全文获取类型
收费全文 | 52篇 |
免费 | 0篇 |
国内免费 | 2篇 |
专业分类
地球物理 | 2篇 |
地质学 | 49篇 |
海洋学 | 2篇 |
天文学 | 1篇 |
出版年
2024年 | 1篇 |
2011年 | 3篇 |
2010年 | 3篇 |
2008年 | 1篇 |
2006年 | 1篇 |
2002年 | 2篇 |
2001年 | 3篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1974年 | 3篇 |
1927年 | 1篇 |
1926年 | 1篇 |
1923年 | 1篇 |
排序方式: 共有54条查询结果,搜索用时 15 毫秒
1.
The Bogosu-Prestea mining district of southwestern Ghana is a 33 km section of the Early Proterozoic Ashanti Gold Belt. Greenschist facies carbonaceous and carbonate-bearing turbidites and greywackes, and mafic dikes host numerous economic mesothermal gold deposits. Structurally higher ores in the Bogosu concession have brittle deformation and consist of disseminated-sulphide lodes in tectonically-disrupted sedimentary rocks and carbonate-altered mafic dikes. Most gold occurs as micrometre-size particles in arsenian pyrite, and as invisible gold in arsenian pyrite and arsenopyrite. The structurally deeper ores of the adjoining Prestea concession are associated with brittle-ductile deformation and consist of extensive crack-seal quartz-veins and graphitic shear zones. Only minor amounts of invisible gold were detected; in these deeper lodes, gold occurs dominantly as abundant microscopic and larger particles in sulphide/arsenide minerals and in gangue. The gold distribution patterns revealed by SIMS microprobe analysis and ion maps, EMP and colour staining suggest that most of the primary gold in the Bogosu-Prestea system precipitated in solid-solution with sulphide/arsenide minerals. However, post-depositional concentration and redistribution occurred, in increasing degree with: 1) increase in metamorphic/hydrothermal gradients in the gold system (depth), 2) decrease in the refractory properties of the host mineral, and 3) increase in the amount of post-depositional, host-mineral recrystallization and deformation. Gold evolved from primary solid-solution within sulphide/arsenide minerals, to colloidal and micrometre-size particles concentrated in voids, fractures and internal grain boundaries, and finally to microscopic and larger particles at sulphide/arsenide grain margins and in the gangue assemblage. The general conclusions presented here are applicable to As-rich gold deposits of all ages, worldwide. The presence of gold in late fractures is insufficient evidence for late-stage introduction of gold in mesothermal gold systems. 相似文献
2.
The partition of Ni between olivine and monosulfide-oxide liquid has been investigated at 1300–1395° C,
=10–8-9–10–6.8, and
=10–2.0–10–0.9, over the composition range 20–79 mol. % NiS. The product olivine compositions varied from Fo98 to Fo59 and from 0.06 to 3.11 wt% NiO. The metal/sulfur ratio of the sulfide-oxide liquid increases with increase in
, decrease in
, and increase in NiS content. The Ni/Fe exchange reaction has been perfectly reversed using natural olivine and pure forsterite as starting materials. The FeO and NiO contents of olivine from runs equilibrated at the same
and
form isobaric distributions with NiS content, which, to a first approximation, are dependent at constant temperature and total pressure on a variable term, –0.5 log (
/
). The Ni/Fe distribution coefficient (K
D3) exhibits only a weak decrease from 35 to 29 with increase in
from the IW buffer to close to the FMQ buffer. At
values higher than FMQ, the sulfide-oxide liquid has the approximate composition (Ni,Fe)3±xS2K
D358. The present K
D3 vs O/(S+O) data define a trend which extrapolates to K
D320 at 10 wt% oxygen in the sulfide-oxide liquid. The compositions of olivine and Ni-Cu sulfides associated with early-magmatic basic rocks and komatiites are consistent, at 1400° C, with a value of -log (
/
) of about 7.7, which is equivalent to 0.0 wt% oxygen in the hypothesized immiscible sulfide-oxide liquid. Therefore, K
D3 would not be reduced significantly from the 30 to 35 range for sulfide-oxide liquids with low oxygen contents. 相似文献
3.
The composition of olivine and nickeliferous sulfide inclusions from a selection of mafic and ultramafre rocks, xenoliths and megacrysts, including picritic basalts from Kilauea Volcano, Hawaii, kimberlite from Fayette County, Pennsylvania, and megacrysts from Mount Shasta, California are compared with the mean experimental value of the distribution coefficient for Ni/Fe exchange (KD3=32). Only nine of the forty five olivipe/bulk-sulfide pairs investigated have compositions consistent with equilibration at high temperature, yielding calculated KD3 values in the range 22 to 41. The remaining pairs have calculated KD3 values which range from 0 to 19. Bulk-sulfides in disequilibrated assem-blages are consistently depleted in nickel and within both indivudual associations and individual petrographic sections they exhibit a wide variation in NiS content. The bulk copper contents of olivine-and groundmass-hosted sulfides from Kilauea Volcano range from 0.5 to 43 at%, and samples from the Kilauea Iki lava lake are more Fe-and Cu-rich and generally have lower KD3 values than those from the eruption itself. As with magmatic Ni–Cu sulfide deposits, most nickeliferous sulfide inclusions in mantle-related rocks and xenoliths and in volcanic rocks do not have pristine early-magmatic bulk compositions, and it would seem to be premature to attribute these sulfides solely to either a mantle or an early-magnatic origin. 相似文献
4.
We propose that within PbO-SiO2 melts the component species PbO(1) and SiO2(1) associate to form a lead orthosilicate complex [Pb2SiO4(1)] according to The association constant (K) for the above reaction is near 30 at 900 and 1000°C On the premises that the enthalpy of the above reaction is the only contributor to the enthalpy of mixing and that three melt species [PbO(1), SiO2(1), Pb2SiO4(1)] mix ideally (Raoult's Law obeyed), the partial molar properties and the integral mixing properties of the melt have been calculated and have been found to accurately reproduce the measured thermochemical data.The conductivity data and density data for PbO-SiO2 melts have been calculated using the association model. The calculated data again are remarkably consistent with the experimental data.Other silicate-melt models have been reinterpreted and that of Toop and Samis is compatible with the proposed model. In fact the Toop and Samis model implicitly assumes the formation of orthosilicate species rather than condensed polymeric species. 相似文献
5.
Pyrite is easily oxidized, and therefore unambiguous evidence of detrital pyrite grains in metasediments is a significant constraint on when an oxygenated atmosphere developed. Compact rounded pyrite in the Witwatersrand gold reefs of South Africa has a detrital habit and is texturally equivalent to and spatially associated with detrital zircon and chromite. X-ray precession photography reveals that petrographically featureless As-poor grains are untwinned single crystals of high diffraction quality. This new evidence from crystallography is consistent with mechanically abraded pyrite from primary lode gold deposits, and excludes an origin by replacement of a pre-existing detrital phase. Further evidence of a detrital origin for the compact rounded pyrite is afforded by isolated grains of arsenian pyrite displaying truncated As-rich growth bands. The geographically extensive Witwatersrand fluvial conglomerates evidently had a matrix of quartz and pyrite sand and pyritic mud in their unconsolidated state and, thus, the late Archean atmosphere of Earth was likely essentially anoxic. 相似文献
6.
Diamonds – rough stones, cut stones, host rocks, historical jewellery, contemporary jewellery, and hi-tech materials – were the stars of an exhibition at the Natural History Museum in London in 2005, the biggest of its kind the Museum had ever staged. Why diamonds are so rare, how they have been valued through history, and the links between the unique properties of diamond and its use were the key themes of the exhibition. 相似文献
7.
8.
Summary Platinum-group mineral (PGM)-bearing amygdule Fe-Ni(±Cu) sulfide has been discovered in samples of amygdaloidal basalt and underlying olivine spinifex-textured basalt from the flow top of Fred's Flow, Munro Township, Ontario. The amygdules are rounded to slightly elongate in shape, up to 10 mm in diameter, filled by chlorite + quartz ± carbonate ± sulfide, and rimmed by relict igneous chromite and clinopyroxene. The sulfide occurs as masses that line and are embedded in the margins of the amygdules. Detailed electron microprobe studies indicate that the sulfide masses are fairly constant (21±4 mol% NiS) in bulk composition and consist of pyrrhotite and pentlandite (Ni-rich) ± minor chalcopyrite rare PGM. The sulfide phases show lamellar intergrowth and are embayed against chlorite. The PGM observed are grains of merenskyite (PdTe2), kotulskite (PdTe), and sperrylite (PtAs2) that are up to 10 m in size, multi-faceted against sulfide, and embayed against chlorite. Whole-rock analyses of the amygdaloidal basalt host rock show strong enrichments in platinum-group elements (PGE + Au = 330 ppb), Ni, Cu, S, and Cr.The textures and spatial associations indicate a genetic relationship between the PGM-bearing sulfide masses and the amygdules. Density considerations, the very close spatial association with the amygdules (vesicles), and the marked enrichment in PGE and related metals and S in the amygdaloidal basalt host rock contradict formation of the sulfide masses as droplets of immiscible sulfide liquid separated from silicate melt. The alteration of the sulfide masses, their association with the vesiculation structures rather than with the pervasive hydrothermal alteration phase assemblage, and lack of evidence for enrichment of Cu and chalcopyrite relative to Ni and Fe-Ni sulfide are inconsistent with formation of the sulfide masses by hydrothermal alteration processes. Alternatively, the mineralogical, textural, spatial association, and whole-rock compositional features can be explained by an igneous degassing-metal diffusion model. It is suggested that prior to emplacement, sulfurous vapor separates from the lava to form vesicles, which float upward to the flow top. Diffusion of PGE and related metals from the lava toward the vesicles as they float upward and reaction of the metals with S within the vesicles forms Fe-Ni-Cu sulfide liquid on the vesicle walls. On quenching, vesicles are trapped in the flow top and the sulfide liquid within them solidifies and sulfide phases and PGM exsolve in the subsolidus.
With 7 Figures 相似文献
Platingruppenminerale mit Flowtop Sulfiden in komatiitischem Basalt, Abitibi Greenstone Belt, Ontario
Zusammenfassung Platingruppenmineral (PGM)-führende Sulfide sind in Blasenräumen von Basaltman delsteinen and darunterliegendem Basalt mit Spinifex-Olivin des Fred's Flow, Munro Township, Ontario beobachtet worden. Die Mandeln sind rundlich bis leicht länglich, haben bis zu 10 mm Durchmesser und Bind mit Chlorit + Quarz ± Sulfid ± Karbonat gefüllt und zeigen einen Rand von reliktischem, magmatischem Chromit und Klinopyroxen. Die Sulfide kommen als Massen, die die Ränder der Mandeln bedecken und in these eingebettet sind, vor. Detaillierte Mikrosondenuntersuchungen zeigen, daß die Gesamtzusammensetzung der Sulfide ziemlich konstant ist (21 ± 4 mol % NiS), und daß she aus Magnetkies und nickelreichen Pentlandit ± Chalcopyrit ± seltene PGM bestehen. Die Sulfidphasen zeigen lamellare Verwachsungen und Einbuchtungen gegen Chlorit. Folgende PGM wurden beobachtet: Merenskyit (PdTe2), Kotulskit (PdTe) and Sperrylit (PtAs2), die bis zu 10 gm groß sind, vielflächig gegen die Sulfide, und eingebuchtet gegen den Chlorit erscheinen. Gesamtgesteinsanalysen des basaltischen Muttergesteins zeigen starke Anreicherungen der Platingruppenelemente (PGE + Au = 330 ppb), Ni, Cu, S, und Cr.Die Texturen und räumlichen Assoziationen weisen auf eine genetische Beziehung zwischen den PGM-führenden Sulfidmassen und den Mandeln hin. Die Dichte, die sehr enge räumliche Assoziation mit den Mandeln, und die deutliche Anreicherung von PGE and verwandten Metallen, Bowie von Schwefel, in den basaltischen Muttergesteinen, sprechen gegen eine Bildung der Sulfidmassen als Tröpfchen einer entmischten Sulfidschmelze, die von der Silikatschmelze abgetrennt wurde. Die Umwandlung der Sulfide, ihre Assoziation mit den Mandeln und nicht mit der umfangreichen hydrothermalen Umwandlungsassoziation und fehlende Hinweise für eine Anreicherung von Cu und Kupferkies relativ zu Ni und Fe-Ni Sulfiden, lassen sich nicht mit einer Bildung der Sulfide durch hydrothermale Umwandlungsprozesse vereinbaren.Die mineralogische, texturelle und raumliche Assoziation und die Zusammensetzung der Muttergesteine kann viel eher durch das Modell magmatischer Entgasung mit Metalldiffusion erklärt worden. Wir regen an, daß vor der Platznahme schwefelreiche Dämpfe von der Lava abgetrennt worden sind und Blasen gebildet haben, welche aufwärts bis zum Top des Basaltergusses migrierten. Diffusion der PGE und verwandter Metalle aus der Lava zu den in Bewegung begriffenen Blasen und Reaktion der Metalle mit Schwefel innerhalb der Hohlräume, führte zur Entstehung einer Fe-Ni-Cu-Schwefel-Schmelze an den Wänden der Mandeln. Bei Abkühlung wurden die Hohlräume in dem oberen Teil des Flows fixiert, die Sulfidschmelze verfestigt sich und Sulfidphasen and PGM entmischen sich im Subsolidus.
With 7 Figures 相似文献
9.
Some of the most vanadium-rich silicate minerals known are present in green mica schist from the Hemlo gold deposit, Ontario, Canada. Vanadium-rich silicate minerals include green mica (up to 17.6 wt. % V2O3), phlogopite (10.1 wt. % V2O3), pumpellyite (25.7 wt. % V2O3), garnet (18.5 wt. % V2O3), epidote-group minerals (9.1 wt. % V2O3), antimonian vesuvianite (4.3 wt. % V2O3), and titanite (18.5 wt. % V2O5). In addition, minor amounts of V (<2 wt. % V2O3) are present in tourmaline, chlorite, talc and tremolite in other lithologies of the Hemlo deposit. The principal substitution that incorporates V into most of these silicate minerals is Al3+=V3+ in octahedral positions. Vanadium is incorporated into phlogopite mainly by the two substitutions: 3Mg2+ =2V3++ and VIMg2++IVSi4+=VIV3+ +IVAl3+, and all of the three substitutions Ti4++O2- =V3++(OH,F)-, Ti4+=V4+, and 5Ti4+=4V5+ + may have operated in titanite.Vanadium-enriched green mica schist from the Hemlo gold deposit is characterized by uniform Ti/Zr ratios, systematically low Ti, Ni, Co and Sc abundances, and low levels of incompatible elements Th, U, Hf and Zr and is distinct in these respects from its Cr-enriched counterpart. These geochemical features, along with textural evidence (relict quartz and oligoclase phenocrysts), indicate that the V-enriched green mica schist from Hemlo was most likely derived mainly from quartz-oligoclase porphyry. However, its anomalously high V and Cr contents were probably introduced metasomatically from local maficultramafic sources and were fixed in green mica and oxides during the waning of a second regional metamorphism. Vanadium was further remobilized, and its concentration probably enhanced, during the late hydrothermal alteration, which resulted in the formation of the characteristic V-rich calc-silicate minerals. 相似文献
10.
Thermal expansion of kyanite at ambient pressure: An X-ray powder diffraction study up to 1000 ℃ 总被引:3,自引:0,他引:3
The thermal expansion coefficients of kyanite at ambient pressure have been investigated by an X-ray powder diffraction technique with temperatures up to 1000 °C. No phase transition was observed in the experimental temperature range. Data for the unit-cell parameters and temperatures were fitted empirically resulting in the following thermal expansion coefficients: αa = 5.8(3) × 10?5, αb = 5.8(1) × 10?5, αc = 5.2(1) × 10?5, and αV = 7.4(1) × 10?3 °C?1, in good agreement with a recent neutron powder diffraction study. On the other hand, the variation of the unit-cell angles α, β and γ of kyanite with increase in temperature is very complicated, and the agreement among all studies is poor. The thermal expansion data at ambient pressure reported here and the compression data at ambient temperature from the literature suggest that, for the kyanite lattice, the most and least thermally expandable directions correspond to the most and least compressible directions, respectively. 相似文献