Abstract:

A blinded ancient gold-bearing placer layer is firstly found at 679.19 m segment of the D7 drilling, in the Muling Formation in Jixi basin, eastern Heilongjiang Province. Heavy minerals in placer layer include native gold, authegenic monazite, clastic monazite, xenotime, zircon, galena, sphalerite, rutile, ilmenite, apatite, biotite, chlorite, pyrite, chalcopyrite, leucoxene, titanite, limonite, hematite, magnetite, Fe-Mn minerals, boehmite, uranium-oxide mineral, native copper and native copper-zinc metals etc.The ancient placer layer is thick about 4.14 m. The volume content of heavy minerals in thin section of  the placer is estimated to 10%-24%. The finding of gold-bearing pacer layer can supply new valuable information for judgement of gold source in this area. Based on sedimentary texture and structure, it is supposed that the ancient placer layer might be formed in coast sedimentary condition. Authors suggest that the magnetic logging method be used to determine the distributing area of blinded ancient placer. Moreover, such minerals as authegenic monazite, framboid pyrite, and native copper-zinc metal in the ancient placer layer indicate that the layer was formed in a favorable sedimentary environment for biomineralization process.

Key words: Jixi basin, Cretaceous, blinded gold-bearing ancient placer, authegenic monazite, gold mines