Origin of Mineralizing Fluids of the Sediment-Hosted Navachab Gold Mine, Namibia: Constraints from Stable (O, H, C, S) Isotopes
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The Navachab gold mine in the Damara belt of central Namibia is characterized by a polymetallic Au-Bi-As-Cu-Ag ore assemblage, including pyrrhotite, chalcopyrite, sphalerite, arsenopyrite, bismuth, gold, bismuthinite, and bismuth tellurides. Gold is hosted by quartz sulfide veins and semimassive sulfide lenses that are developed in a near-vertical sequence of shelf-type metasedimentary rocks, including marble, calcsilicate rock, and biotite schist. The sequence has been intruded by abundant syntectonic lamprophyre, aplite, and pegmatite dikes, documenting widespread igneous activity coeval with mineralization.
The majority of quartz from the veins has δ 18O values of 14 to 15 per mil (V-SMOW). The total variations in δ 18O values of the biotite schist and calcsilicate rock are relatively small (12–14‰), whereas the marble records steep gradients in δ 18O values (17–21‰), the lowest values being recorded at the vein margins. Despite this, there is no correlation between δ 18O and δ 13C values and the carbonate content of the rocks, indicating that fluid-rock interaction alone cannot explain the isotopic gradients. In addition, the marble records increased δ 13C values at the contact to the veins, possibly related to a change in the physicochemical conditions during fluid-rock interaction. Gold is interpreted to have precipitated in equilibrium with metamorphic fluid ( δ 18O = 12–14‰ δ D = −40 to −60‰) at peak metamorphic conditions of ca. 550°C and 2 kbars, consistent with isotopic fractionations between coexisting calcite, garnet, and clinopyroxene in the alteration halos. The most likely source of the mineralizing fluid was a midcrustal fluid in equilibrium with the Damaran metapelites that underwent prograde metamorphism at amphibolite- to granulite-facies grades. Although there is no isotopic evidence for the contribution of magmatic fluids, they may have been important in contributing to the overall hydraulic regime and high apparent geothermal gradients (ca. 80°C/km−1) in the mine area.Research Article| January 01, 1971 Precambrian Rocks of the Lake Hopatcong Area, New Jersey DAVIS A YOUNG DAVIS A YOUNG Department of Geology, Washington Square College of Arts and Science, New York University, New York, New York 10003 Search for other works by this author on: GSW Google Scholar Author and Article Information DAVIS A YOUNG Department of Geology, Washington Square College of Arts and Science, New York University, New York, New York 10003 Publisher: Geological Society of America Received: 22 Jun 1970 Revision Received: 18 Aug 1970 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1971, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1971) 82 (1): 143–158. https://doi.org/10.1130/0016-7606(1971)82[143:PROTLH]2.0.CO;2 Article history Received: 22 Jun 1970 Revision Received: 18 Aug 1970 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation DAVIS A YOUNG; Precambrian Rocks of the Lake Hopatcong Area, New Jersey. GSA Bulletin 1971;; 82 (1): 143–158. doi: https://doi.org/10.1130/0016-7606(1971)82[143:PROTLH]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Precambrian rocks near Lake Hopatcong, New Jersey, form a part of the intensely deformed and metamorphosed Reading Prong. The Lake Hopatcong area is divisible into several northeast-trending fault blocks, each of which contains a mappable stratigraphic sequence of paragneisses and granitic or syenitic rocks.The paragneisses generally are well foliated and well layered. They consist chiefly of biotite-feldspar-quartz gneisses and quartz-oligoclase leucogneisses that are interpreted as metamorphosed potassium-rich sandstones and quartz keratophyres, respectively. A thin well-foliated unit of biotite-plagioclase gneiss is thought to be a metamorphosed sill of gabbroic anorthosite.The granitic and syenitic rocks generally form thick, regionally concordant sheets. They are typically foliated and are composed chiefly of microcline microperthite and plagioclase (or mesoperthite), quartz, and iron-rich hornblende and clinopyroxene. These foliated granitic and syenitic rocks are viewed as syntectonic magmatic intrusives. One regionally discordant, unfoliated sheet of clinopyroxene quartz syenite is probably a late tectonic magmatic intrusive.Mineral assemblages in Lake Hopatcong paragneisses may be assigned to the hornblende granulite subfacies of metamorphism. The presence of Ca-bearing mesoperthite in biotite-feldspar-quartz gneiss indicates that metamorphic temperatures exceeded 700° C, and the assemblage garnet-sillimanite-quartz without cordierite indicates that load pressure was greater than 2.5 kb. The rocks have thus probably been buried to depths in excess of 10 km. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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Protolith
Felsic
Banded iron formation
Greenschist
Basement
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Stable isotope geochemistry is one of new branches of geosciences. In recent years many significant developments have been made in this field, and stable isotope study has become an important tool in solving all kinds of geological and geochemical problems.
In this short comment, a brief discussion on the present status and prospect of stable isotope geochemistry is given in three aspects:
1. On the methodology of stable isotope studies,including the instruments, analytical methods and standards.
2. On the theoretical studies of stable isotopes, including the physical and chemical properties of isotopes and mechanisms of isotope fractionation.
3. On the geological applications of stable isotopes, including the uses of stable isotopes in researches of meteorites,lunar rocks, igneous rocks, sedimen-tal rocks, metamorphic rocks, ore deposits, oil and gas, hydrology, oceanography, atmosphere, environmental problems, hydro thermal springs, volcanics, and so on.
Isotope Geochemistry
Environmental isotopes
Isotopic signature
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The Yaogangxian composite granitic pluton is located in the north of Nanling complex structural belt,hosting the giant Yaogangxian tungsten deposit. The Yaogangxian granites are differentiation S-type granite with the characters of highlyacid,hyperalkaline and peraluminous,belonging to the high-K calc-alkalic series granite. LA-ICP-MS zircon U-Pb dating method was applied to obtain the ages of different types of the Yaogangxian granites. The Yaogangxian composite granitic pluton can be divided into three stages according to their emplacement ages,including coarse-grained two-mica granite forming at 170 Ma,medium-to fine-grained two-mica granite forming at 162 Ma,and fine-grained muscovite granite forming at 157 Ma,indicating that the granitic magma had undergone multi-epoch pulsating emplacement. The element geochemistry and Sr-Nd isopotic characters show that source materials of the Yaogangxian granites might come from pelite in the Paleoproterozoic Era. The Yaogangxian granites formed at 170 Ma to 157 Ma belonging to the Yanshannian Period,occurring in a continental crustal extension and thinning setting. The diagenetic events of the Yaogangxian granites and the metallogenetic events of tungsten deposits were highly consistent in time and space. The granitic magma had experienced high fractional crystallization and produced volatile-rich fluid. So it was indicated that the granites may provide original fluid and material source to mineralization in post-magmatic hydrothermal stage.
Fractional crystallization (geology)
Petrogenesis
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Muscovite
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Yilgarn Craton
Greenstone belt
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The ratios of stable isotopes of certain elements in rocks and minerals have strong regional characteristics that are reflected in atmospheric components, in water, and in the living organisms that form Earth's surface environment as well as in agricultural and fishery products. Geologically derived stable isotope ratios can be used as a tracer for the source of many kinds of substances, with current geochemical techniques allowing the precise determination of numerous stable isotope ratios in both natural and manmade objects. This review presents examples of the use of stable isotopes as tracers within diverse dynamic ecosystems, focusing on Sr isotopes but also including examples of Nd and Pb isotopic analysis, and reviewing the potential of this technique for a wide range of environmental research, including determining the geographic origin of food and archeological materials.
Isotope Analysis
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Zinc(Zn)is a requisite trace element for life,related to human activities,with exceptional biologic and public health importance.In the past decades,the development of sample purification technology and the application of MC-ICP-MS have allowed for precise measurements of Zn isotopic ratios in various environments.Based on the study of Zn isotopes,significant progress has been made on understanding the behavior of Zn in terrestrial and extra-terrestrial reservoirs.In this paper,we give a review of previous studies of Zn isotope and systematically summarize the progresses and/or results in aspects of the analytical methods,experiment and theory of Zn isotopic fractionation,and Zn isotopic compositions in different reservoirs,respectively.We suggest that Zn isotopes could be widely applied in the future in cosmochemistry,environmental geochemistry,paleoclimate reconstruction and environmental health and bio-medical fields,and will greatly increase our awareness on the global biogeochemical cycle of Zn and other metals.
Isotope Geochemistry
Biogeochemical Cycle
Cosmochemistry
Trace element
Isotope Analysis
Biogeochemistry
Paleoclimatology
Isotopic signature
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During the last 10 m.y., the Nanga Parbat Haramosh Massif in the northwestern Himalaya has been intruded by granitic magmas, has undergone high‐grade metamorphism and anatexis, and has been rapidly uplifted and denuded. As part of an ongoing project to understand the relationship between tectonism and petrologic processes, we have undertaken an isotopic study of the massif to determine the importance of hydrothermal activity during this recent metamorphism. Our studies show that both meteoric and magmatic hydrothermal systems have been active over the last 10 m.y. We suggest that the rapid uplift of the massif created a dual hydrothermal system, consisting of a near‐surface flow system dominated by meteoric water and a flow regime at deeper levels dominated by magmatic/metamorphic volatiles. Meteoric fluids derived from glaciers near the summit of Nanga Parbat were driven deep into the massif along the transpressional faults causing δ 18 O and δD depletions in the gneisses and marked oxygen isotopic disequilibrium between mineral pairs from the fault zones. The discharge of these meteoric fluids occurs in active hot springs that are found along the steep faults that border the massif. At deeper levels within the massif, infiltration of low δ 18 O magmatic fluids caused δ 18 O depletions in the gneisses within the migmatite zone. These low δ 18 O fluids were derived from the young (<4 Ma), relatively low δ 18 O granites (∼8‰c) that are found within the core of the massif. Geochronological evidence in the form of fission track and 40 Ar/ 39 Ar cooling ages and U/Pb ages on accessory minerals from the granites and gneisses provide a constraint on the timing of fluid flow in the surface outcrops we examined. Fluid infiltration in the migmatite zone rocks located along the Tato traverse was coeval with metamorphism, granite emplacement, and rapid denudation, in the interval 0.8–3.3 Ma. Finally, we infer from the presence of active hot springs that significant flow systems continue to be active at depth within the central portion of the Nanga Parbat‐Haramosh Massif.
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Leucogranite
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