Abstract
In the Chindwin Basin in northern Burma, there is a system of five Pleistocene terraces in which gold placers with low concentrations of platinum-group minerals (PGM) occur. Samples were taken from four sites in the Chindwin Basin and one from near an ophiolite occurrence on the northeast side of the Chindwin Basin; they were studied under the microscope, with a scanning electron microscope, and an electron microprobe. The main minerals were Pt-Fe and Os-Ir-Ru alloys, usually in a ratio between 2 and 5. In most cases, the shape of the grains allowed a quick distinction between the two types. Sperrylite, laurite, irarsite, cooperite, tulameenite, and isomertieite occur infrequently as individual mineral grains and sometimes as inclusions in the alloy grains. Braggite, platarsite, hollingworthite, bowieite, keithconnite, cuproiridsite, malanite, stibiopalladinite, geversite, kashinite, several unnamed PGM, and Fe, Ni, and Cu sulfides were observed as inclusions, mainly in the Pt-Fe alloys and also to a lesser extent in the Os-Ir-Ru alloys. Lamellar and myrmekite-like intergrowths, oriented exsolution lamellae, and idiomorphic inclusions of sulfides in the alloys indicate a magmatic origin of the PGM. The origin of the PGM is assumed to be ophiolites in northern Burma. A continual decrease in mean grain size occurred during transport.
Zusammenfassung
Im Gebiet des Chindwin Basin in Nordburma ist ein System von fünf pleistozänen Terrassen ausgebildet, in denen Goldseifen mit geringen Anteilen an PGM auftreten.
PGM-Konzentrate von vier Vorkommen des Chindwin Basin und eine weitere Probe aus der Nähe eines Ophiolithvorkommens im Nordosten des Chindwin Basin wurden mit optischer Mikroskopie, Rasterelektronenmikroskopie und Mikrosonde untersucht.
Hauptmineralien sind Pt-Fe-Legierungen und Os-Ir-Ru-Legierungen in einem Verhältnis von 2: 1 bis 5: 1. Ihre Morphologie kugeliger oder plattiger, teilweise idiomorpher Körner erlaubt in den meisten Fällen eine rasche Identifizierung der beiden Typen. Sehr selten treten als Einzelminerale, aber auch als Einschlüsse in Legierungen, Sperrylith, Laurit, Irarsit, Cooperit, Tulameenit und Isomertieit auf. Braggit, Platarsit, Hollingworthit, Bowieit, Keithconnit, Cuproiridsit, Malanit, Stibiopalladinit, Geversit, Kaschinit, einige unbekannte PGM und Fe-, Ni- und Cu-Sulfide wurden nr als Einschlüsse, hauptsächlich in Pt-Fe-Legierungen, weniger in Os-Ir-Ru-Legierungen, beobachtet.
Lamellare und myrmekitische Verwachsungen, orientierte Entmischungen und idiomorphe Einschlüsse von Sulfiden in Legierungen weisen auf eine magmatische Entstehung der PGM hin. Die Herkunft der PGM wird in Ophiolithen Nordburmas vermutet. Beim Transport hat eine kontinuierliche Abnahme der mittleren Korngrösse stattgefunden.
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References
Bannert D, Helmcke D (1981) The evolution of the Asian Plate in Burma. Geol Rdsch 70: 446–458
Bender F (1983) Geology of Burma. Gebriider Bornträger, Berlin Stuttgart, 293 pp
Cabri LJ (1980) Determination of ideal formula for new minerals of the platinum-group. XIth Int Min Assoc Meet Novosibirsk, Proc I, pp 157–165
——,Criddle AJ, Laflamme JHG, Bearne GS, Harris DC (1981) Mineralogical study of complex Pt-Fe nuggets from Ethiopia. Bull Mineral 104: 508–525
——,Feather CE (1975) Platinum-iron alloys: A nomenclature based on a study of natural and synthetic alloys. Can Mineral 13: 117–126
——,Harris DC (1975) Zoning in Os-Ir alloys and the relation of the geographical and tectonic environment of the source rocks to the bulk Pt: Pt + Ir + Os for placers. Can Mineral 13: 266–274
——,Chattopadhyay B, Venkatarama P, Roy DK, Bhattacharyya S, Gosh S (1983) Geology of Naga Hills Ophiolites. Geol Surv India Rec 112, 2: 59–115
Desborough GA, Criddle AJ (1984) Bowieite: A new rhodium-iridium platinum sulfide in platinum-alloy nuggets, Goodnews Bay, Alaska. Can Mineral 22: 543–552
Ford RJ (1981) Platinum-Group Minerals in Tasmania. Econ Geol 76: 498–504
Goossen PJ (1978) The metallogenic provinces of Burma. 3rd Reg Conf Geol Min Res SE Asia, Bangkok, pp 495–536
Harris DC, Cabri LJ (1973) The nomenclature of the natural alloys of osmium, iridium and ruthenium based on new compositional data of alloys from world-wide occurrences. Can Mineral 12: 104–112
Raicevic D, Cabri LJ (1976) Mineralogy and concentration of Au- and Pt-bearing placers from the Tulameen River Area in British Columbia. CIM Bull 770: 111–119
Reiman KU, Aye Thaung (1981) Palynostratigraphic investigation of the Tertiary Chindwin basin. 4th Int Palyn Conf, Lucknow, India (1976–1977), pp 380–395
Rudashevski NS, Menshikov YR, Mochalov AG, Trubkin NV, Shumskaya NI, Zhdanov VV (1985) Cuprorhodsite CuRh2S4 and cuproiridsite CuIr2S4—new natural thiospinels of platinum group elements. Zapiski Vses Mineral Obshch 119: 187–195 (in Russian)
——,Mochalov AG, Menshikov YP, Shumskaya NI (1983) Ferronickel-platinum, Pt2FeNi, a new mineral species. Zapiski Vses Mineral Obshch 112: 487–494 (in Russian)
Stumpft EF, Tarkian M (1973) Natural osmium-iridium alloys and iron-bearing platinum: new electron probe and optical data. N Jb Miner Mh 7/8: 312–322
Tarkian M (1987) Compositional variations and reflectance of the common platinum-group minerals. Mineral Petrol 36: 169–190
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Hagen, D., Weiser, T. & Htay, T. Platinum-group minerals in quaternary gold placers in the upper Chindwin area of northern Burma. Mineralogy and Petrology 42, 265–286 (1990). https://doi.org/10.1007/BF01162695
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DOI: https://doi.org/10.1007/BF01162695