Sample records for alaskites

  1. Occurrence of parsonite, a secondary uranium mineral, in alaskite of the Wheeler Creek pluton, Alaska

    Reconnaissance investigations in the Purcell Mountains of westcentral Alaska in 1977 revealed the presence of parsonite, a hydrous phosphate of lead and uranium with the formula Pb2UO2(PO4)22H2O. This is the first reported occurrence of parsonite in Alaska. The parsonite occurs as a soft, yellow to chocolate brown coating closely associated with green muscovite on fracture surfaces in a shear zone in alaskite of the Wheeler Creek pluton. Thin magnetite veinlets are also present. The identification of parsonite was confirmed by x-ray diffraction. Delayed neutron analysis were run on samples of the Alaskite

  2. Preparation of Zinc Silicate Crystalline Glaze with Alaskite%利用白岗岩制备硅酸锌结晶釉的研究

    蒋述兴; 胡晓林


    利用白岗岩为主要原料,以氧化锌为结晶剂,以二氧化锰、氧化铜或氧化铁为着色剂,成功制备出了硅酸锌结晶釉.以晶核定位的方法解决了晶花生长杂乱的弊端;根据氧化锌、滑石和着色剂等含量不同对釉面花色的影响设计出了较好的配方;同时发现保温时间也是影响结晶大小的重要因素.用XRD对釉层物相进行分析,证明了所制备的样品是硅酸锌结晶釉.%Zinc silicate crystalline glaze was prepared with alaskite as principal raw material, ZnO as nucleation agent, and MnO2, CuO or Fe2O3 as coloring agent. The problem of the disorderly growth of crystals was solved by localizing crystal nuclei. An optimal recipe was designed after considering the influence of the content of ZnO, talcum and coloring agents on glazing effect and a fancy crystalline glaze was prepared. It was found that holding time was an important factor affecting the size of the crystallization. Analyzing the phase of the glaze layer by XRD proved that the prepared sample was zinc silicate crystalline glaze.

  3. Source of the detrital components of uraniferous conglomerates, Quirke ore zone, Elliot Lake, Ontario, Canada

    Mineral and fluid inclusions observed in the quartz pebbles in Elliot Lake uraniferous conglomerate have been investigated. From the results it is concluded that they were derived from a pegmatic, potassic (alaskitic) granite and it is demonstrated that in this source lithology, pebble-sized quartz was spatially associated with radioactive minerals, by inference, uraninite. The postulated characteristics of such a source are remarkably similar in several respects to the uraniferous alaskites of the Roessing deposit of Namibia. (U.K.)

  4. A mineralogical, petrological and geochemical study of a suite of rocks from the Damara Orogenic Belt South West Africa

    This work was a pilot study in which the petrology, mineralogy and geochemistry of a suite of rocks from the Khan/Swakop area of the Damara Orogen were investigated. Petrographic and mineralogical data are presented for about 140 samples. This data (1) assisted in the selection of suitable samples for chemical analysis; (2) aided in the classification of the samples as a basis for geochemical classification; (3) allowed the samples to be correlated with the regional geology of the area. It was found that petrographic examination alone cannot be used to distinguish between mineralised and unmineralised alaskites. Certain features although not exclusive to mineralised and unmineralised alaskites are nevertheless in general characteristic of these rocks types. the X-ray diffraction analysis indicated that mineralised alaskites, even from different localites, produced characteristic X-ray diffractograms which separated them from the rest of the rock-types including the unmineralised alaskites. The geochemical interpretation of the data showed that it was possible to distinguish between the main rock groups using both the major and trace elements. With using the trace elements only this distinction was not possible. Mineralogical relationships within the rock groups could be inferred from the geochemical results thereby complementing the petrographic investigation. It was established that in the main, mineralised alaskites are K-feldspar rich with biotite and no muscovite and that the thorium and rare-earth contents should be high

  5. Results of a paleomagnetic survey undertaken in the Damara mobile belt, South West Africa, with special reference to the magnetisation of the uraniferous pegmatitic granites

    A project study, undertaken by the Geology Division of the AEB, on the correlation between airborne magnetic and radiometric data covering a portion of the Damara Mobile Belt in South West Africa, has revealed that all the known occurrences of uranium in late- to post-tectonic leucogranite (alaskite) of the Damara orogeny are associated with negative geomagnetic anomalies. Although the uranium occurrences themselves do not display marked geomagnetic anomalies, their immediate geological environment is characterised by the negative anomalies, which are semi-regional in extent. To investigate the origin of these anomalies, the Atomic Energy Board and the Geological Survey of South Africa undertook a palaeomagnetic study of the area. Oriented cores were taken from 31 sites in the mobile belt, 18 of which were selected within the negative magnetic zones, mostly in close association with known uraniferous alaskitic granites. Palaeomagnetic evidence suggests that the negative geomagnetic anomalies are associated with a remanent magnetisation, resulting from the Damara orogenic event, whose direction is removed from the earth's present field and which has affected rocks of the Nosib Group. Absence of this stable remanent direction in rocks stratigraphically overlying the Nosib Group accounts for the distinctive geomagnetic signature, in the form of negative anomalies, of the Nosib Group. It is this signature which can be used in airborne surveys to identify rocks of the Nosib Group outcropping, or of shallow suboutcrop, in anticlinal or dome-like structures. Since the uraniferous alaskites are mostly confined stratigraphically to the Nosib Group, the negative geomagnetic anomalies form an important prospecting criterion as they may be used to delineate target areas for further exploration in areas covered by sand, scree and duricrust deposits

  6. Geology of the Spruce Pine District, Avery, Mitchell, and Yancy Counties, North Carolina

    Brobst, Donald Albert


    The Spruce Pine pegmatite district, a northeastward-trending belt 25 miles long and 10 miles wide, lies in parts of Avery, Mitchell, and Yancey Counties in the Blue Ridge Province of western North Carolina. The most abundant rocks in the district are interlayered mica and amphibole gneisses and schists, all of which are believed to be of Precambrian age. These rocks are cut by small bodies of dunite and associated rocks of Precambrian (?) age, large bodies of alaskite and associated pegmatite of early Paleozoic age, and basaltic and diabasic dikes and sills of Triassic (?) age. The rocks of the district have been weathered to saprolite that is locally 50 feet thick. The major structure in the area is a southwestward-plunging asymmetrical synclinorium that has its steeper limb on the northwest side. Feldspar, muscovite as sheet and scrap (ground) mica, and kaolin from the alaskite and associated pegmatite account for over 90 percent of the total mineral production of the district. Amounts of other pegmatite minerals, including quartz, beryl, columbite-tantalite, rare-earth and uranium minerals are an extremely small part of the mineral resources. Actual or potential products from other rocks are olivine, vermiculite, asbestos, talc, chromium and nickel, soapstone, mica schist, garnet, kyanite, dolomite marble, and construction materials.

  7. The Serra do Carambei Granite - PR and the uraniferous anomalism

    The Serra do Carambei Granite forms a pluton relatively homogeneous, covering about 33 km2, cropping out as an elongate retangular body trending NE-SW, being emplaced in the Cunhaporanga Granitoid Complex. Its characteristics indicates a kind of hololeucocratic granite, equigranular, medium to coarse-grained, consisting predominantly of microperthitic alkali-feldspar, quartz and a small amount of biotite (less than 1%), thus being classified as an alaskite. Chemical data allows a classification in the group of granite with high contents of silica (74-76% Wt. SiO2), dominantly alkaline chemism and hypersolvus character, derived from a parental magma under saturated in water with distinguished features of granitoids from the magnetite series and types I and A granites. The pluton shows important chemical variations due to weathering processes. However detailed chemical studies reveal the presence of anomalous concentrations of trace elements such as U, Sn, Nb, Y, Zr, the Serra do Carambei Granite lacks economically important mineralizations because of the absence of well-developed tardi/pos-magmatic processes that could concentrate them. The SW side of the granite is cut by leucocratic rhyolite dykes that show some radiometric anomalies. These rocks, which are highly diferentiated, were emplaced contemporaneously to the Serra do Carambei Granite. Although petrographic and chronological similarities are found between the uraniferous alaskite of Roessing (Namibia) and the Serra do Carambei Granite anyhow it was not possible to establish any lateral continuity with the uranifeous Pan-African Province. (Author)

  8. Airborne radiometric anomalies caused by late kinematic granite rocks in the Molson Lake-Red Sucker Lake area, east-central Manitoba

    Geological mapping with simultaneous ground gamma ray spectrometer surveys in an area with a chain of airborne radiometric anomalies of greater than 2 ppm eU indicate uranium enrichment in late kinematic pink leucogranitic rocks including granites, alaskites, and syenites which form dykes, stocks and small plutons in a batholithic tonalite - granodiorite complex. Field geolocial evidence suggests that the potassium-rich rocks were formed by hydrothermal solutions and that at least some of them are metasomatic replacement bodies. Results of geophysical grid survey over a pronounced anomaly indicate that it is caused by a significant volume of leucogranitic rocks with an unusually high background concentration of uranium averaging 25 ppm eU. The uranium seems to be associated with hematite which coats mineral grains and fills small fractures

  9. Measurement of X-ray mass attenuation coefficients in biological and geological samples in the energy range of 7–12 keV

    Information about X-ray mass attenuation coefficients in different materials is necessary for accurate X-ray fluorescent analysis. The X-ray mass attenuation coefficients for energy of 7–12 keV were measured in biological (Mussel and Oyster tissues, blood, hair, liver, and Cabbage leaves) and geological (Baikal sludge, soil, and Alaskite granite) samples. The measurements were carried out at the EXAFS Station of Siberian Synchrotron Radiation Center (VEPP-3). Obtained experimental mass attenuation coefficients were compared with theoretical values calculated for some samples. - Highlights: • The X-ray attenuation coefficients were measured in biological and geological samples. • The difference between the attenuation coefficients in biological samples reached 47%. • The liver sample had the smallest attenuation coefficients. • The theoretical values for liver sample differ from the experimental ones by 2%

  10. Characteristics and its uranium metallogenic potential of the granite belt between Bange and Jiali county, tibet

    The granite belt between Bange and Jiali county is a composite batholith which intruded at multistage, it con- trolled by several groups of the fault system, the alteration is developed, with the alaskite, aplite, pegmatitic vein intruded, it is type Ⅰ in the beginning of forming, and change to type S in the late time. There is a large of geochemical anomalies of uranium (U>6.8 X 10-6) in Gulu town and Sangba village, of which middle of the granite belt and Bianba county of which east of the granite belt, that anomalies area have 1200 km2, 800 km”2 and 1500 km2. All the anomalies is considered that its forming relate to batholith and its external contact, so it shows that it has favorite geological conditions for granite type uranium metallogenesis. (authors)

  11. Holocene evolution of Dahab coastline - Gulf of Aqaba, Sinai Peninsula, Egypt

    Magdy, Torab


    Dahab was a little Bedouin-village in Sinai Peninsula at the mid-western coast of Gulf of Aqaba approx. 90 km north of Sharm-el-Sheikh City and it means "gold" in Arabic language. But in the past 20 years ago it becomes one of the most tourist sites in Egypt. The basement complex is composed mostly of biotiteaplite-granite, mica-aplitegranite, granodiorite, quartzdiorite, alaskite, and diorite. Based on correlation with similar igneous in the most southern part of Sinai and the Red Sea area. Wadi Dahab composed of igneous and metamorphic rocks and the coastline is formed of the fragments of its rocks, mixed with fragments of coral reef and fluvial deposits of Wadi Dahab. The morphology of Dahab coastline is characterized by hooked marine spit, which composed of fluvial sediments carried by marine current from wadi Dahab mouth, this spit encloses shallow lagoon, but the active deposition on the lagoon bottom will evaluate it into saline marsh. This paper dealing with the evolution of Dahab spit and lagoon during the Holocene in addition to the recent time for last 100 years, and it impacts of the future management of the coast area. The coastline mapping during the period of study depends upon GIS technique for data were collected during field measuring by using total station, aerial photo and satellite image interpretation as well as soil sample dating. Suggested geomorphological evolution of Dahab area during the Holocene depending upon geomorphic investigation of the sedimentological process into 6 stages.

  12. An interpretation of the aeromagnetic data covering the western portion of the Damara orogen in South West Africa/Namibia

    A study of the aeromagnetic data covering the western portion of the Damara Orogen was undertaken in order to determine whether any additional information relating to the occurrence of uraniferous granite in the area could be derived from these data. The study included palaeomagnetic surveys and an interpretation of the regional structure, coupled with computer modelling of a geomagnetic section across the belt. A number of features are evident from this study, viz: (i) All currently known uraniferous alaskitic granite occurrences of economic interest are hallmarked, on a semi-regional basis, by prominent negative geomagnetic anomalies. (ii) A number of structural lineaments and broader lineament zones are apart from the Okahandja Lineament, recognised and named for the first time. Computer modelling studies support the hypothesis that these geomagnetic lineament zones are in fact fault-controlled geanticlinal ridges bounded by relatively rapid monoclinal downfolding of the stratigraphy: (iii) A post-F3 (north-east) structural phase, F4, oriented north-north-east is concluded to be of particular significance to the emplacement of uraniferous granite since, firstly, the major fold axes of the domes and structures with which these occurrences are associated mostly have this orientation and, secondly, the currently known occurrences are exposed along the north-north-easterly trending Welwitschia lineament zone

  13. An interpretation of the aeromagnetic data covering portion of the Damara orogenic belt, with special reference to the occurance of uraniferous granite

    This thesis comprises primarily palaeomagnetic studies within the Damara orogenic belt of South West Africa (Namibia), as well as an interpretation of the regional structure, utilizing published aeromagnetic data. Cursory interpretation of the airborne radiometric data is also undertaken. Gravity traverses, conducted across three dome structures with which uranium mineralisation is intimately associated, are interpreted in order to determine the origin of these structures. A number of features, having an important bearing on both the uraniferous granite occurrences and the regional structure of the area, are recognised for the first time in this study, viz.: a) all currently known uraniferous alaskitic granite occurences of economic interest are hallmarked. b) Virtual geomagnetic poles were derived for the 500 Ma tectonothermal event and for the basement rocks in the area. c) A close correlation exists between positive magnetic anomalies and high radiometric responses over the red granites, reactivated basement and over the Salem Granite Suite and other late- to post-tectonic granites. d) a number of structural lineaments and broader lineament zones are, apart from the Okahandja lineament, identified and named for the first time. e) A post-F3 (northeast) structural phase, F4, is recognised as being a major structural event of particular significance to the emplacement of uraniferous granite. f) The gravity studies indicate that the investigated dome structures result from an interplay between both vertical and lateral stress components

  14. Mid to late proterozoic magmatism within Northeastern North America and its implications for the growth of the continental crust

    Recent studies of the mangerite-charnockite-alaskite suite exposed in the Adirondack Highlands strongly suggest that these rocks were emplaced under anorogenic, or mildly extensional, conditions. The characteristic signatures of the rocks are high (FeO/FeO+MgO) and (FeO/Fe2O3); mildly alkaline to subalkaline and metaluminous trends; high Ga/Al2O3; and within plate concentrations of Nb vs Y, Ta vs Yb, Rb vs (Y+Nb), and Rb vs (Yb+Ta). Evolved members of the series are low in CaO and MgO and high in alkalies and halogens. All of these properties are consistent with anorogenic magmatism comprising acidic crustal melts and mantle derived mafic additions to the crust. Major and minor element trends, as well as field evidence, strongly suggest that the anorogenic acidic suite is coeval, but not comagmatic, with closely associated anorthositic massifs. Present outcrop configurations are consistent with the evolution of the acidic and anorthositic rocks in zoned, bimodal magma chambers cored by the mafic constituents and overlain by explosive, caldera-type volcanism. Age determinations indicate that the emplacement of the anorthosite-charnockite suite extended over approximately 500 Ma in the Grenville and adjacent Nain, Provinces

  15. U-Pb zircon geochronology and evolution of some Adirondack meta-igneous rocks

    Mclelland, J. M.


    An update was presented of the recent U-Pb isotope geochronology and models for evolution of some of the meta-igneous rocks of the Adirondacks, New York. Uranium-lead zircon data from charnockites and mangerites and on baddeleyite from anorthosite suggest that the emplacement of these rocks into a stable crust took place in the range 1160 to 1130 Ma. Granulite facies metamorphism was approximately 1050 Ma as indicated by metamorphic zircon and sphene ages of the anorthosite and by development of magmatitic alaskitic gneiss. The concentric isotherms that are observed in this area are due to later doming. However, an older contact metamorphic aureole associated with anorthosite intrusion is observed where wollastonite develops in metacarbonates. Zenoliths found in the anorthosite indicate a metamorphic event prior to anorthosite emplacement. The most probable mechanism for anorthosite genesis is thought to be ponding of gabbroic magmas at the Moho. The emplacement of the anorogenic anorthosite-mangerite-charnockite suite was apparently bracketed by compressional orogenies.

  16. Magnetite deposits near Klukwan and Haines, southeastern Alaska

    Robertson, Eugene C.


    Low-grade iron ore is found in magnetite-bearing pyroxenite bodies near Klukwan and Haines in Southeastern Alaska. An alluvial fan at Haines also contains magnetite-bearing rock of possible economic significance. The Haines-Klukwan area is underlain by rocks of Mesozoic Including epidote diorite, quartz diorite, and alaskite of the Coast Range batholith, metabasalt (recrystallized lava flows and pyroclastic rocks), and, in the southern part, interbedded slate and limestone. Layering and foliation, where perceptible, generally strike northwest and dip steeply northeast. The iron deposits are found at or near the contact between the metabasalt and epidote diorite; they appear to represent highly-altered lava flows that were metamorphosed during the emplacement of the batholith. Several billion tens of rock containing about 13 percent magnetic iron are included in the pyroxenite body at Klukwan. Sampling and dip-needle data suggest the presence there of two or three tabular aches in which the rock has an average magnetic iron content of 20 percent or more. Pyroxenite bodies outcropping in three areas near Haines apparently are lower in grade than the Klukwan deposit; lack of exposures prevented thorough sampling but reconnaissance traverses with a dip needle failed to reveal important zones of high-grade iron ore. An alluvial fan adjoining the pyroxenite body at Klukwan contains several hundred million tons of broken rock having a magneticiron content of about 10 percent.

  17. International Uranium Resources Evaluation Project (IUREP) national favourability studies: Greece

    Greece, with an area of 131,944 km2, has been actively explored since 1971 under a programme of co-operation with UNDP and IAEA on which close to US $1 million have been spent so far. The programme is focused on the Rhodope Precambrian massif, which is the most attractive structural unit from the geological point of view. The indications available at present, and which have been known for a long time, are also to be found in this unit. They are associated either with Tertiary continental volcanism or with detritic sediments in basins covering this massif. So far there is no evidence of their being of any economic value. The paucity of data available on the basement of the Rhodope precludes any prediction as to the possibility of its containing Pre-cambrian uranium mineralizations. One might perhaps think in terms of mineralizations of the alaskite or alkaline complex type, or also of vein-type deposits. But it is primarily in the deposits associated with tertiary trachy-rhyolitic volcanism that we have most confidence, especially in the Rhodope massif and the Vardar region but possibly elsewhere in the Hellenides as well. All things considered, we place Greece in Group 2 of the IUREP classification. (author)

  18. International Uranium Resources Evaluation Project (IUREP) national favourability studies: Burma

    Kyatpyin, near Mogok; radioactive iron ore at Pangpet, near Taunggyi, Southern Shan States and radioactive fossil wood from Central Burma. From structural point of view the most favourable geological environments for new discoveries are those in the Central, Basin, or as it is named Irrawaddy Basin and Shan Plateau massif. Sedimentary rocks of enormous thickness were formed, in the intramountain Irrawaddy Basin during the Tertiary Period. There is no information about the facies of the sediments but it could be supposed that most of these strata were deposited either in fans or rivers and have features of fluvial facies which is most favourable for uranium concentration leached from surrounding granites and alaskite in Shan plateau massif. The radioactive fossil wood from Central Burma may be an indication for uranium favourability of this basin. The known uranium occurrences in Mogok Belt could be considered, as indicative of some uranium potential of the region mainly of the alaskite and the areas around it. There is also potential in the Tawang Peng area of the Northern Shan States, where the famous multi-metal Bawdwin mine is located in a series of rhyolitic tuffs, lava flows and breccias, interspersed with coarse feldspathic grits of early Paleozoic age. The speculative potential could be about 10,000 tonnes uranium

  19. Investigation of the mineral potential of the Clipper Gap, Lone Mountain-Weepah, and Pipe Spring plutons, Nevada

    The Clipper Gap pluton, composed mostly of quartz monzonite with minor granite, granodiorite, and crosscutting alaskite dikes, intrudes Paleozoic western facies strata. A narrow zone of contact metamorphism is present at the intrusive-sediment contact. No mineral production has been recorded from Clipper Gap, but quartz veins containing gold-silver-copper mineral occurrences have been prospected there from the late 1800's to the present. Areas of the Lone Mountain-Weepah plutons that were studied are located in Esmeralda County about 14 km west of Tonopah, Nevada. At Lone Mountain, a Cretaceous intrusive cuts folded Precambrian and Cambrian sediments. Lead-zinc ores have been mined from small replacement ore bodies in the Alpine district, west of Lone Mountain. Copper and molybdenum occurrences have been found along the east flank of Lone Mountain, and altered areas were noted in intrusive outcrops around the south end of Lone Mountain. Mineral occurrences are widespread and varied with mining activity dating back to the 1860's. The Pipe Spring pluton study area is flanked by two important mining districts, Manhattan to the north and Belmont to the northeast. Mining activity at Belmont dates from 1865. Activity at Manhattan was mainly between 1907 and 1947, but the district is active at the present time (1979). Four smaller mining areas, Monarch, Spanish Springs, Baxter Spring, and Willow Springs, are within the general boundary of the area. The Pipe Spring pluton study area contains numerous prospects along the northern contact zone of the pluton. Tungsten-bearing veins occur within the pluton near Spanish Springs, with potential for gold-tungsten placer in the Ralston Valley. Nickel and associated metals occur at Willow Spring and Monarch Ranch, where prospects may be associated with the margin of the Big Ten Peak Caldera

  20. International Uranium Resources Evaluation Project (IUREP) national favourability studies: Nigaragua

    On invitation of the Nicaraguan Government, the U. S. Atomic Energy Commission conducted a reconnaissance for uranium in March, 1953. Operating and abandoned mines, as well as prospects, formations, contacts, dikes and sills enroute to these mines were tested by scintillometer. Reconnaissance included two mineralized areas exposed in windows within the volcanic belt but did not include the schists and granitic intrusions in the north eastern part of the country. No anomalous radioactivity was detected. No uranium occurrences were discovered during the 1953 reconnaissance and no uranium deposits or prospects are indicated on the metallogenetic map of Central America or in the bibliography of Nicaraguan geology. Information is net available on current exploration in Nicaragua. All subsoil mineral resources besides quarry materials belong to the state. In the interest of national defence, uranium, thorium, lithium and their derivatives, along with certain other mineral substances, may be classified as of temporary strategic interest, and their exploration or exploitation would then be subject to special laws. The Ministry of Economy may establish permanent or temporary national reserves on which mining activities are essentially precluded. Foreign nationals and corporations may acquire mineral concessions although particular regulations may be applicable to such an acquisition. Exploration of any favourable formations has been hindered by volcanic ash cover in western Nicaragua and dense vegetation in the East. Little geologic work has been done on the Paleozoic metamorphic rocks or Todos Santos Formation of the Northern Highlands. These could possibly show some potential for discovery of uranium as might the alaskites near Siuna. The potential resources of Nicaragua are estimated at less than 1,000 tonnes uranium

  1. Paleomagnetism of the Middle Proterozoic Electra Lake Gabbro, Needle Mountains, southwestern Colorado

    Harlan, S.S.; Geissman, J.W.


    The Electra Lake Gabbro is a small 1.435 Ga pluton that intrudes 1.7 to 1.6 Ga gneisses and schists of the Needle Mountains in southwestern Colorado. Paleomagnetic samples were collected from the main phases of the gabbro, diabase dikes, granite, and alaskite dikes that cut the gabbro and from a partially melted zone in gneiss along the southern margin of the pluton. Gabbro, diabase, and some melt zone samples have a single-polarity characteristic magnetization of northeast declination (D) and moderate negative inclination (I). Demagnetization behavior and rock magnetic characteristics indicate that the remanence is carried by nearly pure magnetite. After correction for the minor west dip of overlying Paleozoic strata, we obtain a mean direction of D = 32.1??, I = -41.9?? (k = 94, ??95 = 3.3??, N = 21 sites) and a paleomagnetic pole at 21.1?? S, 221.1 ??E, (K= 89, A95 = 3.4??). This pole is similar to poles from the Middle Proterozoic Belt Supergroup but is located at a higher southerly latitude than poles from other 1.47-1.44 Ga plutons from North America, most of which plot at equatorial latitudes. The reason for this discrepancy is not clear but may result from a combination of factors, including unrecognized tilting of the gabbro, the failure of this relatively small pluton to fully average paleosecular variation, and uncertainties in the overall reliability of other 1.5-1.4 Ga poles of the North American apparent polar wander path.

  2. K-Ar geochronology of basement rocks on the northern flank of the Huancabama deflection, Ecuador

    Feininger, Tomas; Silberman, M.L.


    The Huancabamba deflection, a major Andean orocline located at the Ecuador-Peru border, constitutes an important geologic boundary on the Pacific coast of South America. Crust to the north of the deflection is oceanic and the basement is composed of basic igneous rocks of Cretaceous age, whereas crust to the south is continental and felsic rocks of Precambrian to Cretaceous age make up the basement. The northern flank of the Huancabamba Deflection in El Oro Province, Ecuador, is underlain by Precambrian polymetamorphic basic rocks of the Piedras Group; shale, siltstone, sandstone, and their metamorphosed equivalents in the Tahuin Group (in part of Devonian age); concordant syntectonic granitic rocks; quartz diorite and alaskite of the Maroabeli pluton; a protrusion of serpentinized harzburgite that contains a large inclusion of blueschist-facies metamorphic rocks, the Raspas Formation, and metamorphic rocks north of the La Palma fault. Biotite from gneiss of the Tahuin Group yields a Late Triassic K-Ar age (210 ? 8 m.y.). This is interpreted as an uplift age and is consistent with a regional metamorphism of Paleozoic age. A nearby sample from the Piedras Group that yielded a hornblende K-Ar age of 196 ? 8 m.y. was affected by the same metamorphic event. Biotite from quartz diorite of the mesozonal Maroabeli pluton yields a Late Triassic age (214 ? 6 m.y.) which is interpreted as an uplift age which may be only slightly younger than the age of magmatic crystallization. Emplacement of the pluton may postdate regional metamorphism of the Tahuin Group. Phengite from politic schist of the Raspas Formation yields an Early Cretaceous K-Ar age (132 ? 5 m.y.). This age is believed to date the isostatic rise of the encasing serpentinized harzburgite as movement along a subjacent subduction zone ceased, and it is synchronous with the age of the youngest lavas of a coeval volcanic arc in eastern Ecuador. A Late Cretaceous K-Ar age (74.4 ? 1.1 m.y.) from hornblende in

  3. Origin of the Lyme Dome and implications for the timing of multiple Alleghanian deformational and intrusive events in southern Connecticut

    Walsh, G.J.; Aleinikoff, J.N.; Wintsch, R.P.


    Geologic mapping, structural analysis, and geochronology in the area of the Lyme dome, southern Connecticut provides constraints on the origin of the rocks in the core of the dome, the absolute timing of the principal deformational and thermal events attributed to Alleghanian orogenesis, and the processes that generated the dome. Detrital zircon geochronology in combination with ages on intrusive rocks brackets the deposition of quartzite in the core of the dome sometime between ca. 925 and 620 Ma. Granite and granodiorite intruded the Neoproteorozic metasedimentary rocks in the core of the dome at ca. 620 to 610 Ma. Four major early Permian events associated with the Alleghanian orogeny affected the rocks in the Lyme dome area. Syn-tectonic migmatization and widespread penetrative deformation (D1, ca. 300 - 290 Ma) included emplacement of alaskite at 290 ?? 4 Ma during regional foliation development and aluminosilicate-orthoclase metamorphic conditions. Rocks of the Avalon terrane may have wedged between Gander cover rocks and Gander basement in the core of the Lyme during D1. Limited structural evidence for diapiric uplift of the Lyme dome indicates that diapirism started late in D1 and was completed by D2 (ca. 290 - 280 Ma) when horizontal WNW contractional stresses dominated over vertical stresses. Second sillimanite metamorphism continued and syn-tectonic D2 granite pegmatite (288 ?? 4 Ma) and the Joshua Rock Granite Gniess (284 ?? 3 Ma) intruded at this time. North-northwest extension during D3 (ca. 280 - 275 Ma) led to granitic pegmatite intrusion along S3 cleavage planes and in extensional zones in boudin necks during hydraulic failure and decompression melting. Intrusion of a Westerly Granite dike at 275 ?? 4 Ma suggests that D3 extension was active, and perhaps concluding, by ca. 275 Ma. Late randomly oriented but gently dipping pegmatite dikes record a final stage of intrusion during D4 (ca. 275 - 260 Ma), and a switch from NNW extension to vertical

  4. Gamma-spectrometric surveys in differentiated granites. II: the Joaquim Murtinho Granite in the Cunhaporanga Granitic Complex, Parana, SE Brazil; Levantamentos gamaespectrometricos em granitos diferenciados. II: O exemplo do Granito Joaquim Murtinho, Complexo Granitico Cunhaporanga, Parana

    Ferreira, Francisco Jose Fonseca [Universidade Federal do Parana (UFPR), Curitiba, PR (Brazil). Dept. de Geologia. Lab. de Pesquisas em Geofisica Aplicada; Fruchting, Allan [Votorantim Metais, Sao Paulo, SP (Brazil)], e-mail:; Guimaraes, Gilson Burigo [Universidade Estadual de Ponta Grossa (UEPG), PR (Brazil). Dept. de Geociencias], e-mail:; Alves, Luizemara Soares [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil)], e-mail:; Martin, Victor Miguel Oliveira; Ulbrich, Horstpeter Herberto Gustavo Jose [Universidade de Sao Paulo (USP), SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica], e-mail:, e-mail:


    Detailed mapping at the NW corner of the large Neo proterozoic Cunhaporanga Granitic Complex (CGC), Parana state, SE Brazil, redefined the Joaquim Murtinho Granite (JMG), a late intrusion in CGC with an exposed area of about 10 km{sup 2}, made up mainly by evolved 'alaskites' (alkali-feldspar leuco granites). This unit is in tectonic contact with the Neoproterozoic-Eocambrian volcano-sedimentary Castro Group, to the W, and is intrusive into other less evolved granitic units of the CGC to the E. Petrographically, JMG shows mainly mesoperthite and quartz, with subordinate amounts of altered micas and some accessory phases, mainly zircon. The equi to inequigranular granites are usually deformed with cataclastic textures, are often brecciated, and may have miarolitic structures. Formation of late albite, sericite, carbonate and hematite was caused by deuteric and hydrothermal alteration. A gamma-ray spectrometric survey at 231 stations which measured total counts (TC), Ueq K%, eU ppm and eTh ppm was used to construct several direct and derived maps. Compared to neighboring units the JMG has significant anomalies, especially in the TC, %K, eTh and eU maps, although the differences are less obvious in some derived maps. These evolved granites are enriched in these three elements. Geochemical behavior of K, Th and U is used to analyse the results observed in maps. Enhanced weathering under a subtropical climate with moderate to high average temperatures and heavy rainfall affects mainly feldspars and biotite, and may also destabilize most U and Th-bearing accessory phases. Th is most likely retained in restite minerals in soils, being relatively immobile, while part of U may migrate as uranyl ion in oxidizing media. K is especially affected by feldspar alteration to K-free clays (mainly kaolinite), and may be completely leached. Gamma-ray spectrometric methods are valid tools to study facies in granitic rocks, especially in those that are enriched in K, Th and U

  5. Is there a geochemical link between volcanic and plutonic rocks in the Organ Mountains caldera?

    Memeti, V.; Davidson, J.


    Results from separate volcanic and plutonic studies have led to inconsistent conclusions regarding the origins and thus links between volcanic and plutonic systems in continental arcs and the magmatic processes and time scales responsible for their compositional variations. Some have suggested that there is a geochemical and geochronological disconnect between volcanic and plutonic rocks and hence have questioned the existence of magma mush columns beneath active volcanoes. Investigating contemporary volcanic and plutonic rocks that are spatially connected is thus critical in exploring these issues. The ca. 36 Ma Organ Mountains caldera in New Mexico, USA, represents such a system exposing contemporaneous volcanic and plutonic rocks juxtaposed at the surface due to tilting during extensional tectonics along the Rio Grande Rift. Detailed geologic and structural mapping [1] and 40Ar/39Ar ages of both volcanics and plutons [2] demonstrate the spatial and temporal connection of both rock types with active magmatism over >2.5 myr. Three caldera-forming ignimbrites erupted within 600 kyr [2] from this system with a total erupted volume of 500-1,000 km3 as well as less voluminous pre- and post-caldera trachyte and andesite lavas. The ignimbrite sequence ranges from a crystal-poor, high-SiO2 rhyolite at the base to a more crystal-rich, low-SiO2 rhyolite at the top. Compositional zoning with quartz-monzonite at the base grading to syenite and alaskite at the top is also found in the Organ Needle pluton, the main intrusion, which is interpreted to be the source for the ignimbrites [1]. Other contemporaneous and slightly younger plutons have dioritic to leucogranitic compositions. We examined both volcanic and plutonic rocks with petrography and their textural variations with color cathodoluminescence, and used whole rock element and Sr, Nd and Pb isotope geochemistry to constrain magma compositions and origins. Electron microprobe analyses on feldspars have been completed to

  6. Genesis of rare-metal pegmatites and alkaline apatite-fluorite rocks of Burpala massi, Northern Baikal folded zone

    Sotnikova, Irina; Vladykin, Nikolai


    Burpalinsky rare metal alkaline massif in the Northern Baikal folded zone in southern margin of Siberian Platform, is a of intrusion central type, created 287 Ma covering area of about 250 km2. It is composed of nepheline syenites and pulaskites grading to quartz syenites in the contacts. Veines and dykes are represented by shonkinites, sodalite syenite, leucocratic granophyres, alkali granites and numerous rare metal alkaline syenite pegmatites and two dykes of carbonatites. All rocks except for granites are cut by a large apatite-fluorite dyke rocks with mica and magnetite, which in turn is cut by alaskite granites dyke. The massif has been studied by A.M. Portnov, A.A. Ganzeev et al. (1992) Burpalinsky massif is highly enriched with trace elements, which are concentrated in pegmatite dykes. About 70 rare-metal minerals we found in massif. Zr-silicates: zircon, eudialyte, lovenite, Ti-lovenite, velerite, burpalite, seidozerite, Ca- seidozerite, Rosenbuschite, vlasovite, katapleite, Ca-katapleite, elpidite. Ti- minerals:- sphene, astrophyllite, ramsaite, Mn-neptunite bafertisite, chevkinite, Mn-ilmenite, pirofanite, Sr-perrerit, landauite, rutile, anatase, brookite; TR- minerals - loparite, metaloparite, britolite, rinkolite, melanocerite, bastnesite, parisite, ankilite, monazite, fluocerite, TR-apatite; Nb- minerals - pyrochlore, loparite. Other rare minerals leucophanite, hambergite, pyrochlore, betafite, torite, thorianite, tayniolite, brewsterite, cryolite and others. We have proposed a new scheme massif: shonkinites - nepheline syenites - alkaline syenite - quartz syenites - veined rocks: mariupolites, rare-metal pegmatites, apatite, fluorite rock alyaskite and alkaline granites and carbonatites (Sotnikova, 2009). Apatite-fluorite rocks are found in the central part of massif. This is a large vein body of 2 km length and a 20 m width cutting prevailing pulaskites. Previously, these rocks were regarded as hydrothermal low-temperature phase. New geological and