PEMETAAN GEOLOGI, ALTERASI, MINERALISASI DAN KERAPATAN URAT KUARSA PADA BENCH 210 UNTUK MENGETAHUI PENGARUH KERAPATAN URAT KUARSA TERHADAP MINERALISASI DAN NILAI KADAR TEMBAGA ENDAPAN PORFIRI CU-AU BATU HIJAU, SUMBAWA, NTB

Abstract

Porphyry deposit is one of hydrothermal deposit which has potential to
yield economic minerals such as gold, copper and molybdenum. Studying the
geological concept of porphyry deposit like lithology aspect, type and
characteristic of alteration, mineralization style and vein type can laid to concept
of mineralization environmental that can generate ore. Study of mineralization in
porphyry deposit also need quartz vein density analysis to determine the high
grade and low grade mineralization zone.

This research is purposed to determine the distribution of lithology, zone
of alteration and the relationship between quartz vein density and mineralization
in Batu Hijau Porphyry Deposit. Furthermore the result of the research can be
the consideration for geologist to mine the high grade materials.

The methods that used to analyze the relationship between quartz vein
density and mineralization on Bench 210 Batu Hijau Porphyry Deposit are by
doing highwall mapping on north and east side of Bench 210 open pit and logging
121 geological cores which passed bench 210 (each core’s length 15 meters).

From the approach above, known that lithology from old to young are
Volcanic wallrock, Diorite Intrusion, Intermediate Tonalite Intrusion and Young
Tonalite Intrusion. Megascopic and microscopic observation show that alteration
on research area can be divided into 5 alteration zones, they are: Partial Biotit
Zone (potasic zone), Secondary Biotite Zone(potasic zone), Pale Green Mica Zone
(argilic zone), Chlorite-Epidote Zone (philic zone) and Feldspar Destructive Zone
(propilic zone). Mineralization that occurs in research area is copper-sulfide
mineralization. Bornite (Cu5FeS4) and Chalcopyrite (CuFeS2) are the main
copper sulfide ore and Pyrite as gangue mineral. Quartz vein density zone on
research area is divided to very abudant quartz vein density (10-15%), abundant
quartz vein density (5-9,9%), moderate quartz vein density (3-4,9%) and rare
quartz vein density (0,3-2,9%). There are positive relationship between quartz
vein distribution and Cu assay content. The higher quartz vein density in Bench
210 is the higher Cu assay content and generally occurs in Bornite dominated
zone. And the lower quartz vein density is the lower Cu assay content and
generally occurs in Pyrite dominated zone.