Merlin Diamond Mine
Ashton Mining Limited began open pit trial mining of ore in late 1998 with the first diamonds produced in February 1999. During its operation, the mine produced approximately 500,000 carats from the processing of 2.4 million tonnes of ore, sourced from 9 of the kimberlite pipes. The average value of diamonds produced at this time was approximately US$108/ct.
In March 2004, North Australian Diamonds Ltd acquired the Merlin mineral lease from Ashton Mining Ltd. Reprocessing of sort house tailings commenced shortly after, with trial production of primary kimberlite ore beginning in 2006.
The Merlin kimberlite field has a current indicated and inferred resource of 18.88M tonnes.
Discovery and Development Timeline:
| Ashton Mining Limited |
| 1986 |
E.Mu pipes discovered by CRAE |
| 1990 |
ADEJV follow-up of unresolved chromite anomaly |
| 1991-1994 |
Merlin field discovery |
| 1994-1996 |
Evaluation testing programmes |
| 1996-1998 |
Feasibility study |
| Late 1998 |
Open pit trial mining commences (Excalibur, Palomides-Sacramore) |
| Nov-2000 |
Ashton take-over by Rio Tinto |
| Rio Tinto Pty Ltd |
| 2001 |
PalSac development options - LDC evaluation programme |
| 2002 |
Merlin Project offered for sale |
| 2003 |
Mine closure. 500,000 ct from 2.4 Mt ore |
| North Australian Diamonds Limited |
| 2004 |
NADL acquired Merlin Mining Lease
Data Review: A review of the data allowed an assessment of the diamond under recovery due to poor liberation and inefficient recovery. Based on recalculated grades and increased diamond values, a scoping study completed by AMC Consultants Pty Ltd indicated borderline commercial economics. |
| 2005 |
Grade (Liberation and Recovery Tests): The Company proceeded to test the assumptions on grade as they related to liberation and recovery. To this end the company used a prototype HPGR supplied by Koppern to undertake liberation tests. The results from this test work exceeded expectations, with grades improving 30 – 50%. At the same time the company developed ‘optical sorting’ and magnetic separation techniques for recovery of non-fluorescing diamonds. The sorthouse tailings from previous operations were reprocessed resulting in 14,000cts being recovered, including four +10ct diamonds. High value, non-fluorescing ‘fancy’ yellow diamonds were also recovered. |
| 2006 |
Diamond Value (Trial Production and Sales): Although the data from previous sales was available, the data was compromised due to the liberation and recovery issues. ‘Run of Mine’ diamonds were required to establish current values. As a consequence the company embarked on trial mining and processing, using the larger Bateman processing plant relocated from the Company’s Kimberley project. Sufficient price points were obtained to establish a diamond value model for the Ywain and Gawain pipes. A total of 12,000cts were produced and sold. |
| 2007 |
Scoping Study: A broad scoping study, using information gained from trial mining and
previous mining operations identified a potential large scale commercial
mining project based on the known resources and also including potential
deeper resources contained within the Central and Southern cluster
pipes. Prior to undertaking prefeasibility studies additional resource
definition drilling and grade determination sampling is being undertaken to
increase the resource, compliant with JORC standards, sufficient to
underpin a potential long term mining operation.
Resource Definition Drilling - Gawain Pipe: The first stage of the resource drilling programme commenced in October, 2007 on Gawain pipe. The drilling to date has provided more detailed pipe geometry to a depth of 400m below surface. The deepest drill intersection which provides a kimberlite/wall rock contact is 590m below surface. The drilling has also provided core samples to undertake grade analysis work based on fine diamond analysis. The drilling concluded in late November 2007 after the drilling of 11 holes for a total of 2,390 metres. |
| 2008 |
Resource Definition Drilling -
continuing: The drilling program recommenced on the 20th February 2008. The ongoing work program will include drilling on the larger PalSac pipe. |
Resource Statement:
Inferred and indicated resource grades are based on a bottom slotted screen size of 1.0mm. Grades reflect the variation of grade due to increases in rock density with depth.
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Ywain Trial Production |
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Southern Cluster Pits – (L-R) Launfal, Sacramore, Palomides |
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