Exploration
Bendigo Mining's revised exploration program is targeting the better endowed lines of mineralisation of Garden Gully and New Chum at depths of around 800 m to 1,200 m. Garden Gully and New Chum lines account for some 70% of Bendigo's historic gold production and are the key exploration targets. Drilling is conducted from underground workings at a depth of around 760 m below surface.
Aim
The exploration aim is simple: find bigger reefs than those found to date and interpret
them accurately from drill core. Company geologists are confident they can identify
potential economic grade-ranges and the size of reefs from visual inspection of
the drill core and assay data.
The use of visual inspection is a more fundamental approach which is better suited and appropriate to local conditions. Company geologists now use their accumulated knowledge to make assessments of size and quality of mineralisation based on the visual examination of core. This geological assessment is backed by assays and the knowledge gained from processing over 140,000 t of ore and a reassessment of core drilled through those mined areas.
Targeting
The exploration for mineralised reefs at Bendigo is defined by two key indicators:
prospective stratigraphy and laminated quartz veins.
Prospective Stratigraphy
The Company is able to define stratigraphic units (identifiable packages of rock
or strata) that are favourable hosts for gold mineralisation and use them as targets
for exploration. Attractive sequences of rocks have been identified across the field
from the New Chum to Garden Gully anticlines.
A prospective horizon comprises two main elements, the first and primary one, is the presence of a laminated quartz vein of significant width (>10cm) in secondly, a sequence of sandstones and shales conducive to forming a structural trap/dilation at the anticlinal hinge.
Laminated quartz veins
Laminated quartz veins (LQs) are quartz vein-faults that occur on both east and
west limbs of all anticlines across the Bendigo Goldfield. Reefs have formed in
Bendigo by gold-bearing fluids travelling up the LQs and precipitating gold, quartz,
and traces of other metals in structurally and stratigraphically favourable positions
such as the anticline axes. LQs are a pathway to mineralisation: the width of the
LQ in the limb of the anticline indicates the reef forming potential of the LQ at
the axis of that anticline.
The identification of stratigraphy and laminated quartz veins can enable the exploration to target in on specific zones that have potential to form mineralised reef.
Targets
Current exploration is focused on the Garden Gully and New Chum lines using the
data from historical mining as a guide to the more productive regions. Drilling
is conducted beneath or along from historic mines searching for extensions of mineralisation.
The Company’s two key targets are the central Garden Gully zone (which historically produced some 1.6 Moz at 16 g/t gold from surface down to a depth of approximately 750 m) and the southern portion of New Chum.
The underground drive (North drive) to enable drill access is being developed at a depth of 760 m parallel to the Garden Gully line and offset by around 250 m to the west of the line. The southern end of the New Chum line can be drilled from existing mine openings.
Note. Click the image above to enlarge.
