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J. P. N. Badham 《Mineralium Deposita》1975,10(2):153-175
Polymetallic hydrothermal vein mineralisation of the Ag-Ni, Co Arsenide type, and containing Bi and U, occurs in three mines and five uneconomic veins in the Camsell River area. Each occurrence is described in detail. The veins lie in sulphide-impregnated volcanic rocks of the Aphebian Great Bear Batholith. Large, NE-trending strike-slip faults were initiated during the terminal phases of orogeny (1750 m.y.), and were active intermittently for at least 300 m.y. The veins are located in splays and tension-fractures form the primary faults, and mineralised lenses are found in dilatant zones in these structures. The mineralisation shows a generalised paragenesis of U → Ag+arsenides → Bi, Sulphides, Sulphosalts, but there are variations. A model is presented to explain the temporal and spatial controls of mineralisation and to explain the perturbations in the paragenesis. It is concluded that the mineralisation is of magmatic origin and lateral secretion models are rejected. Discussions of the ultimate origin of the ore elements are not presented here. 相似文献
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David A. Byers 《Geoarchaeology》2002,17(5):417-440
The Fetterman Mammoth locality, eastern Wyoming, U.S.A., produced the remains of a single subadult mammoth and a small lithic assemblage. This paper employs a fine‐grained taphonomic approach to investigate the events responsible for the deposit's creation. No cultural modifications were noted on any of the specimens. Long axis orientations plotted against a reconstruction of the depositional surface suggest limited postdepositional movement of individual disarticulated elements. Weathering patterns based on in situ upside and downside positioning document two discrete episodes of sedimentation. These results suggest that the mammoth remains and the cultural assemblage may be separated by at least one depositional event and, as such, their association is considered equivocal. © 2002 Wiley Periodicals, Inc. 相似文献
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《Journal of Structural Geology》1988,10(8):908-909
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The rocks of the Clough Formation, Black Mountain, New Hampshire,were regionally metamorphosed at 5.5 (±0.5) kb and 495°± 10 °C during the Acadian orogeny. Mineral assemblagesattained chemical equilibrium during metamorphism on the scaleof single sedimentary beds up to 1 m thick. An aqueous, intergranular,metamorphic fluid was probably present; however, the concentrationsof the species H2O, H2, and O2 as well as the abundance of 18Oin the fluid varied from bed to bed. Neither isobaric nor polybaricosmotic equilibrium of H2 was attained between sedimentary beds.Fluid composition was controlled in each bed by the inherentbuffer capacity of the solid phases. Despite the effects ofprogressive dehydration during metamorphism, the buffer capacitiesof the mineral assemblages were sufficiently great that vestigesof premetamorphic heterogeneity of volatile components havebeen preserved. 相似文献
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Lithology and Mineral Resources - 相似文献
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The Square Top intrusion, near Nundle, New South Wales, revealsin its mineralogy and chemistry the transition of analcime-olivinetheralite to analcime tinguaite. Chemical, X-ray, and opticaldata are presented on 2 plagioclases, 9 alkali feldspars, 2nephelines and 3 analcimes, from various members of the differentiationsequence. With differentiation, plagio-clase becomes enrichedin Ab and, to a lesser extent, in Or. The coexisting alkalifeldspars initially reveal enrichment in Ab and trend from sanidineto lime anorthoclase; subsequently in the tinguaites, the sanidinesbecome enriched in Or. Nephelines in the lower theralites havehighly sodic compositions and become slightly enriched in Kin the later differentiates. Replacement of Si by NaAl in theanalcimes decreases with progressive differentiation. The rapidcooling of this relatively small intrusion assisted fractionalcrystallization, and resulted in the preservation of disorderedplagioclase and alkali feldspars. The Square Top feldspar crystallizationtrends are compared with trends presented by Tuttle and Bowen(1958). The location of the feldspar boundary curve in the Ab–An–Orsystem and some general relationships in the undersaturatedportion of the Ne–Ks–Qz system, including the heteromorphicfelsic assemblages developed from the lowest temperature liquids,are also discussed. 相似文献
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Bridget Y. Lynne Kathleen A. Campbell Joseph Moore P.R.L. Browne 《Sedimentary Geology》2008,210(3-4):111-131
Siliceous hot spring deposits from Steamboat Springs, Nevada, U.S.A., record a complex interplay of multiple, changing, primary environmental conditions, fluid overprinting and diagenesis. Consequently these deposits reflect dynamic geologic and geothermal processes. Two surface sinters were examined—the high terrace, and the distal apron-slope, as well as 13.11 m (43 ft) of core material from drill hole SNLG 87-29. The high terrace sinter consists of vitreous and massive-mottled silica horizons, while the distal deposit and core comprise dominantly porous, indurated fragmental sinters. Collectively, the three sinter deposits archive a complete sequence of silica phase diagenetic minerals from opal-A to quartz. X-ray powder diffraction analyses and infrared spectroscopy of the sinters indicate that the distal apron-slope consists of opal-A and opal-A/CT mineralogy; the core yielded opal-A/CT and opal-CT with minor opal-A; and the high terrace constitutes opal-C, moganite, and quartz. Mineralogical maturation of the deposit produced alternating nano–micro–nano-sized silica particle changes. Based on filament diameters of microbial fossils preserved within the sinter, discharging thermal outflows fluctuated between low-temperatures (< 35 °C, coarse filaments) and mid-temperatures ( 35–60 °C, fine filaments). Despite transformation to quartz, primary coarse and fine filaments were preserved in the high terrace sinter. AMS 14C dating of pollen from three horizons within core SNLG 87-29, from depths of 8.13 to 8.21 m (26′8″ to 26′11″), 10.13 to 10.21 m (33′3″ to 33′6″), and 14.81 to 14.88 m (48′7″ to 48′10″), yielded dates of 8684 ± 64 years, 11,493 ± 70 years and 6283 ±60 years, respectively. In the upper section of the core, the stratigraphically out-of-sequence age likely reflects physical mixing of younger sinter with quartzose sinter fragments derived from the high terrace. Within single horizons, mineralogical and morphological components of the sinter matrix were spatially patchy. Overall, the deposit was modified by sub-surface flow of alkali-chloride thermal fluids depositing a second generation of silica, and periodically, by acidic steam condensate formed during periods when the water table was low. Local faulting produced considerable fracturing of the sinter. Hence, the Steamboat Springs sinter experienced a complex history of primary and secondary hydrothermal, geologic and diagenetic events, and their inter-relationships and effects are locked within the physical, chemical and biological signatures of the deposit. 相似文献
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The alpine-type peridotite at Burro Mountain is a partiallyserpentinized harzburgite-dunite body approximately 2 km indiameter. It lies in a chaotic mélange derived from theFranciscan Formation (Upper Jurassic to Upper Cretaceous) ofthe southern Coast Ranges of California. The peridotite is boundedon the east by a vertical fault in the Nacimiento fault zonethat brings sedimentary rocks of Taliaferro's (1943b) AsuncionGroup (Upper Cretaceous) into contact with the peridotite. Theperidotite appears to be one of a number of tectonic lenses,having a wide range in size, that make up the mélange.These lenses include metagraywacke, metachert, greenstone, amphibolite,and blueschist, as well as ultramafic rocks, and represent awide range of pressure-temperature environments. The outer shell of the peridotite is a sheared serpentinitezone 10–15 m thick. The peridotite was tectonically emplacedat its present level as a cold solid mass and had little effecton the mineral assemblages of the Franciscan Formation. Localdevelopment of lawsonite and aragonite in shear zones may berelated to the peridotite emplacement. Foliated harzburgite forms approximately 60 per cent of theperidotite. It is a lithologically uniform rock that has anolivine: orthopyroxene ratio of approximately 75:25. Accessoryclinopyroxene and chromian spinel generally make up less than5 per cent of the harzburgite. Dunite, composed of olivine,accessory chromian spinel (< 5 per cent), and trace amountsof pyroxene, makes up approximately 40 per cent of the peridotiteand occurs as dikes, sills, and irregular bodies in the harzburgite. Olivine and pyroxene show small but significant compositionalvariations and chromian spinel shows a large range in the cationratio Cr/(Cr+Al+ Fe3+). The compositional variations in theseminerals are related to original differences in bulk chemicalcomposition. The following compositional ranges were determinedfor minerals in the harzburgite: olivine, Fo91.1–Fo91.4;orthopyroxene, En89.8–En91.1; clinopyroxene, Ca47.0Mg50.0Fe3.0–Ca48.7Mg48.2Fe3.1;chromian spinel, Cr/(Cr+Al+Fe3+) 0.37–0.55. The pyroxeneshave a range in A12O3 content of 1.3–3.0 wt per cent.Olivine from dunite ranges from Fo91 to Fo92 7 and the chromianspinel has a range in the Cr/(Cr+Al+Fe3+) ratio of 0.30–0.75.Although all the dunites are lithologically similar, three distincttypes are recognized on the basis of composition of coexistingolivine and chromian spinel. Structural relations between thethree types of dunite suggest three periods of emplacement (possiblyoverlapping) of dunite into harzburgite. The evidence indicatesthat the dunite, and probably also the harzburgite crystallizedfrom an ultramafic magma, probably in the upper mantle. After the magmatic episode and crystallization, the peridotitewas subjected to a deep-seated plastic deformation and recrystallization.The first phase of the deformation produced a pervasive, planarstructural element (S1) that crosscuts many harzburgite-dunitecontacts. It is probable that some of the dunite sills wereemplaced during this deformation. The foliation, S1, is definedby layers of different orthopyroxene content in harzburgite,and by discontinuous layers of chromian spinel in dunite. Flowor slip along S1 produced slip folds in harzburgite—dunitecontacts with axial planes parallel to S1. At a later stage,isoclinal folds developed in S1, and the present olivine microfabricwas probably formed by recrystallization in the stress fieldthat produced the isoclinal folding. In the olivine microfabric,X tends to be perpendicular to the axial planes (S2) of theisoclinal folds and Y and Z tend to form double maxima in S2approximately 90° apart. Mg–Fe2+ distribution betweencoexisting mineral pairs yields a calculated temperature offormation of approximately 1200 °C. Although this temperatureis only a nominal value, it indicates that the mineral pairsequilibrated at a significantly high temperature. In view ofthe deformation and recrystallization, the calculated temperaturepossibly represents subsolidus re-equilibration of the mineralsduring this event. The deformation and recrystallization probablyoccurred shortly after crystallization while the peridotitewas still at a high temperature. A later deep-seated deformation produced small scattered kinkfolds in S1 that tend to disrupt the major olivine microfabric.The kink folding was accompanied or followed by the developmentof kink bands in olivine that reflect intragranular glidingon the system T = [Okl], t = [100]. The kink bands probablyformed at a minimum temperature of 1000 °C. Following the deep-seated deformation, which probably took placein the mantle, the peridotite mass was tectonically detachedand moved upward to its present level in the crust. Cleavages,joints, and faults provided channels for water to pervade theperidotite and allow alteration of the primary minerals. 相似文献
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Coal beds of the Upper Cretaceous Fruitland Formation in the San Juan Basin of northwestern New Mexico and southwestern Colorado have significant liquid hydrocarbon generation potential as indicated by typical Rock-Eval Hydrogen Indexes in the range of 200–400 mg hydrocarbon/g organic carbon (type II and III organic matter). Small, non-commercial quantities of oil have been produced from the coal beds at several locations. The oils are characterized by high pristane/phytane (ca 4) and pristane/n-C17 ratios (ca 1.2), abundant C21+ alkanes in the C10+ fraction with a slight predominance of odd carbon-numbered n-alkanes, abundant branched-chain alkanes in the C15+ region, and a predominance of methylcyclohexane in the C4----C10 fraction. The oils are indigenous to the Fruitland Formation coals and probably migrated at thermal maturities corresponding to vitrinite reflectance values in the range 0.7–0.8%. Although the oils found to date are not present in commercial amounts, these findings illustrate the potential of some coals to generate and expel oil under conditions of moderate thermal heating. 相似文献
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C. D. Ollier 《Australian Journal of Earth Sciences》2013,60(3-4):431-435
The Dorrigo Plateau is covered by basalt, which is a remnant of the 18 Ma old Ebor Volcano. The centre of this volcano is an intrusion in the Bellinger Valley. The volcano was erupted on a palaeoplain of moderate relief. Subsequent uplift and tilting led to erosion of the Nambucca Beds, together with much of the volcano, and creation of a major escarpment, part of the Great Escarpment of eastern Australia. In this area the Great Escarpment is younger than 18 Ma. 相似文献