Geological structure and potentiality of Pb-Zn pseudostratified ores in East Bắc Bộ

Nguyễn Anh Tuấn

In East Bắc Bộ, many deposits and occurrences of Pb-Zn pseudostratified ores have been recognized, such as: Sỹ Bình, Bản Lìm, Phia Đăm, Bản Bó, Khuổi Giang and Yên Thổ. In this article, the characteristics of geological structure, mineral composition of ores, geochemical characteristics and forming model of ores in Pb-Zn pseudostratified deposits in above areas are described.

Pb-Zn pseudostratified ore deposits in East Bắc Bộ are distributed nearly along zoning deep-seated faults. These faults are mainly of NW-SE trend, playing the role of ore-conducting canals forming deposits and ore occurrences in the Thái Nguyên, Tuyên Quang, Bắc Cạn, Cao Bằng and Hà Giang Provinces. Ore bodies of seam form were formed mainly in metasomatic (dolomitized, calcitized, quartzified) limestone members which are favourable rock bodies for the formation of lead-zinc ores. The most part of these deposits are distributed in the anticline limbs lying near fault branches having sloping altitude in fractured zones, on pressing planes, bedding surfaces conformably with surrounding rocks of monoclinal structure or in carbonate members underlying beds of clay-sericite shale, quartz-mica schist that play the role of screens.

Ore minerals were formed in the exchange-replacement mode with surrounding altered rocks and ore minerals of the former stage. The paragenetic association consists mainly of sphalerite, galenite, pyrite, pyrrhotine. Secondary minerals are goethite, hydrogoethite, anglesite, smithsonite, etc.. The mineralization has the disseminated, nest, lenticular and filling fissure forms. Ore bodies have uncontinuously extending seam form, lying conformably with surrounding rocks.

Người biên tập: Trần Tất Thắng.