Dart Mining (ASX: DTM) is progressing drilling at the Unicorn Porphyry Mo-Cu-Ag deposit, with the second hole known as DUNDD012 progressing to plan - and intersecting coarse visible molybdenum from 690 metres depth.
Unicorn has similar geological characteristics to the world class Henderson Climax-style primary Mo porphyry mine in Colorado U.S.
At a depth of 420 metres the hole passed out of the brecciated rhyolite and into a porphyritic granite, with minor visible molybdenum.
DUNDD012 is now currently 740 metres from surface with a target depth of below 1000 metres, which is the deepest drilling to date at the project.
The hole was designed to test the depth potential of the system below the current resource. This required the hole to commence to the south of the deposit and progress for some 420 metres generally outside of the scoping study pit.
This is a feature commonly observed in Climax style systems where a single porphyry pulse can transition from strongly mineralised rhyolitic (fine) porphyry at the top of the pulse to a barren central, granitic basal zone.
The Henderson mine in the USA has similar features, with later mineralisation from further down in the system only evident as steep veins within the otherwise barren granitic body.
These steep (radial) veins are often arranged in a radiating pattern (like spokes of a wheel) above the next mineralised porphyry pulse up to 150 metres further below the barren granite. Flat veins, which are often high grade, are known as concentric veins and often occur above and within the mineralised pulse.
A similar style of transition feature from barren granite to strongly mineralised porphyry appears to have been intersected by DUNDD012.
DUNDD012 has passed through 180 metres of sparse molybdenum mineralisation from 420 metres within granitic material before intersecting a major fault zone from 600 - 624 metres.
The hole then passed into typical Unicorn porphyry containing visible molybdenum with a significant increase in the density of quartz stockwork veins below 634 metres as radial veins.
A marked change in rock type occurs at approximately 690m where rhyolitic porphyry appears showing coarse visible molybdenum in a quartz stockwork zone showing minor concentric flat veins.
This open higher grade zone is a further 300 metres below the newly intersected M4 (refer ASX release dated 27 Feb 2013) and illustrates the very continuous nature of the stacked mineralisation zones developed in this style of deposit and provides further evidence to support that Unicorn is a Climax style porphyry intrusive similar to Henderson.
Currently the zone below 600 metres is being logged and sampled with assay results expected in early May. The first 420 metres of the hole has not been systematically sampled providing significant savings on assay costs and sample preparation.
The whole core has been retained for possible future sampling. Drilling progress has been slower than planned with DUNDD012 not expected to reach the target depth of below 1000 metres prior to the end of April.
Unicorn's unique characteristics
The Unicorn Project has a number of unique characteristics. It outcrops, has an extensive high grade zone from surface, is about 20 kilometres from the National Electricity Market infrastructure (hydro generation, switchyards and transmission lines).
The project also has abundant water onsite, road access, an existing logistics chain from mine to market, no known native title, flora or fauna issues and strong Corryong community and government support.
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