论我国微细浸染型金矿床与沉积盆地演化的关系——以右江盆地为例

Relationship Between Sediments-hosted Micro-disseminated Gold Deposits and Basin Evolution: Case Study in Youjiang Basin, South China

对华南右江盆地中某些微细浸染型金矿床开展了系统的地质学、组构学以及矿床地球化学研究。地质学和组构学研究表明 ,这类矿床具有大量的沉积阶段—成岩阶段的成因特征 ,在沉积物沉积—成岩期间就已经成矿。矿化与碳酸盐岩孤台的密切联系和丰富的成岩期软变形组构 ,表明成矿与控制海底地形的同沉积期断裂活动密切相关。而大量泄水构造和液化层理的出现则表明 ,在沉积物成岩阶段 ,沉积柱中曾有大量流体的活动 ,而且这种盆地流体的活动与成矿有密切关系。丰富的生物_有机成因组构则显示 ,成矿与沉积有机质的演化有着密切的内在联系。另外 ,矿床没有显示出与岩浆活动的任何关系。因此 ,右江盆地的微细浸染型金矿床与美国的卡林型金矿床不同 ,可能是离散大陆边缘张性盆地演化过程中盆地流体活动的产物之一。

In the Youjiang basin, South China, numerous sediments_hosted micro_disseminated gold (SMG) deposits occur mainly in Permian_Triassic chert and siliciclastic rocks. Systematic geological, fabric and geochemical researches were carried out. The Youjiang basin is a Devonian_Triassic rift basin on the southern margin of the Yangtze Craton in South China. Strong syndepositional faulting defined the basin_and_range style paleo_topography that further developed into isolated carbonate platforms surrounded by siliciclastic_filled depressions. SMG ores are often auriferous sedimentary rocks with relatively low sulfide contents and moderate to weak alteration. Most of the SMG deposits are remarkably distributed around the carbonate platforms. Accordingly, there are platform_proximal and platform_distal SMG deposits. In the ores and host rocks there are abundant synsedimentary_syndiagenetic fabrics such as lamination, convolute bedding, slump texture, and soft_sediment deformation, indicating submarine hydrothermal deposition and syndepositional faulting. Numerous fluid_escape and liquefaction fabrics imply strong fluid migration during the evolution of sedimentary basin. Magmatic intrusive rocks are rarely found in Youjiang region. Such large_scale geological and fabric evidence implies that SMG ores were formed during basin evolution, probably in connection with basinal fluids. The isolated carbonate platform (as a basin paleo_high) and related syndepositional fault system, together with the unconformity_related facies succession, may have controlled the migration pathway of ore_forming basinal fluids and subsequently determined the location of SMG deposits in the Youjiang basin. SMG mineralization in the Youjiang basin may represent an integral aspect of the dynamic evolution of extensional basins along divergent continental margins. Geochemical study supports this model to various degrees.