Practice of medium-large scale geological mapping for special issues in basic-ultrabasic intrusions:A case study of the Pobei intrusion in northeast Tarim Plate

1:50000 geological mapping is an important foundation geological work. However, there has been little research on geological mapping method of basic-ultrabasic intrusions. With the Pobei Cu-Ni sulfide deposit as the study case, and on the basis of practice of 1:50000 geological mapping for special issues, geological survey by geological mapping, geological physics, remote sensing and geological chemistry, the authors designed a synthetical method combining scientific questions, geological mapping and prospecting. The Pobei basic-ultrabasic intrusion is a magma suite which can be divided into 2 sub-suites according to mineralization type and magma nature, the Cu-Ni sulfide mineralization is related to peridotite facies, whereas the magnetite and ilmentite mineralization occur in gabbro, gabbronorite and pyroxenite. The Pobei basic-ultrabasic intrusion can also be separated into 5 units corresponding to 5 types of lithofacies. The practices on 1:50000 geological mapping are focused on field survey, measured sections, mapping routes arrangement, magma suites and units, structure mapping method, alteration mapping method, mapping process, map layout, prospecting and some other aspects, which provide implications for the present geological mapping for basic-ultrabasic intrusions.