长江中下游成矿带铜多金属矿床中灰泥丘的发现及其意义——以武山和冬瓜山铜矿为例

Discovery and Significance of Carbonate Mud Mounds from Cu-polymetallic Deposits in the Middle and Lower Yangtze Metallogenic Belt: Examples from the Wushan and Dongguashan Deposits

通过对长江中下游成矿带中武山铜矿和冬瓜山铜矿层状硫化物矿体的详细研究,发现了大量具有层圈状构造、层纹状构造或不规则同心环状构造的矿石。在前人研究基础上,经光薄片鉴定、扫描电镜观察和碳氧同位素分析等,认为这类矿石在宏观构造上显示出类似于灰泥丘的孔洞系统,微观上又发现了细菌等微生物结构,判断其属于一种矿化的灰泥丘。资料显示,灰泥丘产出的环境为陆坡相,水深明显大于台地相,并且灰泥丘与热水喷流沉积成矿作用关系密切,在国内外许多热水喷流沉积成因矿床中均发现有灰泥丘。本文所研究的两个矿床中灰泥丘构造矿石保存状况略有不同,冬瓜山铜矿灰泥丘构造矿石保留了大量显示原生热水喷流沉积成因的组构、并发现细菌等微生物结构,碳-氧同位素组成也显示原始沉积特征;而武山铜矿灰泥丘构造矿石则显示出受热液改造的矿石组构和碳-氧同位素组成特征,暂未发现细菌等微生物结构。冬瓜山和武山铜矿灰泥丘构造矿石的发现,有力地佐证了长江中下游成矿带在海西期曾发生过热水喷流沉积成矿作用。

Bedded sulfide orebodies occur in the Wushan and Dongguashan Cu deposits in the Middle and Lower Yangtze mineralization belt.In this study,we found a typical circular or laminated texture in the bedded sulfide ores.Based on microscopic observation of thin sections of the ore samples,carbon and oxygen isotopic analysis,and scanning electron microscope （SEM） observation,we suggested that this type of sulfide ores belongs to a mineralized kind of carbonate mud mound.The macroscopic structures of these sulfide ores are quite similar to those of cavities system of typical carbonate mud mounds,and there are also bacteria structures found in some of the ore samples with SEM analysis.Previous studies show that the carbonate mud mound generally develops in a slope setting with water depth deeper than platform.It is also shown that the occurrence of carbonate mud mound has a close relationship with sea-floor hydrothermal exhalative ore-forming processes.The conservation conditions of the carbonate mud mounds in the two copper deposits are different,in the Dongguashan Cu deposit a lot of primary exhalative sedimentary textures are preserved,bacteria structures are found,and the carbon-oxygen isotopic compositions show primary sedimentary characteristics,while those in the Wushan Cu deposit show hydrothermal altered/overprinted textures,and no bacteria structures have been found so far,the carbon-oxygen isotopic compositions also indicate a hydrothermal reworking.In summary,the discoveries of carbonate mud mounds structure sulfide ores in the Wushan and Dongguashan Cu deposits provide new evidence for the Hercynian sedimentary hydrothermal-exhalative mineralization in the Middle and Lower Yangtze metallogenic belt.