The Seruyung Gold Deposit, North Kalimantan, Indonesia: Exploration History, Evolving Geological Model, and Its Characteristics

Mineralisation Styles

Mr. Ikrar Teguh Mandiri

J Resorces Nusantara

Seruyung is one of epithermal deposit at Kalimantan, Indonesia. Located in the northern part of Kalimantan, Seruyung is situated along NE-trending corridor, known as a part of “the Kalimantan gold belt”, which hosts several other epithermal Au deposits such as Mt. Muro, Kelian, etc. Seruyung Gold Mine, run by J Resources Nusantara since 2011, has been in production since 2014, a more than a two-fold increase on the amount estimated during the feasibility study. This paper describes the discovery and exploration history, and how the geological concept evolved during the life of the mining. It also discusses the characteristics of the gold deposit and the reason why resources increased during the mining stage.

The hydrothermal alteration halo can be divided successively into chlorite-dominant, illite-smectite dominant, alunite-kaolinite dominant and quartz dominant rocks from outer zone inwards. The host rocks of the mineralization are pyroclastic rocks, intrusive andesite, and diatreme breccia. In addition to Au, the elements Ag, As, Pb, Zn, Cu, and Mo are enriched to varying degree within the host rocks and alteration halo. The main ore minerals include pyrite, enargite, bornite, and covellite, with pyrite occurs as the most common sulphide mineral. Gold occurs mostly in fine grained containing an average of low Ag content. Most of the gold grains in the deposit associate with Fe oxide minerals such as hematite, goethite, and jarosite.

The Seruyung deposit is interpreted to belong to the high sulfidation epithermal type. The adjacent hypabyssal intrusion is an obvious source of both hydrothermal fluids and metal. The post mineralization structure is believed as the main control of the mineralization displacement.

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