Kajian geokimia batuan igneus sekitar Gunung Pulai, Johor

The Gunung Pulai area is mainly underlain by igneous rocks and sedimentary rocks. The igneous rocks comprises plutonic and volcanic rocks. Granite is the main rock and consists of biotite granite and hornblende granite. There are also medium to coarse-grained granodiorite. The previous study showed that the age of these granites is early Triassic to early Creataceous. The volcanic rocks belong to the Gunung Pulai volcanic member of the Jurong Fonnation. The volcanic rocks are rhyolite and pyroclastics. The rocks were analysed for Si02, Ti02, AIP3' Fep3' MnO, CaO, Na20, ~O and Pps. The 12 trace elements analysed were As, Ba, Co, Cr, Cu, Ni, Pb, Rb, Sr, V, Zn dan Zr. From XRF analysis, the average (range) for major and minor elements (wt %) are: Si02 74.77 (67.84-79.92), Ti02 0.18 (0.050.53), AIP3 13.63 (11.21-15.93), Fep3 1.96 (0.63-4.97), MnO 0.05 (0.01-0.22), MgO 0.17 (0.02-1.06), CaO 1.54 (0.18-4.19), Nap 3.03 (2.56-3.58), Kp 4.02 (2.74-4.82) dan pps 0.03 (0.01-0.12). Meanwhile, the average (range) for trace elements are: Ba 487 (0-744), Zr 140 (115-186), Sr 99 (40-191), Rb 206(123-336), Pb 28 (4-83), As 18 (1126), Zn 25 (0-91), Cu 19 (13-38), Co 17 (0-42), Ni 5 (1-7), Cr 12 (7-22) dan V 17 (2-59). From geochemical studies, the granitoid are classified as I-type and peraluminous. The calc-alkaline value for the granitoid in the area is 64. Results from geochemical analysis show that granitoid rocks in the study area result from magma evolution from granodiorite to granite. Besides that, the weight percentage (wt%) for major and minor elements of rhyolite is Si02 74.99, Ti02 0.10, AIP3 13.14, Fep3 1.28, MnO 0.02, MgO bdl, CaO 1.31, Nap 2.60, ~O 4.42 and pps 0.01. Meanwhile, the concentration (ppm) of trace elements is Ba 595, Zr 144, Sr 96, Rb 254, Pb 24, As 17, Zn bdl, Cu 16, Co bdl, Ni 3, Cr 9 and V 6.