Exploration
Bendigo Mining's revised exploration program is targeting the better endowed lines of mineralisation of Garden Gully and New Chum. 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 depths of around 800 m below surface.
Aim
The exploration aim is simple: find gold bearing quartz reefs and interpret them accurately from drill core. Recent production and trial mining has increased the ability for Company geologists to confidently identify potential economic grade-ranges and the size of reefs from visual inspection of 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 recent ore processing and the continual assessment of core drilled through 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 (>10 cm) and 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.
Significant research and development work is continuing with the goal of refining the targeting method. Detailed geochemical analysis and structural geology studies are underway with the goal of improving exploration success rates.
