PLACER GOLD DEPOSITS FORMED BY RUNNING WATER IN NORTHEAST CHINA
辽宁、吉林、黑龙江地区流水成因的砂金矿

The formation of placer gold deposits colls for a source with abundant auriferous materials, advantageous exogenetic agencies, opportune neotectonic movement and favourable deposional enviroment.Having been exposured on the surface for a long time and subjected to sustained weathering, the gold-bearing geological bodies broke down and disintegrated. The products were then transported and sorted by running water along valleys, and the gold was finally concentrated to form placer deposits. In valleys, gold was transported in four forms: as single gold grains, by carriers, in"relays"and in solution. Their distances of transportation were different. In the process of transportation, these four forms coexisted but operated in different extent.The gold placers were formed in the early stage of the cycle of erosion of valleys under exogeuitic force in a surficial enviroment (normal temperature and pressure). The formation of the gold placers were directly affected by the current velocity and flow of the streams, character of neotectonic movement, geomorphological features of the valleys, nature of bed rocks of the valley floors, velocity of weatering and erosion and amount of auriferous materials.The placer gold orebodies all occur as zones or bands in sands and gravels and/or debris in the lower part of the valley fills (Figs: 4,5 and 6). The grade of the placer gold orebody varies slightly longitudinally (Fig. 10) but greatly laterally (Fig. 11 and 12). The gold particles are mainly flaky, tabular and granular, and intergrowths with gangues are often seen.When formed, the gold places suffered scouring and reworking due to downward and lateral erosion of the streams and flood currents, which were very favourable for gold enrichment at the bottom of the valleys.