GEOLOGICAL AND GEOCHEMICAL FEATURES AND THEIR SIGNIFICANCE OF THE GEZHEN GOLD ORE ZONE IN WESTERN HAINAN

摘要

The Gezhen gold ore zone crosses sideways the western Hainan. In the zone crop out mainly the Meso-Proterozoic metamorphosed rocks of the Baoban Group, Ordovician epimetamorphosed rocks of the Nanbigou Formation and Indosinian granite. The NE trending Gezhen fault zone which- controlled the contributions of the Tuwaishan, Baoban,Beiniu, Hongpumenling and Bumo gold deposits, etc., is located at the contact between the Baoban Group and the Nanbigou Formation. This zone is 55 km long and 0.5-2.0 km wide. Along the gold ore zone four types of gold mineralization are distinguished as follows: (1) Ptygmatic vein type, formed in Caledonian-Early Hercynian (470.5-342.5 Ma). The veins have gold grade of 0.1 × 10~(-6)-0.3 × 10~(-6)g/ t, and are widespread distributed in the migmatite of the Baoban Group. (2) Mylonite type, formed during Indonisian Period (225-224 Ma), e.g. the Hongpumenling gold deposit. (3) Jiaojia (altered cataclastic rocks) type, formed in Late Indonisian-Early Yanshanian (170-130 Ma), samples are the Baoban and Tuwaishan gold deposits. (4) Quartz vein type, formed during Late Yanshanian (100-80 Ma), sample is the Bumo gold deposit which was dominantly distributed in the P.D.R.T fractures at the sides of the shear zone. The ores of the four types of Au mineralization have similar mineral association, i.e., gold, electrum, arsenopyrite, pyrite, quartz, sericite and so on.