Lithogeochemical characteristics of rocks from borehole No. BS03 in Beishan area, Gansu province

The lithology, petrochemistry and isotopic geochemistry of rocks from borehole No. BS03 have been studied in detail. The results indicate that the dominant lithology of rocks from borehole No. BS03 is the porphyritic monzonitic granite which accounts for 65.35% in the whole section of the borehole. The minor dominant lithology is the quartz diorite and tonalite accounting for 24.28%, and medium to coarse-grained granite, pegmatite and aplite. The ASI index is about 1.0 for the porphyritic monzonitic granite, biotite granite and tonalite. The ASI index for the quartz diorite shows distinct aluminium undersaturation with the ASI value of 0.66-0.68. All kinds of rocks mentioned above are of I-type granite according to their REE patterns. Generally, these rocks have the similar REE patterns meaning certain genetic relationship among them. The Nd, Sr isotopic characteristics reveal that rock-forming materials of granites in this area were originated from the lower crust, possibly, partly from the upper mantle. (authors)