Zircon Mineralogy and Trace Elements Composition of the Metallogenic Granites in the Nanshankeng Mine,Eastern Nanling

1 Introduction Nanshankeng tungsten-tin polymetallic mine,which is located in the eastern Nanling metallogenic belt,is newly discovered by geological investigation and evaluation with prospecting potential(Xiao et

Zircon Geochronology and Trace Element Geochemistry from the Xiaozhen Copper Deposit, North Daba Mountain: Constraints on Albitites Petrogenesis

Albitite often accompanies with various metal and gem mineral deposits and a large number of occurrences have been reported globally, including the South Qinling orogen, China. The Xiaozhen copper deposit is a typical deposit in the North Daba Mountain area of the South Qinling orogen whose distribution is controlled by albitite veins and fractures. As there are few studies on the petrogenesis of albitite in Xiaozhen copper deposit, this paper focuses on the petrogenesis of albitite and its mineralization age. Detailed fieldwork and mineral microscopic observations initially suggest that albitite from the Xiaozhen copper deposit is igneous in origin. Further zircon trace element geochemistry studies indicate that these zircons have high Th/U ratios（〉0.5）, low La content, high（Sm/La）N and Ce/Ce＊values, and a strong negative Eu anomaly, which are commonly seen in magmatic zircons. The chondrite–normalized rare earth element（REE） patterns are consistent with magmatic zircons from throughout the world, and they fall within or near the field of magmatic zircons on discriminant diagrams. The calculated average apparent Ti–in–zircon temperature for young zircons is 780°C, consistent with magmatic zircon crystallization temperatures. Therefore, zircon geochemistry indicates that the albitite origin is magmatic. SIMS U–Pb dating on nine magmatic zircons yielded a concordia age of 154.8±2.2 Ma, which represents the formation of albitite and the metallogenic age. More importantly, it is consistent with the ages of Yanshanian magmatism and metallogenesis in the South Qinling orogen, so formation of the Xiaozhen copper deposit may be a closely related geological event.

Genesis and magma fertility of gold associated high-K granites:LA-ICP-MS zircon trace element and REEs constraint from Bakoshi–Gadanya granites in NW Nigeria

High-K granites dominate the rock units in the Bakoshi and Gadanya areas located in the northwestern Nigerian subshield,part of the Trans-Saharan Belt,West Africa.In this contribution,the LA-ICP-MS zircon trace element revealed the fertility of magma responsible for the high-K granites that hosts the Bakoshi–Gadanya gold mineralization.Two likely metallogenic granites types are 1)Gadanya alkali granite,with high Ce^(4+)/Ce^(3+)(mean 1485)and limited range of Eu anomalies may likely be associated with the gold mineralization,and 2)Bakoshi porphyritic granite,Jaulere biotite granite,Shanono coarsegrained granite,and Yettiti granite,all have low Ce^(4+)/Ce^(3+) ratios(mean\100,except second Bakoshi granite D2-1)with wider ranges of Eu/Eu^(*) values,thus are considered reduced granites.These reduced granites have oxygen fugacity values and Eu anomalies comparable to reduced granites associated with tin belts in Myanmar and Zaaiplaats granites in Bushveld Complex,South Africa.Ti-inZircon thermometric study revealed two thermal regimes during the crystallization of the Bakoshi–Gadanya granites:the high temperature(746–724℃):Shanono coarsegrained granite,Bakoshi granite D2-1,and Jaulere biotite granite;and relatively low temperature(705–653℃):Bakoshi porphyritic granite D1-1,Yettiti medium-grained granite,and Gadanya alkali granite.Zircon trace elements including U,Yb,Y,Nb,and Sc ratios constraint the magma source of Bakoshi–Gadanya granites to an enriched mantle metasomatized during the subduction process before its melting.Except for Gadanya alkali granite,fractionation of titanite and apatite dominate the magma evolution with limited amphibole fractionation.Melt that crystallized Gadanya alkali granite is rather saturated in zircon without accessory titanite or apatite.

Geochronology and zircon geochemistry of auriferous intrusions in the Bumo deposit,Hainan Province,China

Intrusion-related gold deposits(IRGS)are a lowgrade,large-tonnage exploration target.Recently,auriferous magmatic rocks were found in the Bumo deposit of the Gezhen shear zone in Hainan Province,China.However,the geochronology and geochemical characteristics of the intrusions,as well as the mineralization potential,are still unclear.Field and petrographic work show that the sulfidebearing intrusions can be divided into diorite porphyrites,quartz monzodiorites and monzodiorites.Zircon LA–ICP–MS U–Pb dating demonstrates that diorite porphyrites,quartz monzodiorites and monzodiorites were formed at104±1,114±1,114±1 Ma,respectively.In addition,sulfides in Yanshanian intrusion-related gold mineralization haveδ;S values of 0.2–4.4%,lower than those in Hercynian-Indosinian(1.9–9.8%)orogenic deposits(ca.219–378 Ma)in the Gezhen shear zone.In addition,all these intrusions display close correlations between Eu/EuN*with Th/U,consistent with the differentiation of amphibole,apatite and titanite from a hydrous melt.Moreover,zircon Eu/EuN*in the intrusions are higher than0.4,demonstrating that the magmatic rocks have high water contents and oxygen fugacity values,favorable for gold mineralization.Consequently,the Yanshanian magmatic rocks can be a new potential gold exploration target in the Gezhen shear zone.

Proto-Adamastor ocean crust(920 Ma)described in Brasiliano Orogen from coetaneous zircon and tourmaline

Proto-Adamastor ocean bathed Rodinia and successor continental fragments from 1.0-0.9 Ga up to0.75 Ga,and evolved into world Adamastor Ocean at 0.75-0.60 Ga.Mesoproterozoic oceanic crust is poorly preserved on continents,only indirect evidence registered in Brasiliano Orogen.We report first evidence of ophiolite originated in proto-Adamastor.We use multi-technique U-Pb-Hf zircon andδ^11B tourmaline isotopic and elemental compositions.The host tourmalinite is enclosed in metaserpentinite,both belonging to the Bossoroca ophiolite.Zircon is 920 Ma-old,εHf(920 Ma)=+12,HfTDM=1.0 Ga and has’oceanic’composition(e.g.,U/Yb<0.1).Tourmaline is dravite withδ^11B=+1.8‰(Tur 1),0‰(Tur 2),-8.5‰(Tur 3).These characteristics are a novel contribution to Rodinia and associated world ocean,because a fragment of proto-Adamastor oceanic crust and mantle evolved at the beginning of the Brasiliano Orogen.

Temperature and Hf-O isotope correlations of young erupted zircons from Tengchong(SE Tibet):Assimilation fractional crystallization during monotonic cooling

Young zircons from crystal-poor volcanic rocks provide the best samples for the investigations of pre-eruption magmatic processes and for testing a possible relationship between zircon Eu anomalies and crustal thickness.We report trace element chemistry and Hf-O isotope compositions of young zircons from 3 Holocene volcanoes in the Tengchong volcanic field,SE Tibet,in order to provide insights into magma evolution processes and conditions for high-K calc-alkaline volcanic rocks in a post-collisional setting.As decreasing zircon Ti content and falling temperature,zircon Hf content and Yb/Sm increase whereas zircon Eu anomaly and Th/U decrease,indicating fractional crystallization of plagioclase and zircon during magma cooling.More importantly,zircon Hf isotope ratio(sHf values)increases with decreasing zircon Ti content and falling temperature(T),suggesting gradually increasing incorporation of relatively high EHf juvenile materials in the crystallizing zircons during magma evolution.Negative correlations between zirconε_(Hf)and zirconδ^(18)O also support open-system magma evolution.Our data suggest fractional crystallization of a magma with simultaneous contamination by highε_(Hf)and lowδ^(18)O juvenile(immature)crustal materials during monotonic cooling after zircon saturation.The low-T,high-ε_(Hf)and low-δ^(18)O zircons may indicate the involvement of the early Cretaceous juvenile granitic country rocks during shallow magma evolution.Average Eu anomalies in zircons from young Tengchong lavas yield crustal thickness of 40.7±6.8 km,consistent with present crustal thickness(42.5 km)determined by geophysical methods.

NanoSIMS imaging method of zircon U-Pb dating

We report an imaging method of zircon U-Pb dating with NanoSIMS 50 L, which overcomes the significant U-Pb fractionation as the pit was sputtered deeper during conventional spot mode analysis and can be applied to irregular small grains or heterogeneous areas of zircon. The U-Pb and Pb-Pb ages can be acquired simultaneously for 2 μm×2 μm(for small grains) or 1 μm×9 μm(for zoned grains), together with Zr, Y and other trace elements distributions. Using zircon M257 as standard, the U-Pb ages of other zircon standards, including Qinghu, Plesovice, Temora and 91500, were measured to(2σ) as158.8±0.8, 335.9±3.4, 412.0±12 and 1067±12 Ma, respectively, consistent with the recommended values within the analytical uncertainties. Tiny zircon grains in the impact melt breccia of the lunar meteorite SaU 169 were also measured in this study,with a Pb-Pb age of 3912±14 Ma and a U-Pb age of 3917±17 Ma, similar to previous results reported for the same meteorite.The imaging method was also applied to determine U-Pb age of the thin overgrowth rims of Longtan metamorphic zircon, with a Pb-Pb age of 1933±27 Ma and a U-Pb age of 1935±25 Ma, clearly distinct from the Pb-Pb age of 2098±61 Ma and the U-Pb age of 2054±40 Ma for detrital cores.

Discovery of the mid-Cretaceous sedimentary rocks from the ultrahigh-pressure terrane,Dabie Orogenic Belt,and its tectonopaleogeographic implications

The Dabie Orogenic Belt, located in east-central China, is known for the greatest outcrop area of the ultrahigh-pressure metamorphic rocks in the world and is typical for studying deep continental subduction and continent-continent collision. However, since lower-grade metamorphic rock occurrence in the core of the ultrahigh-pressure terrane was reported, it has become a new point of concern. This study reported new results. The so-called lower-grade metamorphic rocks are divided into sedimentary rocks and meta-volcanics.The sedimentary rocks consist mainly of fine-grained turbidites formed under an anoxic deep-water lacustrine basin. Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry U-Pb detrital zircon dating indicates that their maximum deposit age is 119.0 ± 1.1 Ma belonging to the mid-Cretaceous Aptian. U-Pb detrital zircon ages from the sedimentary rocks cluster in three age groups: 1) 2773.8-1550.0 Ma(45.0%);2)868.8-622.3 Ma(23.0%);3) 147.0-100.0 Ma(31.5%). And the provenance and tectonic settings of these sedimentary rocks are discussed by synthesizing U-Pb detrital zircon ages, initial Hf isotope ratios, and trace elements of the zircons. Source rocks of the first group were mainly composed of the Paleoproterozoic basement derived from the reworking of the Paleoarchean-Neoarchean Yangtze continental crust. For the second group, its source rocks consisted of Neoproterozoic volcanics mainly from an island arc system, which derived from the reworking of older continental crust in the northern Yangtze Block. The third group’s source rocks were chiefly composed of Cretaceous rift igneous rocks derived from the derivation through melting of middle-aged continental crust in the Dabie Orogenic Belt. The meta-volcanics have weighted mean U-Pb ages from 751.0 ± 16 Ma to 786.3 ± 5.9 Ma, and their protoliths formed under a Middle Neoproterozoic island arc system in the northern Yangtze Block. The meta-volcanics underwent a Triassic subduction of different depths and then an exhumation, but the sedimentary rocks did not. The findings suggest that the ultrahigh-pressure terrane had suffered violent subsidence during the mid-Cretaceous, and a four-stage evolution model of the Dabie Orogenic Belt was established accordingly.