Hydrothermal Alteration Zonation in Copper-Gold Porphyry Deposition Based on Surface Mapping and Geophysical Exploration at Berambang Prospect, Sekotong Subdistrict, West Lombok, West Nusa Tenggara

Abstract

The research sites are located in the village of Berambang, Sekotong District, West Lombok Regency,
West Nusa Tenggara Province. This area was dominated by volcanic rocks composed of dasitic
volcanic rock, diatrema breccia, and diorite intrusion. Berambang area shows alteration in the form of
potassic, propylitic, advanced argillic, and argillic alterations where in some places accompanied by
pyritisation and stockwork structure, the type of mineralization in this area is a porphyry copper-gold
type. In the potasic alteration zone there are minerals that have a strong anomaly response to the
magnetic due to the presence of oxide minerals magnetite (Fe2O3). Mineral sulfides such as pyrite
(FeS2) and chalcopyrite (CuFeS2) will also provide significant anomalous responses that have an
abundance of 2-5% in the potassic zone. In a propylitic alteration zone characterized by chlorite,
calcite and epidote minerals that do not respond to magnetic anomalies, the presence of pyrite
minerals, hematites and chalcopyrite with abundance of ≤1% will provide some magnetic anomaly in
the propylitic zone. As for advanceargillic alteration zones characterized by mineral andalusite, alunite
and quartz, there will not be any magnetic anomalies, the phenomena was due to the rarity of
mineralization in this zone gives an insignificant anomalous impact. Meanwhile, for the argillic zone
characterized by mineral illite, kaolinite and smectite will not have anomalous magnetic impact, very
rare mineralization in the argillic zone so that the magnetic anomaly is not significant. From the floating
Euler 3D shows an anomalous source from a depth of 0 meters to a depth of more than 400 meters.