内蒙古敖包吐萤石矿床地质和地球化学特征   总被引：2，自引：0，他引：2  

许东青  聂凤军  江思宏  张万益  云飞  杨才  张天俊  吕旭光  林日亮 《地球学报》2008,29(4):440-450

笔者总结了敖包吐萤石矿床的地质特征,并通过萤石的稀土元素的地球化学和Nd同位素研究,探讨了该矿床的成矿作用和成矿物质来源。敖包吐萤石矿床产出于下二叠统大石寨组火山—沉积岩与燕山中期花岗岩的接触带,为单一萤石矿床。萤石矿石的稀土元素的含量(∑REE)变化范围为(8.04～30.04)×10-6,平均为19.42×10-6;轻重稀土LREE/HREE值0.24～0.65,平均0.52;LaN/YbN为0.07～0.62,平均0.26;δEu为0.42～0.90,平均0.60,具Eu负异常和明显重稀土富集的特征。岩矿石的Nd同位素研究表明,萤石矿石的εNd(t)都表现为很大的负值,以成矿主期年龄138Ma计算的εNd(138Ma)为-7.30～-30.55,具有古陆壳的演化特征,暗示其成矿的物质来源主要是壳源物质。在Moller的Tb/La-Tb/Ca成因判别图解中,敖包吐矿床的萤石的结晶作用表现为重新活化的趋势,反映流体具有混源的特征,既有热液成因,又有沉积成因。二叠世的海相火山活动通过海底喷气和喷流的作用形成了初始矿源层,而燕山中期花岗岩浆的侵位与结晶分异,又对初始矿源层的活化和富集提供了流体和热能的来源。成矿流体在经历了长期的演化后在大石寨组的构造薄弱破碎的的部位沉淀析出,形成敖包吐萤石矿床。  相似文献   

贵州梵净山地区震旦系微量元素特征及沉积环境   总被引：4，自引：0，他引：4  

熊国庆  王剑  胡仁发 《地球学报》2008,29(1):51-60

为了详细研究梵净山地区震旦系沉积地球化学特征及沉积环境演化,笔者对该处永义剖面自下而上进行系统采样.样品分析结果表明该处剖面稀土元素呈轻稀土(LREE)富集,重稀土(HREE)亏损,铈总体上表现为亏损,垂向上逐渐变小,铕异常发生3次波动,表明该处震旦系沉积时总体上为氧化环境,局部沉积环境发生变化.而且陡山沱组底部"碳酸盐帽"稀土元素标准化分配模式不同于冷泉碳酸盐岩分配模式,表明两者处于不同的沉积环境,成因上无关.V/Cr、Ni/Co、U/Th及V/V Ni等微量元素比值均表明震旦系沉积时为总体上氧化环境,但垂向上仍有沉积环境及水体分层性的变化.  相似文献   

Rare Earth Deposits of North America     

Stephen B. Castor 《Resource Geology》2008,58(4):337-347

Rare earth elements (REE) have been mined in North America since 1885, when placer monazite was produced in the southeast USA. Since the 1960s, however, most North American REE have come from a carbonatite deposit at Mountain Pass, California, and most of the world’s REE came from this source between 1965 and 1995. After 1998, Mountain Pass REE sales declined substantially due to competition from China and to environmental constraints. REE are presently not mined at Mountain Pass, and shipments were made from stockpiles in recent years. Chevron Mining, however, restarted extraction of selected REE at Mountain Pass in 2007. In 1987, Mountain Pass reserves were calculated at 29 Mt of ore with 8.9% rare earth oxide based on a 5% cut‐off grade. Current reserves are in excess of 20 Mt at similar grade. The ore mineral is bastnasite, and the ore has high light REE/heavy REE (LREE/HREE). The carbonatite is a moderately dipping, tabular 1.4‐Ga intrusive body associated with ultrapotassic alkaline plutons of similar age. The chemistry and ultrapotassic alkaline association of the Mountain Pass deposit suggest a different source than that of most other carbonatites. Elsewhere in the western USA, carbonatites have been proposed as possible REE sources. Large but low‐grade LREE resources are in carbonatite in Colorado and Wyoming. Carbonatite complexes in Canada contain only minor REE resources. Other types of hard‐rock REE deposits in the USA include small iron‐REE deposits in Missouri and New York, and vein deposits in Idaho. Phosphorite and fluorite deposits in the USA also contain minor REE resources. The most recently discovered REE deposit in North America is the Hoidas Lake vein deposit, Saskatchewan, a small but incompletely evaluated resource. Neogene North American placer monazite resources, both marine and continental, are small or in environmentally sensitive areas, and thus unlikely to be mined. Paleoplacer deposits also contain minor resources. Possible future uranium mining of Precambrian conglomerates in the Elliott Lake–Blind River district, Canada, could yield by‐product HREE and Y. REE deposits occur in peralkaline syenitic and granitic rocks in several places in North America. These deposits are typically enriched in HREE, Y, and Zr. Some also have associated Be, Nb, and Ta. The largest such deposits are at Thor Lake and Strange Lake in Canada. A eudialyte syenite deposit at Pajarito Mountain in New Mexico is also probably large, but of lower grade. Similar deposits occur at Kipawa Lake and Lackner Lake in Canada. Future uses of some REE commodities are expected to increase, and growth is likely for REE in new technologies. World reserves, however, are probably sufficient to meet international demand for most REE commodities well into the 21st century. Recent experience shows that Chinese producers are capable of large amounts of REE production, keeping prices low. Most refined REE prices are now at approximately 50% of the 1980s price levels, but there has been recent upward price movement for some REE compounds following Chinese restriction of exports. Because of its grade, size, and relatively simple metallurgy, the Mountain Pass deposit remains North America’s best source of LREE. The future of REE production at Mountain Pass is mostly dependent on REE price levels and on domestic REE marketing potential. The development of new REE deposits in North America is unlikely in the near future. Undeveloped deposits with the most potential are probably large, low‐grade deposits in peralkaline igneous rocks. Competition with established Chinese HREE and Y sources and a developing Australian deposit will be a factor.  相似文献   

REE Abundance and REE Minerals in Granitic Rocks in the Nanling Range,Jiangxi Province,Southern China,and Generation of the REE‐rich Weathered Crust Deposits     

Shunso Ishihara  Renmin Hua  Mihoko Hoshino  Hiroyasu Murakami 《Resource Geology》2008,58(4):355-372

Studies of Mesozoic granites associated with rare earth element (REE)‐rich weathered crust deposits in southernmost Jiangxi Province indicate that they have high‐K to shoshonite compositions and belong to ilmenite‐series I‐type granites. Of the studied rocks at 59–292 ppm of bulk REE content, the highest are seen in the biotite granites of Dingnan (358, 429 ppm) and mafic biotite granite of the Wuliting Granite (344 ppm) near the Dajishan tungsten mine, both areas where weathered‐crust REE deposits occur. REE‐bearing accessory minerals in these granites are mainly zircon, apatite and allanite, and REE‐fluorocarbonates are common. REE enrichment occurs in the rims of apatite crystals, and in fluorocarbonates that occur along grain boundaries of and cracks in major silicate minerals, and in fluorocarbonates that replaced altered biotite. It is therefore thought that a major part of the REE content of these granites was concentrated during deuteric activity, rather than during magmatic crystallization. The crack‐filling REE‐fluorocarbonates could subsequently have been easily leached out and deposited in weathered crust developed during a long period of exposure.  相似文献   

Simulations of 3D DC borehole resistivity measurements with a goal-oriented <Emphasis Type="Italic">hp</Emphasis> finite-element method. Part II: through-casing resistivity instruments     

D. Pardo  C. Torres-Verdín  M. Paszynski 《Computational Geosciences》2008,12(1):83-89

We simulate direct current (DC) borehole resistivity measurements acquired in steel-cased deviated wells for the assessment of rock formation properties. The assumed data acquisition configuration considers one current (emitter) and three voltage (collector) electrodes that are utilized to measure the second difference of the electric potential along the well trajectory. We assume a homogeneous, 1.27-cm-thick steel casing with resistivity equal to 10^− 5 Ω· m. Simulations are performed with two different numerical methodologies. The first one is based on transferring two-dimensional (2D) axisymmetric optimal grids to a three-dimensional (3D) simulation software. The second one automatically produces optimal 3D grids yielded by a 3D self-adaptive goal-oriented algorithm. Both methodologies utilize high-order finite elements (FE) that are specially well-suited for problems with high-contrast coefficients and rapid spatial variations of the electric field, as it occurs in simulations that involve steel-cased wells. The method based on transferring 2D-optimal grids is efficient in terms of CPU time (few seconds per logging position). Unfortunately, it may produce inaccurate 3D simulations in deviated wells, even though the error remains below 1% for the axisymmetric (vertical) well. The method based on optimal 3D grids, although less efficient in terms of CPU time (few hours per logging position), produces more accurate results that are validated by a built-in a posteriori error estimator. This paper provides the first existing simulations of through-casing resistivity measurements in deviated wells. Simulated resistivity measurements indicate that, for a 30° deviated well, measurements in conductive layers 0.01 Ω· m) are similar to those obtained in vertical wells. However, in resistive layers (10,000 Ω· m), we observe 100% larger readings in the 30° deviated well. This difference becomes 3,000% for the case of a 60° deviated well. For this highly-deviated well, readings corresponding to the conductive formation layer are about 30% smaller in magnitude than those in a vertical well. Shoulder effects significantly vary in deviated wells.  相似文献   

A coupling of mixed and discontinuous Galerkin finite-element methods for poroelasticity     

Phillip Joseph Phillips  Mary F. Wheeler 《Computational Geosciences》2008,12(4):417-435

In this paper, we formulate a finite-element procedure for approximating the coupled fluid and mechanics in Biot’s consolidation model of poroelasticity. We approximate the flow variables by a mixed finite-element space and the displacement by a family of discontinuous Galerkin methods. Theoretical convergence error estimates are derived and, in particular, are shown to be independent of the constrained specific storage coefficient, c _o . This suggests that our proposed algorithm is a potentially effective way to combat locking, or the nonphysical pressure oscillations, which sometimes arise in numerical algorithms for poroelasticity.  相似文献   

Fractional crystallization models and B–Be–Li systematics at Mt Somma-Vesuvius volcano (Southern Italy)     

Angelo Paone 《International Journal of Earth Sciences》2008,97(3):635-650

A compilation of B–Be–Li data on rocks that cover the entire eruptive history of Somma-Vesuvius is presented and interpreted in the light of evolution models for the Somma-Vesuvius rocks. Using major and trace element data, fractional crystalllization models are presented for different geochemical units. These data were used to constrain the source mineralogy of the Somma-Vesuvius rocks (ol-opx-cpx-gar-amp of 0.4-0.3-0.1-0.1-0.1), the amount of sediment added (5–10%) and the melt fraction from batch partial melting computations (0.05–0.1). From the B–Li data it is inferred that the main process responsible for the B isotopic signature is sediment recycling. However, the B–Li data show a major variation in Li abundances respect to B which is explained with Li dehydration before the fluid enriched the mantle wedge that produced the arc magmas. The Somma-Vesuvius B isotope composition is intermediate between that of the Campi Flegrei and the broad field of the Eolian Island arc. A low Be isotopes in the recent volcanic rocks can be explained as: (a) the top 1–22 m of the incoming sediment is accreted, (b) large amounts of sediment erosion, (c) a slow rate of subduction which have provoked a long magmatic history for the Vesuvius magma, (d) the sediment component takes several Myr longer than the subducting plate to reach the magma source region beneath Italy.  相似文献   

Platinum-group element distribution in chromite ores from ophiolite complexes: implications for their exploration     

Maria Economou-Eliopoulos 《Ore Geology Reviews》1996,11(6):363-381

Compilation of some new data on ophiolites for Greece and Yugoslavia, and published data from previous studies, indicate that platinum-group element (PGE) and gold concentrations in chromite ores are generally low, ranging from less than 100 ppb to a few hundred ppb. However, samples from several ophiolite complexes exhibit an enrichment (of a few ppm) (a) only in Os, Ir and Ru,(b) only in Pt and/or Pd or (c) in all PGE. This enrichment (up to 10s ppm) is mainly related with chromitites hosted in supra-Moho dunites and dunites of the uppermost stratigraphic levels of the mantle sequence and it seems to be local, independent of the chromitite major element composition and the chromite potential of the ophiolite complexes. The contents of PGE combined with less chalcophile elements (Ni, Co, Cu), the ratios of incompatible/compatible elements, and PGE-patterns provide evidence for discrimination between chromitites derived from primitive magmas and those derived from partially fractionated magmas, although they have a similar major element composition. Thus, they can be used for a stratigraphic orientation in the mantle sequence, and therefore for exploration targets. Moreover, PGE data offer valuable information for the evaluation of the chromite potential in ophiolite complexes. The most promising ophiolites seem to be those which apart from the petrological and geochemical characteristics indicating extensive degree of partial melting in the mantle source contain only one chromite ore type (the other type being only in small proportion) of limited compositional variation, in both major elements and PGE, low ratios of , while PGE-enriched chromitites in the mantle sequence are only occasionally present. In contrast, ophiolites which contain both high-Cr and -Al chromitites, and where their chalcophile element data implies relatively extensive fractionation trend are not good exploration targets for chromite ores, although they are related with a SSZ environment.  相似文献   

A dynamic box model of bioactive elements in the southern Taiwan Strait   总被引：3，自引：0，他引：3  

洪华生  商少凌 《中国海洋湖沼学报》1994,12(2):120-129

A dynamic box model was applied to study the characteristics of biogeochemical cycling of PO_4-P,NO_3-N,AOU,POC and PON in the southern Taiwan Strait region based on field data of the"Minnan Taiwan Bank Fishing Ground Upwelling Ecosystem Study" during the period of Dec.1987-Nov.1988.According to the unique hydrological and topographical features of the region,six boxesand three layers were considered in the model.The variation rates and fluxes of elements induced by hor-izontal current,upwelling,by diffusion,sinking of particles and biogeochemical processes were estimatedrespectively.Results further confirmed that upwellings had important effects in this region.Thenearshore upwelling areas had net input fluxes of nutrients brought by upwelling water,also had high de-pletion rates of nutrients and production rates of particulate organic matter and dissolved oxygen.Theabnormal net production of nutrients in the middle layer(10-30m) indicated the important role of bacte-ria in this high production region.Th  相似文献   

全球不同构造环境蛇纹岩全岩和矿物微量元素组成及非传统稳定同位素(Fe- Zn- Cu同位素)特征     

杨凯  戴紧根  沈洁  张文仓  赵玲玲 《地质学报》2022,96(12):4149-4166

蛇纹岩对地球深部和浅部的元素循环以及氧化还原状态调节具有非常重要的作用。蛇纹岩中的流体活动性元素(fluid- mobile element, FME)是揭示地幔岩石水化、脱水以及元素循环的关键。本文系统收集和分析了前人报道的不同构造环境的蛇纹岩矿物化学、全岩微量元素和非传统稳定同位素(Fe、Zn、Cu)的组成特征，试图从多个角度总结蛇纹岩脱水过程的元素迁移规律及流体性质。蛇纹岩主要矿物蛇纹石微量元素含量具有以下主要特征：① 不同变质程度的蛇纹岩中的蛇纹石既包含轻稀土元素(light rare earth element, LREE)富集，又包含LREE亏损的特征；② 纤蛇纹石的REE和微量元素分布在利蛇纹石和叶蛇纹石的范围内，利蛇纹石重稀土元素(heavy rare earth element, HREE)整体上略高于叶蛇纹石且更加富集FME；③ 通过中度不相容元素与REE含量相结合，能够较好地区分橄榄石和辉石蛇纹石化所形成的蛇纹石，即辉石形成的蛇纹石富集相容元素(如Sc、Zn、Cr、Y和Ti等)并具有较高的HREE，而橄榄石形成的蛇纹石则表现为平坦且整体较低的REE分布型式。在蛇纹岩全岩微量元素和稀土元素(rare earth element, REE)含量方面，不同构造环境的蛇纹岩具有较大范围的重叠，但也有一定的差异：① 慢速扩张的印度洋中脊蛇纹岩REE和微量元素含量要整体高于快速扩张的大西洋中脊和太平洋中脊的蛇纹岩；② 马里亚纳蛇纹岩泥相比于蛇纹岩和蛇纹石化纯橄岩具有更高的REE和微量元素，而蛇纹石化纯橄岩相比于蛇纹岩则具有相对低的REE及流体不活动性元素含量。因此，利用微量元素的含量在区分不同环境的蛇纹岩方面存在一定的困难。但是，碱金属元素与U元素含量及其相应的比值，则可以较明显区分出大洋蛇纹岩和弧前蛇纹岩。目前已发表的蛇纹岩Fe、Zn、Cu同位素数据表明：① 蛇绿岩中的蛇纹岩Fe和Zn同位素的分馏与其变质程度密切相关。蛇纹岩在进变质过程中δ 56Fe值与Fe 3+/∑Fe值呈负相关，而Zn含量和δ 66Zn值则呈现正相关，表明蛇纹岩变质脱水能够释放氧化性流体；② 与橄榄岩相比，蛇纹岩具有明显低的δ 65Cu值，表明橄榄岩蛇纹石化过程中存在氧化性流体的加入。蛇纹岩Fe、Zn、Cu同位素在示踪流体性质和氧化还原状态方面有很大潜力，对壳幔系统的化学循环具有重要意义。  相似文献