| 加拿大安大略省赫姆洛金矿的稳定同位素和痕量元素研究 |
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| 引用本文：丁悌平,H.G.Thode.1991.加拿大安大略省赫姆洛金矿的稳定同位素和痕量元素研究[J].地球学报,12(3):47-62. |
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| 中文摘要:1981年在加拿大安大略省发现的赫姆洛(Hemlo)金矿是目前北美最大的金矿之一,探明储量已超过600t。赫姆洛金矿在太古代晚期地层中沿层产出,矿体形状规则、规模巨大,矿石品位均匀,具有同生层状矿床的特征。但同时,它的元素组合和围岩蚀变又显示出浅成热液矿床的某些特点。所有这些特点,使得赫姆洛金矿成为一个有重大经济价值和科学研究意义的新型矿床。 我们自1985年以来,对赫姆洛金矿的微量元素和各种稳定同位素组成进行了详细的研究,为阐明矿床的成因和晚太古代水圈和大气圈的状况提供了一系列重要依据。 |
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| STABLE ISOTOPE AND TRACE ELEMENT STUDIES ON THE HEMLO GOLD DEPOSIT, ONTARIO, CANADA |
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| Abstract:The Hemlo Gold Deposit is a very interest deposit for its large reserve as well as its unique geological characteristics. It occurs stratigraphically within metamorphosed Archean sedimentary rocks and has many characteristics of syngenetic stratiform deposit:very regular shape of ore bodies, homogeneous distribution of gold in ore formation, large reserve and close association with beded barite. However, it shows also some phenomena of epithermal ore deposit, such as typical chemical composition of epithermal association and obvious country rock alteration. all these characteristics make it a very attractive subject of scientific research and mineral exploration.In this study stable isotope determination and trace element investigation were combined to clarify the genetics of the gold deposit and to throw light on the problems of the conditions of atmosphere and hydrosphere during late Archean period. And some conclusions have been made as following: 1. In the Hemlo gold deposit the content of Au is positively correlated with the contents of Mo, As, Sb and Se, indicating the Au mineralization is closely related to hydrothermal activities.2. The REE pattern of all Au rich samples generally shows the effect of alteration.3. The S content of Au rich samples are normally higher than 5%. This sulphur is mainly contained in sulphides, especially pyrite, having negative δ34S values.4. The Δ34S bar-ps. values are rather constant, indicating an exchange relationship between them. Assuming there is an isotope equilibrium between barite and pyrite, a temperature range from 360-571℃ are obtained by using sulphur isotope geothermometer. This range is in good agreement with that obtained from oxygen isotope geothermometer(434-543℃)and consistent with the fact that the rocks in Hemlo has experinced high grade metamorphism.5. The ratio of sulphide to sulphate, the sulphur isotope compositions of minerals and bulk sample all vary from stratum to stratum It implies that at least most of sulphur in Hemlo deposit was introduced into the rocks before metamorphism 2671 Ma ago and has syngenetic characteristics.6. The δ5 D values of mica in Hemlo rocks are from -35 to - 57(‰5), closing the values of clay mineral equilibrated with sea water. It may indicate that these rocks were originally oceanic sedimentary and volcanic (?).7. The Si isotope compositions of quartz and mica in Hemlo rocks mainly reflect the characters of clastic sedimentary rocks and acidic volcanic rocks. However, a few of gold rich samples has relatively high δ30Si values, falling into the field of siliceous sedimentary rocks of shallow oceanic water and indicating the influence of chemical precipitation on gold mineralization.8. Two kinds of interpretations can be made on the source of sulphur in Hemlo:one assumes there were two or three sulphur sources, i. e.the sulphur from mantle, sulphur form sea water and organic reduced sulphur.The other assumes that there was only one sulphur source--the sulphur from mantle. The first interpretation is more reasonable.9. According to above poinus, it is suggested that the Hemlo gold deposit is an exhaletive deposit of late Archean age, but experinced high grade metamorphism 267lMa ago.10. The sulphur isotope study on Hemlo beded barite indicates that there was some basins having relatively high oxidative environment during late Archean period. |
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