The characteristics of geological and altered rocks of Caijiaying Pb-Zn-Ag ore deposit

Youli Feng, Lijing Yu, and Ruizhong Hu

The Caijiaying Pb-Zn-Ag ore deposit locates at the northwest of Hebei Province, inner margin of northern to North China Craton and it is a large moderate temperature hydrothermal vein filled metasomatism deposit. It is mainly composed of five ore belts and always with buried vein ore body and occurred in the hornblende-biotite-plagioclase granulite of Hongqiyingzi Group, lower Proterozoic, and a few of ore body occurred in volcaniclastic rock of later Jurassic. The occurrence of stratum in the ore district is reversal monocline with north dipping. There is exposed pyrogranite-porphyry, quartz porphyry which has close relation with mineralization. The metallogenesis of Caijiaying Pb-Zn-Ag ore deposit is the product of the identity structural-thermal event between the turn of stronger structural system and magma fluid metallization initiated by extensional process during in Mesozoic era in the eastern of North China Craton.

The Caijiaying Pb-Zn-Ag ore deposit is duplex vein type and the main ore minerals as follows: marmatite, Fe-bearing sphalerite, sphalerite, galena, chalcopyrite and minor gold and silver- bearing minerals etc. There are many periods of wall rock alteration, but no obvious space zoning and the main type is green rock with characteristic minerals assemblage of epidote- actinolite-chlorite-carbonate. There are different altered rocks developed such as pyrite sericite quartz rock and sericitization. The sequence of wall rock alteration as follows: epidote- actinolite- chlorite; carbonate- sericite quartz rock- silicification, then later carbonate.

There exist positive dependency relation between the Fe2++AlIVand Fe/(Fe+Mg) value of the chlorite in the hydrothermal deposit and there are obvious different ratio value in chlorite in different deposit (ore district). There are obvious different of AlIV and AlVI value of chlorite in Caijiaying deposit and it demonstrates that this deposit has absolute property. The types of chlorite are medium amount of iron and brunsvigite and seldom Fe-rich chamosite in Caijiaying. The changes of chemical composition of chlorite depend on the forming environment such as temperature, pressure, acidity etc. The different types of chlorites in Caijiaying show the acid forming environment. There exist positive dependency relations among frequency difference of vibration zone in infra-red spectrum, iron amount and mineralizing degree in thuringite of Caijiaying.