11.1 million tonnes
The Merlin diamond mine is located approximately 100km-south of Borroloola and is the only diamond mine in Australia’s Northern territory. Merlin contains the second biggest diamond resources and reserve base in Australia and is also the third diamond producing mine in Australia.
North Australian Diamonds, now known as Merlin Diamonds, purchased the Merlin property from Rio Tinto in 2004. The mine is expected to have a life of more than 15 years.
Diamond production at the Merlin mine commenced in September 2013 with the processing of the historic stockpiles. Borehole extraction of diamond ore from the Ywain kimberlite pit was also commenced simultaneously. The trial production was conducted in 2010 recovering 10,600ct of diamonds. The diamonds sale generated approximately $1.86m.
Merlin diamond mine location, geology, and mineralisation
The Merlin diamond mine is located within the Merlin property, which was developed and initially operated by Ashton Mining and later taken over by Rio Tinto. The property comprises of the diamond mine and the surrounding exploration tenements (Merlin Orbit) extended in approximately 2,286km2.
The Merlin property is made up of 14 kimberlite pipes divided into four clusters in which nine deposits were subject to bore hole mining from 1998 to 2003 producing approximately 507,000ct of diamonds. The property was known for top quality white diamond and large specials; the biggest diamond weighed 104.73ct.
The property hosts diamond-bearing kimberlite pipes that are believed to have intruded the sedimentary rocks of the southern McArthur Basin and northern Georgina Basin. Much of the diamond mineralisation is disseminated in volcanic rocks. The mineralisation occurs as Cratier-facies sequences comprising of country rock with minor juvenile material.
Merlin diamond mine reserves and resources
Probable ore reserves, as of 2004, were estimated to be 11.1million tonnes of ore containing 2.9million carats of diamonds. The contained measured and indicated resources are estimated to be 4.31million carats.
Diamond mining and processing at Merlin mine
Borehole open pit mining is being conducted at the Ywain kimberlite pit in the central cluster, which will be followed by Gawain, Excalibur and Palsac pits. Borehole method reduces the need for drill and blast, hauling and re-handling of ore thus minimising the usage of mining fleet, and labour and capital costs.
The borehole method involves the usage of high pressure hydraulic water jetting tool to cut and break the kimberlite rock formations with in the pit. The resultant slurry is pumped to the surface via a hydraulic lifting system. The ore is then directly delivered to a 75tph capacity processing plant.
Processing methods such as HPGR and optical sorting were applied for diamond liberation and recovery during the pre-production trials.
Contractors involved with the development of Australian diamond mine
Jet Mining was awarded the contract to provide engineering and project management services for the diamond mine. It will also provide borehole mining equipment for the mine. The contract for operating the borehole mining rig, which provides access for the downhole mining tool, was awarded to Gorey and Cole Drillers.
DRA Group was engaged to upgrade and recommission the processing plant. AMC Consultants and Consulmet conducted the pre-feasibility study for the mine. Consulmet was awarded a contract in August 2011 to conduct the definitive feasibility study.
Cater Care Group was awarded the contract to provide catering and camp management services for the diamond mine. Merlin Diamonds teamed up with Kinley Exploration for conducting the borehole mining.