Platinum-group elements distribution and spinel composition in podiform chromitites and associated rocks from the upper mantle section of the Neoproterozoic Bou Azzer ophiolite, Anti-Atlas, Morocco

The distribution of platinum-group elements (PGEs), together with spinel composition, of podiform chromitites and serpentinized peridotites were examined to elucidate the nature of the upper mantle of the Neoproterozoic Bou Azzer ophiolite, Anti-Atlas, Morocco. The mantle section is dominated by harzburgite with less abundant dunite. Chromitite pods are also found as small lenses not exceeding a few meters in size. Almost all primary silicates have been altered, and chromian spinel is the only primary mineral that survived alteration. Chromian spinel of chromitites is less affected by hydrothermal alteration than that of mantle peridotites. All chromitite samples of the Bou Azzer ophiolite display a steep negative slope of PGE spidergrams, being enriched in Os, Ir and Ru, and extremely depleted in Pt and Pd. Harzburgites and dunites usually have intermediate to low PGE contents showing more or less unfractionated PGE patterns with conspicuous positive anomalies of Ru and Rh. Two types of magnetite veins in serpentinized peridotite, type I (fibrous) and type II (octahedral), have relatively low PGE contents, displaying a generally positive slope from Os to Pd in the former type, and positive slope from Os to Rh then negative from Rh to Pd in the latter type. These magnetite patterns demonstrate their early and late hydrothermal origin, respectively. Chromian spinel composition of chromitites, dunites and harzburgites reflects their highly depleted nature with little variations; the Cr# is, on average, 0.71, 0.68 and 0.71, respectively. The TiO₂ content is extremely low in chromian spinels, <0.10, of all rock types. The strong PGE fractionation of podiform chromitites and the high-Cr, low-Ti character of spinel of all rock types imply that the chromitites of the Bou Azzer ophiolite were formed either from a high-degree partial melting of primitive mantle, or from melting of already depleted mantle peridotites. This kind of melting is most easily accomplished in the supra-subduction zone environment, indicating a genetic link with supra-subduction zone magma, such as high-Mg andesite or arc tholeiite. This is a general feature in the Neoproterozoic upper mantle.     

Mineralogical and chemical evolution of the Ernest Henry Fe oxide–Cu–Au ore system, Cloncurry district, northwest Queensland, Australia

The Ernest Henry Cu–Au deposit was formed within a zoned, post-peak metamorphic hydrothermal system that overprinted metamorphosed dacite, andesite and diorite (ca 1740–1660 Ma). The Ernest Henry hydrothermal system was formed by two cycles of sodic and potassic alteration where biotite–magnetite alteration produced in the first cycle formed ca 1514±24 Ma, whereas paragenetically later Na–Ca veining formed ca 1529 +11/−8 Ma. These new U–Pb_titanite age dates support textural evidence for incursion of hydrothermal fluids after the metamorphic peak, and overlap with earlier estimates for the timing of Cu–Au mineralization (ca 1540–1500 Ma). A distal to proximal potassic alteration zone correlates with a large (up to 1.5 km) K–Fe–Mn–Ba enriched alteration zone that overprints earlier sodic alteration. Mass balance analysis indicates that K–Fe–Mn–Ba alteration—largely produced during pre-ore biotite- and magnetite-rich alteration—is associated with K–Rb–Cl–Ba–Fe–Mn and As enrichment and Na, Ca and Sr depletion. The aforementioned chemical exchange almost precisely counterbalances the mass changes associated with regional Na–Ca alteration. This initial transition from sodic to potassic alteration may have been formed during the evolution of a single fluid that evolved via alkali exchange during progressive fluid-rock interaction. Cu–Au ore, dominated by co-precipitated magnetite, minor specular hematite, and chalcopyrite as breccia matrix, forms a pipe-like body at the core of a proximal alteration zone dominated by K-feldspar alteration. Both the core and K-feldspar alteration overprint Na–Ca alteration and biotite–magnetite (K–Fe) alteration. Ore was associated with the concentration of a diverse range of elements (e.g. Cu, Au, Fe, Mo, U, Sb, W, Sn, Bi, Ag, F, REE, K, S, As, Co, Ba and Ca). Mineralization also involved the deposition of significant barite, K(–Ba)–feldspar, calcite, fluorite and complexly zoned pyrite. The complexly zoned pyrite and variable K–(Ba)–feldspar versus barite associations are interpreted to indicate fluctuating sulphur and/or barium supply. Together with the alteration zonation geochemistry and overprinting criteria, these data are interpreted to indicate that Cu–Au mineralization occurred as a result of fluid mixing during dilation and brecciation, in the location of the most intense initial potassic alteration. A link between early alteration (Na–Ca and K–Fe) and the later K-feldspathization and the Cu–Au ore is possible. However, the ore-related enrichments in particular elements (especially Ba, Mn, As, Mo, Ag, U, Sb and Bi) are so extreme compared with earlier alteration that another fluid, possibly magmatic in origin, contributed the diverse element suite geochemically independently of the earlier stages. Structural focussing of successive stages produced the distinctive alteration zoning, providing a basis both for exploration for similar deposits, and for an understanding of ore genesis.     

扬子地台西南缘朱家坝辉绿岩地球化学特征及其地质意义

近年来在扬子西缘大量的早—中元古代岩浆岩证据显示扬子地台内形成的断陷盆地及早中元古代岩浆岩与全球性的Columbia超大陆裂解事件有着密不可分的联系。这种联系主要表现在区内早中元古代的岩浆岩地球化学特征上。为了探讨武定裂陷槽朱家坝辉绿岩的地球化学特征及其意义,以12块朱家坝辉绿岩的地球化学分析数据为基础,在分析了其主微量和稀土元素的特征之后发现朱家坝辉绿岩w(SiO_2)为44.16%～48.08%,w(K_2O+Na_2O)为3.54%～4.26%,在化学成分上属于钙碱性岩石;其稀土元素的总量为183.1×10^-6～206.91×10^-6,LREE/HREE=1.44～1.96,表明在其形成过程中发生了明显的地壳混然或者是岩浆分异作用,其化学成分基本可以反映出岩浆源区的化学组成特征。基于此,对朱家坝辉绿岩进行了源区性质、构造环境和可能的成因机制探讨,认为朱家坝辉绿岩形成于拉张环境之中,很有可能是在昆阳裂谷形成初期形成,其岩浆来源于较富集的地幔源区,形成过程中几乎没有地壳物质参与。     

陕蒙交界地区碎屑岩风化成因浅析

陕蒙交界地区基岩均具强风化,由此造成当地环境恶化、下游地区生态破坏和灾害积累。其形成机理应与岩石本身的物质组成、自然地理环境、地质构造状况、水文地质条件及其物理化学条件有关。而南部地区,由于上述诸因素的差别,基岩风化微弱。     

关于蓟县型中、上元古界沉积环境及内蒙地轴的性质

内蒙地轴和燕辽坳都是华北地台北缘的二级大地构单元,本文在对蓟县型中、上元古界沉积环境和对内蒙地轴演化历史的初步研究基础上,认为蓟县型中、上元古界沉积盆地于长城－蓟县期,在北部与广海相连,属于陆表海发展,在青白口期,由于北部逐渐抬升,该沉积盆地才具有陆内盆地性质,内蒙地轴在长城－蓟县期总体处于水下环境,青白口爰开始抬升为古陆,其大规模抬升可能是在古生代或更晚。     

长白山天池火山区长白-敦化剖面结晶基底的探测和研究

时间项分析法中，应用广义最小二乘法进行反演，对长白山天池火山区岩浆系统的长白—敦化(L1)剖面的Pg波到时进行了计算处理，得到了Pg波时间项及基底速度值；取上部地壳的介质平均速度为4．5km/s，经反演求得了各点的深度值，给出了长白山天池火山区结晶基底的厚度分布。结晶基底厚度一般在2．0km左右，而在长白山天池下方结晶基底最厚处接近4．0km；在万宝和敦化附近各有一不太明显的凹陷，其原因可能与在这两个位置处有几条断裂穿过有关。     

沉积盆地、结晶基底和油、气成因理念与第二深度空间勘探和开发

在石油、天然气的勘探和开发研究中,涉及到深部空间的介质、结构和属性,在沉积建造上涉及到陆相沉积、海相沉积和火山岩相,在油、气成因理论上涉及到有机成因和无机成因,在机制上涉及到深部流体的分异、调整、运移和动力作用.这些本质性问题的研究和探讨是人们十分关注的科学领域.基于油、气生、储和形成的理论、应用和成效的研究提出,有几个基础性的理念问题必须重新认识,特别是沉积建造与古老变质岩结晶基底;双相（海相和陆相）沉积建造与盆地的内涵和双基（有机和无机）混合油、气成因理念.清晰地厘定这些认识不仅有益于对油、气形成、聚集和勘探及开发给出一个更为科学的深部空间,即第二深度空间（5000~10000 m）的油、气勘探,而更为重要的是基于对这些理念的重新认识和深化研究可构建新的思路或理论,且在新的理念导向下,强化油、气深部勘探,以期能在理论研究和实践应用中取得新的成效,发现大型与超大型油、气田.     

合肥盆地安参1井前侏罗纪基底地层的孢粉组合特征与时代归属

大别山北缘的安参1井是合肥盆地最深的一口参数井,钻遇前侏罗纪基底地层达千米以上,为一套不含煤层(线)或灰岩以泥岩为主的地层,与周缘华北陆块和大别造山带等构造单元的地层对比困难。因缺少宏观化石记录和明确的定年依据,其时代归属一直存在争议,制约了对这一套特殊地层所反映的地质信息的进一步挖掘。为进一步明确该套特殊地层的地质时代,本项研究对安参1井4160~5152m井段大量岩心和岩屑样品进行了微古化石分析,在其中5块样品中发现了保存良好的孢粉化石647粒,共计23属51种及部分未定种。根据对孢粉化石的类型、属种和含量的分析,将其自下而上划分为两个孢粉化石组合:Ⅰ.Densosporites reynoldburgensisLaevigatosporites perminutus;Ⅱ.Triquitrites-Macrotorispora media。孢粉组合Ⅰ中蕨类植物孢子以平均含量87.67%占绝对优势,代表分子有Laevigatosporites perminutus,Lycospora rotunda,Patellisporites meishanesis等,裸子植物花粉均为单囊粉属Florinites;孢粉组合Ⅱ中,蕨类植物孢子平均含量降低至53.78%,其中蕨类孢子Lycospora rotunda消失,Leiotriletes adnatus,Triquitrites,Crassipora等含量下降,并有特征分子大一头沉孢属Macrotorispora出现,裸子植物花粉含量和丰富度明显增加,以柯达粉属Cordaitina为主。经过与华北其他地区孢粉组合特征的对比分析,上述两个孢粉组合分别与华北陆块晚古生代二叠系太原组和上石盒子组具有明确的相似性,与早期和中晚期华夏植物群面貌相一致,反映了裸子植物逐渐繁盛、属种越来越丰富的过程,孢粉组合Ⅰ和Ⅱ的地质时代分别为晚石炭世晚期至早二叠世早期和晚二叠世,为安参1井前侏罗纪基底存在石炭—二叠系提供了直接证据,也为合肥盆地沉积环境和古气候分析提供了新资料。     

大岭子金矿地质特征及选矿浸出率

大岭子金矿V1矿体赋存于中元古界高黎贡山群变质岩中,受韧性剪切带控制,矿石类型以氧化矿石为主。提出选矿依据。     

河南省栾川县马圈一带银铅锌多金属找矿方向探讨

马圈一带出露的主要地层为上元古界栾川群和中元古界官道口群 ,是Pb、Zn、Ag的主要含矿地层。燕山期花岗岩在空间上与矿化关系密切。矿体主要受北西向断裂控制 ,常分布在北西、北东向断裂构造交汇部位。根据地球化学特征、矿产分布规律和找矿标志 ,划分出百炉沟西凹—东凹—磨沟、百炉沟—黄花北沟—杨树凹等两个一级和银窝沟—大石渣沟—小石渣沟、板岔沟等两个二级找矿预测区。