大沟谷钠长石岩型金矿床Pb、S、Sr同位素特征初探

STUDY ON THE Pb, S AND Sr ISOTOPIC CHARACTERISTICS OF DAGOUGU ALBITITE-HOSTED GOLD DEPOSIT IN WESTERN GUANGDONG PROVINCE

大沟谷金矿床产于震旦系乐昌峡群钠长石岩带底部陡倾斜钠长石岩中。金矿床铅同位素组成变化大 ,2 0 6Pb/2 0 4 Pb 1 7.3 56～ 1 9.3 0 6,2 0 7Pb/2 0 4 Pb 1 5.3 3 0～ 1 5.862 ,2 0 8Pb/2 0 4 Pb 3 7.53 2～ 3 9.957。μ值在8.2 3～1 0 .67之间 ,黄铁矿δ3 4S值在 5.1‰～ 1 3 .4‰之间 ,铅同位素组成具线性相关关系 ,2 0 6Pb/2 0 4 Pb与2 0 7Pb/2 0 4 Pb线性方程 y=0 .2 4x +1 1 .1 9,r=0 .83 ,2 0 6Pb/2 0 4 Pb与2 0 8Pb/2 0 4 Pb方程为 y=1 .3x +1 4 .8,r=0 .93 ,黄铁矿铅硫同位素组成具负相关关系。钠长石岩Rb、Sr含量较低 ,87Sr/86Sr值为 0 .72 2 63～ 0 .73 1 50 ,平均 0 .72 595。综合铅、锶、硫同位素特征 ,可以认为大沟谷金矿床成矿物质主要来自高 μ值基底碎屑沉积岩及钠化基性火成岩。

Dagougu gold ore\|bodies occurred in the vein\|filling albitite in the lower part of the stratabound albitite hosted by the Lechangxia Group schist of the Sinian period. Lead isotope ratios vary considerably with \{\}\+\{206\}Pb/\+\{204\}Pb: \{17.356\}～\{19.143\}, \{\}\+\{207\}Pb/\+\{204\}Pb: \{15.330\}～\{15.862\}, and \{\}\+\{208\}Pb/\+\{204\}Pb: \{37.532\}～\{39.957\}. The lead isotopic composition shows a positive linear correlation with r=\{0.83\} for \{\}\+\{206\}Pb/\{\{\}\+\{204\}Pb\} vs. \{\}\+\{207\}Pb/\{\{\}\+\{204\}Pb\} and r=\{0.93\} for \{\}\+\{206\}Pb/\+\{204\}Pb vs. \{\}\+\{208\}Pb/\{\}\+\{204\}Pb. Lead and sulfur isotopic composition displays a negative correlation. The gold\|hosted albitite has low contents of Rb and Sr and its \{\}\+\{87\}Sr/\+\{86\}Sr is in the range of \{0.72263\}～\{0.73150\} with an average of \{0.72595\}, similar to the initial strontium isotope ratio of ore fluid for the Dagougu gold deposit. On the basis of lead\|, sulfur\|, and strontium isotopic composition, in conjunction with geological background information, it is concluded that the source rocks of the Dagougu gold deposit are the old metamorphic clastic rocks with high μ values and the basic rocks suffering from sodium alteration (e.g. spilite), which are common in the Proterozoic basement in western Guangdong to eastern Guangxi.