Study of the Genesis and the Enrichment Regularity of Fengpinzi Placer Gold Deposit

The study area of the lower reach of Bailongjiang river is located in Longnan area and belongs to southern Qinling folded belt of western Qinling complex structural zone. Bikou group of lower Silurain (Slbk) developed very well, which is a set of greenschist series metamorphosed by clastic rock, volcanic rock and carbonate rock of marine facies, and is the source rock of the placer gold. A lot of evidences on neotectonism indicate that Bailongjiang valley had been risen, and the strata were weathered and denuded since Quaternary Period, provided a favourable tectonic condition for migration and enrichment of the placer gold. The negative locations such as fault depression and tectonic valley become the storing site of the placer gold. Moreover, the warm, moist climate and powerful hydrodynamic power also provide a favourable condition for enrichment of the placer gold. According to the analytical results of heavy concentrate samples which collected from alluvial flat at Fengpingzi, grade of the placer gold increaes with the depth at vertical section, 3. 5 - 5m and 7. 5m -11m are enrichment section of the placer gold; the outside point bar, near midchannel is the distributive zone of high grade at transverse section. So the deep mining is suitable for the placer gold deposit of alluvial flat in lower reach of Bailongjiang.