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1.
Age determinations mostly by Rb/Sr whole rock isochrons of the Precambrian rocks of Rajasthan in northwest India are summarized
and discussed. On present sampling and subject to its possible bias, the following conclusions can be made. The Untala Granite
believed to be intrusive into the gneissic terrain (bgc) east of Udaipur has the oldest age, 2.95 b.y. yet measured for a granite in Rajasthan. This, coupled with the lead isochron
age of 3.5 b.y. for detrital zircon from the Aravalli schists by Vinogradov and others extends the basement of Rajasthan well
into the Archaean. The time equivalence of thebgc east of Udaipur with the Berach Granite dated only at 2.55 b.y. is not tenable. No satisfactory radiometric age control exists
for the onset and duration of the Aravalli Supergroup, believed to be an early Proterozoic linear belt.
Heron’s original Delhi Supergroup has recorded acid magmatism widely separate in space and time. The earliest activity between
1700 and 1500 m.y. is recorded mainly in the Alwar basin in northeastern Rajasthan while the younger activity between 850
and 750 m.y. is represented by the ‘Erinpura type’ granites in the central and southern Aravalli sector. This younger event
not only has let its thermal overprinting on the older Alwar rocks but also marks the onset of emplacement of the Malani Igneous
suite in the trans-Aravalli terrain. This raises the new possibility that the Delhi rocks of Heron represent atleast two chronologically
independent sequences with varying geographical extent. The trans-Aravalli terrain is most probably floored by partly reworked,
crystalline basement and developed along linear rift zones which acted as loci for high heat flow and igneous activity since
about 800 m.y. ago. 相似文献
2.
Partial melting experiments on Nigerian charnockitic monzonite associated with migmatised gneisses provide consanguineous liquids from which the metaluminous and peraluminous younger granites may be derived. After 40–60% melting at 750–800° C the liquids are metaluminous with hastingsite-fayalite granite affinities. On cooling towards the granite system minimum these liquids can evolve into metaluminous hastingsite-biotite granite and peraluminous biotite granite compositions. These experiments show that partial melting of charnockitic monzonites cannot yield peralkaline liquids at the specified conditions (750–850° C).Syenitic rocks of this province may either reflect the action of late stage albitising fluids on residual charnockitic material after partial melt extraction or the collection of feldspar floated from a hastingsite-fayalite granite liquid. 相似文献
3.
Claude J. Allègre Francis Albarède Marc Grünenfelder Dr. Viktor Köppel 《Contributions to Mineralogy and Petrology》1974,43(3):163-194
Based on regular arrays in a U-Pb diagram of data points of zircons from polymetamorphic rocks of the Alps quantitative models are developed that include several episodic lead losses, continuous lead losses during discrete periods and combinations of both.The data from the Alps can be explained by assuming an initial age of the zircons of 2000 and/or 2500–2600 m.y. and three episodic lead losses 520–580 m.y., 300 m.y. and 30 m.y. ago with regionally varying intensities of the events as can be seen from the efficiency parameters which define the shape of the discordia. On the other hand, zircon data from North American basement rocks satisfy a model assuming a discrete interval of continuous lead loss that starts with the time of uplift of the rocks.The Th-U-Pb diagrams are valuable for recognising whether the history of the zircons and their host rock is a complex one or not which is not always noticeable in a U-Pb diagram. 相似文献
4.
The Neoproterozoic Malani magmatism of the northwestern Indian shield: implications for crust-building processes 总被引：1，自引：0，他引：1
Kamal K. Sharma 《Journal of Earth System Science》2004,113(4):795-807
Malani is the largest event of anorogenic felsic magmatism (covering ∼50, 000 km2) in India. This magmatic activity took place at ∼750 Ma post-dating the Erinpura granite (850 Ma) and ended prior to Marwar
Supergroup (680 Ma) sedimentation. Malani eruptions occurred mostly on land, but locally sub-aqueous conditions are shown
by the presence of conglomerate, grits and pillow lava. The Malani rocks do not show any type of regional deformation effects.
The Malanis are characterised by bimodal volcanism with a dominant felsic component, followed by granitic plutonism and a
terminal dyke phase. An angular unconformity between Malani lavas and basement is observed, with the presence of conglomerate
at Sindreth, Diri, and Kankani. This indicates that the crust was quite stable and peneplained prior to the Malani activity.
Similarly, the absence of any thrust zone, tectonic mélange and tectonised contact of the Malanis with the basement goes against
a plate subduction setting for their genesis. After the closure of orogenic cycles in the Aravalli craton of the northwestern
shield, this anorogenic intraplate magmatic activity took place in a cratonic rift setting under an extensional tectonic regime. 相似文献
5.
The Teplá–Barrandian unit (TBU) of the Bohemian Massif shared a common geological history throughout the Neoproterozoic and Cambrian with the Avalonian–Cadomian terranes. The Neoproterozoic evolution of an active plate margin in the Teplá–Barrandian is similar to Avalonian rocks in Newfoundland, whereas the Cambrian transtension and related calc-alkaline plutons are reminiscent of the Cadomian Ossa–Morena Zone and the Armorican Massif in western Europe. The Neoproterozoic evolution of the Teplá–Barrandian unit fits well with that of the Lausitz area (Saxothuringian unit), but is significantly distinct from the history of the Moravo–Silesian unit.The oldest volcanic activity in the Bohemian Massif is dated at 609+17/−19 Ma (U–Pb upper intercept). Subduction-related volcanic rocks have been dated from 585±7 to 568±3 Ma (lower intercept, rhyolite boulders), which pre-dates the age of sedimentation of the Cadomian flysch (
t
chovice Group). Accretion, uplift and erosion of the volcanic arc is documented by the Neoproterozoic Dob
í
conglomerate of the upper part of the flysch. The intrusion age of 541+7/−8 Ma from the Zgorzelec granodiorite is interpreted as a minimum age of the Neoproterozoic sequence. The Neoproterozoic crust was tilted and subsequently early Cambrian intrusions dated at 522±2 Ma (T
ovice granite), 524±3 Ma (V
epadly granodiorite), 523±3 Ma (Smr
ovice tonalite), 523±1 Ma (Smr
ovice gabbro) and 524±0.8 Ma (Orlovice gabbro) were emplaced into transtensive shear zones. 相似文献
6.
Isotopic age determinations on granitic rocks from Tasmania 总被引：1，自引：1，他引：0
Potassium‐argon and rubidium‐strontium isotopic age measurements show that emplacement of granitic rocks in Tasmania occurred during the Late Devonian and Early Carboniferous and in pre‐Devonian times, possibly in the Cambrian. In addition, a Precambrian granite, dated at about 750 m.y., has been recognized on the west coast of King Island. The granitic bodies of pre‐Devonian age include the Murchison River Granite, the Dove River Granite and its correlatives, and the adamellite on the southwest coast of Tasmania at Elliott Bay. These rocks were deformed during the Devonian Tabberabberan Orogeny with the result that leakage of radiogenic daughter products has occurred from minerals. Hence the indicated ages are younger than the true ages. Possibly these granitic rocks were emplaced during the Jukesian Movement of the Tyennan Orogeny, in the Late Cambrian, although a Precambrian age cannot be excluded for some of the bodies. As recognized by earlier workers the most important period of emplacement of granitic rocks in Tasmania was in the Middle Palaeozoic. The measured dates for this group of rocks range from 375 to 335 m.y., and indicate that intrusion occurred over an extended period from the Late Devonian to the Early or possibly Middle Carboniferous. There are distinct concentrations of measured ages at about 370 and 340 m.y. The granitic bodies of northeast Tasmania mainly yield the older age, whereas those of northwest Tasmania give the younger age. As the granites are post‐tectonic bodies the older age of about 375 m.y. provides a younger limit to the time of completion of the main folding in the Tabberabberan Orogeny, and this is consistent with the stratigraphic evidence. The evidence suggests that generation of granitic magma was initiated during the main folding associated with the Tabberabberan Orogeny, but that emplacement of the granites into the upper crust continued over a long period subsequently to the main folding phase. Alternatively, the younger granitic bodies, dated at about 340 m.y., may indicate that these rocks are related to the Early Carboniferous Kanimblan Orogeny recognized in Victoria and New South Wales; however, there is no field evidence to support such a proposition. 相似文献
7.
The mafic magmatic rocks associated with 1720–1700 Ma albitised A-type granites in the northern segment of the Aravalli orogen, NW India show evidence of metasomatism. It is, however, not clear whether the metasomatism of mafic rocks is related to the cooling of these associated granites or whether it took place much later after the emplacement of the granites on a regional scale. For this, we have investigated the mafic magmatic rocks, which occur in close association with these granites. In the Biharipur intrusive, the mafic rocks are intensely commingled with the A-type granites, whereas in the vicinity of the Dosi intrusive, the mafic rocks (clinopyroxenite) do not show any evidence of granite mingling. The commingled and metasomatised Biharipur mafics occur in contact with the albitised granites instead of original granite, indicating that the mafics were metasomatised along with the granites. This is supported by the similarity in REE and spider patterns of the intermixed mafic rocks and the albite granites. On the other hand, the Dosi mafic rocks, free from granite commingling, are scapolitised where the original diopside has been partly transformed to chlorine-rich marialites with a meionite component ranging from Me14.0 to Me16.0. The scapolite, occurring as anastomosing veins, within these rocks is also of similar composition, and the undeformed nature of these veins suggests that the scapolitisation postdates regional metamorphism in the region. Mineralogical, geochemical and Nd isotopic characteristics of the mafic rocks indicate that originally, these were clinopyroxenites, which have been altered to a monomineralic actinolite-bearing rock. The immobile incompatible trace element ratios indicate a continental tholeiite affinity for the mafics, which is in consonance with the A-type nature of the associated granites. During this metasomatic event, the mafic magmatic rocks experienced albitisation and scapolitisation, although the dominance of these processes varied on a local scale depending on the fluid composition.A whole-rock-mineral (clinopyroxene and scapolite) Sm–Nd isochron of the scapolitised clinopyroxenite at Dosi yields an age of 831 ± 15 Ma. Synthesis of this age data along with previously published geochronological data indicate an important Early Cryogenian (850–830 Ma) metasomatic event in the northern Aravalli orogen, which is also synchronous with the Erinpura granite event in the southern Aravalli orogen. 相似文献
8.
9.
Hydrochemical baseline condition of groundwater at the Mizunami underground research laboratory (MIU) 总被引：2，自引：0，他引：2
Hydrochemical conditions up to depths of 1000 m below ground level around the Mizunami Underground Research Laboratory were investigated to construct a “baseline condition model” describing the undisturbed hydrochemical environment prior to excavation of the underground facilities at Mizunami, Gifu, Japan. Groundwater chemistry in this area was classified into a Na–Ca–HCO3 type of groundwater in the upper part of sedimentary rock sequence and a Na–(Ca)–Cl type of groundwater in the deeper part of the sedimentary rock sequence and basement granite. The residence time of the groundwaters was estimated from their 14C contents to be approximately 9.3 ka in the middle part of the sedimentary rock and older than 50 ka in the deep part of the granite. The evolution processes of these groundwaters were inferred to be water–rock interactions such as weathering of plagioclase, dissolution of marine sulphate/sulphide minerals and carbonate minerals in the Na–Ca–HCO3 type of groundwater, and mixing between “low-salinity water” in the shallow part and “higher-salinity water” in the deeper part of the granite in the Na–(Ca)–Cl type of groundwater. The source of salinity in the deeper part of the granite was possibly a palaeo-hydrothermal water or a fossil seawater that recharged in the Miocene, subsequently being modified by long-term water–rock interaction. The Cl-depth trend in granitic groundwater changes at a depth of −400 m below sea level. The hydrogeological properties controlling the groundwater flow and/or mixing processes such as advection and diffusion were inferred to be different at this depth in the granite. This hydrochemical conceptual model is indispensable not only when constructing the numerical model for evaluating the hydrochemical disturbance during construction and operation of the MIU facility, but also when confirming a hydrogeological model. 相似文献
10.
A.P. Tewari 《Tectonophysics》1981,73(4):285-294
To the south of the Great Himalaya Range in Kashmir, a group of metasedimentary rocks with altered ultrabasic rocks occur physically over the migmatitic complex, as a klippe. The best exposure of it is met with in the Kudi nala, west of Sumjam, where lensoid outcrops of basic and ultramafic rocks, comprising actinolite—tremolite rock intruded by garnetiferous amphibolite occur within the marble, calc-gneiss and graphitic schist-gneiss. These rocks occur at an altitude of 5000–5500 m and the underlying rocks comprise gneiss, migmatite, schist, etc.The klippe of the metasedimentaries with the basic and ultrabasic suite of rocks, shows a synclinal disposition with a sheared northern contact. The southern contact of this klippe is also sheared and a tectonic “melange” zone is exposed in certain outcrops. This unusual geological set up, along with the absence of a deep-seated fault in the area of investigation, had led the author to believe that this suite of metasedimentaries has no stratigraphic relation with the underlying rocks which they override. These are very much akin to some of the rock suites of the Indus ophiolitic zone outcropping far in the north, particularly those of the Suru valley (Kargil tehsil) and they appear to have been transported during post-Cretaceous times as a thrust mass. This is the first record of an exotic thrust nappe in the Kashmir Himalaya to the south of the Great Himalaya Range. 相似文献
11.
The reported age of 1,100 ± 50 m.y. for the Albany Granite is taken as marking the waning stages of the main orogeny in the south coast of Western Australia. The high initial 87Sr/86Sr for this granite, 0.7118 ± 0.0064, suggests an anatectic or rheomorphic origin which is consistent with petrographic evidence for the absence of a later metamorphism. Shales from the Stirling Range Beds indicate a metamorphic event at 1,150 ± 40 m.y. which is considered to be the time of upthrusting of rocks of higher metamorphic grade to their present position adjacent to the Stirling Range Beds. The minimum age of deposition for the Stirling Range Beds is postulated as 1,340 m.y. 相似文献
12.
Structural studies on Proterozoic rocks belonging to the Lunavada Group, Southern Aravalli Mountain Belt (SAMB), India, have shown that they underwent three episodes of deformation which have led to the formation of various regional scale interference patterns. Whilst the northern parts of the SAMB underwent brittle-ductile deformation, the southern portion underwent more ductile deformation. On the basis of structural as well as metamorphic studies it has been established earlier that the region was subjected to uplift orogenesis during its evolutionary history. In the present paper an attempt is made to visualize the possible causes that led to deformation of the SAMB, the structural geology of which has been established by the authors, and to constraint the timing of these events on the basis of already available geochronological data. A “working-hypothesis” is proposed according to which it is suggested that deformation of the SAMB is a result of the accretion of the three protocontinents viz. Aravalli, Dharwar and Singhbhum during the Mesoproterozoic. It is envisaged that the accretion of Aravalli and Singhbhum Protocontinents occurred between 1600 and 1400 Ma along the NE-SW trending Son Suture and this event led to development of NE-SW trending structures in the SAMB. Suturing of Aravalli and Dharwar Protocontinents between 1400 and 935 Ma along the E-W Narmada Suture was responsible for the E-W to NW-SE trending D3 structures of the SAMB. It is postulated that the Satpura orogeny which resulted in deformation of rocks in Satpura mountain range lying to the south of Narmada Suture was coeval with the accretion of Aravalli and Dharwar Protocontinents. 相似文献
13.
From alternating-field and thermal demagnetization studies on two dolerite “Traps” in the Gwalior Series (Central India), dated at 1830 ±200 m.y., three different palaeomagnetic directions could be distinguished. The characteristic magnetization component, which is considered as the primary magnetization, has a mean direction: D=78°, I=+34.5°, α95=5°, k=369, N=4 (Pole): 155.5°E19°N, dp=3°, dm=5.5°.A comparison of the presented data with other Precambrian and Phanerozoic data from the Indian subcontinent might suggest that the Indian subcontinent underwent a continuous anticlockwise rotational movement during the last 1800 m.y. 相似文献
14.
Carlos Garza-Gonzlez Antoni Camprubí Eduardo Gonzlez-Partida Germn Arriaga-García Fernando Rosique-Naranjo 《Journal of Geochemical Exploration》2006,89(1-3):124
The Tiámaro deposit in Michoacán state has been dated as Lower Cretaceous (Valanginian), though most of the porphyry deposits in central Mexico were dated or have an attributed Eocene–Oligocene age. The host rocks belong to a volcanoplutonic complex overlain by red conglomerates. These rocks were intruded by pre-Valanginian plutonic and hypabissal rocks. Propylitic, phyllic, and argillic alteration assemblages developed, and their superimposition draws the evolution of the deposit. Stage I is represented by propylitic assemblages, stage II contains the main ore forming stockworks and both phyllic and argillic assemblages, and stage III contains late carbonatization assemblages. The obtained temperatures and salinities from inclusion fluids are low for a porphyry-type deposit, but we interpret that the known part of the deposit represents the shallow portion of a bigger deposit. The evolution of mineralizing fluids draws a dilution trend of brines from “porphyry-like” to “epithermal-like” stages. The richest ore zone is roughly located between the 300 and 350 °C isotherms, though unnoticed resources may occur at depth. 相似文献
15.
During the Itkillik Glaciation the Brooks Range supported an extensive mountain-glacier complex that extended for 750 km between 141° and 158°W longitude. Individual ice streams and piedmont lobes flowed as much as 50 km beyond the north and south margins of the range. Glaciers in the southern Brooks Range were longer than those farther north because of a southerly precipitation source, whereas those in the central and eastern part of the range were larger than glaciers at the extremities of the mountain system because of higher and more-extensive accumulation areas. Glacier equilibrium-line altitudes (ELAs) at the time of greatest advance were depressed 600 ± 100 m below present levels, whereas during a less-extensive late-glacial readvance (Alapah Mountain) ELA depression was about 300 ± 30 m. Radiocarbon dates indicate that Itkillik drift correlates with Late Wisconsin drift along the southern margin of the Laurentide Ice Sheet and with drift of Cordilleran glaciers in southern Alaska and the western conterminous United States deposited during the last glaciation. Itkillik I moraines represent the maximum ice advance under cold full-glacial conditions between about 24,000 and 17,000 14C y. a. Itkillik II sediments, probably deposited close to 14,000 y. a., are characterized by abundant outwash and ice-contact stratified drift implying a milder climate than that of the Itkillik I phase. Alapah Mountain moraines at the heads of valleys draining high-altitude (≥1800 m) source areas record a possible late Itkillik readvance that is not yet closely dated. Itkillik glaciers may have largely disappeared from Brooks Range valleys by the beginning of the Holocene. 相似文献
16.
A radiometric estimate of the duration of sedimentation in the Adelaide geosyncline,south Australia 总被引：1，自引：1，他引：0
The Adelaide System forms the uppermost Precambrian sequence in South Australia and the Wooltana Volcanics lie near its base. Though affected by Palaeozoic metamorphism, the least‐altered samples give a minimum age of 850 ± 50 m.y., so that the base of the System is about 900 m.y. old or more. The unmetamorphbsed Roopena Volcanics of northeastern Eyre Peninsula are 1,345 ± 30 m.y. old and if correlated with the Wooltana Volcanics the base of the system becomes about 1,400 m.y. old. The data for the Wooltana Volcanics are consistent with this, provided that even the least‐altered total‐rock samples were open systems during the later metamorphism. Ages of basement in the Mount Painter and Olary districts (1,600 m.y.) and data for Willouran shales overlying the Wooltana Volcanics can fit both minimum and maximum estimates for the Volcanics. Lower Cambrian shales give a range of 530–690 m.y.; though some Palaeozoic isotopic movement occurred, the ages are approximately correct. Shales from the top of the Torrensian Series range from 660–840 m.y. (700 m.y. preferred value). If the base of the system is at 1,400 m.y., this is surprisingly young. It suggests either a hiatus between the Wooltana Volcanics and the Torrensian or that the correlation of the former with the Roopena Volcanics is wrong (and that the base is at about 900 m.y.). Alternatively, the shales may be abnormally updated. The Gawler Range Volcanics of Eyre Peninsula have been dated accurately at 1,535 ± 25 m.y. and illitic shale from the penecontemporaneous Corunna Conglomerate gives nearly the same value. These ages indirectly set a maximum for the age of the base of the system, as stratigraphy suggests that they are older. Granites underlying the Gawler Range Volcanics are about 1,600 m.y. old; some may be 1,800 m.y. old. Final Palaeozoic metamorphism in the northern Flinders Ranges was at 465 m.y. The ages of several post‐orogenic intrusions are given. 相似文献
17.
Jun-Ichi Matsuda Kenji Notsu Jun Okano Katsumi Yaskawa Leonard Chungue 《Tectonophysics》1984,104(1-2)
Sr isotopes and K-Ar ages were determined for volcanic rocks from three islands, Samoa, Rarotonga and Rurutu in the Austral-Gilbert-Marshall chain. We have established that Rurutu originated from the same “hot spot” as Tubuai and Raivavae in the Cook-Austral chain as indicated by its 11 m.y. K-Ar age and (
) ratios. The (
) ratios for Rurutu, Tubuai and Raivavae lie in the restricted range 0.7026–0.7035. K-Ar ages of all volcanic rocks from Samoa and Rarotonga are all less than 4 m.y. and their (
) ratios are much higher than those in Rurutu, Tubuai and Raivavae. These findings suggest that Samoa and Rarotonga did not originate in a single hot spot for the Cook-Austral islands. 相似文献
18.
J.G. Raith 《Precambrian Research》1995,70(3-4)
The 1.1 Ga Concordia Granite Gneiss (CGG) is part of the late to postorogenic Spektakel Suite in the western Namaqualand Metamorphic Complex, South Africa. It intruded synkinematically, with respect to the main (D2) deformation event, into lower to middle crustal rocks and granite emplacement was more or less coeval with the peak of granulite-facies metamorphism ( > 800°C, 5 kbar). Several genetically related rock types, megacrystic garnet-bearing granite, minor aplitic leucogranites and pegmatites are distinguished. All varieties are SiO2-rich (69–79 wt.%) peraluminous granites and show subalkaline-monzonitic magma characteristics. Geochemical differences in whole-rock chemistry between megacrystic granite and aplitic leucogranites (e.g., lower Al2O3, MgO, CaO, Ba, Zr; higher K2O, Rb, Nb, W, Rb/Sr, Ga/Al) and the decrease of e.g., CaO, MgO, Fe2O3, Ba, Zr, Th/U with increasing SiO2 in the megacrystic granites as well as the variation in Fe/Mn of magmatic garnets are best explained with crystal fractionation processes. Fractional crystallization of plagioclase produced potassium- and silica-rich residual melts characterised by very high Rb/Sr, Rb/Ba, U/Th, Mn/Fe ratios and higher concentration of W, Cu and Zn. Crystal fractionation processes also resulted in a relative LREE depletion and HREE enrichment (megacrystic granite: La/Lu)cn = 8.87−31.67; aplitic leucogranite and pegmatites: La/Lu)cn = 0.71−1.44) and evolution of pronounced negative Eu-anomalies. The crystallization sequence (near-solidus crystallization of biotite prior to alkali feldspar) suggests that the CGG magmas were H2O-undersaturated over a long period of their evolution. Water saturation during late-stage crystallization is, however, indicated by coarse late-stage eutectic mineral textures, pegmatites and WMo-bearing siliceous rocks. Furthermore the economic potential of the CGG is supported by its geochemical signature (e.g., high U, Th contents) which is similar to evolved high heat production (HHP) granites. The granitic magmas are attributed to partial melting of peraluminous crustal source rocks and are tentatively interpreted as fractionated S-type granites. The WMo deposits represent vein-type and pegmatitic deposits genetically related to a deep-seated granitic system. 相似文献
19.
Structural, stratigraphic and petrologic studies between Amet and Sembal in the Udaipur district of southcentral Rajasthan indicate that all the rocks belonging to the Banded Gneissic Complex, the Aravalli Group and the Raialo Formation have been involved in isoclinal folding on a westerly trend, co-axial refolding, and upright folding on a north to north-northeast trend. There is neither an unconformity nor an overlap between the Aravallis and the Raialos. The conglomerates supposed to mark the erosional unconformity above the Banded Gneissic Complex near Rajnagar is a tectonic mélange of folded and torn quartz veins in mica schist within the Aravalli Group. The Aravalli—Raialo metasediments have been migmatized synkinematically with the first folding to give rise to the Banded Gneissic Complex; the gneissic complex does not have any separate stratigraphic entity. By contrast, there is an undoubted erosional unconformity between the type Aravalli rocks and the underlying Sarara granite to the south. These relations, coupled with the continuity of the Aravalli rocks of Udaipur northward to the metasedimentary rocks of the Sembal—Amet area along the strike, and a comparable structural history, point to granitic rocks of at least two generations in the Early Precambrian of central and southern Rajasthan. Preliminary radiometric dating of rocks of known stratigraphic—structural relationship seems to confirm the presence of granitic rocks of two ages in the Early Precambrian, and of a considerable interval between the deposition of the Aravalli—Raialo rocks and the Delhi rocks. The Udaipur granite, post-dating the first deformation but preceding the upright folding on the northerly trend, provides evidence for granitic activity of a third phase before the deposition of rocks of the Delhi Group. 相似文献
20.
The Owl Creek Gold Mine is located in Hoyle Township, approximately 18 km northeast of Timmins, Ontario, Canada. The open-pit mine exposes a sequence of altered and mineralized mafic tholeiitic volcanics bounded to the north and south by greywacke and argillite. Gold occurs in the free state in quartz veins, often with graphite, and as fine gold on surfaces of, and within fractures in, pyrite.The study was designed to determine the distribution and distance of transport of Au in overburden down-ice from subcropping Au mineralization. This required an understanding of the glacial history of the area.The Quaternary stratigraphy at Owl Creek was studied and sampled by means of 17 sonic and 15 reverse-circulation overburden drill holes near the open pit, and several overburden exposures in the open-pit walls. Nonmagnetic heavy-mineral concentrates (specific gravity >3.3) were made from the <2000 μm (−10 mesh) fraction of all overburden samples from the drill hole and section sampling. The heavy-mineral concentrates were analyzed for Au by neutron activation. A till pebble lithology study was done on the >2000 μm (−10 mesh) fraction of the sonic drill core.Our stratigraphic studies indicate that there were three major Wisconsinan (Weichselian) ice advances and one minor, late readvance in the Timmins area. The transport and deposition of sediments comprising the “Oldest”, “Older”, Matheson and Cochrane stratigraphic “packages” (oldest to youngest) are related to three ice advances and one readvance which moved towards 240° ± 10°, 150° ± 5°, 170° ± 5° and 130° ± 5°, respectively.Geochemically anomalous levels of Au in the overburden define two dispersal trains down-ice of the Owl Creek Gold Mine. One, in the “Older” lodgement till, is 400–500 m long. The other in Matheson ablation and waterlain tills, is approximately 700 m long.The till pebble lithology study showed that pebble counting can be used to approximate bedrock contacts, but may not necessarily identify the source rock type of the matrix. 相似文献