重要的地球化学"信息库"

金红石是各种岩石特别是地壳组成岩石中重要的副矿物,它在成岩、风化和各种不同程度的变质过程中均能保持极大的稳定性。同时,除主要成分TiO₂外,金红石还含有为数众多的其它微量元素(例如: Nb, Ta, Zr, Hf, Sn, Mo, Sb, Cr, V, W, U和Pb等),这些微量元素的变化特征,对于包含金红石的主体岩石所经历的地质过程具有非常重要的指示意义。近二十年特别是近十年来,金红石已成为地球化学研究领域的一个热点。对各种元素和同位素在金红石中变化特征的调查,被广泛地应用于对各种地质过程的了解,其研究应用的范围涉及到了整体地球的元素平衡、大陆地壳的形成机制、含金红石岩石的形成源区、变质岩石的温压条件和形成时代的研究等多个方面,同时其所包含的各种同位素体系也被广泛用于各种地质过程的示踪。本文综合近年来金红石研究的最新进展,系统表述了金红石作为一个近年来发展起来的重要地质信息储库,在地球化学研究中各个方面的应用。     

云南弥渡黄矿厂铅银矿矿床成因

矿区位于三江地槽褶皱系和扬子准地台之间的丽江—大理台缘过渡带南缘,大地构造位置特殊,地质构造复杂,岩浆活动强烈而频繁,成矿地质条件较好。认为矿床成因为火山喷流沉积型透镜状-似层状铅银多金属矿床。     

云南永善长坪铁多金属矿矿床成因

矿体赋存于上二叠统宣威组下段铝土质粉砂质泥岩中。赤铁矿为主,次为磁铁矿、菱铁矿等。矿体与底板围岩呈突变关系,赤铁矿化强烈。     

老挝琅勃拉邦爬奔金矿矿床地质及成因探讨

琅勃拉邦省位于“三江”成矿带南延部分,爬奔金矿为受剪切带控制的低温热液矿床,矿体产出空间符合里德尔剪切裂隙规律,进一步工作后该矿区应有中型以上规模。     

东川稀矿山式铁铜矿控矿条件新认识

落因背斜两翼地层构造、地层岩相、含矿的差异性,证明背斜轴部存在生长断层。凡有长断层出现,因民组、落雪组岩相剧变,伴随碱性火山喷发-喷溢活动形成细碧岩、基性熔岩、角砾岩之处成为成矿必要条件。     

红河车古铁金多金属矿矿化特征及成因探讨

红河县车古铁多金属矿为近期新发现的金矿点,通过矿区已发现的三处矿化体的综合研究,并与典型矿床进行对比,认为本区金矿化体均为热液成因。     

Geology and hydrothermal resources in the northern Lake Abaya area (Ethiopia)

The northern Lake Abaya area located in the southern part of the Main Ethiopian Rift (MER) evidently contains an advective hydrothermal system. Regional extensional tectonics and subsidence that began in Late Miocene was followed by rift margin rhyolitic volcanism which produced extensive ignimbrite succession and rift shoulder trachytic volcanism in Pliocene. The extensional axis of the MER became the locus of volcanic activity in the Quaternary with bimodal basalt – rhyolitic volcanic products in the rift floor. Shallow crustal magma chambers feeding the axial volcanic complexes provide heat for the hydrothermal system which reside in Tertiary volcanic succession and is capped by lacustrine and volcanoclastic graben infill sediments. Duguna Fango rhyolitic volcanic complex which has extruded as much volume of volcanic products as all the other felsic centers put together is the most important heat source for the hydrothermal system and related manifestations. The closed drainage basin centered at Lake Abaya with adjacent plateau receiving over 1500 mm annual precipitation maintains a stable recharge for the prevailing hydrothermal system. Regional ground water flow direction is to the southwest following Bilate River which is the major river draining into the lake flowing parallel to the major NNE-SSW structural pattern of MER.Analyses of remote sensing data provided some insight into how the structural fabric had a control on the distribution of the groups of hydrothermal manifestations identified as hydrothermal fields. Thermal infrared image showed distinct thermal signature over the rift floor where hydrothermal fields are situated as compared to the plateau and areas covered by the cap-rock. A hydrothermal field around Duguna Fango volcanic complex has volcanological favorable setting despite lower inferred reservoir equilibrium geothermometer temperatures on the thermal springs. About 30 km to the south two other hydrothermal fields are located at a latitudinal distance of less than 15 km between each other. The near boiling point spring #6 of Northwest Abaya discharge mature water with highest geothermal fluid – host rock equilibrium geothermometer temperatures which together with a nearby fumarolic activity may be explained as an outflow. Across Chewkare graben the Bolcho and northeast Abaya hydrothermal fields located between Bilate and Gidabo rivers geochemically appear to be from a different high-enthalpy geothermal reservoir probably related to the cluster of felsic volcanic centers such as Chericho, Kilisa, Donga and Werencha. The high temperature springs indicate the existence of at least two geochemically distinct hydrothermal reservoirs in the study area. It remains to be proven weather an up-flow of an advective hydrothermal system centered to the north around Duguna Fango have long distance concealed out flows to the south on the northern shores of Lake Abaya which is the hydrologic depocenter.     

塔里木盆地下古生界热液白云岩储层的主控因素及识别特征

塔里木盆地下古生界中热液活动多,相应地也发育较多的热液白云岩储层.认为该类储层的规模具有局限性,更多的是对前期已经形成的储层进行叠加改造,但由于盆地内热液影响的范围大,对储层的改造作用也相当可观.对大量的岩心、薄片及露头的研究表明,具有一定孔渗性的石灰岩和白云岩地层为热液白云岩储层的发育提供了物质基础,高角度深大断裂为...     

http://www.sciencedirect.com/science/article/pii/S1674987111000478

Convective heat transfer associated with the circulation of pore-fluid in porous rocks and fractures within the upper crust of the Earth is substantial when the temperature gradient is sufficiently high.In order to understand the process of Sn-polymetallic mineralization in the Dachang ore district of Guangxi,a finite element method has been used in this study to simulate both pore-fluid flow and heat transfer in this district.On the basis of related geological,tectonic and geophysical constraints,a computational model was established.It enables a computational simulation and sensitivity analysis to be carried out for investigating ore-forming pore-fluid flow and other key factors that may affect hydrothermal ore genesis in the district.The related simulation results have indicated that:(1) permeable fault zones in the Dachang ore district can serve as preferential pathways for pore-fluid flow on a regional-scale;and(2) the pore-fluid flow can affect the salinity distribution.This latter factor is part of the reason why Sn-polymetallic mineralization has taken place in this district.     

Architecture of a forced regressive systems tract in the Turonian Ferron “Notom Delta”, southern Utah, U.S.A.

The large-scale stratigraphic architecture of forced regressive deposits has been documented in many previous studies. Bed-scale facies architectural analyses of these deposits, however, are still very limited. The Cretaceous Ferron “Notom Delta” in southern Utah, U.S.A. contains a 20 km dip-oriented exposure of a stepped, forced regressive systems tract. The main focus of this paper is to reconstruct the paleogeography and depositional history of the systems tract based on detailed stratigraphic and facies architectural analysis using 23 geological sections, photomosaics, and walking out of beds.Internally, the systems tract consists of 6 parasequences, 11f to 11a from the oldest to the youngest. During the progradation of parasequences 11f to 11b the paleoshorelines were wave-dominated, as indicated by the abundance of HCS and/or SCS beds, wave-ripple cross-laminated beds, and the occurrence of diverse and robust ichnological suites attributable to the Skolithos and Cruziana Ichnofacies. Progradation of the wave-dominated shorelines resulted in more homogeneous and laterally continuous sand bodies. From 11b to 11a, however, there is a distinct change in paleoshoreline regime from wave-dominated to tide-influenced as indicated by the common occurrence of tidal facies in 11a, including: (1) lenticular, wavy, and flaser bedding and bidirectional dipping cross strata; (2) reactivation surfaces, double-mud drapes, and ripple cross lamination with opposing dips at the toe of large dune-scale cross sets; (3) inclined heterolithic strata (IHS) and sigmoidal bedding with tidal rhythmites; and (4) cyclic vertical variation in facies and bed thickness and the common occurrence of sand-mud couplets. These tide-influenced facies show overall lower bioturbation intensity (BI 0-3). Progradation of the tide-influenced shoreline results in more heterolithic delta-front facies. Tidal and/or tidal-fluvial channels further dissect delta-front sandstones, forming more isolated sand bodies.Data from this study, as well as previous work, show that width and thickness of the forced regressive parasequences are small, typically less than 5 km and 20 m respectively. In subsurface studies, identifying and correlating such small-scale parasequences using sparse data involve significant uncertainties. A combination of the diagnostic features indicating forced regression and different data sets is essential to better constrain the geometry and architecture these small-scale bodies.