粤西震旦系含金建造及与金矿的关系

SINIAN GOLD-BEARING FORMATION AND ITS RELATION WITH GOLD MINERALIZATION, WEST GUANGDONG PROVINCE

粤西震旦系Z^b组和Z^c组是重要的含金建造。原岩为一套陆源碎屑岩,其中夹有少量中酸性凝灰岩。建造中的金丰度高于克拉克值2-4倍,金的丰度及其分布主要受变质岩的基性程度,硫化物及有机质数量控制。

This paper has studied in detail the geochemical characteritics of Sinian metamorphic rocks in west Guangdong province and condsiders the Sinian metamorphic rocks this area as an important gold-bearing formation. The microscopic analysis shows that the normal terrigenous clastic rocks in the Sinian gold-bearing formation often contain some volcanic clastic substances. For the metamorphic rocks with high grade, the following methods are used to restore primary rocks, namely, Negery tetrahedron diagram, 〔 (al+fm)-(alk+c)〕 - si diagram, K%-A% diagram, (al-alk)-c diagram and ratio of trace element pairs. The results from various methods all show that the primary rocks of Sinian metamorphic rocks are mainly a set of terrigenous clastic rocks containing some volcanic clastic rocks. Sinian gold-bearing formation commonly shows a higher content of gold. The gold concentration is 13.21 ppb in Zcgroup and 7.67 ppb in Zbgroup . From the sandstone and shale to the schist, the gold concentration decreases from 20.3 ppb to 8.2 ppb, Showing that the gold in Sinian gold-bearing formation was leached out gradually as the regional metamorphism developed. The δ34S data of pyrites in ore bodies change from -3.06 to -1.73, the mean is -2.24. It is considered that the sulphur in ore bodies was from Sinian metamorphic rocks, which would have been homogenized during the regional metamorphism and migmatization. In 206pb / 204Pb- 207pb / 204pb diagram, there is dearly a fine linear relationship of projection dots of Pb isotope in all geologic bodies. The projection dots of Pb isotope in Sinian metamorphic rocks are located in the right upper part of the line, the projection dots of Pb isotope in granites and pegmatites are located in the left lower part of the line, and the projection dots of Pb isotope in gold ore bodies are located in the middle of the line, showing that the Pb in gold ore bodies came from Sinian metam orphic rocks and Hercynian-Indosinian granites. The δ18O and δD data show that the ore-forming solutions were of the mixture of metamorphic water and meteoric water. Finally, the author suggests a metallogenic model for three types of gold deposits in this area. The flysch formation containing volcanic clastic rocks, which formed during Sinian period, is the most important gold-bearing formation in the area. The regional metamorphism caused gold in the gold-bearing formation to activate and transport and to form sedirnentary-metamorphic gold deposits. Migmatization and mylonitization caused further enrichment of gold. Magmatic activity of Hercynian-Indosinian granites caused gold further to transport and precipitate, and then, migmatizatic gold deposit (e.g. Hetai gold deposit) formed. Probably, all gold-bearing bodies could develop into gold placer due to long action of weathering.