Tectonic Isotope Geochemistry—Further Study on Sulphur Isotope of Jiaodong Gold Concentration Area

摘要

(1) Statistics of sulphur isotope data from 500 ore samples has shown that the sulphur isotopic composition of gold deposits in western Jiaodong area are remarkably characterized by small variance and concentrated on ~(34)S. Different mineralization types of gold deposits are of its own characteristics of δ~(34)S value; Mid Yanshanian (140～100Ma) mesothermal quartz vein type gold deposits are of 4per thousand～7per thousand; altered rock type gold deposits are 7per thousand～12per thousand; Late Yanshanian epithermal gold, silver, and Pb-Zn deposits are -4per thousand～4per thousand. From the statistic aspect, the higher of δ~(34) S value, stronger the intensity of gold mineralization and larger the scale of gold deposits, thus the δ~(34)S value of ore deposit maybe used as the major geochemistry indices for the evaluation of gold prospecting in Western Jiaodong. (2) Early Pre-Cambrian metamorphic rock system (Jiaodong Group, Jingshan Group), Metasomatic-anatectic granite (including Linglong/Kunyushan type gneissic biotite granite, Guojialing potash feldspar porphyroblastic grano-diorite and Luanjiahe medium-coarsed adm-ellite) and late Yanshanian syntectic granite (Aishan grano-diorite) are all characterized by different degree of concentrated ~(34)S. From Neo Archean Jiaodong Group to early Proterozoic Jingshan Group, δ~(34)S value varied from 5. 4per thousand～7.4per thousand increased to 9. 2per thousand～10.1per thousand, this is in line with the sudden change regularity of sulphur isotopic composition during the earth evolution history from Archaeozoic to Proterozoic. From the basement metamorphic rock system to metasomatic granite (migmatitic granite), the δ~(34)S value from 5. 4per thousand～7. 4per thousand increased to 7. 3per thousand～9. 5per thousand, it shows that there are concentration process of ~(34)S associated with migmati-zation (deep source alkalic alteration) and resulted the increasing of δ~(34)S value. From metasomatic granite to anatectic granite to syntectic granite, the δ~(34)S value decreased, i. e, from 11. 7per thousand, (Kunyushan granite) to 9. 5per thousand (Linglong granite) to 8. 9per thousand (Luanjiahe granite) to 6. 7per thousand (Guojialing granite) to 6. 6per thousand (Aishan granite) to 2. 4per thousand (intermediate basic dykes). This shows the former two types (metasomatic and anatectic granite) pertain to crustal source sulphur type and the latter types (syntectic granite) are mainly mantle source sulphur.