Shoshonitic lamprophyre dykes and their relation to mesothermal Au---Sb veins at Hillgrove, New South Wales, Australia   总被引：5，自引：0，他引：5  

P.M. Ashley  N.D.J. Cook  R.L. Hill  A.J.R. Kent 《Lithos》1994,32(3-4):249-272

The Hillgrove mineral field, in the southern part of the New England Orogen of northeastern New South Wales, Australia, contains numerous mesothermal Au---Sb vein systems. Calc-alkaline (shoshonitic) lamprophyre (CAL) dykes are also associated with mineralisation with dilational lode structures acting as conduits for dyke intrusion, which has occurred before and after major quartz-stibnite veining. Dykes include minette and vogesite compositions and were emplaced in the late Permian (247–255 Ma), at the same time as regionally extensive I-type magmatism in the New England Orogen. Least-altered dykes are enriched in Mg, K, Ba, Rb, Sr, Zr, Th, Cr and Ni relative to I-type intrusives although chemical affinities are evident between lamprophyres and the more mafic members of the high-K Moonbi Plutonic Suite.

Hillgrove lamprophyres are commonly enriched in Sb, As, Hg, Au, W and Bi with respect to average CAL compositions. Evidence indicates this is most likely due to contamination of magma during intrusion through mineralised structures, rather than a primary magmatic feature. Partially resorbed xenocrystic stibnite occurs in dykes which have intruded lode structures, probably facilitated by the low melting point of stibnite (550°C) and its incorporation into the magma. Carbon and oxygen isotopic data from carbonates in least-altered, post-lode lamprophyres are indistinguishable from carbonate in altered dykes and veins, implying that hydrothermal interaction continued after dyke intrusion. Although it is unlikely that lamprophyre dykes have been a direct source for mineralisation at Hillgrove, the close temporal and spatial relation of dykes, mesothermal Au---Sb veins and I-type intrusions are interpreted to be manifestations of the post-collisional setting and influx of mantle-derived heat and partial melts into the New England Orogen during the late Permian.  相似文献   

Preparations for a new absolute determination of gravity at the National Physical Laboratory Teddington     

A. H. Cook 《Journal of Geodesy》1959,33(1):63-71

The proposed method involves the timing of the flight of a ball projected upwards and allowed to rise and fall freely under gravity and the principle, the advantages and the difficulties of the method are discussed. Means of locating a ball in flight to i μ are considered and the results of some studies of the adopted scheme are given. The probable layout of the apparatus is outlined.  相似文献   

Deep Natural Gas Resources     

Dyman  T. S.  Wyman  R. E.  Kuuskraa  V. A.  Lewan  M. D.  Cook  T. A. 《Natural Resources Research》2003,12(1):41-56

From a geological perspective, deep natural gas resources generally are defined as occurring in reservoirs below 15,000 feet, whereas ultradeep gas occurs below 25,000 feet. From an operational point of view, deep may be thought of in a relative sense based on the geologic and engineering knowledge of gas (and oil) resources in a particular area. Deep gas occurs in either conventionally trapped or unconventional (continuous-type) basin-center accumulations that are essentially large single fields having spatial dimensions often exceeding those of conventional fields.Exploration for deep conventional and continuous-type basin-center natural gas resources deserves special attention because these resources are widespread and occur in diverse geologic environments. In 1995, the U.S. Geological Survey estimated that 939 TCF of technically recoverable natural gas remained to be discovered or was part of reserve appreciation from known fields in the onshore areas and state waters of the United States. Of this USGS resource, nearly 114 trillion cubic feet (Tcf) of technically recoverable gas remains to be discovered from deep sedimentary basins. Worldwide estimates of deep gas also are high. The U.S. Geological Survey World Petroleum Assessment 2000 Project recently estimated a world undiscovered conventional gas resource outside the U.S. of 844 Tcf below 4.5 km (about 15,000 feet).Less is known about the origins of deep gas than about the origins of gas at shallower depths because fewer wells have been drilled into the deeper portions of many basins. Some of the many factors contributing to the origin and accumulation of deep gas include the initial concentration of organic matter, the thermal stability of methane, the role of minerals, water, and nonhydrocarbon gases in natural gas generation, porosity loss with increasing depth and thermal maturity, the kinetics of deep gas generation, thermal cracking of oil to gas, and source rock potential based on thermal maturity and kerogen type. Recent experimental simulations using laboratory pyrolysis methods have provided much information on the origins of deep gas.Technologic problems are among the greatest challenges to deep drilling. Problems associated with overcoming hostile drilling environments (e.g. high temperatures and pressures, and acid gases such as CO₂ and H₂S) for successful well completion, present the greatest obstacles to drilling, evaluating, and developing deep gas fields. Even though the overall success ratio for deep wells (producing below 15,000 feet) is about 25%, a lack of geological and geophysical information continues to be a major barrier to deep gas exploration.Results of recent finding-cost studies by depth interval for the onshore U.S. indicate that, on average, deep wells cost nearly 10 times more to drill than shallow wells, but well costs and gas recoveries differ widely among different gas plays in different basins.Based on an analysis of natural gas assessments, deep gas holds significant promise for future exploration and development. Both basin-center and conventional gas plays could contain significant deep undiscovered technically recoverable gas resources.  相似文献   

Preface – Special Issue: Telluride and selenide minerals in gold deposits – how and why?     

C. L. Ciobanu  N. J. Cook  P. G. Spry 《Mineralogy and Petrology》2006,87(3-4):163-169

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Gold scavenged by bismuth melts: An example from Alpine shear-remobilizates in the Highiş Massif, Romania     

C. L. Ciobanu  N. J. Cook  F. Damian  G. Damian 《Mineralogy and Petrology》2006,87(3-4):351-384

Summary Gold mineralization occurs in the Şoimuş Ilii vein, the main Cu prospect in the Highiş Massif, Western Apuseni Mts., Romania. The Highiş Massif is part of the Highiş Biharia Shear Zone, a 320–300 Ma Variscan greenschist belt, with a 114–100 Ma Alpine overprint. In Highiş, phyllonites enclose an igneous core consisting of an Early Permian basic complex intruded by Middle Permian granitoids. The vein is hosted within basalt hornfels at its contact with the 264 Ma Jernova granite. Gold is not only present as native gold, but also as jonassonite (ideally AuBi₅S₄). The latter occurs as inclusions 1–30 μm in size in chalcopyrite; microanalysis gives the empirical formulae Au_1.02(Pb_0.47Bi_4.51)_4.98S_4. The two Au minerals are spatially associated with Bi–(Pb) sulfosalts (oversubstituted bismuthinite, cosalite) and sulfotellurides/selenides (ingodite, ikunolite and laitakarite) in blebs/patches, mainly hosted in chalcopyrite. This Au–Bi–Te association overprints an earlier, chalcopyrite-quartz assemblage, occurring as trails along discrete zones of brecciation that crosscut former mineral boundaries. Curvilinear and cuspate boundary textures within the blebs/patches suggest deposition in a molten form. Mineral associations in combination with phase relations indicate that the Au–Bi–Te association formed as a result of melting of pre-existing native Bi (and possibly sulfosalts) at 400 °C under sulfidation conditions. These melts incorporated Au, Pb, Te and S as they moved in the vein during shearing and were locked within dilational sites. Native Bi occurs as coarse aggregates along vein margins, but in the Au–Bi–Te association, it is present only as small droplets in shear gashes, never together with other Bi- and Au-minerals. The Bi-derived melts are part of an internal remobilizate which also includes chlorite and adularia. Minerals in the system Au–Bi–Te were deposited from a neutral low reducing fluid during Alpine shearing in the Early Cretaceous. The fluid also assisted solid-state mobilisation of chalcopyrite and cobaltite. This study illustrates the significant potential of Bi, a low melting-point chalcophile element (LMCE), to act as Au scavenger at temperatures as low as 400 °C.  相似文献   

Analysis of a vertical dipole tracer test in highly fractured rock   总被引：1，自引：0，他引：1  

Sanford WE  Cook PG  Dighton JC 《Ground water》2002,40(5):535-542

The results of a vertical dipole tracer experiment performed in highly fractured rocks of the Clare Valley, South Australia, are presented. The injection and withdrawal piezometers were both screened over 3 m and were separated by 6 m (midpoint to midpoint). Due to the long screen length, several fracture sets were intersected, some of which do not connect the two piezometers. Dissolved helium and bromide were injected into the dipole flow field for 75 minutes, followed by an additional 510 minutes of flushing. The breakthrough of helium was retarded relative to bromide, as was expected due to the greater aqueous diffusion coefficient of helium. Also, only -25% of the total mass injected of both tracers was recovered. Modeling of the tracer transport was accomplished using an analytical one-dimensional flow and transport model for flow through a fracture with diffusion into the matrix. The assumptions made include: streamlines connecting the injection and withdrawal point can be modeled as a dipole of equal strength, flow along each streamline is one dimensional, and there is a constant Peclet number for each streamline. In contrast to many other field tracer studies performed in fractured rock, the actual travel length between piezometers was not known. Modeling was accomplished by fitting the characteristics of the tracer breakthrough curves (BTCs), such as arrival times of the peak concentration and the center of mass. The important steps were to determine the fracture aperture (240 microm) based on the parameters that influence the rate of matrix diffusion (this controls the arrival time of the peak concentration); estimating the travel distance (11 m) by fitting the time of arrival of the centers of mass of the tracers; and estimating fracture dispersivity (0.5 m) by fitting the times that the inflection points occurred on the front and back limbs of the BTCs. This method works even though there was dilution in the withdrawal well, the amount of which can be estimated by determining the value that the modeled concentrations need to be reduced to fit the data (approximately 50%). The use of two tracers with different diffusion coefficients was not necessary, but it provides important checks in the modeling process because the apparent retardation between the two tracers is evidence of matrix diffusion and the BTCs of both tracers need to be accurately modeled by the best fit parameters.  相似文献   

Mineralogy and textural relationships among sulphosalts and related minerals in the Bleikvassli Zn-Pb-(Cu) deposit, Nordland, Norway     

N. J. Cook  P. G. Spry  F. M. Vokes 《Mineralium Deposita》1998,34(1):35-56

Several distinct assemblages of Pb-Sb, Pb-As, Cu-Pb-Sb and Cu-Fe-Zn-Sn sulphosalts are identified in sulphide samples from Bleikvassli mine, Norway. Detailed optical microscopy and electron probe microanalysis have permitted investigation of textural relationships between minerals and compositional variations between different ore types. Tetrahedrite, typically containing 10–16?wt.% Ag (rare freibergite containing 25–30?wt.% Ag has also been identified in two samples), stannite (Cu₂(Fe>Zn)SnS₄), and meneghinite, CuPb₁₃Sb₇S₂₄, are widely distributed as trace constituents throughout massive pyritic and galena-rich ores. Native antimony and pyrargyrite occur in trace amounts in all ore types, as the breakdown products of earlier sulphosalts. Several distinct types of wall-rock mineralisation are present at Bleikvassli. Of considerable mineralogical interest are the coarse-grained sulphide mobilisates within the wall rock which contain a distinct?and characteristic suite of Pb-As sulphosalts:?tennantite?+?jordanite (Pb₁₄As₆S₂₃)?+?seligmannite (CuPbAsS₃) ± dufrenoysite (Pb₂As₂S₅). Bournonite (CuPbSbS₃) is the only Sb-bearing sulphosalt recognised in significant amounts within the mobilisates, meneghinite and tetrahedrite being conspicuously absent. These mobilisates display considerable Au enrichment; electrum can be confirmed, intimately associated with jordanite and tennantite. Appreciable Sb (up to 3?wt.%) is contained within galena in the mobilisates, in contrast to galena from massive ores which contains only negligible Sb. Contents of Ag and Bi in galena vary considerably in all ore types, but confirm earlier suggestions that galena is a major Ag-carrier at Bleikvassli. Boulangerite (Pb₅Sb₄S₁₁), jamesonite (FePb₄Sb₆S₁₄) and gudmundite (FeSbS) occur in trace amounts. Sn-sulphosalts are represented by kësterite, (Cu₂(Zn> Fe)SnS₄), but commonly zoned with respect to Zn/Fe ratio, in the mobilisates, rather than by stannite. A rare type of mobilisate, also in the wall rock, in which chalcocite and bornite are the main minerals, contains native Ag, stromeyerite (AgCuS), mckinstryite ((Ag,Cu)₂?S), Ag-free tetrahedrite, an unnamed Cu-Ag-Fe sulphide (Cu₃Ag₂FeS₄) and native Bi, myrmekitically intergrown with chalcocite. Although a comprehensive genetic model for the wall-rock mineralisation at Bleikvassli is largely impossible given the limitations in the present state of knowledge regarding mechanisms involved in remobilisation processes, a multi-stage model of remobilisation during regional metamorphism is considered to best explain the observations. An interplay of different solid- and liquid-state remobilisation mechanisms, in various combinations, is required to account for the macro- and microscopic observations. Remobilisation probably began during the earlier stages of metamorphism, with crystallisation and further remobilisation taking place during the entire metamorphic cycle, giving rise to the extensive chemical and mineralogical diversity observed today. Preserved mineral assemblages and their textural relationships reflect a complex sequence of replacement and decomposition reactions taking place during the latest phase of late-metamorphic crystallisation and subsequent cooling.  相似文献   

Fractals in deep crustal seismic reflection profiles     

K. Vasudevan  Q. Li  F. A. Cook 《International Journal of Earth Sciences》1996,85(1):44-49

Application of a syntactic pattern recognition technique, seismic skeletonization, to deep crustal seismic reflection data allows attributes such as energies, lengths and dips to be associated with individual reflection events. Some of these attributes exhibit fractal properties, e.g. the relationship between seismic event lengths and their spatial distribution throughout the crust. This approach provides a new technique to analyse complex geometry on seismic reflection data.Dedicated to Professor William George Laidlaw on his SIXTIETH birthday  相似文献   

The $\text{D}\text{H}$ ratios of sap in trees: Implications for water sources and tree ring $\text{D}\text{H}$ ratios     

James W.C. White  Edward R. Cook  James R. Lawrence 《Geochimica et cosmochimica acta》1985,49(1):237-246

Measurements of $\text{D}\text{H}$ ratios of tree sap can be used to determine the source water for a tree. Based on these measurements, trees can be separated into three categories: those which rely solely on summertime rainfalls, those which rely solely on groundwaters and those which utilize both water sources. For trees in the last category, $\text{D}\text{H}$ ratios of sap can be used to quantify the relative contributions to the tree's source water of summertime rainfalls and groundwaters. These measurements can be used to select trees for tree ring isotope studies. Single source trees, those which rely solely on summertime rain or groundwaters, appear to be the best choices for measuring long records of tree ring $\text{D}\text{H}$ ratios.  相似文献   

Petrology of a suite of sedimentary rocks associated with some cole-bearing basins in northwestern Thailand     

N.R. Sherwood  A.C. Cook  M. Gibling  C. Tantisukrit 《International Journal of Coal Geology》1984,4(1):45-71

A number of basins in northwestern Thailand contain thick sequences of Cenozoic sedimentary rocks. Oil shales and coals are prominent lithologies within these sequences and occur together in some basins. Most of the sequences are, however, dominated by either oil shales or coals. The major oil shale deposit is in the Mae Sot Basin but oil shales also occur in the Ban Huay Dua, Mae Moh, Ban Pa Ka Li, Mae Teep, Ban Na Hong and Jae Hom Basins.Drilling and detailed mapping, in the Mae Sot Basin indicate thick sequences of oil shales and organic petrological studies show that they contain abundant lamalginite. Trace amounts of telalginite, liptodetrinite, bitumen/resinite and huminite/inertinite are also present in some of the rocks. The parts of the sequences rich in authigenic minerals are, in general, petrographically similar to Green River Formation lamosites. Where clay/silt-sized epiclastics are more abundant, similarities exist to Australian Tertiary lamosites. Vitrinite reflectance date from the oil shales and associated coals indicate a low level of maturity.Oil shales from the other basins are, petrographically similar to the Mae Sot lamosites, however some differences do exist. The Mae Sot and other lamosites were deposited in lacustrine environments that probably had highly variable water depths.  相似文献