Geology and Lead-Isotope Study of the Baiyinnuoer Zn-Pb-Ag Deposit, South Segment of the Da Hinggan Mountains, Northeastern China

The Baiyinnuoer deposit (32.74 Mt ore with grades of 5.44% Zn, 2.02% Pb and 31.36 g t^?1 Ag), the largest Zn‐Pb‐Ag deposit in northern China, is hosted by crystalline limestone and slate of the Early Permian Huanggangliang Formation. Detailed cross‐section mapping indicates stratigraphic and fold structural controls on the mineralization. The Zn‐Pb‐Ag mineralization is hosted predominantly by skarn, which occurs as bedding‐parallel lens that pinch out at the margins of the main economic zone. Three skarn stages are identified at the deposit: (i) garnet‐clinopyroxene; (ii) sulfides; and (iii) carbonate‐epidote. Lead isotopic compositions were determined for galena and sphalerite of the ores, whole rock samples of the Yanshanian granite and granodiorite, Permian marble and tuff, and Jurassic volcanic and subvolcanic rocks in and around the Baiyinnuoer area in order to discuss the sources of ore‐forming materials and the relationship between the ore formation and these whole rocks. Galena and sphalerite of the Baiyinnuoer ore have uniform isotopic ratios (²⁰⁶Pb/²⁰⁴Pb, 18.267–18.369; ²⁰⁷Pb/²⁰⁴Pb, 15.506–15.624; ²⁰⁸Pb/²⁰⁴Pb, 38.078–38.394) consistent with the granite and granodiorite (²⁰⁶Pb/²⁰⁴Pb, 18.252–18.346; ²⁰⁷Pb/²⁰⁴Pb, 15.504–15.560; ²⁰⁸Pb/²⁰⁴Pb, 38.141–38.320), whereas the ratios for Jurassic volcanic and subvolcanic rocks are variable and radiogenic (²⁰⁶Pb/²⁰⁴Pb, 18.468–18.614; ²⁰⁷Pb/²⁰⁴Pb, 15.521–15.557; ²⁰⁸Pb/²⁰⁴Pb, 38.304–38.375). These results indicate that the mineralization was not related to the Jurassic volcanism, but to the Yanshanian magmatism. The Permian strata may have a slight contribution to the mineralization. All features show that the Baiyinnuoer deposit is related to the Yanshanian granitic magmatism, and can be classified as a zinc‐lead‐silver skarn deposit.     

Petrogenesis of basalt–trachyte lavas from Olmoti Crater, Tanzania

Olmoti Crater is part of the Plio-Pleistocene Ngorongoro Volcanic Highland (NVH) in northern Tanzania to the south of Gregory Rift. The Gregory Rift is part of the eastern branch of the East African Rift System (EARS) that stretches some 4000 km from the Read Sea and Gulf of Aden in the north to the Zambezi River in Mozambique. Here, we (1) characterize the chemistry and mineral compositions of lavas from Olmoti Crater, (2) determine the age and duration of Olmoti volcanic activity through ⁴⁰Ar/³⁹Ar dating of Olmoti Crater wall lavas and (3) determine the genesis of Olmoti lavas and the relationship to other NVH and EARS volcanics and (4) their correlation with volcanics in the Olduvai and Laetoli stratigraphic sequences.Olmoti lavas collected from the lower part of the exposed crater wall section (OLS) range from basalt to trachyandesite whereas the upper part of the section (OUS) is trachytic. Petrography and major and trace element data reflect a very low degree partial melt origin for the Olmoti lavas, presumably of peridotite, followed by extensive fractionation. The ⁸⁷Sr/⁸⁶Sr data overlap whereas Nd and Pb isotope data are distinct between OLS and OUS samples. Interpretation of the isotope data suggests mixing of enriched mantle (EM I) with high-μ-like reservoirs, consistent with the model of Bell and Blenkinsop [Bell, K., Blenkinsop, J., 1987. Nd and Sr isotopic compositions of East African carbonatites: implications for mantle heterogeneity. Geology 5, 99–102] for East African carbonatite lavas. The isotope ratios are within the range of values defined by Oceanic Island Basalt (OIB) globally and moderate normalized Tb/Yb ratios (2.3–1.6) in these lavas suggest melting in the lithospheric mantle consistent with other studies in the region.⁴⁰Ar/³⁹Ar incremental-heating analyses of matrix and anorthoclase separates from Olmoti OLS and OUS lavas indicate that volcanic activity was short in duration, lasting 200 kyr from 2.01 ± 0.03 Ma to 1.80 ± 0.01 Ma. The age of Olmoti activity overlaps with ages reported for Ngorongoro Caldera, implying contemporaneous activity of multiple NVH volcanic centers during part of the eruption interval.Olmoti is considered the source for the bulk of interbedded volcanics and volcaniclastic deposits that comprise much of the upper Bed I section of nearby Olduvai Gorge, and part of the Laetoli sequence, both known for their well preserved fossils and archaeological remains. Age and chemical data reported here are compatible with those derived from tephra and lava interbedded in Bed I at Olduvai Gorge and from the Olpiro Beds at Laetoli.     

腾冲明光老波厂铅锌矿围岩蚀变及找矿标志

矿体产于白垩纪马头窝单元（K1^7M^λπ）石英斑岩与石炭系上统空树河组三段二层（C2k^3-3）地层的石英砂岩、长石石英砂岩接触带上,或上述两类岩石的破碎带中,矿体与围岩界线常呈波状起伏,呈突变或渐变接触。矿区围岩蚀变明显,有进一步找矿的前景。     

吉林荒沟山铅锌矿床地质特征及矿床成因探讨

吉林荒沟山铅锌矿床赋存于中元古界老岭群珍珠门组白云石大理岩中,层控特征明显.通过对矿床地质、成矿元素Zn/Pb比值、方铅矿和闪锌矿中的微量元素、硫和铅同位素组成特征、矿物包裹体成分特征,矿源层特征等的讨论,认为本矿床为沉积改造型层控矿床.沉积作用是本矿床成矿物质来源的基础,改造作用是形成本矿床的主要因素.珍珠门组是提供成矿物质来源的重要矿源层.     

Accumulation of Phosphorus and Heavy Metals in the Peel-Harvey Estuary in Western Australia: Results of a Preliminary Study

Concentrations of P and of heavy metals (Zn, Cd, Pb, Cu) were determined in sediment cores from the Peel-Harvey Estuary in Western Australia. Two cores were extracted, each representing one of the two basins of the estuary. Sediments were dated by surplus²¹⁰Pb, by¹³⁷Cs and by changes in the Fe/S ratio. Increasing exports of P from the mainly agricultural catchments have resulted in more than a doubling of both total P and acid extractable inorganic P in sediments of the estuary. Accumulation of P in the estuary is less than expected for complete retention of inputs of P from the major tributaries. Historical data show that since 1950 average concentrations of dissolved inorganic P have approximately doubled in the Peel Inlet and increased by times seven in the Harvey Estuary. Increases in concentrations in surface sediments of acid extractable Zn, Cd, Pb and Cu are noticeable in the Peel Inlet, and of Zn and Cd in the Harvey Estuary. The greatest increase, relative to background, is shown by Zn. Concentrations of extractable Zn and Cd in surface sediments are similar to those estimated from average concentrations in the water column for equilibrium adsorption to organic matter in sediments. Extractable Pb is greater than estimated for equilibrium adsorption to sediments. Extractable Cu is of the order of what can be expected for equilibrium adsorption to sediments in the Peel Inlet, but is less than expected in the Harvey Estuary.     

台湾海峡西部海底及毗邻陆域铅铜元素丰度与转换机制

台湾海峡西部海底及毗邻福建陆域Ｐｂ元素丰度较高,而Ｃｕ较对比值低上当。二才的转换形成机制不同,受元素特性、岩石化学成分、地表风化特点及人海沉积差异等因素控制,在含量分布中构成一组颇具意义的工模式。     

陕西略阳铜厂铜矿床Sr,Pb同位素组成特征及其意义

结合岩体产出环境,时代及其与碧口火山岩的关系,认为铜厂石英闪长岩体是由碧口火山岩的局部熔融作用形成的。铜厂铜矿硫化物Ｐｂ同位素特征显示出以浅源的地壳铅为主,并与碧口火山岩铅同位素组成的壳源端员重合,指示矿质与碧田火山岩之间存在密切关系。由于岩体与火山岩的同源性,所以脉状铜矿石既可能来自岩体也可能来自围岩。     

黑龙江镜泊湖地区第四纪玄武岩的Sr、Nd、Pb同位素组成及其地幔源区特征

本文首次对黑龙江镜泊湖地区第四纪玄武岩的Sr、Nd、Pb同位素组成进行了系统研究。结果表明,尽管不同时代、不同空间上生成的玄武岩在岩石化学、稀土和微量元素特征上差别明显,但其Sr、Nd、Pb同位素组成却有明显的相似性,均具有低Sr、Pb和相对高的Nd同位素值（87Sr/86Sr=0.70396～0.704537;143Nd/144Nd=0.512656～0.512786;206Pb/204Pb=17.0856～1 7.5034;207Pb/204Pb=15.2689～15.3461;208Pb/204Pb= 37.0999～37.4363）,由此指示了该区玄武岩的源区是DMM和EMI二 端元混合的结果。本文将其解释为与含有再循环的下地壳物质的地幔柱活动引起该区软流圈地幔的部分熔融有关,但在部分熔融之前发生了交代作用。     

庐枞火山岩系与偏碱性石英正长岩带的同源特征及成因探讨

庐枞火山岩系与由黄梅尖、城山和大龙山3个岩体组成的偏碱性石英正长岩带在野外紧密共生,他们的RbSr等时线年龄在分析误差范围内相当一致,约为135 Ma,87Sr／86Sr初始比和Nd、Pb同位素组成也很相似,显示了成因上的渊源关系以及成岩物质来源较深且受到了上部地壳的混染等特征,反映了深部地质构造条件对岩浆活动的制约。     

滇西芒市地区石板村黑云母二长花岗岩的年代学、地球化学特征及地质意义

滇西芒市地区石板村黑云母二长花岗岩分布于芒市粱河县南部勐养村—芒市石板村一带,主要由黑云母二长花岗岩组成。石板村黑云母二长花岗岩大部分是作者通过1∶5万区域地质填图,从原高黎贡山群中解体出来的。为了限定该地区中生代岩浆事件的准确时间,本文对该黑云母二长花岗岩进行了LA-ICP-MS锆石U-Pb定年。测定结果显示,石板村黑云母二长花岗岩的锆石U-Pb年龄加权平均值为125.60±1.0Ma。表明该花岗岩体的形成时代属于早白垩世。岩石地球化学研究表明,该区早白垩世黑云母二长花岗岩具有高Si02(70.70%~76.14%),高碱(K20+Na20=7.35%~9.00%),中—高钾(K20/Na20=1.12~2.37)的特征。铝饱和指数(A/CNK)为0.67~1.17,岩石属钾玄岩—高钾钙碱性过铝—强过铝S型花岗岩。岩石总体上富集大离子亲石元素Rb、Th、U、Nd、Sm和Pb等,明显亏损高场强元素Nb、Ce、Sr、Eu、Zr、Hf等。稀土元素总量(ΣREE)为80.55×10-6~362.85×10-6,平均为171.97×10-6,稀土元素配分曲线呈右倾型,LaN/YbN介于5.11~18.80之间,δEu=0.28~1.08,显示弱到中等程度的负铕异常,具有较明显的轻稀土富集,重稀土亏损的特征。根据地球化学特征和微量元素构造判别图解判别结果表明,该花岗岩是以含粘土的变质杂砂岩部分熔融形成的,岩浆可能来源于本区中—新元古代高黎贡山群为代表的地壳物质的部分熔融。是一种典型的壳源成因类型,具后碰撞花岗岩特征,形成于板块间从挤压体制向拉张体制转变的后碰撞构造环境。冈底斯—滕冲构造带早白垩世构造岩浆事件与羌塘—保山板块与冈底斯—腾冲板块之间俯冲、碰撞、成弧造山作用密切相关。早白垩世花岗岩体的发现及其形成时代的厘定,为进一步探讨腾冲地块构造演化提供了新证据。