Abstract
In mineral exploration, collection of structural data is important in order to understand the
intricate interplay of structures and their impact on the mineralisation. Valuable
structural information can be gained from drill cores and it is important to extract all these
information. The best way to maximise the structural data from drill core is through core
orientation. Various methods are currently available for core orientation including:
Spear, Ezy Mark®, Ball Mark®, and Ace Core Tool®. The current study used simple
Spear-method utilising Chinagraph pencil. A procedure was developed in-house in
marking, preserving marks, drawing bottom of hole lines, and alpha and beta readings of
structures. Processing and analysis of alpha and beta readings is facilitated through
GeoCalc and GeoOrient softwares.
The core orientation procedure was applied in the definition drilling of the Bundulipu
Gold prospect in Avocet’s Totopo Project, Gorontalo, Indonesia. Combined with logging
of vein mineralogy, vein textures and cross-cutting relationships, Avocet geologists were
able to come-up with a feasible interpretation of the structural paragenesis and its impact
on the gold mineralisation.
The Bundulipu prospect is characterised by epithermal quartz-sulphide veins hosted by
Pliocene dacitic to rhyolithic pyroclastic rocks. It was originally interpreted that these
veins were developed within a pair of NW-SE trending sinistral faults forming a small
pull-apart basin. Mineralised quartz-sulphide veins form within this pull-apart basin.
Structural measurements in drill cores showed that mineralised veins occur as moderate
to steep, northwest dipping veins trending ENE-WSW to NE-SW. Unmineralised veins,
on the other hand, have gentle to moderate dips to the north-northeast and west. The
structural readings of these veins and their spatial distribution confirmed the regional
structural interpretation of a dominant E-W stress field and the development of veins in a
small pull-apart basin. Vein paragenesis and fault readings indicate that this stress field
has a protracted history that outlived the mineralisation event. This interpretation helped
significantly in the delineation of the vein system at Bundulipu.
By: Eddy Da Costa/ Boyet Bautista
PT. Avocet Bolaang Mongondow
Jl. Kol Sugiono no 24 – Kotabangon
Kotamubagu – Sulawesi Utara
Phone : 0434 – 2628776
Fax : 0434 – 22965