemical similarity, suggesting that they may represent magmatism associated with the earliest stages of Midcontinent rifting. [ABSTRACT FROM AUTHOR]

The Philippine Mobile Belt is a complex plate boundary with multiple terranes in Southeast Asia, yet its early tectonic evolution is still not fully understood due to a scarcity of solid evidence. Here we report new whole rock geochemical, Sr-Nd isotopic, and zircon U-Pb-Hf isotopic data for Cretaceous-Miocene arc magmatic rocks from the Cebu and Bohol Islands, Philippine Mobile Belt. Bulk geochemical data display arc affinities with enriched large ion lithophile elements (e.g., Sr and Ba) and depleted high field strength elements (e.g., Nb, Ta, and Ti). The high positive εNd(t) (+4.6 to +9.1) values and low initial 87Sr/86Sr ratios (0.7032--0.7048) suggest that these igneous rocks were generated by partial melting of mantle wedge in an arc setting. U-Pb dating of zircons revealed Cretaceous (ca. 120-90 Ma), middle Eocene to early Oligocene (ca. 43-30 Ma), and middle Miocene (ca. 14 Ma) crystallization ages for the arc magmatism with abundant Permian-Triassic zircon xenocrysts clustering at ca. 250 Ma. The Permian-Triassic grains show dominantly negative εHf(t) values ranging from -16.2 to -6.6, which are similar to those of coeval rocks in Eastern Indochina. Combined with previous paleomagnetic studies, we propose that an Eastern Indochina-derived continental fragment was involved during the formation of arcs in the Cebu and Bohol Islands, which highlights the potential contribution of ancient continental materials in the formation of intra-oceanic arcs. This scenario does not support the previously proposed model that the Cretaceous arc in the Philippine Mobile Belt formed in the northern margin of the proto-Philippine Sea Plate and Australian margin. [ABSTRACT FROM AUTHOR]

Mafic intrusions on the NE shoulder of the Midcontinent Rift (Keweenawan LIP), including Cu–PGE mineralized gabbros within the Coldwell Complex (CC), and rift parallel or radial dykes outside the CC are correlated based on characteristic trace element patterns. In the Coldwell Complex, mafic rocks are subdivided into four groups: (1) early metabasalt; (2) Marathon Series; (3) Layered Series; (4) Geordie–Wolfcamp Series. The Marathon Series are correlated with the rift radial Abitibi dykes (1140 Ma), and the Geordie–Wolfcamp Series with the rift parallel Pukaskwa and Copper Island dykes. U–Pb ages determined for five gabbros from the Layered and Marathon Series are between 1107·7 and 1106·0 Ma. Radiogenic isotope ratios show near chondritic (CHUR) εNd(1106 Ma) and 87Sr/86Sri values that range from –0·38 to +1·13 and 0·702537 to 0·703944, respectively. Distinctive geochemical properties of the Marathon Series and Abitibi dykes, such as Ba/La (14–37), Th/Nb (0·06–0·12), La/Sm (3·8–7·7), Sr/Nd (21–96) and Zr/Sm (9–19), are very different from those of the Geordie–Wolfcamp Series and a subset of Copper Island and Pukaskwa dykes with Ba/La (8·7–11), Th/Nb (0·12–0·13), La/Sm (6·7–7·9), Sr/Nd (5–7·8) and Zr/Sm (18–24). Each unit exhibits covariation between incompatible element ratios such as Zr/Sm and Nb/La or Gd/Yb, Sr/Nd and Ba/La, and Nb/Y and Zr/Y, which are consistent with mixing relationship between two or more mantle domains. These characteristics are unlike those of intrusions on the NW shoulder of the MCR, but resemble those of mafic rocks occurring in the East Kenya Rift. The results imply that an unusual and long-lived mantle source was present in the NE MCR for at least 34 Myr (spanning the 1140 Ma Abitibi dykes and the 1106 Ma Marathon series) and indicate potential for Cu–PGE mineralization in an area much larger than was previously recognized. [ABSTRACT FROM AUTHOR]

The Miocene Cuonadong leucogranites in the easternmost section of the Tethyan Himalaya, Southern Tibet, are characterized by two types of tourmaline. Tourmaline occurs as needle-like crystals in the two-mica ± tourmaline granites (Tur G) and large patches in the pegmatites (Tur P). Both the granite and the pegmatites yield Miocene ages (ca. 20 Ma) based on monazite U(-Th)-Pb dating, whereas 40Ar/39Ar geochronology of the coarse-grained tourmalines (Tur P) crosscut by pegmatite veins yielded an Eocene mini-plateau age of 43 ± 6 Ma. Major element concentrations of tourmaline indicate that both Tur P and Tur G belong to the schorl group with a magmatic origin, but trace elements such as V indicate that they are not cogenetic. Boron isotopes suggest that Tur P (average –9.76‰) was derived from typical crustal sources, whereas Tur G (average –7.65‰) contains relatively more mafic input. The capture of Eocene tourmaline by the Miocene leucogranites at Cuonadong suggests that the crustally derived Eocene magmatism may have occurred in the southern Tethyan Himalaya. Identification of the inherited magmatic tourmaline (Tur P), although not common, challenges the current application of tourmaline chemistry to the investigation of magmatic-hydrothermal systems. [ABSTRACT FROM AUTHOR]

The Andes of central Chile are composed mostly of Cenozoic volcanic rocks, erupted during the opening and subsequent inversion of the intra-arc volcano-tectonic Abanico Basin. Until recently, the internal segmentation of this inverted basin was poorly understood. Based on a combination of U-Pb geochronology, (U-Th)/He thermochronology, whole rock geochemistry and structural data, we propose that the Abanico Basin can be divided into two main segments, separated by the NW-striking Piuquencillo fault and conjugate, NE-striking faults. Stratigraphic units defined in the northern segment (Abanico and Farellones formations) cannot be correlated with the rocks of the southern segment (Coya-Machali Formation and Teniente Volcanic Complex) in terms of lithofacies, depositional ages and geochemistry. The northern and southern segments also show temporal differences in their tectonic evolution. An early deformation event beginning at ~ 22 Ma affected only the northern segment and is associated with the formation of progressive unconformities between the Abanico and Farellones formations, and also with crustal thickening as reflected in the geochemistry of the Farellones Formation. A second stage of crustal thickening and exhumation began at ~ 12 Ma, as suggested by a sharp increase of the La/Yb ratios in the northern segment. In the southern segment, this event is reflected by only a moderate increase of La/Yb ratios, and by the transition between the Coya-Machali Formation and the Teniente Volcanic Complex. Finally, a third stage of exhumation and crustal thickening beginning at ~ 7 Ma affected both the northern and southern segments. This last stage was the main exhumation event affecting the rocks of the Andes of central Chile, and is recorded in the geochemistry of igneous rocks by a sharp increase in the La/Yb ratios in the southern segment. [ABSTRACT FROM AUTHOR]

Although the magmatism in the North American Midcontinent Rift System (MRS) is generally accepted to have formed via partial melting of the Keweenaw Plume (i.e., the plume that impinged on the MRS), the long duration of this magmatism and paleomagnetic evidence has led some authors to suggest a passive rifting model. Discerning between these two models (i.e., active vs. passive rifting) has been challenging, however, given that many of the earliest volcanic and intrusive rocks of the MRS have been variably contaminated by crustal material, masking the relative contributions of magmas derived from the plume and subcontinental lithospheric mantle (SCLM). Understanding these contributions, however, is critical to developing a genetic model for the early history of the MRS. Here, we assess these contributions by combining new Re Os isotope data of early MRS diabase sills (Nipigon, McIntrye, Inspiration sills), mafic–ultramafic sills (Shillabeer and Jackfish sills) and intrusions (Eva Kitto and Seagull), and subaerial volcanics (Wolfcamp and Coubran basalts) with previously determined Sm Nd and Rb Sr isotopes, and whole-rock geochemistry. The γOs i values of the early MRS rock suites range from slightly depleted (−10) to highly radiogenic (3857), with Initiation Stage melts (Eva Kitto and Seagull intrusions, Jackfish sill) exhibiting the smallest variability (4 to 50) and Early Stage melts (Nipigon sills, Wolfcamp basalt, and Thunder intrusion) exhibiting the greatest variability (−10 to 3857). This range of Os isotope compositions could not have resulted from variable degrees of partial melting, garnet retention in the mantle, or crystal fractionation as the values do not correlate with proxies for these processes (e.g., La/Sm, Gd/Yb, and MgO, respectively). Considering the variably elevated Th/La–Th/Nb and radiogenic εNd i –Sri values, it is possible that SCLM and/or crustal material contributed to the magmatic evolution of these rock suites. Based on mixing models in γOs i –εNd i space, the negative εNd i and slightly radiogenic γOs i of the mafic–ultramafic intrusions and sills indicates that they likely crystallized from hybrid magmas representing mixtures of enriched SCLM-derived melts with lesser plume-derived melts; these hybrid magmas were contaminated by limited amounts (<10%) of crustal material during emplacement. An SCLM source for these early MRS intrusions implies that rifting of the North American continent likely initiated passively. Given their negative to highly positive γOs i values, the diabase sills and subaerial lavas are suggested to have crystallized from melts derived from a depleted source region of the Keweenaw Plume and, with the exception of those that formed Wolfcamp basalt, were contaminated to variable degrees by crustal material. Although variable contamination can explain the negative εNd i values, it cannot independently explain the range of γOs i values because i) not all of the rock suites are contaminated (e.g., Wolfcamp basalt) and ii) the highly radiogenic γOs i values would require unrealistically high degrees of contamination. Rather, the variability likely also stems from segregation of sulfide liquid or crystallization of Os-bearing platinum-group minerals. This study demonstrates that the early MRS rock suites did not all crystallize from plume-derived melts as may be expected in a model whereby rifting initiated as a result of plume impingement. Rather, the earliest rock suites (>1109 Ma) crystallized from melts derived from the SCLM, indicating that rifting likely initiated passively. • The Keweenaw Plume must have contained source regions that were isotopically depleted. • The magmas from which the earliest MRS rock suites crystallized originated largely from the subcontinental lithospheric mantle. • Rifting of North America was not initiated by plume impingement, but rather initiated passively. • The radiogenic γOs i composition of the early MRS rock suites resulted from a culmination of several processes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Porphyry- and epithermal-style mineralization is associated with ∼ 130 Ma magma event. • The mineralizing fluids were predominantly magmatic water with addition of meteoric water. • Metal deposition resulted from cooling, sulfidation, neutralization, and boiling of fluids. The Naozhi deposit in the Yanbian district of northeastern China contains polymetallic epithermal veins and subeconomic porphyry-style Cu mineralization within 2 km of each other. These two mineralization styles are genetically associated with 130–126 Ma andesites and dioritic–granitic intrusions. Isotopic ages determined on sericite (128.2 ± 2.9 Ma; 40Ar–39Ar plateau age) and sulfide (124.6 ± 2.7 Ma; Rb–Sr isochron) associated with the epithermal mineralization constrain the hydrothermal activity to at approximately 128 Ma. Three types of fluid inclusions, including halite-bearing, vapor-rich, and liquid-rich inclusions were trapped in quartz from porphyry-style veinlets associated with an assemblage of K-feldspar–biotite–magnetite. Based on microthermometry and the homogenization behavior of halite-bearing inclusions, they were trapped at lithostatic pressures of > 500 bars and at temperatures of ≥ 350 °C, whereas the vapor- and liquid-rich inclusions were trapped at pressures and temperatures of 110 ± 35 bars and ≤ 350 °C. Epithermal mineralization comprises four vein stages, which, from oldest to youngest, are quartz–pyrite, quartz–base metal sulfide, quartz–precious metal, and quartz–carbonate. The ore assemblage precipitated from low-salinity fluids (<10 wt% NaCl equiv.) at temperatures and pressures of ≤ 350 °C and ≤ 100 bars. The δ18O H2O (2.5 to −2.4 ‰) and δD H2O (−85 to −114 ‰) compositions of fluids related to porphyry- and epithermal-style mineralization indicate a mixture of magmatic and meteoric waters. The δ34S H2S (−3.1 to 4.5 ‰) values of fluids become isotopically heavier from the quartz–pyrite stage to the quartz–base metal sulfide stage, reflecting continuous reduction during epithermal mineralization. The mineral assemblage and chemical composition of sulfide minerals indicate a transition from oxidizing, high sulfidation porphyry-style fluids to reducing, intermediate–low sulfidation epithermal fluids, with log ƒO 2 values ranging from −31 to > −33, and log ƒS 2 values ranging from −7.0 to ≤ −13.4 during the epithermal veining stage. Metal deposition in the Naozhi magmatic–hydrothermal system resulted from cooling, sulfidation, neutralization, and boiling of predominantly magmatically sourced hydrothermal fluids that mixed with meteoric water. [ABSTRACT FROM AUTHOR]

Stratabound ore has been recognized as an end-member of porphyry copper systems, but pyrite chemistry has not been widely applied to linking stratabound ore with the related porphyry and skarn system. Stratabound ore is commonly developed around porphyry-skarn systems in eastern China, and is characterized by abundant colloform pyrite; however the origin of the colloform pyrite has been contentious. Xinqiao deposit is ideal for study of pyrite geology and geochemistry with the aim of elucidating formation of the stratabound ore and to decipher the evolution of pyrite compositions in a porphyry-skarn environment. The colloform pyrite paragenesis and S isotopes indicate that it formed during early skarn mineralization, based on its occurrence in stockwork veins cutting skarn minerals, and that it is replaced by later hypogene sulfides; the δ34S of colloform pyrite (average 6.12‰) is close to the δ34S value of both porphyry- (average 5.06‰) and skarn-type pyrite (average 4.65‰). The colloform texture formed as an aggregate of nanometer- or micrometer-sized (<0.2 μm) pyrite cubes produced by rapid crystallization from a high-fS2, low-temperature, and supersaturated fluid. Supersaturation of the fluid was probably produced by rapid decompression that triggered fluid boiling and cooling when the magmatic-hydrothermal fluid (derived from Cretaceous magma) flowed along the Devonian-Carboniferous unconformity. Subsequently, the colloform pyrite was replaced by later stage pyrite with distinctive trace elements (Co, Ni, and Se), indicating that the stratabound ore at Xinqiao formed from multiple pulses of magmatic-hydrothermal fluids derived from an Early Cretaceous stock. Co, Ni, and Se enrichment in porphyry- and proximal skarn-type pyrite suggests they formed at relatively high temperature, whereas the colloform pyrite shows trace element contents (Cu, Pb, Zn, Ag, and Bi) similar to those in distal skarn pyrite, suggesting that they may have formed in the same fluid environment. The trace element variations in pyrite from stratabound, skarn and porphyry ore probably resulted from decreasing fluid temperature and increasing pH away from the source. Our data, combined with previous studies, show that Co and Ni in pyrite increase toward porphyry and skarn ore, whereas As, Sb, Pb, Ag, and Bi are enriched in pyrite in distal stratabound ore, which extends for 1–2 km away from the intrusion. A plot of As/Se vs. Co discriminates the three ore types that occur associated with porphyry-skarn Cu systems in the Middle and Lower Yangtze belt (MLYB). These results indicate pyrite chemistry can be effective in discriminating the genesis of different deposit types related to porphyry-skarn systems and can potentially be used as a vectoring tool during exploration in the MLYB and elsewhere. [ABSTRACT FROM AUTHOR]

The petrogenesis of the world famous Koktokay No. 3 pegmatite in the Chinese Altai Mountains is still enigmatic due to its superenrichment of rare metals and the apparent absence of a parental granite. We present results from a granite apophysis that was recently discovered in the No. 3 pegmatite open pit. Results show that it has low K/Rb (32.35-38.76), Zr/Hf (13.78-23.30), Nb/Ta (1.00-6.02), and extremely low K2O/Na2O (0.12-0.20) ratios, which, together with its mica composition and the occurrences of garnet, indicate that it is a highly evolved muscovite albite granite. Columbite and apatite from the granite apophysis yielded U-Pb ages of 182.3 ± 1.0 Ma and 184.9 ± 4.3 Ma, respectively, which are younger than the Triassic ages (ca. 210 Ma) of the main magmatic stage but fall into the age range of the No. 3 pegmatite series (220-175 Ma). Both the granite and the apatite grains within it share nearly identical rare earth element patterns with the magmatic stage of the No. 3 pegmatite. The whole-rock εHf(t) values (t = 183 Ma) range from -0.11 to +1.32, consistent with those of the No. 3 pegmatite and indicating a similar source. We propose that the Jurassic granite represents a late pulse of magma injected as apophyses from a deep-seated magma chamber (perhaps from the lower crust), which overlapped with the early pegmatite and promoted the rare metal mineralization. The No. 3 pegmatite and the Jurassic granite may represent a continuous magmatic system with a 50 m.y. melting process, generating this unusual giant pegmatite intrusion with abundant rare metals. [ABSTRACT FROM AUTHOR]

Abstract: New radiogenic isotope data are presented for intrusive rocks of the Mesoproterozoic Midcontinent Rift from the north shore of Lake Superior. These mafic rocks are amongst the older portions of the rift sequence and offer insights into the early development and evolution of the rift. Two sill suites are recognized within the study area, an earlier, spatially restricted ultramafic unit termed the Riverdale sill and the predominant Logan sills, as well as three dike sets, the north-east trending Pigeon River swarm, the north-west trending Cloud River dikes and the Mt Mollie dike. In addition an enigmatic extrusive unit termed the Devon basalts is also present. The Logan sills are characterized by 87Sr/86Sri values of 0.7048–0.7119, with 143Nd/144Nd values from 0.512012 to 0.512187, whereas the Riverdale sill is characterized by 87Sr/86Sri values ranging from 0.7037 to 0.7078 and 143Nd/144Nd of 0.511938–0.511984. Both the Cloud River and Pigeon River dikes show a range of isotope data with the Cloud River dikes having 87Sr/86Sri values ranging from 0.7042 to 0.7064 and 143Nd/144Nd values from 0.512222 to 0.512379 whereas the Pigeon River dikes have 87Sr/86Sri values from 0.7041 to 0.7243 and 143Nd/144Nd from 0.511640 to 0.512383. The Mt. Mollie dike is characterized by 87Sr/86Sri of 0.7041–0.7074 and 143Nd/144Nd values range from 0.512014 to 0.512371. The majority of samples are characterized by negative ɛNdT, which are interpreted to be the result of contamination of a plume-related mantle source by older crustal material. The lack of correlation with other indices of fractionation (e.g., SiO2) for the majority of samples implies interaction with subcontinental lithospheric mantle, either through assimilation or melting of the mantle, rather than contamination during emplacement. However, a small number of samples appear to have assimilated material during emplacement resulting in strongly negative ɛNdT values. The radiogenic isotope data are consistent with a suite of rocks that have undergone complex contamination histories requiring variable crustal residence times and assimilation of material both at depth, in large magma chambers, and during emplacement. [Copyright &y& Elsevier]

Abstract: The ∼3Ga North Caribou greenstone belt comprises a package of volcanic and sedimentary rocks metamorphosed from greenschist to upper amphibolite grade, surrounded by ∼2.7–3.0Ga granitoids and gneisses and is host to the Musselwhite gold mine, a large orogenic gold deposit. New U–Pb (zircon, monazite), Ar–Ar (biotite) and Sm–Nd (garnet) ages for volcanic, sedimentary and intrusive rocks from the Musselwhite mine and surrounding plutons have been obtained. Felsic volcanic rocks yielded ages of 2972.4±1.6 and 2982.4±0.8Ma, broadly consistent with existing ages for volcanic rocks and plutonism. An age of 2857.3±1.4Ma for the Schade Lake gneiss is consistent with published plutonic and volcanic ages. A younger, and previously unrecognized, plutonic event is represented by three granites dated at 2723.1±0.8, 2727.7±1.0 and 2729.4±7.1Ma. An Sm–Nd age of 2690±9Ma for garnets associated with gold mineralization is bracketed by peraluminous granites with ages of 2668.8±1.1 and 2715.8±1.6Ma. Ar–Ar ages range from 2420±11.97 to 2658±13.46Ma, broadly synchronous with the youngest intrusive age, and are consistent with progressive resetting due to metamorphism. The new geochronological data for the NCGB show that volcanism in the Opapimiskan Lake area spanned 10 million years from 2982.4 to 2972.4Ma, allow for new stratigraphic interpretations of the belt and are broadly correlative with other greenstone belts in the North Caribou terrane. The new data for the NCGB and associated plutons are consistent with ∼3Ga plume-related activity forming a proto-craton that was the site of successive sedimentary basins over the next ∼150 million years. Subsequent plutonism is consistent with supra-subduction zone processes at the margins of this proto-continent by ∼2.87Ga and is best interpreted as the result of horizontal tectonic processes consistent with those operating in the Phanerozoic, with the plutons emplaced behind continental margin arcs on the edges of the craton. Sm–Nd ages of garnets that are coeval with mineralization suggest that the orogenic gold mineralization at the Musselwhite mine was broadly synchronous with the ∼2700Ma orogeny caused by the collision of the Oxford-Stull domain with the North Caribou terrane ∼75km northeast of the Musselwhite mine and furthermore argues that S-type granites may play a greater role in the formation of some orogenic gold deposits than has been previously recognized. [Copyright &y& Elsevier]

Abstract: Attempts to decipher the petrogenesis of Archean Trondhjemite–Tonalite–Granodiorite (TTG) and establish trends in their compositions over time typically do not assess the possible role of assimilation–crystal fractionation processes. Studies of TTG suites worldwide, however, demonstrate that reprocessing of older crust is common. Felsic volcanic and intrusive rocks from the North Caribou Lake area, located in the nucleus of the Superior Province, exhibit a range of compositions that are not accounted for by variable degrees of amphibolite melting alone. Characteristic of Archean TTG, the rocks mainly fall in the lower right hand quadrant of a Nb/Ta vs Zr/Sm plot but they also show clear trends between εNdT and ratios such as Al2O3/TiO2, Th/Nb, [Tb/Yb]N and Eu/Eu*. The lowest Nb/Ta values in the TTG likely result from crystal fractionation including titanite, which strongly partitions and fractionates these elements. [Copyright &y& Elsevier]

Abstract: The Midcontinent Rift (MCR) of North America comprises a series of basaltic sheets, flows and intrusive rocks emplaced in the Lake Superior region during the Mesoproterozoic. The mafic rocks preserved on the northern flank of Lake Superior represent the older portions of the rift sequence and offer insights into the early development of the rift. New geochronological, geochemical and paleomagnetic data are presented for the dikes and sills located in and south of Thunder Bay, Ontario. Three sill suites are recognized within the study area; an earlier, spatially restricted ultramafic unit termed the Riverdale sill, the predominant Logan sills and Nipigon sills in the north of the study area. In addition three dike sets are recognized, the north-east trending Pigeon River swarm, the north-west trending Cloud River dikes and the Mt. Mollie dike. The geochemical data demonstrate that the majority of sills south of Thunder Bay are of Logan affinity and distinct from those of broadly similar age in the Nipigon Embayment to the north. The Pigeon River dikes that intrude the sills are geochemically coherent but distinct from the Logan sills and could not be feeders to the sills. The new age of 1109.2±4.2Ma for the Cloud River dike and its R polarity are consistent with published magnetostratigraphy. The Mt. Mollie dike age (1109.3±6.3Ma) indicates that it is not coeval with the spatially associated Crystal Lake gabbro as previously thought. The complexity of the dike and sill suites on the northern flank of suggests that the early phases of rifting occurred in distinct and changing stress fields prior to the main extensional rifting preserved in younger rocks to the south. The geochemistry and geochronology of the intrusions suggest a long-lived and complex magmatic history for the Midcontinent Rift. [ABSTRACT FROM AUTHOR]

[Display omitted] • Three types of scheelite were recognized from the different skarn stages of Machangqing. • Mo contents indicate temperature and fO 2 variations in different skarn stages. • The REE pattern and Eu anomaly of scheelite inherited from the metallogenic fluids. • Higher fO 2 lead to a larger deposit size at Beiya compared to Machangqing. The Machangqing Cu-Mo (-Au) deposit lies in the middle of the Jinshajiang-Ailaoshan alkaline porphyry metallogenic belt, and skarn is one of the main mineralization styles in the deposit. Scheelite from the Machangqing skarn occurs as discrete grains present in the early to late skarnization stages of the deposit, which can be divided into three types based on their occurrence: scheelite I in the prograde skarn, scheelite II (including the early scheelite II-a and the late scheelite II-b) in the retrograde alteration and scheelite III in the quartz-sulfide stages. In the CL images, scheelite grains of all three types have core- (mantle-) rim textures displaying CL-dark cores and CL-bright rims. The REE content could act as quenchers reducing CL intensity of the Machangqing scheelite. The Mo content of these scheelite types ranges from 0.5% to 13.6%, and Scheelite II-b is significantly enriched in MoO 3 compared to other scheelite. Scheelite I and scheelite II-b exhibit right-dipped REE patterns, whereas scheelite II-a and scheelite III exhibit slightly middle rare MREE enriched patterns and flat REE patterns, respectively. The Eu anomaly differs between different types of scheelite, most of which exhibit variable negative Eu anomalies. Our study reveals that the substitution mechanism of REE for Ca in the Machangqing scheelite was probably 3Ca2+ =2REE3+ + □Ca and 2Ca2+ = REE3+ + Na+. The ore-forming fluids may be magma-derived. Mo contents of the Machangqing scheelite are generally controlled by the temperature and fO 2 of the ore-forming fluids. The Mo variations in scheelite from different stages indicate a temperature decrease from the prograde to the early retrograde skarn stages, followed by fO 2 increasing from the early retrograde to the late retrograde skarn stages, then decreasing to the quartz-sulfide stage. The Eu anomaly of scheelite was probably inherited from the ore-forming fluids and not dependant on the fO 2 of hydrothermal fluids in the Machangqing deposit. [ABSTRACT FROM AUTHOR]

The Lake Nipigon Region Geoscience Initiative (LNRGI) was a 3-year collaborative geoscience data acquisition and compilation project that focussed on Lake Nipigon in Ontario and involved partnerships between mineral industry, university, and provincial and federal government geoscientists. A major objective of the initiative was to collect new geoscience information to better understand the geological history of the Nipigon region to inform land-use planning, identify areas of high mineral potential, and attract mineral exploration. The Special Issue on the LNRGI highlights the scientific successes of the Initiative in the fields of geology, petrology, geochemistry, geochronology, stratigraphy and basin analysis, mineral deposits, and surficial geology and geochemistry. [ABSTRACT FROM AUTHOR]

The ca. 1110–1120 Ma diabase sills of the Nipigon Embayment represent the oldest phase of the Midcontinent Rift recognized to date. The sills can be subdivided into five geochemically distinct suites: Nipigon, McIntyre, Inspiration, Shillabeer, and Jackfish. Sm–Nd, Rb–Sr, and Pb–Pb isotope data for the sills can be used to evaluate the source regions and emplacement histories of these sills. The εNdT values for all the sill suites are consistently negative (–0.5 to –6.6) but show coherent variations both within and between suites. The negative εNdT values can be interpreted as the result of contamination of a plume-related mantle source by older crustal material. The initial strontium (Sri) values (0.7032–0.7068) for the sills indicate that at least two distinct contaminants are required: (1) a source with strongly negative εNdT and lower Sri, likely Archean metasediment or granite, and (2) one with elevated Sri, likely sedimentary rocks of the Proterozoic Sibley Group. The Pb data for the Nipigon and Inspiration sills form distinct linear arrays consistent with variable contamination of a source comparable to that of other igneous suites of the Midcontinent Rift. The radiogenic isotopes preserve a complex contamination history best interpreted as the result of <5% contamination by a variety of Archean and Proterozoic sources. The ultramafic Jackfish sill shows the least evidence of contamination and is interpreted to have been emplaced along a crustal-scale fault with little interaction with crustal material. In contrast, the other sill suites have undergone complex contamination histories requiring variable crustal residence times and assimilation of material both at depth in large magma chambers and during emplacement. [ABSTRACT FROM AUTHOR]

The Mesoproterozoic 1108–1105 Ma Osler Group, a 3 km thick succession of basaltic flows and sedimentary units on the north shore of Lake Superior, is among the oldest expressions of the Midcontinent Rift. Basal sediments of the Simpson Island Formation (new name) deposited by braided fluvial systems record westward transport of debris eroded from local Archean and Proterozoic rock units. Strata deposited by this fluvial system are intercalated with, and overlain by, ocean-island basalt (OIB)-like basalts, which become increasingly contaminated up section (εNd(1100Ma) = +0.3 to –5.3). The light rare-earth element (LREE) enriched (La/Smn = 1.5–3.9) and heavy REE (HREE) fractionated (Gd/Ybn = 1.5–3.7) subaerial flows are divisible into two units that correlate with other sections of the Osler Group to the east, but simple correlations with more distant sequences are difficult. The volcanic rock dominated portion of the succession is overlain by a thin (25 m thick) conglomerate–sandstone assemblage representing southeast progradation of an alluvial fan in a semi-arid climatic setting. Clast lithologies and geochemistry indicate no extra-rift detritus was delivered from the hinterland of the fan. Various lines of evidence in both volcanic and sedimentary rocks support a scenario where early, pre-1108 Ma, subsidence along a north–south axis from the western arm of the rift to the Nipigon Embayment was replaced by subsidence along the east–west rift axis between 1108 and 1105 Ma. [ABSTRACT FROM AUTHOR]

Abstract: A compositionally diverse group of basaltic flows are present in the 2.7 Ga St. Joseph assemblage of the St. Joseph greenstone belt, Uchi Subprovince. A spectrum of light rare earth element (LREE) depleted to enriched patterns corresponds to low-, medium- and high-K series (LKS, MKS, HKS) basalts, shoshonites and leucitites of some modern arcs. More primitive, tholeiitic LKS and MKS basalts plot with counterparts from modern intraoceanic arcs, such as the South Sandwich Islands, and show no evidence of contamination by continental crust. Consequently they are interpreted to have erupted in an oceanic setting. There is an array from low Nb with high Zr/Nb (29) to high Nb but lower Zr/Nb (15) indicative of a mantle wedge similar to average mid ocean ridge basalts (MORB; average Zr/Nb=32). These basalts also show positive to negative Nb, Hf and Zr anomalies. Negative anomalies are interpreted as the product of first stage melting, where LREE and MREE are added to the mantle wedge from dehydration of the slab, leaving a residue with high Nb/La, Hf/Nd and Zr/Nd. Second stage melts inherit the high HFSE/REE ratios. Within the Birch–Uchi greenstone belt, basalts of the ∼2.8 Ga Woman assemblage includes both LKS and HKS. These are characterized by similar Nb–Zr/Nb and HFSE/REE systematics, signifying that these are general features of sub-arc mantle wedges that developed over 100 Ma in Uchi subprovince arcs. Enriched St. Joseph assemblage basaltic rocks cannot stem from sediment melting on the slab, as Th/Ce ratios are generally <0.1. Neither can they derive from an ocean island basalt component because Nb anomalies do not correlate with La/Ybn. Rather, the trend from primitive LKS through MKS to HKS, leucitite and shoshonite is interpreted to reflect progressively lower degrees of partial melting at increasing depths and/or less depleted mantle wedge. [Copyright &y& Elsevier]

The Mesoproterozoic English Bay Complex consists of a granite-rhyolite assemblage outcropping on the shores of Lake Nipigon in western Superior Province, Canada. It intrudes Neoarchean rocks and is disconformably overlain by a rift–infracratonic basin sedimentary succession recording subsidence following a heating event. The granites and rhyolites are characterized by light rare-earth element (LREE) enrichment (La/Smn = 2.8–5.1) and only weakly fractionated heavy REE (HREE; Gd/Ybn = 1.1–1.6). The felsic igneous rocks are high-K, enriched in Zr, Nb, Y, and REE satisfying all the criteria for an A-type suite. Trace element geochemistry, particularly the absence of any negative Nb anomalies, indicates this melt did not originate in a suprasubduction zone setting, unlike the St. Francois Mountain Complex to the south. The English Bay Complex may record the northern portion of a Mesoproterozoic plume track— a plume that possibly led to earlier igneous activity and infracratonic basin formation to the north and would later interact with a suprasubduction zone margin to the south. [ABSTRACT FROM AUTHOR]

The ∼2.89 Ga Pickle Crow assemblage of the Pickle Lake greenstone belt is located within the central Uchi subprovince of the Superior Province. Tholeiitic basalts at the base of the assemblage have uniform SiO2 contents and MgO spanning 10.5–3.1 wt.%. They plot with modern intraoceanic arcs in Ce–Yb co-ordinate space. There are positive to negative Nb, P and Hf anomalies, but negative anomalies dominate. Ti anomalies are systematically negative and Nb and Hf anomalies are correlated. These features are consistent with a two stage melting regime in a convergent margin. During first stage melting LREE are more mobile than Nb, P, Hf and Ti, generating basalts with negative anomalies of these elements and a refractory residue with complementary positive anomalies; as a result second stage melts inherit positive anomalies of Nb, P and Hf. The basalts plot on a hyperbolic mixing array from a high Nb (4–8 ppm), high La/Ybn, but low Zr/Nb member to a low Nb (2–4 ppm), low La/Ybn, but high Zr/Nb counterpart, indicative of a heterogeneous subarc mantle source, as depleted to slightly enriched compared to mid ocean ridge basalts, the source of which is prevalent in modern arcs. Collectively, the data can be interpreted as a paired arc–back arc where first stage melting in the back arc (low Zr/Nb), generated higher Nb basalts, and the depleted residue (high Zr/Nb) was drawn by induced convection beneath the arc where second stage melting produced lower Nb basalts. Alternatively, there was a single arc with a heterogeneously depleted subarc mantle wedge. [Copyright &y& Elsevier]

Geochemical data from the ∼2.9-Ga Northern Pickle assemblage of the Pickle Lake greenstone belt in the northern Superior Province distinguish three distinct volcanic suites. Suite I, from the north of the assemblage, comprises tholeiitic basalts with unfractionated rare earth elements (REE). Suite II basalts are light REE (LREE)-enriched with negative mantle-normalized Nb anomalies relative to Th and La, similar to the CA suite of Sajona et al. [J. Petrol. 37 (1996) 693]. Basalts from Suite III are also LREE-enriched but lack negative Nb anomalies. Normalized Nb abundances are either similar to or higher than Th and La, comparable to Nb-enriched basalts (NEB) from Phanerozoic arcs. Variable high field strength elements and heavy REE (HREE) systematics support the subdivision of Suite III basalts into two spatially distinct suites. Suite IIIa is interpreted to have melted at relatively shallow depths in the presence of Nb–Ti-bearing silicates whereas Suite IIIb melted in the presence of garnet. Variations in the geochemistry of the three suites can be accounted for by interaction among primitive mantle, adakite melts, and subduction-modified mantle. The association of the three suites is interpreted to be the result of rifting in a back-arc environment, characterized by Suite I tholeiites, permitting asthenospheric upwelling of subduction-modified NEB and associated arc-like volcanic rocks (Suites II and III). The association of arc-like basalts (Suite II) with NEB (Suite III) in the Northern Pickle assemblage extends the known occurrence of Archean NEB beyond the ∼2.7-Ga age of previously recognized examples. [Copyright &y& Elsevier]

Provides insights on the evolution of the Trans-Hudson orogen prior to amphibolite-grade metamorphism in Canada. Evaluation of the tectonic setting of magma generation between 1840 and 1820 Ma.; Stages of continental collision; Geologic history of the Kisseynew domain granitoids.

[Display omitted] • Yuleken porphyry Cu-Mo deposit is a superimposed porphyry deposit. • Rb-Sr isotopes of chalcopyrite show that it formed during deformation. • The trace element and in situ -S isotope of chalcopyrite can distinguish distinct episodes of mienralization. The Yulekenhalasu porphyry Cu–Mo deposit is located ca. 40 km southwest of Qinghe, in the Chinese Altay-East Junggar section of the Central Asian Orogenic Belt, NW China. The belt preserves multistage tectonic-hydrothermal and porphyry Cu-Mo mineralization events associated with arc to syn- and post-collision environments over 87 m.y. The 359 Ma deformed granitic porphyries are characterized by positive ε Nd(t) (+0.62 to + 3.77) and (87Sr/86Sr) initial values (0.704304–0.705960), and old crustal model ages of 747 to 1216 Ma, whereas a 272 Ma sample from late chalcopyrite–molybdenite–pyrite–magnetite–feldspar–calcite–gypsum veins yielded (87Sr/86Sr) initial values of 0.704415 to 0.705764, high ε Nd(t) values (+5.81 to + 5.88) and young crustal model ages (715 to 614 Ma) suggesting an increasingly juvenile mantle source over time. Seven fragments of a single deformed chalcopyrite grain yielded an Rb-Sr isochron age of 358.6 ± 4.8 Ma (2σ, MSWD = 1.8), which is consistent with the 360 Ma recrystallized zircon grains in the deformed host granitic porphyries. Eight fragments of chalcopyrite from the chalcopyrite–molybdenite–pyrite–magnetite–feldspar–calcite–gypsum veins formed along cleavage planes yielded a younger Rb-Sr isochron age of 272.2 ± 2.6 Ma (2σ, MSWD = 1.8). The younger age is interpreted as the lower age limit for the Mo and Cu mineralization in the post-collisional stage. The heterogeneous initial Sr isotopic compositions of chalcopyrite in the Yulekenhalasu deposit are likely the result of phyllosilicate inclusions. Disseminated chalcopyrite crystals in the granitic porphyry have different trace elemental contents than chalcopyrite in the deformed granitic porphyry and late chalcopyrite veins. Our Rb-Sr and trace element data for chalcopyrite grains constrain the age and geochemistry of multistage mineralization in porphyry Cu-Mo deposits. In-situ S isotope data of chalcopyrite from the deformed granite porphyries and chalcopyrite-feldspar-quartz-muscovite veins display a similar mantle origin. The 272 Ma mineralization event at Yulekenhalasu is coeval with the formation age of the Cu-Ni-(PGE) sulfide deposit in the Chinese Altay, indicating that hydrothermal mineralization like that in porphyry deposits can form proximal to ultramafic–mafic rocks and potentially may have a genetic relationship with mantle-derived Cu-Ni-(PGE) sulfide deposits. [ABSTRACT FROM AUTHOR]

[Display omitted] • Scheelite in the Jiaodong orogenic deposits is similar to that from orogenic gold deposits in other greenstone belts. • Eu anomaly of the Xiadian and Majiayao scheelite is controlled by REE substitution and/or fluid compositions. • Sr isotope signature of scheelite is significantly influenced by meta -sedimentary rocks. • Pb isotope represents a result of remobilization Pb from old lithologies. • Metals of the Jiaodong gold deposits are associated with large-scale fluid-rock interaction at shallow crustal levels. Orogenic gold deposits in the Jiaodong Peninsula contain >5000 t of known gold resources. Precambrian metamorphic rocks and Mesozoic granite represent the main host rocks for these deposits, but gold deposition (~120 Ma) is significantly younger and it remains unclear whether some of the metals are sourced from the local country rock to these mineral systems. This study uses in situ geochemistry and isotope signatures of scheelite (Sr isotopes) and galena (Pb isotopes) at the Xiadian and Majiayao gold deposits to determine the role, if any, of country rock compositions on the formation of gold ore systems in the Jiaodong Peninsula. Scheelite from the two gold deposits occurred as part of a syn -mineralization stage with quartz, siderite, ankerite, and pyrite in the main orebody and/or its footwall. New results show that scheelite yields high Sr (>200 ppm) and low Mo (<40 ppm) and As (<5 ppm) concentrations, bell to flat REE profiles, and variable Eu anomalies. These scheelite compositions are very similar to previously published results from orogenic-style gold deposits in greenstone belts, indicating fluids with similar geochemical properties. The Xiadian scheelite with negative Eu anomalies may be controlled by REE substitution mechanisms and the composition of parent fluids that may have interacted with graphitic formations of the Jingshan Group, while the Majiayao scheelite with positive Eu anomaly is most likely the result of crystallographic controls on REE partition. New scheelite Sr isotope results for the Xiadian (87Sr/86Sr: 0.71258–0.71540) and Majiayao (87Sr/86Sr: 0.71568–0.71930) deposits further support interaction between hydrothermal fluids and local to distal country rocks. The high radiogenic Sr isotope signature of scheelite from the Majiayao deposit is primarily derived from the regional Jingshan and/or Penglai Group meta -sedimentary rocks. Galena in the Xiadian deposit, which occurs with pyrite in the syn -mineralization stage, has Pb isotope signatures of 206Pb/204Pb: 17.185 ± 0.004 that may reflect mixing between the Linglong granite and/or metamorphic rocks. The Majiayao galena yields the least radiogenic Pb isotope results (206Pb/204Pb: 16.554 ± 0.040), which are consistent with sulfide in the Jiaodong Group meta -volcanic rocks (206Pb/204Pb: 16.270–16.718) and suggest remobilization of Pb from sulfide within the previously metamorphosed formation. New geochemistry and isotope results document a mixed metal contribution that likely occurred as a consequence of fluid-rock interaction between ore-forming fluids and wall rocks at shallow crustal depths (<10 km). Such processes may have played a critical role in generating similar metallogenic features of the Jiaodong gold deposits as well as syn -metamorphic orogenic gold deposits in other greenstone belts. Our study highlights that the remobilization and precipitation of metals (Pb, Sr, W, and possible Au) scavenged from country rocks are perhaps ubiquitous processes, whether in syn- and/or post-metamorphism orogenic gold systems. [ABSTRACT FROM AUTHOR]

Cerium (Ce) anomalies can be used to distinguish diagenetic and hydrogenetic nodules, making them an important discriminator for the genesis of marine ferromanganese nodules. To understand the enrichment and adsorption mechanisms of Ce in different types of ferromanganese nodules, we conducted mineralogical and geochemical studies on ferromanganese nodule layers formed through both hydrogenetic and early diagenetic processes as well as adsorption experiments on synthetic δ-MnO 2 to monitor the Ce uptake during the different processes. The major and trace element contents of natural ferromanganese nodule layers were investigated by SEM, EPMA and LA-ICP-MS analysis. The marine nodule studied in this study consisted of a core of fish tooth and a rim that could be divided into the hydrogenetic (type I) and early diagenetic (type II) layers based on their mineralogy and Mn/Fe ratios. The Mn oxide mineral assemblage is composed of todorokite, buserite, birnessite, and vernadite (δ-MnO 2) and occurred in both type I and II layers. The type I layer has laminated structures with a low Mn/Fe ratio (1.1–3.2; averaging at 1.7), and low Cu, Ni and Mg contents consistent with a hydrogenetic genesis. The type II layer has a columnar and stromatolitic structure with a high Mn/Fe ratio (5.1–54.0; averaging at 23.3) and high Cu, Ni and Mg contents that are similar to early diagenetic nodules. The ΣREE contents in type I and type II layers are 1405–3506 ppm (averaging at 2091 ppm) and 199–1232 ppm (averaging at 674 ppm), respectively, indicating that the REE is enriched in the hydrogenetic type I layers. Strong positive Ce anomalies are present type I layers ranging from 1.2 to 2.5 (averaging 1.9), but only slightly positive are seen in type II ranging from 0.4 to 2.4 (averaging at 1.0). Synthetic experiments to monitor the Ce uptake process show that Ce can be adsorbed onto δ-MnO 2 with the XRD and FTIR patterns suggesting that the structure of δ-MnO 2 did not change significantly, consistent with Ce behavior in hydrogenetic nodules. The results suggest that Ce is predominantly concentrated in hydrogenetic nodules in an oxic environment, whereas in the early diagenetic layer, there is less oxidation and fixation of Ce due to the suboxic conditions. Our findings are consistent with Ce anomalies in marine Fe-Mn nodules being the result of Mn oxide oxidation adsorption and then fixation (oxidation) after adsorption. [Display omitted] • Morphology and geochemistry results confirm the hydrogenetic and diagenetic genesis of the ferromanganese nodule. • LA-ICP-MS analysis shows that Ce anomalies are distinctly different in hydrogenetic and diagenetic nodules. • Adsorption experiments suggest that Ce is adsorbed on the surface of δ-MnO 2. [ABSTRACT FROM AUTHOR]

Presents information pertaining to the influence of the long-lived mantle on an Archean protocontinent, with reference to the 3 Ga Lumby Lake greenstone belt, Ontario, Canada. Important consequences of the recognition of the complex geodynamic settings in the Archean; Information on the Archean rock record; What investigations of mantle-flow dynamics indicates.

• Sulfide-rich fibrous veins and miarolitic cavities represent the magmatic–hydrothermal transition in porphyry systems. • Fractional crystallization process could induce the exsolving of sulfur from magma to porphyry systems. • Color cathodoluminescence can be used to unravel the paragenesis of ore-bearing in porphyry deposit. The Qiongheba porphyry Cu deposit is characterized by geochemical features of island arc and adakitic intrusions with fractional crystallization playing a key role in the formation of the ore-bearing rocks. Calculated sulfur concentrations in silicate melts at sulfide saturation show that two-thirds of the sulfur was exsolved during the fractional crystallization process to contribute to the formation of sulfides. The ore-bearing rocks in the Qiongheba area yielded U-Pb zircon ages of 414–412 Ma coeval with the 412 Ma Re-Os age of molybdenite indicating that sulfide mineralization is broadly coeval with magmatic crystallization. The color cathodoluminescence of quartz (purple) and K-feldspar (pink) in the fibrous veins and miarolitic cavities (Qtz-2 and Kfs-2) are the same as those (Qtz-1 and Kfs-1) in the granitic porphyry whereas the hydrothermal quartz (Qtz-3) and K-feldspar (Kfs-3) are black and green, suggesting that the color cathodoluminescence can be used to unravel the paragenesis of PCD. The oxygen isotopic values of Qtz-1 and Qtz-2 range from 9.15 to 10.1‰ and 8.93 to 10.4‰ with calculated equilibrium fluid compositions of 9.86 to 11.7‰ and 10.5 to 12.0‰, respectively, indicating a magma-dominated fluid composition, whereas Qtz-3 veins have very low oxygen isotopic values from −4.60 to −1.25‰ with corresponding fluid compositions of −3.51 to −0.17‰, implying that the fluid formed via the mixing of magmatic and meteoric water. Titanium-in-quartz thermometry constrains the magmatic crystallization to 580–627 °C, whereas the magmatic to hydrothermal transition occurred at 523–613 °C. [ABSTRACT FROM AUTHOR]

The origin of stratabound deposits in the Middle-Lower Yangtze River Valley Metallogenic Belt (MLYRB), Eastern China, is the subject of considerable debate. The Xinqiao Cu-Fe-Au deposit in the Tongling ore district is a typical stratabound ore body characterized by multi-stage magnetite. A total of six generations of magnetite have been identified. Mt1 is commonly replaced by porous Mt2, and both are commonly trapped in the core of Mt3, which is characterized by both core-rim textures and oscillatory zoning. Porous Mt4 commonly truncates the oscillatory zoning of Mt3, and Mt5 is characterized by 120° triple junction texture. Mt1 to Mt5 are commonly replaced by pyrite that coexists with quartz, whereas Mt6, with a fine-grained foliated and needle-like texture, commonly cuts the early pyrite as veins and is replaced by pyrite that coexists with calcite. The geochemistry of the magnetite suggests that they are hydrothermal in origin. The microporosity of Mt2 and Mt4 magnetite, their sharp contacts with Mt1 and Mt3, and lower trace-element contents (e.g., Si, Ca, Mg, and Ti) than Mt1 and Mt3 suggest that they formed via coupled dissolution and reprecipitation of the precursor Mt1 and Mt3 magnetite, respectively. This was likely caused by high-salinity fluids derived from intensive waterrock interaction between the magmatic-hydrothermal fluids associated with the Jitou stock and Late Permian metalliferous black shales. The 120° triple junction texture of Mt5 suggests it is the result of fluid-assisted recrystallization, whereas Mt6 formed by replacement of hematite as a result of fracturing. The geochemistry of the magnetite suggests that the temperature increased from Mt2 to Mt3 and implies that there were multiple pulses of fluids from a magmatic-hydrothermal system. Therefore, we propose that the Xinqiao stratiform mineralization was genetically associated with multiple influxes of magmatic hydrothermal fluids derived from the Early Cretaceous Jitou stock. This study demonstrates that detailed texture examination and in situ trace-elements analysis under robust geological and petrographic frameworks can effectively constrain the mineralization processes and ore genesis. [ABSTRACT FROM AUTHOR]

The question of whether the high U and Th concentrations in zircon are primary or secondary is often difficult to resolve, and a clear understanding of the modification processes of secondary U- and Thrich zircon is lacking. Zircon crystals from two well-studied, highly evolved granites, the Jiangjunshan muscovite granite in the Chinese Altai Mountains and the Cuonadong leucogranite in the Eastern Tethyan Himalaya, have been investigated and classified into two types. Type I exhibits typical igneous growth zoning, and type II has "diffuse" or "spongy" internal structures. These textures, along with compositional data, indicate that the type II zircon crystals formed through hydrothermal modification of magmatic zircon (type I) by infiltrating hydrothermal fluids. During hydrothermal modification, the U and Th concentrations increase from type I to type II in the Jiangjunshan muscovite granite but decrease from type I to type II in the Cuonadong leucogranite. The Raman spectra of type II zircon crystals from Jiangjunshan muscovite granite have broader peaks (i.e., measured as the full width at half maximum, FWHM) with decreased intensities than their type I counterparts, which indicates that the former are affected by significant accumulated radiation damage. However, the preserved radiation damage in both the type I and II zircon measured by Raman spectroscopy is less than that expected from the total dose of alpha particles calculated from the U and Th contents, which indicates variable degrees of annealing. We propose that late magmatic-hydrothermal alteration was responsible for the modification of magmatic zircon grains in highly evolved granites and resulted in the enrichment or redistribution of U and Th. The calculated radiation dose of the Cuonadong leucogranite zircon is far below that required for metamictization, which indicates that metamictization is not always responsible for diffuse and spongy textures. [ABSTRACT FROM AUTHOR]

Exploitable or potentially exploitable deposits of critical metals, such as rare-earth (REE) and high-field-strength elements (HFSE), are commonly associated with alkaline or peralkaline igneous rocks. However, the origin, transport and concentration of these metals in peralkaline systems remains poorly understood. This study presents the results of a mineralogical and geochemical investigation of the Na-metasomatism of alkali amphiboles and clinopyroxenes from a barren peralkaline granite pluton in NE China, to assess the remobilization and redistribution of REE and HFSE during magmatic-hydrothermal evolution. Alkali amphiboles and aegirine-augites from the peralkaline granites show evolutionary trends from sodic-calcic to sodic compositions, with increasing REE and HFSE concentrations as a function of increasing Na-index [Na#, defined as molar Na/(Na + Ca) ratios]. The Na-amphiboles (i.e., arfvedsonite) and aegirine-augites can be subsequently altered, or breakdown, to form hydrothermal aegirine during late- or post-magmatic alteration. Representative compositions analyzed by insitu LA-ICPMS show that the primary aegirine-augites have high and variable REE (2194-3627 ppm) and HFSE (4194-16,862 ppm) contents, suggesting that these critical metals can be scavenged by alkali amphiboles and aegirine-augites. Compared to the primary aegirine-augites, the presentative early replacement aegirine (Aeg-I, Na# = 0.91-0.94) has notably lower REE (1484-1972) and HFSE (4351-5621) contents. In contrast, the late hydrothermal aegirine (Aeg-II, Na# = 0.92-0.96) has significantly lower REE (317-456 ppm) and HFSE (6.44-72.2 ppm) contents. Given that the increasing Na# from aegirine-augites to hydrothermal aegirines likely resulted from Na-metasomatism, a scavenging-release model can explain the remobilization of REE and HFSE in peralkaline granitic systems. The scavenging and release of REE and HFSE by Na-metasomatism provides key insights into the genesis of globally significant REE and HFSE deposits. The high Na-index of the hydrothermal aegirine might be useful as a geochemical indicator in the exploration for these critical-metals. [ABSTRACT FROM AUTHOR]

Widespread crust-derived granitoids in North China provide evidence of Mesozoic lithospheric thinning and destruction of the North China Craton. However, the link between lower crust and lithospheric mantle reactivation remains poorly understood. We present whole-rock geochemistry and zircon O-Hf isotopes for Early Cretaceous peralkaline A-type granites (i.e., Xiwanzi, Xiangshan, and Yansehu) from the Yanshan Mountains of the eastern block of the North China Craton. The Xiwanzi granite has a U-Pb age of 134.3 ± 0.4 Ma, with homogeneous whole-rock Nd isotopes [εNd(t) = -7.7 to -7.5] but highly variable zircon O-Hf isotopes [δ18O = 5.1‰ to 7.2‰ and εHf(t) = -7.7 to +9.6]. Such isotopic variations likely resulted from a hybrid juvenile source consisting of partial melting of newly underplated basaltic rocks derived from both the metasomatized ancient and juvenile sub-continental lithospheric mantle. In contrast, the Xiangshan (117.4 ± 1.0 Ma) and Yansehu (116.3 ± 1.4 Ma) granites have relatively uniform isotopic compositions [whole-rock εNd(t) = -12.2 to -10.8, zircon δ18O = 5.2‰ to 6.4‰, and εHf(t) = -17.1 to -4.7], close to those of the Proterozoic mafic granulite xenoliths from the ancient lower crust. The isotopic variations of the Early Cretaceous A-type granites suggest a continuous change in the melting model from the underplated juvenile lowermost crust to the overlying ancient lower crust at high temperatures in an extensional environment. Our results indicate that A-type granites can be used to probe the nature and reactivation of the lower crust of an Archean craton. Significantly, large-scale continuous thinning of lower continental crust provides key insights into the generation of the widespread Mesozoic crust-derived granitoids in North China. [ABSTRACT FROM AUTHOR]

A combination of zircon U–Pb ages, whole-rock geochemistry, Sr–Nd isotopes, and in situ zircon Hf isotope, for newly found felsic igneous rocks from the Hongshanliang copper deposit district in the Aqishan-Yamansu belt, NW China, are presented to investigate the petrogenesis and tectonic or even crustal evolution of the Eastern Tianshan during the Late Paleozoic to the Early Mesozoic. Zircon U–Pb ages show two phases of igneous activity in the Early Carboniferous (348.8 ± 2.1 Ma and 343.3 ± 2.3 Ma for rhyolite and granite porphyry) and the Triassic (250.2 ± 3.5 Ma and 235.7 ± 2.4 Ma for (monzonitic) granodiorite and monzogranite) in the Hongshanliang copper deposit district. The Carboniferous granitic rocks are enriched in Rb, Ba, and Pb, and depleted in Nb and Ta, with low Sr/Y ratios, showing arc-related affinities. Dominantly positive ε Hf (t) values (+2.55 to +7.15 and +1.54 to +5.03 for the rhyolite and granite porphyry, respectively), crustally-derived geochemical elements ratios (e.g., Nb/Ta, Th/U, Ta/U, and Th/La) and Mg# values (< 37), combined with ε Nd (t) values (−0.1 to +0.6 and −0.3 for the rhyolite and granite porphyry), suggest the Carboniferous granitic rocks were derived from partial melting of the Mesoproterozoic lower crust with mantle-derived magmas involvement. The Triassic (monzonitic) granodiorite and monzogranite are medium-K calc-alkaline, enriched in LILE, and depleted in HFSE, with high SiO 2 , Al 2 O 3 , Sr, and Sr/Y, and low Y and HREE values, characteristic of adakite-like rocks. The Triassic granitoids have low MgO, TiO 2 , Cr, Co, and Ni contents and high Fe 2 O 3 T/MgO ratios (3.07–3.23), with geochemical features of juvenile crust (e.g., low Nb/U and Ta/U ratios and depleted ε Hf (t) values) and mantle-derived magmas (e.g., high Th/U and Th/La ratios and Mg# values), which suggests that the Triassic granitoids were derived from partial melting of thickened juvenile lower crust with minor mantle-derived components. Integrating published cognition and our work, we propose that the Aqishan-Yamansu belt underwent a tectonic transition from an Early Carboniferous fore-arc basin extensional setting to a Triassic within-plate one. Early Carboniferous granitic magmas were emplaced during the southward subduction of the Kangguer oceanic slab and Triassic granitoids were formed after later collision between the Dananhu-Tousuquan island arc and the Yili-Central Tianshan block. Moreover, we also conclude that the major crustal growth in the Eastern Tianshan occurred at ca. 444–270 Ma and was accompanied by abundant Fe–Cu–Ni–Au mineralization, with crustal reworking at ca. 250–200 Ma. Unlabelled Image • Two phases of igneous activity documented in the Hongshanliang copper deposit area. • Carboniferous granitic rocks mainly formed by partial melting of the Mesoproterozoic lower crust. • Triassic granitoids predominantly formed by re-melting of thickened juvenile lower crust. • The Aqishan-Yamansu belt underwent a Carboniferous to Triassic tectonic transition. • The Eastern Tianshan underwent crustal growth (444–270 Ma) and reworking (250–200 Ma). [ABSTRACT FROM AUTHOR]

[Display omitted] • Pyrite-bearing veins at Qulong can be divided into seven subclasses. • The contents of Co and Ni and the ratios of Co/Ni and Ni/Se in pyrite can be used to investigate the evolution of fluid composition, temperature and oxygen fugacity. • Changes in trace elements and S isotopes in pyrite can be used to investigate the evolution of magmatic-hydrothermal fluids. The post-collisional Qulong porphyry Cu-Mo deposit is the largest in the Gangdese Cu belt, southern Tibet. Despite many previous studies, the evolution of ore-forming fluids in the Qulong deposit remains controversial. Pyrite-bearing veins at Qulong can be divided into seven subclasses, including Mt-type, Bt-type, A-type, B-type, C-type, D-type, and E-type veins. To decipher the evolution of magmatic-hydrothermal fluids at Qulong, in situ LA-ICP-MS trace element and sulfur isotope compositions of pyrites from different veins were analyzed. The δ34S values (+1.01‰ to + 4.28‰) for pyrites indicate a magmatic sulfur source and the high Se/S ratios of pyrite at Qulong are consistent with hydrothermal fluids being mainly magma-derived. The low Co/Ni ratio (0.01–0.1) of pyrite in Mt-type vein suggests that the earliest magmatic-hydrothermal fluids may have contributed from mafic magma injection. From Mt- to Bt- to A-type veins, the δ34S values in the hydrothermal fluids decrease as the temperature decreases, whereas the Cu and Co contents increase and the As and Ni contents decrease. In B- and C-type veins, the relatively high and stable Co and Ni contents and the range of δ34S isotope values in pyrite indicate the existence of multiple-stages of magmatic-hydrothermal fluids during the main mineralization period. During the late stages of mineralization, the decrease of Co, Ni and As contents and increase of Cu in pyrite in D- and E-type veins, as well as the narrow range of δ34S values, may be due to decreasing temperature as a result of fluid dilution caused by mixing with meteoric waters. The slightly negative δ34S fluid values for chalcopyrite (-1.56‰ to −0.75‰) in sample Q711-1968 also suggests the addition of external water at Qulong. [ABSTRACT FROM AUTHOR]

Continental collision–related porphyry copper (Cu) deposits provide significant global copper resources, but their genesis remains controversial because it is not clear whether remelting of remnant arc-derived lower-crustal Cu-rich cumulates is critical to their formation. We investigated zircon and apatite compositions of the Jiru porphyry Cu deposit in the Gangdese belt of southern Tibet, which is characterized by weaker early Eocene mineralization and more pronounced Miocene mineralization. Our data demonstrate that apatite hosted in zircon can record the volatile compositions of magma before fluid exsolution. Zircon-hosted apatites from the early Eocene granite that have low XF/XCl ratios (≤3) and are interpreted to have crystallized from volatile-undersaturated magma have Cl contents of 0.96–2.14 wt% (1.86 ± 0.38 wt%; n = 15) and SO3 contents of 0.01–0.14 wt% (0.08 ± 0.04 wt%; n = 15). In contrast, zircon-hosted apatites from the Miocene porphyry that have low XF/XCl ratios (≤10) and are interpreted to have crystallized from volatile-undersaturated magma have Cl contents of 0.40–0.56 wt% (0.47 ± 0.06 wt%; n = 11) and SO3 contents of 0.20–0.92 wt% (0.59 ± 0.29 wt%; n = 11). In addition, the early Eocene magma was relatively reduced (ΔFMQ = 0.86 ± 0.55, where FMQ is fayalite-magnetite-quartz) compared with the oxidized Miocene magma (ΔFMQ = 2.04 ± 0.43). The contrasting magmatic oxidation states and apatite/melt S contents were likely critical in controlling the different scales of Cu mineralization during the early Eocene and Miocene, as more highly oxidized magma can dissolve much larger amounts of sulfur and metals (e.g., Cu). Melt Cl content may not play a critical role in magma fertility, since the Jiru early Eocene granite had higher melt Cl contents than the Miocene porphyry. Magmatic sulfides (pyrrhotite, chalcopyrite, and pyrite) were not recognized in the Miocene zircons but did occur in the early Eocene zircons, and these sulfides were demonstrated to have crystallized before fluid exsolution in the shallow magma reservoir. The Jiru early Eocene magmatic sulfide saturation might not have enhanced the amount of copper available to hydrothermal fluids during the early Eocene. Late-stage sulfide saturation in the previous arc magmas might reduce the potential for collision-related porphyry Cu mineralization that is associated with remelting of the previous arc lower crust. [ABSTRACT FROM AUTHOR]

Abstract Two populations of zircons are present in the F-rich highly evolved 300 Ma Shuangji granites, Xinjiang, eastern Tianshan, China. Zircon I comprise a very small proportion of the population. They show characteristics of primary igneous zircons and yield an age of ca. 300 Ma. Zircon II are the dominant type and are weakly luminescent under cathodoluminescence (CL) but show a range of complex textures in back-scattered electron (BSE) images. Zircon II are characterized by Th-U-rich mineral inclusions not seen in zircon I and can be divided into zircon IIa and zircon IIb. Autometasomatism during the magmatic-hydrothermal phase of the highly evolved Shuangji granites, fluids rich in F interacted with zircon I through a coupled dissolution-reprecipitation process forming pores and cracks in the zircon grains. The simultaneous alteration of U-rich euxenite, released high amounts of U and Th into the fluids. Interaction of these fluids with porous zircon I resulted in the precipitation of U- and Th-rich inclusions in the zircon I grains. Radiation damage resulted in the formation of metamict zircons. Later hydrothermal alteration affected the metamict zircons, forming nanoscale baddeleyite in the amorphous zone. Subsequent radiation damage accumulated continuously resulting in the final textures of zircon II. Highlights • Primary and altered zircons can coexist in one granitic system. • Zircons could be hydrothermally altered rather than hydrothermal zircons. • The magmatic-hydrothermal transition could be traced by zircons. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Tuwu overprinting chlorite are depleted in Mg and K, and enriched in Fe and Al relative to propylitic chlorite. • Compared with metamorphic chlorite, Tuwu propylitic chlorite shows higher Mg and K, lower Fe, Al and As concentrations. • Sc, V, Ti and Ga are enriched, and Li, Sr, Mn and Zn are depleted in Tuwu propylitic chlorite proximal to the orebody. Abstract Chlorite is one of the most widely developed minerals in propylitic alteration around porphyry deposits and can be used to investigate element transport and enrichment processes during hydrothermal alteration. The Paleozoic Tuwu porphyry Cu deposit (metal reserve: 0.7 Mt Cu @ 0.67%), located in the southern margin of the Central Asian Orogenic Belt, is one of the most economical and largest porphyry Cu deposits in NW China. The Tuwu porphyry Cu deposit comprises an early porphyry Cu mineralization (including potassic, propylitic and phyllic alteration stages) and later overprinting Cu mineralization periods with chlorite found in both. Chlorite from the propylitic zone at Tuwu is geochemically similar to propylitic chlorite in younger Cenozoic porphyry systems, but enriched in Mg and K and depleted in Fe and Al relative to the overprinting chlorite. Scandium, V, Ti and Ga are enriched, and Li, Sr, Mn and Zn are depleted in the Tuwu propylitic chlorite proximal to the orebody, consistent with Cenozoic deposits. Compared with metamorphic chlorite from Proterozoic metamorphic terranes in Australia, Tuwu propylitic chlorite has higher Mg and K, lower Fe, Al and As. Our results suggest propylitic alteration in the Tuwu district is probably the product of cooling of fluids derived from the magmatic-hydrothermal system, but not from peripheral waters, and trace element variations in chlorite are mainly controlled by temperature although other factors such as fault development could affect variation trends. The common elemental features of chlorite in both Paleozoic and Cenozoic porphyry Cu deposits indicate it could act as a potential tool for mineral exploration. [ABSTRACT FROM AUTHOR]

The Shapinggou molybdenum deposit is located in the Qinling-Dabie Orogen, which hosts the world's largest molybdenum belt. The igneous rocks at Shapinggou can be divided into two stages (136–127 Ma and 118–114 Ma), the early suite of felsic (136–127 Ma, SiO 2  = 58.0 to 72.9 wt%) and mafic rocks (133–128 Ma, SiO 2  = 45.2 to 57.0 wt%), and a later suite comprising syenite (117 Ma, SiO 2  = 64.2 to 65.0 wt%), quartz syenite porphyry (116 Ma, 62.5 to 70.0 wt%), granite porphyry (112 Ma, SiO 2  = 75.5 to 77.6 wt%) and diorite porphyry (111 Ma, SiO 2  = 56.6 to 59.7 wt%). The early-stage felsic rocks display high SiO 2 , Al 2 O 3 , Na 2 O, K 2 O, Sr, LREE contents, and Sr/Y, (La/Yb) N ratios, initial Sr isotope ratios of 0.7076 to 0.7089, but low MgO, FeO T , Y, Yb contents and negative ε Nd (t) values, consistent with partial melting of the lower continental crust. The early-stage mafic rocks exhibit low SiO 2 , high MgO, Ni and Cr contents, consistent with an upper mantle source, but trace element and isotope data suggest a role for crustal contamination. The late-stage syenite and quartz syenite porphyry show high abundances of Na 2 O, K 2 O, Al 2 O 3 , HFSEs (e.g., Th, U, Zr, Hf) and significant negative Eu anomalies. The late-stage granite porphyry displays high SiO 2 contents, and depletions in Ba, Sr, Eu and Ti. The geochemical features of the late-stage intrusions are similar to A-type granites. Crystal fractionation of plagioclase, K-feldspar, biotite/ muscovite, amphibole/ garnet and Fe-Ti oxides controlled the evolution of the magma. The geochemical and isotopic data suggest that the rocks at Shapinggou were likely derived from a mixed source of lithospheric mantle, subducted continental crust of the Yangtze Block (Kongling Group) and partial melts of the Dabie Complex. Early stage rocks represent melts of the source with a lower proportion of Dabie Complex materials, whereas late stage rocks were derived from a source with a higher proportion Dabie Complex component. The geochemical and isotopic variations of the intrusions at Shapinggou were controlled by both source characteristics and fractional crystallization. Although the Shapinggou deposit is located in a continental collision orogen, the magmas formed in an intraplate extension setting, with an increase in the amount of extension from the early to late stages. As well, both stages intrusions at Shapinggou were generated by the addition of heat, due to lithospheric delamination, mantle upwelling and rapid mantle convection, related to the far-field effects of the westward subduction of the paleo-Pacific Plate beneath the Asian continent. The geochemistry and setting suggest that the formation of a giant Mo deposit does not require a Mo-rich magma source, but rather an efficient convection mechanism for the transport of volatiles and Mo in a granitic magma system. The fluids derived from the granite porphyry at Shapinggou were more oxidised than that from the barren intrusions. [ABSTRACT FROM AUTHOR]

The Shapinggou deposit, located in the Dabie Orogenic Belt, eastern China, is one of the largest Mo-only porphyry deposits in the world. Alteration types associated with Shapinggou include silicic, potassic-silicic, phyllic, propylitic and argillic. The phyllic alteration can be subdivided into quartz and sericite (mainly muscovite) phases whereas the argillic alteration is distinguished by poorly crystallized kaolinite (kaolinite PX), muscovite and phengite. The ore-forming event can be divided into quartz-K-feldspar, quartz-molybdenite, quartz-sericite and quartz-fluorite-gypsum stages, with molybdenite deposited in the first three stages but mainly in the second. The molybdenites in Shapinggou represent either the 2H 1 and/or the 2H 1  + 3R polytype, and can be subdivided into two groups (group one and group two), Group 1 is associated with stage 1 alteration whereas Group 2 is found with stages 2 and 3. There is an increase in the Re values from group one to group two with the Re contents likely controlled by both the crustal metal source and temperature. With decreasing temperature, the contents of Re and the ratios of Mo/Cu in molybdenites in Shapinggou decrease gradually, whereas the contents of Cu and W + Sn, and the ratios of Re/Cu, Co/Ni increase. The Pb + Zn values in molybdenite are higher in the porphyry Mo deposit associated with Pb-Zn deposits than in porphyry Cu-Mo/Mo deposits not associated with Pb-Zn deposits. The ratios of Cl − /F − , SO 2 /H 2 S, and H + /K + in the Shapinggou fluids, increasing over time, suggest that the fluids became more oxidised. The initial ore-forming fluid, was >500 °C, carried ions of Mo, Ca, Na, K, Cl, F, S and caused potassic-silicic alteration with deposition of only small amounts of molybdenite. As the temperature dropped down to ∼400 °C, the amounts of Mo, K, Cu and Cl ions in the fluid decreased leading to silicic-sericitic and propylitic alteration and the deposition of the majority of the molybdenite. As the temperatures decreased to ∼300 °C, the fluid contained ions of Ca and F, and Pb-Zn was deposited distally around the main Mo ore-body. [ABSTRACT FROM AUTHOR]

Carbonate-replacement Zn-Pb deposits are formed through fluid circulation within carbonate rocks and are an important global source of Zn and Pb. The Caixiashan carbonate-replacement deposit is one of the largest Zn-Pb systems in China. The Mesoproterozoic syn-sedimentary stage (I) of the Caixiashan deposit is characterized by sulfides with negative δ 34 S values (−25.3 to −8.6‰) generated by organic sulfate reduction, which co-precipitated with the host rocks. The Neoproterozoic main sulfide precipitation stage (II) was caused by thermo sulfide reduction resulting in positive δ 34 S values (7.9–12.3‰). Carbonates from stage I have δ 13 C PDB of −1.2 to 2.8‰ and δ 18 O SMOW of 17.1–24.0‰, similar to those of marine carbonate rocks. Dolomite and calcite from stage II have δ 13 C PDB ranging from −5.1 to −0.2‰ and δ 18 O SMOW of 14.1–19.7‰, consistent with dissolution of carbonate rock. In contrast dolomite and calcite from stage III have mantle C-O signatures with the δ 13 C PDB ranging from −7.5 to 0.4‰ and δ 18 O SMOW from 5.8 to 13.2‰. C-O isotopic signatures suggest that the original carbonates were dissolved by the acid generated from sulfide precipitation consistent with the sulfide precipitation process. Subsequent precipitation of carbonates created large volumes of dolomite alteration that coated the sulfides and possibly contributed to the preservation of the ore, as dolomite would dissolve more slowly than calcite. Carboniferous magmatism (stage III) resulted in a magmatic overprint on the stage II sulfide. The metal sources of these sulfide ore packets are mainly derived from the Mesoproterozoic carbonate rocks as indicated by the lead isotopes of sulfides and also C-O isotopes of carbonates. The deposit is characterized by a complex paragenesis with multiple overprinting sources of hydrothermal fluids and sulfide over 700 m.y. The syn-sedimentary stage (∼1019 Ma) and main mineralization stage (859–837 Ma) at Caixiashan are chronologically and tectonically associated with the assembly and break-up of the Rodinia supercontinent, whereas the magmatic-hydrothermal modification stage (∼353 Ma) is associated with the closure of the Paleo Asian Ocean during the Early Carboniferous. [ABSTRACT FROM AUTHOR]

Abstract: Melting and dehydration of subducted oceanic slabs dominate element recycling within the subduction factory, but the role of recycled oceanic crust in the source of intraplate magmas is poorly understood. In situ zircon O‐Hf isotope data from two Early Cretaceous alkaline A‐type granites that are genetically related to large‐scale extension of eastern China in the Late Mesozoic (circa 125 Ma) yield low δ18O (1.8 ± 0.3‰ to 5.1 ± 0.3‰, 2σ) and positive εHf(t) (1.5 ± 1.2 to 17 ± 1.2, 2σ). This suggests the contribution of altered oceanic crust and an enriched mantle component in the source region. Elevated initial 87Sr/86Sr and 206Pb/204Pb ratios, and εHf(t) whole rock values with relatively constant εNd(t) values beyond the normal mantle array, require a component that underwent seawater interaction in the source of protolith. The geochemical data require a complex source region for the alkaline A‐type granites in NE China involving more than 40% recycled oceanic crust. This altered oceanic crust beneath the Late Mesozoic lithospheric mantle likely represents remnants of multiple subduction and collision events between microblocks from the Late Paleozoic to Early Mesozoic in northeastern China. Recycling of subducted oceanic crust represents a novel exotic source for the origin of alkaline A‐type granites in intraplate extensional settings. [ABSTRACT FROM AUTHOR]

Deep-sea sediments rich in rare earth elements and yttrium (REY) are promising mineral resources that are believed to be associated with the burial of fish debris. However, the nature of the REY enrichment is poorly understood, in part due to a lack of robust age constraints. We report bioapatite U-Pb ages from an Ocean Drilling Program (Leg 199, Hole 1218A) core and a REY-rich sedimentary core from the Pacific Ocean, which yielded U-Pb ages rang- ing from 22.8 to 18.2 Ma and 6.5 to 2.2 Ma, respectively. The U-Pb fish teeth ages from the 1218A core are consistent with biostratigraphic constraints, shed light on the application of the U-Pb bioapatite chronometer, and yield an absolute time scale for stratigraphy, especially for sequences deposited below the calcite compensation depth (CCD), where there is an ab- sence of fossil carbonate. The successful measurement of U-Pb ages from REY-enriched fish teeth in the REY-rich sediment core suggests the mineralization occurred no later than the Miocene in the western Pacific Ocean. Uranium is positively correlated with REY, suggesting that the U and REY were incorporated into the fish teeth lattice simultaneously, making the bioapatite U-Pb chronometer suitable for constraining the timing of REY mineralization. When combined with published data, our study suggests that the Miocene REY accumula- tion event in the western Pacific Ocean was influenced by high P2O5 and MnO2 contents correlated with oxic bottom water. [ABSTRACT FROM AUTHOR]

The Zijinshan mineral field is a large porphyry-epithermal Cu Au Mo Ag ore system located in the southwestern Fujian Province, China. The Southeast (Cu Mo) Ore Segment (SOE) is a newly discovered section located in the southeastern portion of the Zijinshan mineral field. Zircon U Pb and molybdenite Re Os ages, as well as the geochemical compositions of intrusive and volcanic rocks and zircon Hf isotope data are used to constrain the timing, petrogenesis, tectonic setting and the relationship between magmatism and metallogenesis in the SOE and Zijinshan mineral field. Major and trace element geochemistry indicates that igneous rocks from SOE are mainly shoshonitic granitoids that are LILE enriched (Rb, Ba, Th, U) with HFSE depletion (Nb, Ta, Zr, Hf and Y), indicating a subduction related setting. New U Pb zircon analyses yield weighted mean ages of ca. 160 Ma for the Caixi pluton, ca. 110 Ma for the Sifang granodiorite, ca. 107–105 Ma for the Luoboling granodiorite porphyry, ca. 105 Ma for the quartz diorite porphyry, ca. 108–105 Ma for the dacite porphyry, ca. 98 Ma for the rhyodacite, and 97 Ma for the rhyolite in the SOE. These dates, integrated with previous geochronological data, indicate that there were two main magmatic events in this area: (1) a Middle to Late Jurassic event (165–150 Ma), and (2) a Cretaceous event (110–95 Ma) which can be further divided into two groups, i.e., the late Early Cretaceous event (110–105 Ma) and the early Late Cretaceous event (100–95 Ma). The late Early Cretaceous intrusions contain higher ε Hf (t) values (0.1 to − 3.6), with T DM2 varying from 1.4 to 1.0 Ga, which may come from mixing between crustal and subduction-related mantle derived melts in contrast to the Middle to late Jurassic intrusions that may come from the partial melting of the Cathaysia Block basement. The early Late Cretaceous intrusions display a broader range of ε Hf (t) values (− 0.9 to − 9.4), with T DM2 varying from 1.8 to 1.2 Ga, suggesting a similar source to the late Early Cretaceous rocks but with more crustal material. The molybdenite Re Os ages for mineralization range from 110 Ma to 105 Ma, consistent with ages of the late Early Cretaceous rocks. Zircon trace elements analyses imply that the early Late Cretaceous rocks (Ce 4 + /Ce 3 + = 113–1800) are characterized by higher oxygen fugacity with higher mineralization potential than the late Early Cretaceous (Ce 4 + /Ce 3 + = 9–545) and the Middle to Late Jurassic rocks. Variability in ages, geochemistry and oxygen fugacity indicate that the Middle to Late Jurassic magmatic event represents pre-mineralization intrusions whereas the late Early Cretaceous is syn-mineralization and the early Late Cretaceous intrusions post-mineralization. We propose that both the Middle to Late Jurassic and the Cretaceous magmatic events may relate to the subduction of the Pacific slab, and the changing direction of the subducted slab may result in the different sources for the two magmatic events. [ABSTRACT FROM AUTHOR]

[Display omitted] • LA-ICP-TOFMS was used for rapid and high-resolution element maps of Fe-Mn nodules. • 10 * 9 mm2 and 700 * 350 µm2 size area took 2.27 h and 0.62 h, respectively. • Macro area element maps indicate that the nodule underwent mineral maturation. • LA-ICP-TOFMS element mapping is suitable for soft, porous samples. Polymetallic nodules are one of the most ubiquitous critical metal reservoirs in the deep sea during early diagenesis. Trace elements including REY (Rare earth elements + Y), can provide a wealth of information to document the source-to-sink (STS) processes and critical metals enrichment regimes. Element imaging is an important "see-through" technique to display the distribution of multi-elements to understand the respective concentration relationship. However, traditional elemental mapping of macro (several millimeters) and micro (tens of micrometers) areas has remained a major challenge due to the long analytical time and low lateral resolution. Here, we apply inductively coupled plasma time-of-flight mass spectrometry (ICP-TOFMS), coupled to laser ablation (LA) with a low-dispersion two-volume sample cell and a dual concentric injector at both the macro- and micro-scales. LA-ICP-TOFMS mapping was applied to an entire polymetallic nodule (size of 10 * 9 mm2 @ 40 µm2 spot size, 1300 µm/s scan speed and 15 Hz frequency) and microdomains with microlayers (size of 700 * 350 µm2 @ 1 µm2, 200 µm/s and 200 Hz), respectively. The intra-nodule distribution patterns of elements are mainly controlled by the occurrence minerals. For example, the distribution patterns of some metals (e.g., Cu, Co, Ni) are similar to that of Mn, indicating these metals host in Mn-phase minerals. There is a trend of decreasing and then increasing of these elements from the inner to the outer layer, suggesting that the redox environment may have undergone a process from oxic to suboxic and then to oxic during the growth process. Our results demonstrate the feasibility of LA-ICP-TOFMS analysis on soft and porous materials, whose advantages include a shorter time and higher lateral resolution compared with traditional LA-ICP-QMS, expanding the geochemical mapping techniques for deep-sea early diagenetic sediments samples. [ABSTRACT FROM AUTHOR]

The Fe-Cu mineralization of the Laoshankou district is located in the Dulate Late Paleozoic island arc at the northern margin of East Junggar terrane, Northwest China and is hosted by volcanic rocks of the Middle Devonian Beitashan Formation. LA-ICP-MS U–Pb dating of zircon constrains the timing of crystallization of biotite diorites and quartz syenites in the Laoshankou district to 379 ± 2 Ma and 376 ± 2 Ma, respectively. The volcanic rocks are calc-alkaline in composition and are characterised by LILE and LREE enrichments and HFSE depletions, consistent with a subduction-related affinity. The relatively depleted Nb, Ta, Zr, Hf and Th, enriched Sr and Ba, elevated Mg#, positive ε Nd (t) values (5.5 and 5.6), low ( 87 Sr/ 86 Sr) i ratios (0.7042 and 0.7044) and MORB-like Pb-isotope characters all suggest that they were derived from a depleted mantle wedge metasomatized by slab-derived fluids, without crustal contamination. The biotite diorite shows slightly metaluminous compositions and is geochemically similar to the volcanic rocks, suggesting that they were derived from the same depleted mantle source. The lack of correlation between SiO 2 and initial Sr, Nd ratios suggests that fractional crystallization dominated the petrogenesis of the biotite diorite with only weak crustal contamination. The geochemical characteristics of the quartz syenite are distinct from the volcanic rocks and the biotite diorite. The positive ε Hf (t), ε Nd (t), high Th/La (0.17–0.53), Th/Yb (1.62–4.39), low Ce/Th (2.87–10.13) ratios and positive trends of SiO 2 versus ( 87 Sr/ 86 Sr) i and ( 143 Nd/ 144 Nd) i indicate the quartz syenite is likely the product of a depleted mantle wedge metasomatized by slab-derived fluids and subducted sediment-derived melts that underwent crustal contamination during passage through the crust. The low abundance of Th, Yb, Ta and La, indicate that all the intrusive rocks from 379 to 376 Ma in the Laoshankou district formed in an island arc rather than a continental margin arc. The northern margin of East Junggar was related to the southward subduction of the Kuerti-Erqis Ocean (a branch of the Paleo-Asian Ocean) between the Altay and the Dulate arcs in this period, consistent with the presence of Nb-enriched basalts and boninites in the north of the Dulate arc and the island arc rather than back arc setting of the igneous rocks in the Laoshankou district. For metallogenesis in the northern margin of East Junggar, arc-related Fe-Cu-Au and porphyry Cu mineralization was dominated. There is large potential to find several Late Paleozoic arc-related Fe-Cu-Au mineralizations in North Xinjiang. [ABSTRACT FROM AUTHOR]

The East Junggar terrane (NW China) is an important constituent of the Central Asian Orogenic Belt (CAOB). From the Devonian to Permian, regional magmatism evolved from mainly calc-alkaline (I-type) to alkaline (A-type). The Qiaoxiahala Fe-Cu deposit, located in the Late Paleozoic Dulate island arc (northern margin of the East Junggar), is hosted in the volcanic rocks of the Middle Devonian Beitashan Formation. Two magmatic stages were identified in the deposit, the Qiaoxiahala diorite porphyry (380 ± 4.0 Ma) and a younger aplite (331 ± 3.1 Ma). The (high-K) calc-alkaline Beitashan Formation basaltic rocks are characterized by LILE and LREE enrichments and HFSE depletions, pointing to a subduction-related affinity. The high Mg# (42–75), elevated Ce/Th and Ba/Th, depleted Nb, positive ε Nd (t) (6.6), low ( 87 Sr/ 86 Sr) i (0.7037) and MORB-like Pb isotope characters all suggest an origin involving partial melting of a MORB-like depleted mantle wedge (metasomatized by slab-derived fluids) with little evidence of crustal contamination. The calc-alkaline (I-type) diorite porphyry, characterized by LILE and LREE enrichments and HFSE depletions, may have formed from fractional crystallization of the basaltic rocks, with its parental magma derived from the same depleted mantle wedge. The negative ε Hf (t) (−8.26), Hf model age ( T DM C ) of 1406 Ma and the presence of inherited zircons (ca. 470 and 506 Ma) indicate that the diorite has assimilated older crustal material. The alkaline, metaluminous (A-type) aplite is characterized by HFSE enrichment and depletions in Sr, P and Ti, distinct from the basaltic rocks and diorite porphyry at Qiaoxiahala. The low Mg# (35–38), positive Zr and Hf, positive ε Hf (t) (4.77–9.75) and ε Nd (t) (6.85–6.86) and low T 2DM (538–520 Ma) suggest a juvenile lower crustal source due to partial melting of basaltic lower crust as a result of underplating of mantle-derived melts and accompanied by magma mixing. The tectonic evolution of the Paleozoic East Junggar was associated with the initiation of subduction of the Paleo-Asian Ocean, with the formation of an island arc during the Early to Middle Devonian and generation of the coeval arc-related Fe-Cu (-Au) and porphyry Cu mineralization. Collision between the Chinese Altay and East Junggar happened in the Late Devonian with Early Carboniferous post-collisional tectonics likely explaining the synchronous Cu-Mo mineralization, while the late-Early to Late Carboniferous post-orogenic event ended without related mineralization in Qiaoxiahala. [ABSTRACT FROM AUTHOR]

The timing of hydrothermal activity is a key factor in any predictive genetic model of skarn mineralization, but direct dating is often hindered by the absence of suitable minerals to date. Vesuvianite, a common mineral in skarn deposits, can incorporate U and has a high Pb closure temperature (>650 °C), and consequently may be suitable for dating for skarn deposits. Vesuvianite collected from nine Chinese skarn deposits, including the Jinchuantang Sn Bi, Shizhuyuan W–Sn–Mo–Bi polymetallic, Jiepai Cu W, Dashunlong Sn, Xianghualing Sn, Furong Sn, and Huangshaping W–Sn–Mo–Cu polymetallic deposits in Nanling Range (Southern China), and the Kaerqueka and Saishitang Cu deposits in East Kunlun Orogen (Northwestern China), have high U concentrations (median 66.8 ppm for 460 LA-ICP-MS analysis spots). The flat and stable time-resolved signal spectra for U during LA-ICP-MS analysis, combined with the absence of nanoscale mineral inclusions, porosities, or lattice defects in the JCT vesuvianite, with high and consistent U concentrations, revealed by the HAADF-STEM images, and the marked positive relationships between U and REE collectively suggest that the U incorporation into vesuvianite was primarily controlled by replacement of Ca2+ in eight-fold coordination, confirming that vesuvianite may be a suitable U Pb geochronometer. The JCT vesuvianite is characterized by high and consistent U concentrations (260–526 ppm, median 307 ppm) and homogeneous internal texture and elemental distribution, and yields an ID-TIMS U Pb concordia age (2σ, 153.9 ± 0.2 Ma, MSWD = 1.6, n = 11), demonstrating that it can be taken as a potential LA-ICP-MS U Pb reference material, which can be freely distributed to other laboratories. Using the JCT vesuvianite as a U Pb reference material, the Kaerqueka, Saishitang, Jiepai, Dashunlong, Xianghualing, Furong, and Shizhuyuan vesuvianite yielded well-defined LA-ICP-MS U Pb ages (239.0–152.1 Ma, 2σ), consistent with previously published age constraints of mineralization and cogenetic igneous rocks. Vesuvianite from the Huangshaping W–Sn–Mo–Cu polymetallic deposit, yielded U Pb ages of 157.3 ± 1.4 Ma (2σ, MSWD = 1.8) and 161.0 ± 1.3 Ma (2σ, MSWD = 1.9), providing reliable constraints on the overprinting sequence of the skarn W–Sn–Mo and Cu mineralization events at Huangshaping, which was not previously detectable using other mineralization chronometers. Combined, these ages suggest that vesuvianite is a robust and reliable geochronometer, and offers a new tool for dating skarn deposits. [ABSTRACT FROM AUTHOR]

The Halasu porphyry copper belt situated in the East Junggar is one of the major porphyry copper belts in Xinjiang Uygur Autonomous Region, northwest China. Copper and molybdenum mineralization occurs as disseminated sulfides or veinlets mainly in granodiorite porphyry and diorite porphyry, with the intense development of zoned alteration from potassic, through sericitic to an outer zone of propylitic alteration. New LA–ICP-MS zircon U–Pb dating reveals that magmatism in the belt can be divided into three periods during the Middle Devonian and Early Carboniferous, namely the pre-mineralization stage of 390 Ma, syn-mineralization stage of 382–372 Ma, and post-mineralization stage of 350–320 Ma. The syn-mineralization intrusions are calc-alkaline, whereas pre- and post-mineralization intrusions are shoshonitic and high-K calc-alkaline. The syn-mineralization intrusions are enriched in highly incompatible trace elements but depleted in Nb, Ta, Hf and Ti relative to the pre- and post-mineralization intrusions. Zircon trace elements analyses demonstrate a negative correlation between Ti-in-zircon temperatures and oxygen fugacity. Ore-bearing syn-mineralization granitoids are characterized by higher water content, oxygen fugacity and low temperatures with higher mineralization potential than pre- and post-mineralization ones. These characteristics, together with the geochemical signature of the intrusions, suggest that the ore-bearing porphyries are derived from relative high ƒH 2 O magma reservoir. The remarkably homogeneous Hf isotopic compositions (εHf(t) = 8 to 13) from syn-mineralization intrusions span over 10 m.y., suggesting the existence of a long-lived reservoir beneath Halasu belt during the Middle Devonian. All the intrusions have low initial 87 Sr/ 86 Sr values (0.703935 to 0.707172), high εNd(t) values (4.7 to 5.5) and young crustal model ages (650 to 750 Ma). Combined with the mantle-derived Pb isotope characteristics, the Sr–Nd–Hf data suggest that the parental magma was probably derived from flat subduction triggered partial melting of juvenile crust generated during subduction–accretionary process with no significant input of old crust, whereas pre-mineralization and post-mineralization intrusions are supposed to emplaced in immature island arc setting and post-orogenic setting, respectively. [ABSTRACT FROM AUTHOR]