1989 Fiscal Year Final Research Report Summary
Chronological application of Re-Os system to sulfide ores
| Project/Area Number |
62430009
|
|---|
| Research Category |
Grant-in-Aid for General Scientific Research (A)
|
| Allocation Type | Single-year Grants |
|---|
| Research Field |
分析・地球化学
|
|---|
| Research Institution | University of Tokyo |
|---|
Principal Investigator |
MASUDA Akimasa Univ. Tokyo, Fac. Sci., Professor, 理学部, 教授 (40030788)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
NAKAI Shun-ichi Univ. Tokyo, Fac. Sci., Res. Associate, 理学部, 助手 (50188869)
SHIMIZU Hiroshi Univ. Tokyo, Fac. Sci., Associate Prof., 理学部, 助教授 (60090544)
|
|---|
| Project Period (FY) |
1987 – 1989
|
| Keywords | Re-Os geochronometer / sulfide ore minerals / ICP mass spectrometer / isotopic equilibrium / mass discrimination / gas-mist merging introduction / molybdenite |
|---|
| Research Abstract |
For the studies of sulfide ore deposits, chronological studies of them are of much significance. However, such studies of formation ages of sulfides have been retarded, since there remain some problems concerning Re-Os dating which has been expected to be a promising geochronometer. In the present work, we tried to examine the problems underlying the practical and wide application of Re-Os clock to the sulfide ore minerals, from basic points of view involving the technical improvement, where the mass spectrometer with inductively coupled plasma (ICP) ion source was employed. Our results are summarized below:
(1) A new method has been developed to make a correction about the effect of mass discrimination which takes place in ICP mass spectrometer. By combination of this correction method with isotope dilution employing highly enriched Os-192, we succeeded in simultaneous determination of (Os-187)/(Os-186) ratio and Os abundance. In this connection, an apparatus was devise to treat Os as
… More
tetroxide which has very high volatility.
(2) Also we succeeded in enhancing the sensitivities of Os and Re. In this method, the vapor of OsO_4"or Re_2O_7 generated from a specially designed small furnace merges into the "pure" mist produced by a conventional nebulizer. Thus, Os or Re is introduced into the plasma torch without substantial loss or discard. In use of the customary introduction employing the simple nebulization of aqueous solution of element(s), 50-100 ng Os was required, whereas -10 ng Os is sufficient amount according to our system.
(3) We recognized that the Re content in molybdenite is different from portion to portion. This problem is solved by careful pulverization. Besides, it was found out that it is difficult for us to attain the isotopic equilibrium between the radiogenic Os and the Os spike added. This isotopic problem can be solved by distillation for 5 hours, in which the distillate is collected separately for each hour and isotopic measurement of Os distilled is made for each fraction. As a result, we could obtain the correct age. Less
|
