Weighted Mean Age Research Articles

Breast cancer receptor subtypes in East Africa: A systematic review and meta-analysis.

e19074 Background: Estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) are determinants of both treatment and mortality for patients with breast cancer (BC). With a mortality to incidence ratio of 0.51, mortality rates for breast cancer in East Africa are among the world’s highest. Building on a meta-analysis of BC receptor subtypes in sub-Saharan Africa (2014) and including all recently available PubMed literature, our meta-analysis aims to investigate the differences among receptor subtype distribution in five East African countries. Methods: Receptor distributions for female samples >30 in all BC articles for Ethiopia, Kenya, Rwanda, Tanzania and Uganda were obtained from PubMed, January 1, 1998 - June 30, 2019. Outcomes were proportions of ER+, PR+, and HER2+ and/or molecular subtypes. Data included study characteristics and mean/median patient age (weighted by observations). Using metaprop for STATA 16, we estimated pooled proportions (ES) with 95% confidence intervals (CI) and assessed I2 statistics for heterogeneity across studies. Results: Among 35 BC studies with receptor data, 21 met criteria. Overall, the weighted mean age was 47.5 years (SD 3.2) and median, 48. For ER+ (18 studies/n=2,875), the overall ES was 0.55 (95% CI 0.47, 0.62), I2 of 94.4%, p<0.001, ranging from 0.62 in Ethiopia (95% CI 0.52, 0.72) to 0.42 in Uganda (95%0.36, 0.49). For HER2+ (18 studies/n=2,689), the overall ES was 0.23 (95% CI 0.20, 0.26), I2 of 70.2%, p<0.001, and ranged from 0.27 in Ethiopia (95% CI 0.18, 0.36) to 0.21 in both Tanzania and Uganda (95% CI 0.13/0.14, 0.28). For triple negative (TN, 15 studies/n=2,510), the overall ES was 0.28 (95% CI 0.23, 0.32), I2 of 84.0%, p<0.001, varying from 0.21 in Ethiopia (95% CI 0.15, 0.27) to 0.46 in Tanzania (95% CI 0.32, 0.60). Conclusions: We found differences between countries, e.g. lower distribution of TN in Ethiopia (21%) compared to Uganda (35%) and Tanzania (46%), and high between-study heterogeneity. Consistent with former studies, ER+, 55%, was the dominant subtype, particularly in Ethiopia, Kenya and Rwanda, indicating the need to prioritize hormonal treatment. Overall rates of HER2 subtype, 23%, approached overall rates of TN, 28%, yet HER2 testing is often not performed due to the cost and unavailability of anti-HER2 therapy, hence this subtype often goes untreated. These findings highlight the benefit of testing and reporting of receptor subtypes at the country level to promote delivery of more effective treatment to reduce the mortality disparity.

Petrogenesis of the Lijiagou spodumene pegmatites in Songpan-Garze Fold Belt, West Sichuan, China: Evidence from geochemistry, zircon, cassiterite and coltan U-Pb geochronology and Hf isotopic compositions

Spodumene and other pegmatites in the Lijiagou area are located in the central Songpan-Garze Fold Belt (SGFB), West Sichuan. These pegmatites are hosted within the giant Songpan-Garze polymetallic belt. A lack of precise geochronological constraints on the magmatic crystallization of the pegmatite suite and nearby plutonic granitoids has precluded definitive statements on genetic links between spodumene ore formation and the magmatic suite. Systematic zircon, cassiterite and coltan U-Pb dating, Hf isotope and whole-rock geochemical analysis were undertaken. Two-mica granite and muscovite albite granite have S-type granite affinities and chemical compositions suggesting a post-orogenic setting, and the albite spodumene pegmatites belong to the LCT (Li-Cs-Ta) group of pegmatites. Zircon LA-MC-ICP-MS U-Pb dating of the two-mica granite, muscovite albite granite, albite pegmatite and albite spodumene pegmatite give crystallization ages of 219.2 ± 2.3 Ma (MSWD = 0.55), 217 ± 2.8 Ma (MSWD = 0.47), 202.8 ± 4.9 Ma (MSWD = 3.9) and 200.1 ± 4.6 Ma (MSWD = 3.1), respectively. Zircons from the same units yield εHf(t) values of −39.17 to 6.81, −22.73 to −2.83, −11.17 to 8.14, and −4.92 to −2.4, respectively, consistent with mixed crustal sources for the pegmatite and granite magmas. Cassiterite from albite spodumene pegmatite yields a concordia intercept age of 211.4 ± 3.3 Ma (MSWD = 2.9), while coltan yields a weighted mean age of 211.1 ± 1.0 Ma (MSWD = 0.97). The U-Pb zircon ages of the two-mica granite and muscovite albite granite are interpreted as ages of magmatic crystallization. Metamictization of zircon in both albite and albite spodumene pegmatites makes their U-Pb zircon ages liable to inaccuracy due to Pb loss. The coltan U-Pb age is regarded as an accurate measure of the magmatic crystallization age of the albite spodumene pegmatite. Given the differences in magmatic ages and εHf(t) ranges between albite spodumene pegmatite and both the two-mica granite and the muscovite albite granite, the albite spodumene pegmatites probably represent anatectic melts and not fractionation products of either of the granitic magmas. U-Pb coltan and U-Pb cassiterite dating are more likely to provide accurate crystallization ages of albite spodumene pegmatites than U-Pb zircon ages.

The 127 Ma gold mineralization in the Wulong deposit, Liaodong Peninsula, China: Constraints from molybdenite Re-Os, monazite U-Th-Pb, and zircon U-Pb geochronology

The Wulong deposit is a large tonnage deposit (>80 t of Au), characterized by quartz vein style of gold mineralization in the Liaodong Peninsula, China. The auriferous quartz veins are mainly hosted by Late Jurassic gneissic two-mica granite (165–157 Ma) and Early Cretaceous granodiorite (129 Ma) and are structurally controlled by NNE- and NW-trending faults. Previous attempts to date the gold mineralization yielded ambiguous results (135–112 Ma). Here we report the first in-situ and direct age constraint for gold mineralization at Wulong. Five molybdenite samples from Mo-bearing quartz ± pyrite veins yielded an isochron age of 127.6 ± 2.3 Ma. In-situ SIMS U-Th-Pb dating of hydrothermal monazite that coexists with gold-bearing pyrite and quartz yielded a 208Pb-232Th age of 126.7 ± 3.2 Ma. These robust ages, together with new age data of the Wulong host intrusion and post-ore dike, allow for a better interpretation of the ore genesis of the Wulong deposit relative to a well constrained sequence of regional geological events. Zircon U-Pb dating of the Wulong host intrusion (gneissic two-mica granite), representing the oldest magmatic event at Wulong, gave a weighted mean age of 159.3 ± 1.4 Ma that is interpreted to be the magma emplacement age. Subsequent magmatic events are recorded by the Early Cretaceous dikes with zircon U-Pb ages between 127 and 113 Ma. A post-ore diorite porphyry dike that crosscuts the Early Cretaceous dikes has a U-Pb zircon age of 121.5 ± 1.5 Ma. All the lines of geochronology evidence suggest a distinct genetic link between the gold mineralization and the Early Cretaceous magmatism in the Wulong orefield. This episode of magmatism and mineralization corresponds to the lithospheric thinning within the northeastern North China Craton, which is triggered by the subduction of the Paleo-Pacific plate.

Petrogenesis of Late Triassic mafic enclaves and host granodiorite in the Eastern Kunlun Orogenic Belt, China: Implications for the reworking of juvenile crust by delamination-induced asthenosphere upwelling

Late Triassic granitoids containing abundant mafic microgranular enclaves (MMEs) occur widely in the Eastern Kunlun Orogenic Belt (EKOB). In this work, we present mineral chemistry, zircon U-Pb ages and L-Hf isotopes, whole-rock chemistry and S-Nd isotope compositions of the MMEs and host granodiorite from the Huda pluton in the Elashan area within the easternmost domain of the EKOB. These rocks contain inherited (Meso- to Neoproterozoic) and xenocrystic (ca. 240 Ma) zircon grains that yield apparent older ages, whereas the magmatic zircons from MMEs and granodiorite yield similar weighted mean ages around 224 Ma, which are interpreted as their crystallization ages. The MMEs have low SiO2 but high TiO2, TFe2O3, CaO, MgO and MnO concentrations with relatively high Mg# values (48–54) and 100MnO/(MnO + MgO + TFe2O3) ratios (1.2–1.6). They display identical Sr-Nd-Hf isotope compositions to the host granite. Combined with petrological evidence, we suggest that the MMEs are cognate cumulates that formed by pressure quenching during the late stage of magma evolution from the same parental magma of the host granodiorite, rather than a magma mixing origin. The granodiorite is calc-alkaline to high-K calc-alkaline, metaluminous I-type granite. They show relatively low SiO2 and MnO, but high MgO, Al2O3, CaO and TFe2O3 contents with Mg# values of 45–50. They are enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), such as Rb, Th, K and Pb, and are depleted in P and high field strength elements (HFSE) including Nb, Ta and Ti. These rocks display slightly negative Eu anomalies and low Sr/Y and La/Yb ratios. Together with the rim-ward chemically evolved nature of some phenocrysts, the comparatively high initial Sr isotope (0.70888–0.70912), low whole-rock εNd(t) (−5.6 to −6.0) and zircon εHf(t) (−3.3 to −0.1) values, and low Nb/Th (0.11–0.26) and Ta/U (0.53–0.68) ratios, we suggest that the granodiorite magma was sourced from the lower crust. Considering their comparatively young two-stage Nd and Hf model ages (1.42–1.49 Ga and 1.13–1.42 Ga, respectively) and same trace element character with the juvenile crust beneath the EKOB, we interpret the juvenile lower crust as the dominant source rocks for the granodiorite. Based on our data and regional geological evidence, we suggest that the partial melting of juvenile crust resulted from delamination-related asthenosphere mantle upwelling. The latter process resulted in extensive melting of the lower crust, producing a major Late Triassic magmatic flare-up event in the EKOB.

Timing of carbonatite-hosted U-polymetallic mineralization in the supergiant Huayangchuan deposit, Qinling Orogen: Constraints from titanite U–Pb and molybdenite Re–Os dating

The newly-discovered supergiant Huayangchuan uranium (U)-polymetallic (Sr, Se, REEs, Ba, Nb and Pb) deposit is located in the Qinling Orogen, central China. The deposit underwent multistage mineralization, with the main carbonatite ore stage being the most important for the U, Nb, REE, Sr and Ba endowments. According to the mineral assemblages, the main carbonatite ore stage can be divided into three substages, i.e., sulfate (Ba–Sr), alkali-rich U and REE-U mineralization.Main-stage titanite from the Huayangchuan igneous carbonatite are rich in high field strength elements (HFSEs, e.g., Zr, Nb and REEs), and show clear elemental substitutions (e.g., Ti vs. Nb ​+ ​Fe ​+ ​Al and Ca ​+ ​Ti vs. Fe ​+ ​Al ​+ ​REE). High-precision LA-ICP-MS titanite dating yielded a U–Pb age of 209.0 ​± ​2.9 ​Ma, which represents the main-stage mineralization age at Huayangchuan, and is coeval with the local carbonatite dyke intrusion. This mineralization age is further constrained by the Re–Os dating of molybdenite from the Huayangchuan carbonatite, which yielded a weighted mean age of 196.8 ​± ​2.4 ​Ma. Molybdenite Re contents (337.55–392.75 ​ppm) and C-O-Sr-Nd-Pb isotopic evidence of the Huayangchuan carbonatite both suggest a mantle origin for the carbonatite. Our study supports that the Late Triassic carbonatite magmatism was responsible for the world-class U-Mo-REE mineralization in the Qinling Orogen, and that the regional magmatism and ore formation was likely caused by the closure of the Mianlue ocean and the subsequent North China-South China continent-continent collision.

Zircon U–Pb geochronology and clockwise P–T evolution of garnet-bearing migmatites from the Qinling complex in the Weiziping area of the Qinling Orogen, Central China: Implications for thermal relaxation after crustal thickening

Zircon U–Pb dating and phase equilibrium modeling in the Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O2 system were carried out to garnet-bearing migmatites from the Qinling Complex in the Weiziping area of the Qinling Orogen, Central China, to constrain their metamorphic P–T path and elucidate the tectonic setting and geodynamic mechanism of Early to Middle Devonian high-temperature (HT) metamorphism in the North Qinling Belt. The mesosomes of the migmatites are composed of garnet-bearing biotite–hornblende–plagioclase and biotite–plagioclase gneisses, and the leucosomes can be divided into two types: wide leucosomes that were deformed, and narrow penetrative leucosomes. Laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) zircon U–Pb analyses yielded weighted mean 206Pb/238U ages of 398.8 ± 4.7, 394.6 ± 2.6, 399.5 ± 7.3, 372.5 ± 4.2, 370.8 ± 4.3, and 368.5 ± 4.2 Ma for metamorphic zircons within the sampled mesosomes, and a weighted mean age of 408.7 ± 5.7 Ma for igneous zircons within a deformed leucosome. Based on the published data and the results in this study, the timing of granulite-facies metamorphism is constrained to be ca. 409–395 Ma. The mesosome sample (garnet-bearing biotite–hornblende–plagioclase gneiss) has a peak mineral assemblage of garnet, biotite, plagioclase, hornblende, quartz, ilmenite, and melt, which equilibrated at P–T condition of 8.5–9.7 kbar at 745–820 °C as constrained by isopleths of XAn and XPy in a P–T pseudosection, suggesting that these gneisses underwent medium-pressure granulite-facies metamorphism. Conventional garnet–biotite–plagioclase–quartz (GBPQ) geothermobarometry yielded P–T conditions of 703 °C at 10 kbar and 685–748 °C at 7.1–8.9 kbar, which correspond to prograde and retrograde metamorphic stages, respectively. On the basis of these P–T results, the studied samples document a clockwise P–T path characterized by temperature increase and pressure decrease during the prograde stage, and temperature decrease and pressure decrease during the retrograde stage. Ti-in-zircon thermometry yielded a temperature range of 781–793 °C for metamorphic zircons from the mesosomes, further demonstrating that they underwent granulite-facies metamorphism at ca. 409–395 Ma. The prograde metamorphic stage characterized by temperature increase and pressure decrease suggests that thermal relaxation after crustal thickening has induced the partial melting and migmatization. Thus, the crustal thickening that may be caused by continental collision between the North China Block and the South China Block should occur no later than ca. 409 Ma.

Tourmaline 40Ar/39Ar geochronology and thermochronology: Example from Hadean-zircon-bearing siliciclastic metasedimentary rocks from the Yilgarn Craton

We present 40Ar/39Ar ages and boron isotopes of tourmalines from a quartz-tourmaline intrusion cross-cutting the Hadean detrital-zircon-bearing metasedimentary rocks from the Mt. Alfred and Brooking Hills localities of the Illaara Greenstone Belt, Western Australia. Concordant 40Ar/39Ar plateau ages on the tourmalines at Mt. Alfred give a weighted mean age of 2935 ± 9 Ma (2σ). These results are the first reported Archean 40Ar/39Ar ages directly obtained on tourmaline, and provide a minimum depositional age for this sequence, placing constraints on the depositional timing of detrital Hadean zircons to between 2935 ± 9 Ma and c.a. 3250 Ma (youngest detrital zircon age in sequence). This is the last known occurrence of abundant detrital Hadean zircons having been directly deposited in a sedimentary sequence, and thus suggests that most Hadean zircon sources have been exhausted by this time. The 2935 ± 9 Ma tourmalines occur within a quartz-tourmaline intrusion with associated stratiform layers and veins, inferred to have grown during a hydrothermal fluid circulation event. A younger generation of tourmalines from the Brooking Hills, 30 km south of Mt. Alfred yielded concordant 40Ar/39Ar plateau ages with a weighted mean age of 2624 ± 16 Ma. These tourmalines occur within and along the margins of post-kinematic quartz veins, parallel to the foliation fabric and marks the end stage of high temperature tectono-thermal events within the Illaara Greenstone Belt. The retention of 2935 ± 9 Ma tourmaline ages within the Illaara Greenstone Belt shows that the K/Ar system of tourmaline remained closed throughout repeated upper-greenschist metamorphic events (∼450 °C) between the ages of c.a. 2930 to 2630 Ma in contrast to muscovite recording plateau ages of about 2600 Ma. This is in agreement with an approximate Ar closure temperature between ∼534 and 628 °C experimentally determined in this study.

HYPOGENE ALUNITE FROM THE EL SALVADOR DISTRICT, CHILE, INDICATES POTENTIAL FOR A BLIND PORPHYRY COPPER CENTER

AbstractSurface samples of hypogene alunite that cement late breccia bodies from the El Salvador porphyry copper district of Chile were recently dated. One alunite sample over the principal Turquoise Gulch porphyry deposit has a 40Ar/39Ar total gas age of 40.64 ± 1.04 Ma, overlapping the age of a late latite intrusion. Two other samples associated with quartz-alunite replacement of rhyolite, ~750 m southwest of the collapse zone over the block cave of the porphyry copper deposit, are distinctly younger, at 38.12 ± 0.66 and 38.04 ± 0.22 Ma (averages of duplicate analyses, with ±2σ errors).Previously reported U/Pb ages of zircons from 15 Eocene-age diorite, granodiorite, and granite porphyry intrusions have weighted mean ages that range from about 44 to 41 Ma, with peak magmatic flux interpreted at 44 to 43 Ma. Porphyry copper ores in the El Salvador district formed at about the same time as porphyry intrusions, with intrusive centers that migrated in a south-southwest direction, from the small deposits at Cerro Pelado (~44.2 Ma), to Old Camp (~43.6 Ma) and M Gulch-Copper Hill (~43.5–43.1 Ma), to the main ore deposit at Turquoise Gulch (~42 Ma). The granodiorite porphyry intrusions at Turquoise Gulch are associated with ~80% of the known copper ore of the district; they record waning stages of magmatism at 42.5 to 42.0 Ma, followed by weakly altered latite dikes at 41.6 Ma. Molybdenite in quartz veins returned Re-Os ages of 41.8 to 41.2 Ma.The two alunite samples from our study with coincident dates of ~38 Ma provide evidence for magmatic-hydrothermal activity younger than any recognized to date, consistent with the alteration overprint of quartz-alunite on older muscovite after erosion. This younger activity must have been associated with a blind intrusion, likely located south of the Turquoise Gulch deposit, based on the distribution of alteration minerals, and offset from the zoning associated with the Turquoise Gulch center. Stable isotope values (δ34S, δ18O, δD) of the ~38 Ma alunite indicate a high-temperature hypogene origin, consistent with formation in a lithocap environment that typically is located at shallow levels over and on the shoulders of porphyry copper deposits. Both observations—alteration overprint and markedly younger age of alunite—indicate the potential for porphyry copper mineralization south of Granite Gulch, as much as 1,000 m below the level of the coeval outcropping quartz-alunite replacement, perhaps near ~2,000-m elevation; this is hundreds of meters deeper than the known copper ore of Turquoise Gulch.

The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XX. Ages of Single and Multiple Stellar Populations in Seven Bulge Globular Clusters

Abstract In the present work we analyzed seven globular clusters (GCs) selected from their location in the Galactic bulge and with metallicity values in the range −1.30 ≲ [Fe/H] ≲ −0.50. The aim of this work is first to derive cluster ages assuming single stellar populations and second to identify the stars from first (1G) and second generations (2G) from the main sequence, subgiant, and red giant branches, and to derive their age differences. Based on a combination of UV and optical filters used in this project, we apply the Gaussian mixture models to distinguish the multiple stellar populations. Applying statistical isochrone fitting, we derive self-consistent ages, distances, metallicities, and reddening values for the sample clusters. An average age of 12.3 ± 0.4 Gyr was obtained both using DSED and BaSTI (accounting atomic diffusion effects) isochrones, without a clear distinction between the moderately metal-poor and the more metal-rich bulge clusters, except for NGC 6717 and the inner halo NGC 6362 with ∼13.5 Gyr. We derived a weighted mean age difference between the multiple populations hosted by each GC of 41 ± 170 Myr adopting canonical He abundances; whereas for higher He in 2G stars, this difference reduces to 17 ± 170 Myr, but with individual uncertainties of 500 Myr.

A possible linkage between highly fractionated granitoids and associated W-mineralization in the Mesozoic Yaogangxian granitic intrusion, Nanling region, South China

The Yaogangxian (YGX) W deposit in the central Nanling W province, South China, is one of the largest W deposits worldwide. Both vein-type wolframite and skarn-type scheelite orebodies were exposed in YGX. These scheelite and wolframite mineralization are spatially associated with the YGX granitic intrusion. The exposed intrusion contains two main intrusive phases: lower zone, coarse-grained two-mica granite and upper zone, fine-grained muscovite granite. An integrated study of whole-rock geochemistry, LA ICP-MS zircon U–Pb geochronology, and zircon Hf isotopic geochemistry of the YGX granitic intrusion was undertaken to constrain its magmatic source and petrogenesis. Cassiterite LA ICP-MS U–Pb dating was also undertaken to constrain the connection between the intrusion and hydrothermal W mineralization. Zircon U–Pb dating yielded weighted-mean ages of 161 ± 3 and 157 ± 2 Ma for the two-mica and muscovite granites, respectively. Cassiterite crystals from wolframite–quartz veins display growth zonation under cathodoluminescence, and have a weighted-mean zircon U–Pb age of 158 ± 2 Ma. The formation of the muscovite granite and related W mineralization in the YGX deposit was thus initiated during the early Yanshanian. The YGX granites display typical metaluminous to strongly peraluminous characteristics with high SiO2 (73.5–79.1 wt%) and K2O (3.0–5.0 wt%) contents. They are enriched in heavy rare earth elements (REEs) comparative to light REEs. Notably, they exhibited strong negative Eu anomalies, and are depleted in Sr, Ba, P, and Ti. In addition, muscovite granites in YGX are more significantly enriched in heavy REEs relative to light REEs than two-mica granites, indicating that the former experienced higher degree fractionation than the latter. Zircon grains of the YGX granitoids have strongly negative εHf(t) (–15 to –10.3), with two-stage Hf model ages of 2.15–1.86 Ga, indicating a magma source of reworked ancient crustal material without obvious involvement of juvenile materials. The results of petrology and geochemistry indicate that the YGX granitic intrusion is a highly fractionated S-type granite emplaced during widespread 160–150 Ma granitic magmatism in the Nanling region. Further evolution to late stage for multiphase YGX granitic intrusion is needed to enrich ore-forming elements after magmatic emplacement. It is suggested that the extensional environment of continental lithosphere caused by the northwest subduction of the paleo-Pacific plate may play an key role in the genesis of YGX S-type granite. W-rich Proterozoic basement rocks and fractional crystallization may provide material for the formation of the granite-related tungsten mineralization.

40Ar/39Ar geochronology constraints on formation of the Tuwaishan orogenic gold deposit, Hainan Island, China

The Tuwaishan deposit is an orogenic gold deposit that is structurally controlled by the NE-trending Gezhen shear zone in the western part of Hainan Island, south China. It is part of a belt of numerous similar deposits hosted in Mesoproterozoic granitoids and lesser Paleoproterozoic to Mesoproterozoic schists. The Tuwaishan gold orebodies comprise auriferous quartz veins and disseminated gold in sulfidized granitic mylonite. The veins consist of early quartz-pyrite-arsenopyrite-pyrrhotite with minor gold, middle stage quartz-gold-base metal sulfides, and barren late quartz-carbonate. New 40Ar/39Ar dating of muscovite from wallrock schists yielded a minimum age of 356.8 ± 0.9 Ma, suggesting the youngest possible age estimate for amphibolite facies regional metamorphism of the Baoban Group country rocks. The 40Ar/39Ar dating of sericite from auriferous quartz veins yielded a weighted mean age of 243.4 ± 2.3 Ma, representing the ore-forming age of the Tuwaishan gold deposit. The formation of the shear-hosted gold deposits along the Gezhen gold belt was likely related to the Early to Middle Triassic convergence between the Indochina and South China Blocks. Based on the widely accepted metamorphic devolatilization model for orogenic gold deposit formation, most Au tends to be released into the ore-forming fluid in the source region when country rocks were firstly metamorphosed from greenschist to amphibolite facies. Therefore, it is highly unlikely that the immediate country rocks of the Baoban Group, which were at amphibolite facies by early Carboniferous, were the source for fluids and metals along the Gezhen shear zone.

Genesis of Volcanic Rocks in the Zijinshan Ore District, SE China: Implications for Porphyry-Epithermal Mineralization

Volcanic rocks, as the extrusive counterparts of the mineralized intrusions, can provide important information on the magma source, petrogenesis, and metallogenic conditions of the coeval porphyry-epithermal system. Shanghang Basin volcanic rocks are spatially and temporally related to a series of adjacent porphyry-epithermal Cu–Au deposits, and they can be used as a window to study the related deposits. Two laser-ablation–inductively coupled plasma–mass spectrometry zircon U–Pb analyses of the volcanic rocks yield weighted mean ages of ~105 Ma, identical to the age of the coeval porphyry-epithermal mineralization. Rocks have SiO2 contents of 55.4 to 74.8 wt % and belong to the high-K to shoshonitic series, characterized by strong differentiation of light rare-earth elements (REEs) relative to heavy REEs (mean LaN/YbN = 16.88); enrichment in light REEs, Rb, Th, and U; and depletion in Nb, Ta, Zr, Hf, and Ti. The volcanic rocks display (87Sr/86Sr)i values of 0.709341 to 0.711610, εNd(t) values of −6.9 to −3.3 εHf(t) values of −3.95 to −0.30, and δ18O values of 6.07‰–6.79‰, suggesting that the parental magmas were derived from a mantle source enriched by subduction-related progress. SiO2 content shows a strong negative correlation with the contents of some major and trace elements, indicating that fractional crystallization played an important role in the generation of these rocks. A binary mixing model of Hf–O isotopes gives an estimated degree of crustal contamination of 30%. In addition, magnetite crystallized early, and the samples showed high zircon EuN/EuN* values (0.48–0.68), indicating that the parental magma had a high oxygen fugacity. The inferred suppression of plagioclase crystallization and increasing hornblende crystallization during magma evolution suggest that the magma was water rich. The high-water content and high oxygen fugacity of the magma promoted the dissolving of sulfides containing Cu and Au in the source area and contributed to the migration of ore-forming elements.

Geochronology, geochemistry, and Hf isotopes of mafic rocks from Dalabute ophiolitic mélange in West Junggar, Xinjiang (NW China): Implications for the magmatic source and tectonic setting

Several Palaeozoic ophiolitic mélanges distributed in the West Junggar, Xinjiang, are remnants of the Paleo‐Asian Ocean evolution. They are important keys for studying the component, tectonic evolution, and crust–mantle interaction of the Central Asian Orogenic Belt (CAOB). This paper presents petrology, zircon U‐Pb chronology, geochemistry, and Hf isotope data of mafic rocks from the Dalabute ophiolitic mélange, West Junggar. The zircon U‐Pb chronology data of gabbro in the Dalabute ophiolitic mélange can be divided into two groups. The first group magmatic zircons yield a weighted mean age of 389.7 ± 7.7 Ma. It suggests that gabbros of the Dalabute ophiolitic mélange were formed during the period of Early‐middle Devonian, which represents the main period that the Dalabute back‐arc ocean basin expanded. The second group inherited zircons with ages ranging from 910 to 975 Ma were interpreted as Neoproterozoic materials of basement entered its magmatic source. Geochemical characteristics show that the mafic rocks from the Dalabute ophiolitic mélange can be subdivided into alkaline and tholeiite series. Whole‐rock and Hf isotopic data indicate that alkaline basalts have the signatures of typical OIB and formed in the oceanic island or seamount settings related to mantle plume, which were most likely derived from an enriched mantle source. Besides, tholeiitic rocks exhibit the features of MORB and generated in an immature back‐arc basin in the supra‐subduction zone. Their magmas originated from a depleted mantle that had been metasomatized by subduction‐related fluids and contaminated by materials with crustal nature. Therefore, Dalabute ophiolites are supposed to be generated from a back‐arc oceanic basin, which is relate to intra‐subduction and with mantle plumes developed within it. These results jointly provide convincing evidence for the evolution and property of the Dalabute ophiolite in the West Junggar and further supply reference and base for reconstruct the evolutionary history of the CAOB.

Low–pressure granulite–facies metamorphism in the Southern Chinese Altay orogenic belt, NW China: P–T estimates, U–Pb ages and tectonic implications

The Chinese Altay orogenic belt formed in the Paleozoic is an important part of the Central Asian Orogenic Belt (CAOB), accompanying with remarkable metamorphism. Its tectono–metamorphic evolution history is still a controversial topic. In this contribution, we investigate the petrography, metamorphic peak P–T conditions and zircon geochronology of the newly discovered garnet–absent metapelitic and felsic gneisses at Wuqiagou area in the southern Chinese Altay. They are characterized by an assemblage of orthopyroxene + biotite + plagioclase + quartz + Fe–Ti oxides ± cordierite ± K–feldspar, in which most K–feldspar grains have transformed into perthites with thin albite lamellae. The Wuqiagou garnet–absent gneisses experienced pervasive partial melting, as testified by microstructures such as mineral pseudomorphs after melt films or pockets. Phase diagram modelling constrains the peak P–T conditions to 3.5–5.5 kbar and 800–900 °C, with possible geothermal gradients of 45–75 °C/km, indicative of a prominent low–pressure granulite–facies metamorphic event in the southern Chinese Altay. SIMS zircon U–Pb dating results show a weighted mean age of 255.8 ± 1.8 Ma. This age is interpreted to represent the timing of this low–pressure granulite facies metamorphism, which is highly coeval with the timing of their hosted mafic granulite lenses (∼255 Ma) and nearby mantle–derived mafic intrusions (∼257 Ma). Based on available petrological, geochemical and chronological data, we propose that the Permian low–pressure granulite–facies metamorphic event in the southern Chinese Altay was likely associated with the intrusions of deep–derived mafic magma at a relatively shallow crustal level (12–18 km) in a post–orogenic extensional setting, with a possible link with the Tarim mantle plume activity.

40Ar/39Ar geochronology of the Pongkor low sulfidation epithermal gold mineralisation, West Java, Indonesia

The Pongkor gold deposit located approximately 90 km southwest of Jakarta is well known as the typical low sulfidation (LS) epithermal gold deposit and the largest gold vein deposit in Indonesia. The Pongkor gold mineralisation has been the subject of several geological studies. Determination of the duration of gold mineralisation events, however, is less well understood. The mineralisation events are important for understanding the genesis of ore deposits. This study presents 40Ar/39Ar age results for four adularia samples from Ciguha gold-bearing quartz vein yielding plateau ages of 1.80 ± 0.03 Ma, 2.33 ± 0.32 Ma, and 1.88 ± 0.02 Ma, plus one weighted mean age of 1.95 ± 0.04 Ma. Adularia from the Kubang Cicau gold-bearing quartz veins yielded a 40Ar/39Ar plateau age of 2.02 ± 0.03 Ma. The period of adularia growth in the Ciguha vein may have extended from ca. 2.07 to 1.77 Ma that includes the ages of 1.95 ± 0.04 Ma and 1.88 ± 0.02 Ma. The time interval indicates multiple generations of the adularia. The data suggest that mineralisation of Ciguha may have continued episodically or continuously. The age of adularia from the Kubang Cicau gold-bearing quartz vein (2.02 ± 0.03 Ma) is within the error of the Ciguha vein age and the adularia growth of Kubang Cicau vein reveals at the beginning of Ciguha’s adularia growth. The data suggest that gold mineralisation in the Pongkor deposit for Kubang Cicau and Ciguha veins was initiated at the relatively similar time. The 40Ar/39Ar adularia ages of this study are within error of the previously reported 40Ar/39Ar results (Milesi et al., 1999) but significantly younger than the previously reported K-Ar adularia dating result (Kageyama, 1999 in Rosana and Matsueda, 2002).

Association Between Serum Cotinine and Severe Abdominal Aortic Calcification in US Adults.

This study aims to explore the association between serum cotinine and severe abdominal aortic calcification (AAC) in the US adults. We examined 2840 participants with a weighted mean age of 57.4 years from the National Health and Nutrition Examination Survey 2013-2014. Serum cotinine was analyzed as the main exposure both continuously and categorically (tertiles). Abdominal aortic calcification detected with dual-energy X-ray absorptiometry was quantified using the Kauppila score system. Severe AAC was detected in 252 (8.9%) participants. The multivariable-adjusted odds ratios and 95% confidence intervals (CIs) of the middle and top cotinine categories were 1.14 (0.79-1.64) and 1.80 (1.21-2.68), respectively, P for trend = .004. Per unit increase in log-transformed serum cotinine was associated with 10% (95% CI: 6%-15%) higher odds of severe AAC when serum cotinine was analyzed as a continuous variable. The association was consistent across sex and ethnic groups. In conclusion, elevated serum cotinine level was associated with higher odds for severe AAC in a representative sample of US adults.

Outcomes and Incidence of Complications Following Endoscopic Gastrocnemius Recession: A Systematic Review.

Introduction: Equinus contracture of the ankle can lead to a multitude of foot and ankle pathologies. The gastrocnemius recession has been used to address equinus deformity via various methods, including either an open or an endoscopic approach. Open techniques require increased intraoperative time and complication risks of sural nerve injury, wound complications, and poor cosmesis. Resultantly, the aim of the current study is to review the complications and outcomes of the endoscopic gastrocnemius recession. Methods: A systematic review of electronic databases was performed. The authors compiled data from retrospective and prospective patient studies including general patient demographics, outcomes, qualitative scoring measures, complications, and surgical technique. Results: Eleven studies met our inclusion criteria. A total of 697 feet in 627 patients were included in the current systematic review. The weighted mean age was 45.3 years and weighted mean follow-up was 18.4 months. The most common indication for an endoscopic gastrocnemius recession was equinus contracture. The weighted mean preoperative ankle range of motion was -2.3° and the weighted postoperative ankle range of motion was 10.9°. The most common complications included plantarflexion weakness of the ankle at 3.5%, a sural nerve injury of 3.0% and wound complication rate was 1.0% with no deep infection. The overall complication rate was 7.5%. Conclusion: The endoscopic gastrocnemius recession is a valuable surgical tool in the treatment of ankle equinus. The endoscopic approach has satisfactory outcomes including low incidence of plantarflexion weakness and sural neuritis. Patients should be counseled on these risks preoperatively. Compared with previously reported systematic review of the open technique, the endoscopic approach has a lower overall incidence of complications. Prospective clinical trials comparing open and endoscopic techniques are warranted.Levels of Evidence: Level IV.

Pyrite Rb-Sr, Sm-Nd and Fe isotopic constraints on the age and genesis of the Qingchengzi Pb-Zn deposits, northeastern China

Sr-Nd-Fe isotopes are reported for pyrites and whole rocks of ores and associated rocks for the Qingchengzi Pb-Zn deposits in the northeasern China, to investigate the age, sources and processes of the Pb-Zn mineralization. Rb-Sr leaching isotopic dating of pyrites that crystallized coeval with galena and sphalerite from five subsamples of ores yields isochron ages of 143 ± 12 Ma to 159 ± 12 Ma with a weighted mean age of 151.8 ± 5.2 Ma. This age can be interpreted to be the timing of Pb-Zn mineralization, coeval with the emplacement of Late Jurassic granites in the region. The pyrites have negative εNd (152 Ma) values of −17.6 to –22.0, among the Neoarchean TTG rocks, Paleoproterozoic meta-sedimetary rocks (i.e., wall rocks) and granites, and Mesozoic mafic dykes and granites. However, the initial 87Sr/86Sr ratio of 0.7188 ± 0.0004 is similar to those of Late Jurassic granites and Paleoproterozoic rocks (0.7082–0.7183), distinct from those of mafic dykes (0.7069–0.7110), indicating the ore-forming materials (i.e., Pb and Zn) were mainly derived from wall rocks and Late Jurassic granites. Combined with the previously-published H-O isotopes, the new age and Sr-Nd isotopic data indicate that the mineralizaing fluids were mainly derived from dehydration of granitic magmas, interacted with meteoric water that extracted Pb and Zn from the wall rocks. The δ56Fe values of pyrites in the Pb-Zn ores and Paleoproterozoic meta-sedimentary rocks range from +0.23‰ to +1.09‰ and −0.49‰ to +0.17‰, respectively, distinct from those of Paleoproterozoic basement rocks and Mesozoic rocks (−0.03‰ to +0.28‰). Combined with Nd isotopes, the large range of δ56Fe values for pyrites would be the result of rapid precipitation of pyrites in the wall rocks and contemperal deposition of pyrites in the residual fluids during interaction between wall rocks and ore-forming fluids. Collectively, our new Sr-Nd-Fe isotopes of pyrites not only constrain the age and sources of Pb and Zn mineralization, but also reveal the detailed mineralization processes, providing a new method to constrain the genesis of hydrothermal Pb-Zn deposits.

U–Pb (zircon) geochronologic constraint on tectono-magmatic evolution of Chaur granitoid complex (CGC) of Himachal Himalaya, NW India: implications for the Neoproterozoic magmatism related to Grenvillian orogeny and assembly of the Rodinia supercontinent

Many elongated, lenticular intrusive granitoids of various ages are scattered within the Lesser Himalayan metamorphic belt, all along the ~ 2500 km length of the Himalaya. The Neoproterozoic Chaur granitoid complex (CGC) of Chaur area is characterized by foliated and non-foliated peraluminous granites occurring as an isolated granitoid body within the Jutogh group. In this work, we present the whole-rock geochemical data of six samples and U–Pb (zircon) geochronology of two different granites of the CGC and one granitic gneiss sample of Jutogh group from Himachal Pradesh of NW Himalaya. Our newly obtained results of U–Pb (zircon) geochronological age populations from all granitoid sample yield age between 766 and 1080 Ma with few younger phases and older inherited ages. We obtained U–Pb (zircon) ages from two sample of the CGC, out of which one gives the two prominent age spectra for 206Pb/238U with weighted mean age of 826 ± 4.97/9.74 Ma, MSWD = 0.65, n = 8) and 868 ± 6.21/12.17 Ma, MSWD = 1.28, n = 7). Similarly, another granite of CGC gives the weight mean age of 929 ± 6.48/12.70 Ma (MSWD = 1.28, n = 11). The granitic gneiss of the Jutogh group also gives two prominent age spectra for 206Pb/238U, with weighted mean age of 861 ± 8.27/16.21 Ma (MSWD = 0.31, n = 10) and 932 ± 10.0/19.6 Ma (MSWD = 1.57, n = 8). The whole-rock geochemical data show calc-alkaline composition of all six samples and suggest a subduction-related accretion setup. The depletion in the Nb, Sr, P and Ti in CGC indicates a magmatic arc type magma. U–Pb (zircon) ages of all three samples have a similar phase of crystallization and we defined as ~ 930 Ma age of crystallization of CGC. The whole-rock geochemical data suggest that all the three samples possibly came from the same magma source during the Neoproterozoic magmatic events in the northern marginal part of the Indian plate. It is envisaged that the unknown microcontinents present in the northern margin collide with the Indian plate and the subduction process coincides with the onset of the Grenvillian orogeny during the Neoproterozoic. The extension of these minor collision orogen may have been connected with Lhasa, Trim as well as Greater India blocks. In this collisional process, the crustal melt was generated and intruded in the form of CGC within the pre-existing Paleoproterozoic crust of Indian plate. The whole process indicates that the subduction of unknown microcontinent under the Indian plate may be correlated with the Grenvillian orogeny and formation of the Rodinia supercontinent during Neoproterozoic.

Petrogenesis and geodynamic significance of Kayinde gabbro in the Ashele Basin, Altay Orogenic Belt, Xinjiang, Northwest China: Constraints from geochronological and geochemical data

Mafic‐ultramafic intrusions occur sporadically but are pivotal to constrain the tectonic evolution of the Chinese Altay, a key part of the Central Asian Orogenic Belt. The tectonic setting of the Early‐Middle Devonian is well documented, but that of the Late Devonian remains a matter of ongoing debate. The Kayinde gabbro occurs in the Ashele Basin of the South Altay. This paper reports petrologic, zircon U‐Pb geochronological, geochemical, and Sr‐Nd isotopic data of the Kayinde gabbro, with the aims to investigate its formation time, petrogenesis, and geodynamic significance. Zircons separated from the gabbro yield a cluster of concordant data points and a weighted mean age of 373.1 ± 4.1 Ma, representing a Late Devonian emplacement. Geochemically, the Kayinde gabbro is subalkaline, tholeiitic, and characterized by high Mg# values (68–73), enrichment in large‐ion lithophile elements (including Ba, Sr, Rb, and U), depletion in high‐field‐strength elements (including Nb, Ta, Zr, and Hf), fairly flat REE patterns, low (87Sr/86Sr)i (0.70366–0.70440) and positive εNd(t) (3.4–5.4) values. The geochemical characteristics collectively suggest that the Kayinde gabbro was derived from a spinel‐stable lithospheric mantle source, which was depleted by previous magma extraction and metasomatized by later slab‐derived fluids or melts in an island arc setting. The geochemical similarities between the Kayinde gabbro and other contemporary mafic‐ultramafic intrusions reveal that the subduction continued during the Late Devonian in the Chinese Altay. In combination with the published research, we favour a two‐unit arc system composed of a continental arc and an island arc, spanning across the Early to Late Devonian. The Ashele Basin can be considered to be an oceanward setting in this model.