Fluid inclusion and H–O isotope study of the Jiguanshan porphyry Mo deposit,Xilamulun Metallogenic Belt: implications for characteristics and evolution of ore-forming fluids

We studied the fluid inclusions of the Jiguanshan Mo deposit in China, which is a large porphyry deposit located in the southern Xilamulun Metallogenic Belt. The irregular Mo ore body with various types of hydrothermal veinlets is hosted by Late Jurassic granite porphyry. Intense hydrothermal alterations in the deposit from the core to margin are silicification–potassium feldspar alteration,pyrite–quartz–sericite–fluorite alteration, and propylitic alteration. Based on the mineral assemblages and crosscutting relationships of ore veins, the ore-forming process were divided into three stages and two substages: quartz–pyrite veins(stage I) associated with potassic alteration;quartz–molybdenite–chalcopyrite–pyrite veins(substage Ⅱ-1) and quartz–molybdenite–fluorite veins(substage Ⅱ-2)associated with phyllic alteration; and fluorite–quartz–carbonate veins(stage Ⅲ) with carbonation. Five majorfluid inclusions(FIs) types were distinguished in the quartz associated with oxide and sulfide minerals, i.e. polyphase brine(Pb-type), opaque-bearing brine(Ob-type), solid halite(S-type), two-phase aqueous(A-type), and vapor(Vtype) inclusions. The FIs of stage I were composed of liquid-rich S-, A-, and V-type FIs with homogenization temperatures and salinities of 490 to 511 °C and 8.9 to 56.0 wt% NaCl equiv., respectively. The FIs of substage Ⅱ-1 are composed of Pb-, Ob-, S-, A-, and V-type FIs with homogenization temperatures and salinities of 352 to460 °C and 3.7 to 46.1 wt% NaCl equiv, respectively. The FIs of substage Ⅱ-2 are Ob-, S-, A-, and V-type FIs with homogenization temperatures and salinities of 234 to309 °C and 3.7 to 39.2 wt% NaCl equiv, respectively. The FIs of stage Ⅲ are A-type FIs with homogenization temperatures and salinities of 136 to 172 °C and 1.1 to 8.9 wt%NaCl equiv, respectively. Fluid boiling, which resulted in the precipitation of sulfides, occurred in stages I and Ⅱ. The initial ore-forming fluids of the Jiguanshan deposit had high temperature, high salinity, and belonged to an F-rich NaCl ± KCl–H_2O system. The fluids gradually evolved to low temperature, low salinity, and belonged to a NaCl–H_2O system. Studies of the hydrogen and oxygen isotope compositions of quartz(δ~(18)O_(H2O)=-7.3 to 6.3%,δD_(H2O)=-104.3 to-83.3%) show that the ore-formingfluids gradually evolved from magmatic water to meteoric water.     

Geochemical evidence for contribution of ore-forming materials from peraluminous granite basement —— Taking Fucheng pluton and No. 6722 uranium deposit in southern Jiangxi Province as examples

Source of ore-forming material is always one of the fundamental subjects in the study of mineral deposits. Recently, in order to probe deep sources of ore-forming materials, many interna-tional and Chinese investigators have paid much attention to the rel…     

Geothermal and fluid flowing simulation of ore-forming antimony deposits in Xikuangshan

1 Introduction The Mid-Hunan Basin is located in the south mar- gin of the Ancient Island Arc of Dong’an-Xuefeng and the north part of the interarc basin of Hercynian- Indosinian in Hunan-Guangxi. The basement rock of the basin, which is mainly distributed along the mar- ginal area of the basin and some interior sub-uplifts, is composed of pre-Devonian epimetamorphic-clastic rocks in great thickness, and the cap rock of the basin are dominated by carbonate rock and clastic rocks of Paleo…     

Zircon and apatite fission track analyses on mineralization ages and tectonic activities of Tuwu-Yandong porphyry copper deposit in northern Xinjiang, China

The mineralization ages reported in the past in the Tuwu-Yandong copper district not only are different,but also fall into the Hercynian epoch.This study has achieved 9 zircon and 7 apatite fission track analysis results.The zircon fission track ages range from 158 Ma to 289 Ma and the apatite ages are between 64 Ma and 140 Ma.The mineralization accords with the regional tectonics in the copper district.We consider that the zircon fission track age could reveal the mineralization age based on annealing zone temperature of 140―300℃ and retention temperature of ～250℃ for zircon fission track,and metallogenetic temperature of 120―350℃ in this ore district.Total three mineralization epochs have been identified,i.e.,289―276 Ma,232―200 Ma and 165―158 Ma,and indicate occurrence of the min-eralization in the Indosinian and Yanshan epochs.Corresponding to apatite fission track ages,the three tectonic-mineralizing epochs are 140―132 Ma,109―97 Ma and 64 Ma,which means age at about 100℃ after the mineralization.The three epochs lasted 146 Ma,108 Ma and about 100 Ma from ～250℃ to ～100℃ and trend decrease from early to late.It is shown by the fission track modeling that this district underwent three stages of geological thermal histories,stable in Cretaceous and cooling both before Cretaceous and after 20 Ma.     

REE and εNd of clay fractions in sediments from the eastern Pacific Ocean:Evidence for clay sources

The surface sediments from the eastern Pacific Ocean are mainly composed of biogenetic fossils, silicate detritus, ferromanganese spherolites and clay fractions. Among them, the clay fractions with grain size less than 2 μm (mainly clay minerals) are mostprevalent, especially in the non-calcareous sediments (the content of calcareous fossils is less than 5%), the clay fraction contents often exceed 70%[1―5]. Because of the influences of Antarctic Bottom Water (AABW), equatorial currents, …     

Genesis and metallogenic characteristic of Dongnan Cu–Mo deposit associated granitoids: LA-ICP-MS zircon U–Pb dating and isotope constraint from Zijinshan ore field in southeastern China

The Dongnan Cu–Mo deposit, located in the southeast of the Zijinshan ore field(the largest porphyry–epithermal system in Southeast China), represents the complex magmatic and metallogenesis events in the region. The petrogenesis and metallogenesis of granitoids from the deposit are not determined, especially the interactions between ore-bearing(granodiorite porphyry) and barren samples(granodiorite and diorite). In the paper, the whole rock geochemical features shared a similar affinity to the m...     

Geochemistry of ore-forming fluids and geological significance of the Kuoerzhenkuola gold field in Xinjiang, China

The Kuoerzhenkuola gold field (including the Kuo- erzhenkuola and the Buerkesidai gold deposits), lo- cated 68 km east of Jimunai County in northern Xing- jiang, China, is an important component of the Sawuer gold belt which is the eastward extending part of the Zarma-Sawur gold-copper belt in Kazakhstan. Some studies are concerned with the geology of the gold ores[1―3], the associated volcanic rocks[4], radiogenic isotope[5―8], and the ore-forming environment[8]. Most researchers inferr…     

Evidence of microstructures and fluid inclusions for the origin of polycrystalline quartz ribbons in high-grade metamorphic rocks in Daqingshan region

Polycrystalline quartz ribbons in high-grade metamorphic rocks from the Daqingshan region, are typi- cal microfabrics of, and provide information for, deep crust deformation and metamorphism. The quartz ribbons have straight boundaries and extend stably along gneissosity. They truncate other mineral grains in the rocks and may contain inclusions of such minerals that are lens-shaped and oriented. They frequently end into branching termination. Analysis fluid inclusions in polycrystalline quartz rib- bons reveal that the complex types of fluid inclusions are inhomogeneously distributed. They are ob- viously different from inclusions captured at granulite facies, in both fluid compositions and T-P esti- mations. Based on microfabric and fluid inclusion analysis, the polycrystalline quartz ribbons are suggested to be formed by SO2-rich fluids filling micro-fractures that are parallel to early gneissosity. The SO2 composition is derived from the deformed host rocks. The fluid phase has significant effects on the rheological characteristics, fracturing of rocks, and formation of quartz ribbons.     

Evidence for solar forcing of climate variation from δ18O of peat cellulose

There have been a number of investigations for examining the possible link between long-term climate variability and solar activity.A continuous δ18O record of peat cellulose covering the past 6000 years and the response of climate variation inferred from the proxy record to solar forcing are reported.Results show that during the past 5000 years the abrupt climate variations,including 17 warming and 17 cooling,and a serious of periodicities,such as 86,101,110,127,132,140,155,207,245,311,820 and 1050 years,are strikingly correlative to the changes of solar irradiation and periodicity.These observations are considered as further evidence for a close relationship between solar activity and climate variations on time scales of decades to centuries.     

Electron microscopy study of the sakhaite from endogenous borate deposit in Hunan, China

Sakhaite was first discovered by Ostrovskaya, Pertsev and Nikitina at Siberia in the former Soviet Union. By using the X-ray diffraction technique, they proved that the crystal system of sakhaite was cubic (a = 1.464 nm), its possible space groups were Fm3m, F432, F43m, Fm3, F23, and its crystal chemical for-mula was Ca48Mg16(CO3)16(BO3)28Cl4(OH)8 4H2O[1]. Chichagov, Simonov and Belov studied the crystal structure of synthetic sakhaite and determined that its space group was F4132, …     

Re-Os age for molybdenite from the Gangdese porphyry copper belt on Tibetan plateau: Implication for geody- namic setting and duration of the Cu mineralization

It is recognized that there are at least two sorts of significant environments for porphyry copper deposits, i.e. magmatic arcs and collisional orogens[14]. The deposits in the former environments are exampled by the circle-Pacific porphyry copper belt, such as An-dean-type deposits, which mainly formed in the period of the Andean tectonic cycle characterized by trans- pressional and transtensional movements along the arc-parallel strike-slip fault zone in the Late Eo-cene-Early Oligocene[5…     

Origin of the deep fluids in the paleosubduction zones in western Tianshan: Evidence from Pb- and Sr-isotope compositions of high-pressure veins and host rocks

Fluids in the deep subduction zones play an impor-tant role in the process of crust-mantle interaction. This has been proved by a large number of studies on the geochemistry of island arc volcanic rocks[1―9]. Study on high-pressure metamorphic rocks within orogen shows that the dehydration and devolatilization of subducted oceanic crust and sediments can release amounts of water during progressive metamorph- ism[10―13]. The origin of the fluids in the subduction zones provides important info…     

Climacogram versus autocovariance and power spectrum in stochastic modelling for Markovian and Hurst–Kolmogorov processes

Three common stochastic tools, the climacogram i.e. variance of the time averaged process over averaging time scale, the autocovariance function and the power spectrum are compared to each other to assess each one’s advantages and disadvantages in stochastic modelling and statistical inference. Although in theory, all three are equivalent to each other (transformations one another expressing second order stochastic properties), in practical application their ability to characterize a geophysical process and their utility as statistical estimators may vary. In the analysis both Markovian and non Markovian stochastic processes, which have exponential and power-type autocovariances, respectively, are used. It is shown that, due to high bias in autocovariance estimation, as well as effects of process discretization and finite sample size, the power spectrum is also prone to bias and discretization errors as well as high uncertainty, which may misrepresent the process behaviour (e.g. Hurst phenomenon) if not taken into account. Moreover, it is shown that the classical climacogram estimator has small error as well as an expected value always positive, well-behaved and close to its mode (most probable value), all of which are important advantages in stochastic model building. In contrast, the power spectrum and the autocovariance do not have some of these properties. Therefore, when building a stochastic model, it seems beneficial to start from the climacogram, rather than the power spectrum or the autocovariance. The results are illustrated by a real world application based on the analysis of a long time series of high-frequency turbulent flow measurements.     

U–Pb dating and geochemistry of granite porphyry dykes in the Xicha gold–(silver) deposit,southern Jilin Province,China,and their metallogenic significance

We report U–Pb dating of zircon,as well as geochemical and Hf isotope data,in order to constrain the formation time,magma source,and tectonic setting of granite porphyry dykes in the Xicha gold–(silver) district in southern Jilin Province,Northeast China.The zircon grains are euhedral–subhedral,display oscillatory growth zoning and have Th/U ratios varying between 0.11 and 0.78,which together imply a magmatic origin.The dating results indicate the porphyry formed in the Early Cretaceous (122±1 Ma)and it contains SiO_2=70.64–72.31 wt%,Al_2O_(3-)=13.99–14.64 wt%,K_2O+Na_2O=6.96–7.81 wt%K_2O/Na_2O=1.24–2.10,and A/CNK=1.11–1.41.Chemically,the porphyry belongs to a high-K calc-alkaline S-type granite.Chondrite-normalized rare earth elements (REE)patterns show LREE enrichment,light rare earth elements(LREE)/heavy rare earth elements (HREE)=9.93–11.97(La/Yb)_N=11.08–15.16,and d Eu=0.69–0.95.On the trace element spider diagram,large ion lithophile elements such as Rb,Ba,K,Th,and U are enriched,whereas the high field strength elements Ti and P are depleted.The e Hf(t) values of zircon from the granite porphyry vary between-17.1 and-13.2,and their Hf two-stage model ages vary from 2.01 to 2.26 Ga,implying that the magma was derived from partial melting of old lower crust.The granite porphyry dykes and many A-type granites in the region formed at the same time,suggesting an extensiona environment.The combination of the occurrence of strong magmatism,large-scale mineralization,and extensiona tectonics throughout much of Eastern China indicate that the Early Cretaceous was a period of significant lithospheric thinning.The southern Jilin Province,therefore,experienced lithospheric thinning during the Early Cretaceous.     

Evidence for solar forcing of climate variation from δ18O of peat cellulose

There have been a number of investigations for examining the possible link between long-term climate variability and solar activity. A continuous δ¹⁸O record of peat cellulose covering the past 6 000 years and the response of climate variation inferred from the proxy record to solar forcing are reported. Results show that during the past 5 000 years the abrupt climate variations, including 17 warming and 17 cooling, and a serious of periodicities, such as 86, 101, 110, 127, 132, 140, 155, 207, 245, 311, 820 and 1 050 years, are strikingly correlative to the changes of solar irradiation and periodicity. These observations are considered as further evidence for a close relationship between solar activity and climate variations on time scales of decades to centuries.     

Evidence from isotopic geochemistry as an indicator of eutrophication of Meiliang Bay in Lake Taihu, China

In this paper, Lake Taihu, a large shallow freshwater lake in China, is chosen as an example of reconstruction of eutrophication through the comparison between stable isotopes from dissolved nutrients and plants and water column nutrient parameters and integration of multiple proxies in a sediment core from Meiliang Bay including TN, TP, TOC, C/N,δ15N,δ13C, etc. Differences in aquatic plant species and trophic status between East Taihu Bay and Meiliang Bay are indicated by their variations inδ13C andδ15N of aquatic plants andδ15N of NH4 . A significant influence of external nutrient inputs on Meiliang Bay is reflected in temporal changes inδ15N of NH4 and hydro-environmental parameters. The synchronous change betweenδ13C andδ15N values of sedi-mented organic matter (OM) has been attributed to elevated primary production at the beginning of eutrophication between 1950 and 1990, then recent inverse correlation between them has been caused by the uptake of 15N-enriched inorganic nitrogen by phytoplankton grown under eutrophication and subsequent OM decomposition and denitrification in surface sediments, indicating that the lake has suffered from progressive eutrophication since 1990. Based on the use of a combination of stable isotopes and elemental geochemistry, the eutrophication of Meiliang Bay in Lake Taihu could be better traced. These transitions of the lake eutrophication respectively occurring in the 1950s and 1990s have been suggested as a reflection of growing impacts of human activities, which is coincident with the instrumental data.     

Vertical migration of Daphnia galeata – Evidence for the use of an alternative resource from a lethal environment

Metazoans normally avoid anaerobic environments, at least when they are combined with toxic stress due to hydrogen sulfide. In Lake Speldrop, a small but deep gravel pit lake at the Lower Rhine, Daphnia galeata was found not only to dominate the zooplankton community, but was also regularly found in anoxic and even sulfidic layers during summer. We conducted field experiments with a newly developed “Zooplankton In-situ Incubator”, simulating vertical migrations of D. galeata. When daphnids were exposed to sulfidic conditions, mortality increased with exposure time, revealing LT₅₀-values between 129 and 42 min in relation to increasing concentrations of sulfide. Additionally, those experimental individuals originating from 12.5 m depth showed significantly higher mortality rates than those from 7.5 m depth. Further migration experiments showed that an interruption period of sulfidic exposition in less stressful environments reduced mortality rates significantly. Daphnids found in the hypolimnion belonged partly to moribund parts of the population; however, the majority of daphnids showed regular mowing activity and was able to withstand sulfidic conditions in the hypolimnion for a limited time. It is so far unclear what maybe the major ultimate factor for this type of short term migratory behavior, to seek for shelter or to use high amounts of sulfur bacteria as an alternative food resource.     

Carbon–oxygen isotopic covariations of calcite from Langdu skarn copper deposit,China: implications for sulfide precipitation

The Langdu skarn copper deposit in the Zhongdian area, Yunnan Province, China, has an average Cu grade of 6.49 %. The deposit is related to a porphyry intrusion(*216 Ma), which was emplaced in the Upper Triassic sedimentary rocks of the Tumugou and Qugasi Formations.At the Langdu skarn copper deposit, carbon and oxygen isotope ratios of fresh limestones(d18O = 3.0–5.6 % relative to V-SMOW; d13 C = 24.5–25.7 % relative to PDB)and partly altered limestones(d18O = 27–7.2 to-1.9 %;d13C = 11.8–15.2 %) indicated that the deposit was a typical marine carbonate source. Oxygen and carbon isotope values for calcites formed at different hydrothermal stages are-9.1 to 0.2 and 10.1–16.3 %, respectively. Moreover,the carbon–oxygen isotopic composition of an ore-forming fluid(d18O = 5.0–9.5 %, d13 C =-7.3 to-5.3 %) suggested the presence of magmatic water, which most likely came from the differentiation or melting of a homologous magma chamber. The deposition of Calcite I may arise from metasomatism in an open system with a progressively decreasing temperature.Later, the minerals chalcopyrite, pyrrhotite, quartz and Calcite II were precipitated due to immiscibility. Water–rock interaction could potentially be responsible for Calcite III precipitation in the post-ore stage.     

Tectonic evolution of the Western Kunlun orogenic belt in northern Qinghai-Tibet Plateau:Evidence from zircon SHRIMP and LA-ICP-MS U-Pb geochronology

The Western Kunlun Range in northern Qinghai-Tibet Plateau is composed of the North Kunlun Terrane,the South Kunlun Terrane and the Karakorum-Tianshuihai Terrane. Here we report zircon SHRIMP and LA-ICP-MS U-Pb ages of some metamorphic and igneous rocks and field observations in order to pro-vide a better understanding of their Precambrian and Palaeozoic-early Mesozoic tectonic evolution. Based on these data we draw the following conclusions: (1) The paragneisses in the North Kunlun Terrane are likely of late Mesoproterozoic age rather than Palaeoproterozoic age as previously thought,representing tectonothermal episodes at 1.0―0.9 Ga and ～0.8 Ga. (2) The North Kunlun Terrane was an orogenic belt accreted to the southern margin of Tarim during late Mesoproterozoic to early Neopro-terozoic,the two episodes of metamorphisms correspond to the assemblage and breakup of Rodinia respectively. (3) The Bulunkuole Group in western South Kunlun Terrane,which was considered to be the Palaeoproterozoic basement of the South Kunlun Terrane by previous studies,is now subdivided into the late Neoproterzoic to early Palaeozoic paragneisses (khondalite) and the early Mesozoic metamorphic volcano-sedimentary series; the paragneisses were thrust onto the metamorphic vol-cano-sedimentary series from south to north,with two main teconothermal episodes (i.e.,Caledonian,460―400 Ma,and Hercynian-Indosinian,340―200 Ma),and have been documented by zircon U-Pb ages. (4) In the eastern part of the South Kunlun Terrane,a gneissic granodiorite pluton,which intruded the khondalite,was crystallized at ca. 505 Ma and metamorphosed at ca. 240 Ma. In combination with geochronology data of the paragneiss,we suggest that the South Kunlun Terrane was a Caledonian accretionary orogenic belt and overprinted by late Paleozoic to early Mesozoic arc magmatism.