云南墨江金矿床成矿作用探讨

云南墨江金矿床位于“三江”褶皱带哀牢山板块结合带北段的墨江 -九甲断裂带中。矿体分布于金厂超基性岩体西侧的金厂组烂山段含火山物质的硅质岩、变余粉砂岩和板岩中 ,矿体由含金石英脉、含金硅质岩组成 ,金矿体受层位和岩性控制。在矿区还分布晚于金矿化形成的镍矿体。金镍矿体共同存在于同一矿区 ,矿区围岩蚀变种类多 ,与金矿化有关的围岩蚀变主要有硅化、黄铁矿化等。矿体的空间分布与穿插关系表明 ,金成矿作用开始于晚三叠世以前。含金硅质岩具有沉积作用形成的地质特征 ,其稀土元素、氧、硅同位素地球化学特征与热水沉积作用形成的硅质岩一致 ;含金石英脉的矿物组成、结构和构造特征、稀土元素、硅同位素、微量元素组成与含金硅质岩相似 ,可能与硅质岩具有相似物质来源或形成作用。金矿石中金与镍、铬等元素的相关性很低。推断金矿床成矿作用可能开始于中石炭世含金硅质岩的热水沉积作用 ,在早三叠世以前 ,成矿热液通过充填和交代作用在硅质岩和上部的岩石中形成含金石英脉。后来的区域变质作用、超基性岩自变质作用及镍矿化作用可能使金矿体的金含量提高 ,但没有产生具有工业意义的独立金矿化。

ON THE FORMATION OF MOJIANG GOLD ORE DEPOSIT,YUNNAN PROVINCE-A DISCUSSION

The Mojiang gold ore deposit is located in the Mojiang\|Jiujia fault zone in the Ailaoshan integrating belt of slab tectonics of the \!Three River" fold zones. The gold ore bodies are hosted by cherts, metasiltstones and slates of the Lanshan member of the Jincang Formation (C\-2j\ 1), consist of auriferous quartz veins and cherts, and are stratabound. In the gold ore deposit, there exist nickel orebodies formed later than gold mineralization. For the co\|existence of gold and nickel mineralization in the same deposit, the alterations are complex. Alterations related to gold mineralization include silicification, pyritization, etc. Spatial distribution of mineralization shows that gold metallogenesis began before Late Triassic. The auriferous cherts have the geological characteristics of sedimentation; the REE, Si and O isotopes of the cherts are unanimous with hot\|water sedimentary cherts. It is indicated that the auriferous cherts and quartz veins are of similar origin and formation process. The correlation coefficients of Au and Ni, Cr are small in the gold ores. It is deduced that gold mineralization began simultaneously with hot\|water deposition of the auriferous cherts during Carboniferous. Thereafter, hot\|water activity continued in the area and gold quartz veins were deposited by filling and replacing the cherts and upper rocks below the water\|rock surface. The gold orebodies were predominantly formed from hot\|water, ranging from Middle Carboniferous to Early Hercynian. Later regional metamorphism, autometamorphism of ultrabasic rocks and nickel mineralization might have contributed gold to the orebodies, but could not generate independent gold orebodies.