REE distribution in grandites from the Crown Jewel gold skarn deposit: A LA-ICP-MS study
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Abstract The Huaixi copper-gold polymetallic deposit of SE Zhejiang Province, China, is a typical hydrothermal-vein ore body. The Caomen K-feldspar granite porphyry, the dominant intrusion in the mining district, has been dated by laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) analyses of zircon, which yielded a weighted mean 206Pb/238U age of 101.6 ± 0.9 Ma (MSDW = 1.3). Rb-Sr dating of fluid inclusions in auriferous quartz from ore bodies yielded an isochron age of 101 ± 2 Ma. These results indicate that intrusion of the Caomen pluton and Cu-Au mineralization was contemporaneous and corresponds to the third episode of Mesozoic magmatism and metallogenesis in South China. Calculated δ18O values of fluid inclusions from ore-bearing quartz range from −0.89 to −1.98‰ and δD from −42.60 to −60.20‰, suggesting that the ore-forming fluids are derived from a mixed source of magmatic and meteoric waters. δ18S values of 8 pyrites range from −2.14 to +4.14‰ with a mean of +1.67‰, similar to magmatic sulphur. These isotope data support a genetic relationship between the Huaixi copper-gold deposit and the Caomen alkaline granite and probably indicate a common deep source. Petrography and chemical compositions show that the Caomen alkaline granite crystallized from shoshonitic magmas characterized by high SiO2 (75.64–78.00%) and alkali (K2O + Na2O = 7.96–8.82%) but low FeOT (1.34–3.31%), P2O5 (0.05–0.13%) and TiO2 (0.12–0.18%). The granitic rocks are enriched in Ga, Rb, Th, U, and Pb but depleted in Ba, Nb, Sr, P, and Ti. REEs are characterized by marked negative Eu anomalies (Eu/Eu* = 0.06–0.13) and exhibit right-dipping ‘V’ patterns with LREE enrichment. These are similar to the Late Cretaceous alkaline granites in the coastal areas of Zhejiang and Fujian provinces, implying that the Caomen granite formed in a post-collisional extensional tectonic setting. Combined with previous studies, we interpret the Huaixi copper-gold deposit and the associated Caomen alkaline granite as related to back-arc extension due to high-angle subduction of the palaeo-Pacific plate, caused by northward movement of the Indian plate. Keywords: LA–ICP–MS zircon U-Pb datingRb-Sr datingalkaline graniteback-arc extensionHuaixi copper-gold vein depositSE China Acknowledgements This study was financially supported by the Programme for Innovative Research Team in University (IRT0755), the Programmes of Superseding Resources Prospecting in Crisis Mines in China (No. 2006020035 and 2007020047) and the Key Laboratory of Geological Progress and Mineral Resources (GPMR), China University of Geosciences (CUG). We acknowledge the kind help of Mr Roger Mason and Mr Jianwei Li, CUG, for reading through the paper and providing numerous corrections in the usage of English that led to great improvement in the presentation of the paper. Ms Yafei Ge from CUG and Dr Jiajia Zheng from the University of Queensland are acknowledged for their constructive suggestions. We also thank Ms Haihong Chen and Mr Shu Zheng, GPMR, for their analytical support and No. 11 Geological Team of Zhejiang Bureau of Geology and Mineral Resource for their help in the field work.
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Abstract Although REE (lanthanides + Sc + Y) mineralization in alkaline silicate systems is commonly accompanied with Zr mineralization worldwide, our understanding of the relationship between Zr and REE mineralization is still incomplete. The Baerzhe deposit in Northeastern China is a reservoir of REE, Nb, Zr, and Be linked to the formation of an Early Cretaceous, silica-saturated, alkaline intrusive complex. In this study, we use in situ laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of zircon and monazite crystals to constrain the relationship between Zr and REE mineralization at Baerzhe. Three groups of zircon are identified and are differentiated based upon textural observations and compositional characteristics. Type Ia zircons display well-developed oscillatory zoning. Type Ib zircons are darker in cathodoluminescence images and have more irregular zoning and resorption features than type Ia zircons. In addition, type Ib zircons can locally occur as overgrowths on type Ia zircons. Type II zircons contain irregular but translucent cores and rims with oscillatory zoning that are murky brown in color and occur in aggregates. Textural features and compositional data suggest that types Ia and Ib zircon crystallized at the magmatic stage, with type Ia being least-altered and type Ib being strongly altered. Type II zircons, on the other hand, precipitated during the magmatic to magmatichydrothermal transition. Whereas the magnitude of the Eu anomaly is moderate in the barren alkaline granite, both magmatic and deuteric zircon exhibit pronounced negative anomalies. Such features are difficult to explain exclusively by feldspar fractionation and could indicate the presence of fluid induced modification of the rocks. Monazite crystals occur mostly through replacement of zircon and sodic amphibole; monazite clusters are also present. Textural and compositional evidence suggests that monazite at Baerzhe is hydrothermal. Types Ia and Ib magmatic zircon yield 207Pb-corrected 206Pb/238U ages of 127.2 ± 1.3 and 125.4 ± 0.7 Ma, respectively. Type II deuteric zircon precipitated at 124.9 ± 0.6 Ma. The chronological data suggest that the magmatic stage of the highly evolved Baerzhe alkaline granite lasted less than two million years. Hydrothermal monazite records a REE mineralization event at 122.8 ± 0.6 Ma, approximately 1 or 2 million years after Zr mineralization. We therefore propose a model in which parental magmas of the Baerzhe pluton underwent extensive magmatic differentiation while residual melts interacted with aqueous hydrothermal fluids. Deuteric zircon precipitated from a hydrosilicate liquid, and subsequent REE mineralization, exemplified by hydrothermal monazite, correlates with hydrothermal metasomatic alteration that postdated the hydrosilicate liquid event. Such interplay between magmatic and hydrothermal processes resulted in the formation of discrete Zr and REE mineralization at Baerzhe.
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Granitic rock
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在从在在从 Laowan 花岗石的石英的河南省省和那的 theLaowan 金牌沉积物的主要阶段的石英和黄铁矿的 REE 的作文被诱导地联合的 plasma-mass-spectrometry (ICPMS ) 决定跟踪形成矿石的材料的来源。同时，存款矿石，花岗石和变形的墙岩石的 REE 作文也详细为比较研究被考虑。从存款矿石的石英和黄铁矿的 ΣR EE 的范围是 4.18x 10 ~(-6)～ 30.91 x 10 ~( ΣR EE 的一般水准是的-6), 13.39 x 10 ~(-6),和在 Laowan 花岗石的石英的 ΣR EE 的一般水准是 6.68 x 10 ~(-6)。没有在存款矿石石英和花岗石石英之间的 REE 参数的不同差别。在金沉积物的石英他是的一样的 REE 特别参数从 Laowan 花岗石的石英例如δ_( Eu )，δ_( Ce )，( La/Yb ) _N 并且( La/Sm ) _N ，到 HREE 的 LREE 的分区度，特别使球粒状陨石正常化的 REEpatterns ，但是从变形的墙岩石的到那些的类似，它显示出那 ore-forminghydrothermal 液体都不主要是来自 Laowan 花岗石岩浆，而非变形液体的液体。同时，比较在矿物质的 REE 特征能作为形成矿石的液体性质和来源的指示物服务的沉积物表演从沉积物矿石和相关地质的身体在在矿物质之间的 REE 特征上学习，当体积的 REE 特征取样时(例如沉积物矿石，花岗石和墙岩石)不能确切跟踪 ore-formingmaterials 的来源。
Rare-earth element
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گارنتهایاسکارنخوت در باختر یزد در نتیجه فعالیت گرمابی تودههای نفوذی کالکآلکالن الیگومیوسن تشکیل شدهاند. ترکیب شیمیایی گارنتها دراسکارن خوت به دو نوع متفاوتمحلول جامد گروسولاریت-آندرادیت و آندرادیت تقریبا خالص تقسیمبندی میشوند. گارنتهای غنی از آهن (And>96)همسانگرد بوده در حالی که گارنتهای گروسولاریت- آندرادیت (And74.3Gr24.8-And32.1Gr66.6)ناهمسانگرد بوده و زونبندی ترکیبی و ماکل قطاعی را نشان میدهند. زونبندیترکیبی گارنتهای ناهمسانگرد میتواند در نتیجه برهمرشدیهای گرمابی بر روی کانیهای دگرگونی مجاورتی، تغییرات در دما، فشار، اکتیویته CO2 تغییرات غلظتAl و Fe3+ و عوامل سینتیک رخ دهد. نتایجLA-ICP-MSنشان داد که گارنتهای همسانگرد روندهای غنیشدگی از LREE و تهیشدگی از HREE همراه با بیهنجاری مثبت یوروپیم را نشان میدهند. این نوع گارنتها در نسبتهای بالای آب به سنگ (W/R)از سیالهای مشتقشده ماگمایی در طی متاسوماتیسم تراوشی به سرعت رشد میکنند در حالی که گارنتهای ناهمسانگرد غنیشدگی کمتری از عناصر کمیاب خاکی سبک داشته و بیهنجاری منفی ضعیفی از یوروپیم را نشان میدهند. این نوع گارنتها توسط برهمکنش طولانی مدت سیالهای منفذی با سنگهای میزبان در طی فرایند متاسوماتیسم انتشاری شکل میگیرند.
Laser Ablation
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