Dart Mining NL (ASX: DTM) has made progress with pre-feasibility metallurgical and geotechnical drilling with the completion of five large diameter (83.5mm PQ) diamond drill holes, to test the variability of the metallurgy across the deposit and to determine rock strength / stability properties for mine pit design.
As previously announced on 17 January 2013, DUNDD008 intersected the northern edge of the target porphyry system at 586m and then passed through some 27m of lower grade surrounding rhyolite before intersecting the host sediments at 613m. The hole was extended to 695.8m and remained within sediments.
Final geological interpretation and assay data now available indicates that the new M4 mineralisation zone (22m @ 0.1% MoEq1 including 12m @ 0.12% MoEq1 from 482m) was intersected near the northern edge of the porphyry system before the hole entered the lower grade surrounding rhyolite which is consistent with previous drilling. Promisingly, the brecciated porphyry / rhyolite contact in DUNDD008 contained intersections of up to 4m @ 0.12% MoEq1.
DUNDD008 has confirmed that the Unicorn porphyry body dips to the south rather than being sub vertical. This is common for these types of porphyry systems and, with the intersection of another stacked high grade zone in M4 within DUNDD008, Dart Mining remains confident that Unicorn is a climax-style porphyry similar in nature to Henderson.
Pre-feasibility metallurgical testing is underway following the completion of five large diameter PQ diamond drill holes located across the deposit. Approximately 7 tonnes of samples from the four main ore types has been shipped to the AMML laboratory in Gosford (NSW) to undergo a series of grinding, flotation and recovery optimisation testing. These studies will supply the key data to allow detailed plant and tailings dam design and provide pre-feasibility level mine planning to commence.
These metallurgical holes were also geotechnically logged, together with some previous diamond holes. Initial indications from Coffey Mining, who supervised the logging program, are that overall batter angles of up to 55 degrees, consistent with the scoping study, can be used in pre-feasibility mine design.
The second deep diamond drill hole (DUNDD012) has now commenced from surface and has been located to stay within the porphyry body down to approximately 1200m, having taken into account that Unicorn is interpreted to dip to the south. The hole started in brecciated sediments and passed into the main porphyry zone at 126 m as anticipated and is currently at approximately 300m. It is expected that this second deep hole will reach 1200m by the end of March.
At approximately 270 metres down DUNDD012 and some 170 metres below the current scoping study pit boundary, a 1 metre intersection of brecciated porphyry containing strong veining of molybdenum has been encountered. Encouragingly the brecciated material is cemented by molybdenum rich fluids rather than the usual silca which has not been seen before at Unicorn. Brecciated porphyry is an indicator of deep seated volcanic activity which is the likely source of mineralisation into Unicorn.
It is expected that this second deep hole will be at approximately 1200m by the end of March.