A Nigerian national was Sunday arrested for possessing ganja and amphetamine valued at Rs.4.6 lakh, Goa Police said here.Accused Elvis Okeke was nabbed at Taleigao, a Panaji suburb with 69 gm of amphetamine colloquially known as "Speed" and 1.2 kg of ganja. Okeke has been booked under relevant sections of the Indian Penal Code and the Narcotics Drugs and Psychotropic Substances Act.