赣闽浙三省接合区砂金资源的分布与沉积学特点

THE RESOURCES DISTRIBUTION AND SEDIMENTOLOGICAL CHARACTERISTICS OF PLACER GOLD IN THE JOINT AREA OF JIANGXI, FUJIAN AND ZHEJIANG PROVINCES

赣闽浙三省接合区砂金资源分布广泛,尤以赣东北乐安江、昌江水系最富。本文是在对该区野外调查,取样分析和典型砂金矿床、矿点地质环境分析的基础上,认为冲积型砂金富集与矿源层分布,水系发育规模及地貌条件,含金物质搬运距离,水动力条件,沉积界面微地貌及合金物质沉积后埋藏状况有密切关系,掌握砂金沉积学特点有利于资源的勘探和开发。

The enrichment conditions and depositional characteristics of placer gold in the joint area of Jiangxi, Fujian and Zhejiang Provinces are dealt with as follows:1.In this areas, there is a high concentration of placer gold in the drainages of the Lean-jiang and Chanjiang Rivers, which are located in Northeast Jiangxi Province, and the placer gold distributes almost in the whole region of the main river systems. The material sources derive mainlf from the metamorphic rock of m ddle proterozoic era. This stratum is rich in gold and covers 63% of the area, providing a good material condition.2.The distribution of the stratum of Green Stone is so wide that many mineral deposits and enrichment spots of placer gold are found and the gold-bearing layers are thick. The gold-bearing depositional areas are essentially in the valleys of the main rivers and their large tribu-taries.3.According to the heavy sand analysis, the enrichment of placer gold has close relation with its transport distance. In general, the anomaly area of gold-bearing sand is found not more than 10-20 km apart from the source, and the gold content gradually decreases with the tran-spor distance due to the effects of mechanical attrition and water sorting along the way.4.In the mineralization environment the variation in river dynamics is the main factor of gold enrichment. In the transitional section between the upper reaches and middle reaches of the river, the formation of various sedimentary bodies in the channel is due to sudden decrease in longitudinal river gradient, widening of river valley, abrupt reduction of current speed, and meander migration. These bodies have thicker gold-bearing materials, coarser gold grain size, and higher gold content.5.Microtopography plays a significant role in placer gold enrichment. The placer gold has a high content in ancient buried channel, grooves of selective erosion of the bedrock, and various corrosion depressions in the karst basin. The fill depth of placer gold in weathered cracks of the bedrock generally reaches 30 to 50cm.