Gaya APA
Sumartono, . et al (1987).
Mineral Exploration of The Sigalala Area, Sumatra Utara, Northern Sumatra .
Bandung:
Pusat Sumber Daya Geologi.
Gaya MLA
Sumartono, . et al.
"Mineral Exploration of The Sigalala Area, Sumatra Utara, Northern Sumatra".
Bandung:
Pusat Sumber Daya Geologi,
1987.
Geokimia.