Monday, 10 May 2010

New developments increase optimism for Cornwall's South Crofty mine

Last December I reported that South Crofty, Europe's last working tin mine, which closed 12 years ago, was on the brink of reopening as a polymetallic mine, working orebodies containing copper, zinc, silver, lithium and indium, as well as tin.

Only last week the mine's owners, Western United Mines, announced a potentially lucrative new source of income- gold, assaying abouth 1.6g per tonne.

Jon and I decided to take the short trip to South Crofty from Falmouth, and talk to John Webster (near left with Jon), WUM's chief operating officer, and one of my past-CSM students.

It's a fascinating and highly complex project. The old South Crofty tin mine worked, in most cases, narrow veins of tin ore in the granite country rock, but exploration of the surrounding killas, a term for highly metamorphosed sedimentary and volcanic rocks, which underlies two thirds of Cornwall, had not, until now, been carried out.

The present historic resource consists of 53 identified potential orebodies in the South Crofty area, containing varying amounts of copper, zinc, silver, indium, tungsten and uranium, and now gold, as well as, of course, tin.

There are also lithium brines in the groundwater, which may be exploited not only for this light metal, but also for its heat; the high geothermal gradient could mean that the mine water has potential for sale to local housing and industries for heating purposes.

John took me and Jon to look at a couple of the exploratory drives, where drilling is producing cores, which are rigorously analysed every 10cm by a portable InnovX XRF analyser. The next stage is a complete mineralogical assessment of the core samples, which will be undertaken using the Camborne School of Mines extensive facilities, including XRD, Ion probe and QEMSCAN.

It is early days yet, but John envisages the orebodies being treated underground by some form of modular processing plant, such as Gekko's Python Underground Processing Plant, designed to operate in a 5m x 5m tunnel and produce a high-grade concentrate that can be pumped to the surface. Such keyhole plants have been installed in the Central Rand Gold Mine in South Africa (MEI Online). The shallow orebodies in the district are found as low as 40m from the surface so the decline ramps are ideally suited for this purpose. The target is to mine around 2500 tpd from 2-3 satellite deposits and pump the bulk concentrate from the keyhole processing plants to a surface storage facility where tankers will transport the crude mixed concentrate to a central processing plant at the South Crofty site for separation into saleable concentrates or metal.

The 63-strong workforce all seem highly motivated and confident that this project will come to fruition within the next few years, so please watch this space for further developments!

7 comments:

  1. I remember talk of an underground mill at crofty about 6-7yrs ago. Is this the same ownership as back then? Its good to see that they've switched the idea over to those portable processing units working on numerous stopes rather than a full on mill...

    Any idea of the resource tonnes and grades?

    Certainly would be exciting to see form of some hard rock mining restarting in Camborne.

    You never know - they may even move CSM back there! ;)

    DM

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  2. Hi there,

    The idea of underground processing is not new but fits this project very well.
    The company presently holds over 150 km2 of mineral rights and we are going to be surface scout drilling outside the main district in the next couple of weeks.
    We are targeting polymetallic targets primarily Cu, Zn & Sn but with significant Ag & In.
    Due to the layered nature both across the zones and with distance from the granite we work on a $/t value algorithm as there is low levels of correlation between various metals.
    However we would be targeting in-stope value of ~ $150/t with a cut off grade ~$45/T which equates even in the old Crofty stopes to be an average of 3-4m widths.
    We are looking at using an Alimak based stoping method which gives excellent control with low dilution and high tonnes per manshift.
    This coupled with mobile underground bulk concentrate production and immediate paste tails disposal gives low predicted in-mine costs.
    This is an area we need to focus on over the next year or so, but we are close to completion of a JORC standard recalculation of the old Crofty data which is showing ~45-55,000 tonnnes of in-ground tin which we are target drilling underground to find up-dip extensions (which we have had some success) and this is also around 4m wide and carrying 3-4% Cu as well as ~1% Sn.

    All in all quite a challenge especially with limited funding, but that is what it is going to take to get this project off of the "Tin Junkie" not-so-merry-go-round!

    Thanks for your interest in the project - watch this space

    Cheers

    John Webster
    Dip CSM
    COO
    Western United Mines

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  3. Sounds like the perfect project for the Python……..
    Processing underground with the Python is definitely an option not only from an environmental perspective but it also makes good financial sense. The Python came about from the application of LEAN principles to mining, looking at where the largest cost benefits can be gained in mining operations – the transport and handling of ore and waste was an obvious target. Not only do you reduce the energy taken to get the rock to the surface but if you use the Python to produce backfill underground you get double the benefit!

    Another spin-off of using the Python underground is that it may allow less selective mining methods to be used, as you’re not transporting the ore/waste so far. Ultimately this can unlock further reserves by allowing mining of previously uneconomic areas, effectively lowering the cut-off grade.

    Look forward to following the rebirth of South Crofty.

    Ben Murphy
    Gekko Systems

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  4. I have never heard of the Python processor before, but it sounds an interesting concept. Maybe this is a naive question, but what happens to the tailings from the Python? I can see the point of concentrating underground if the tailings are used as backfill, but if they are unsuitable for this, or there are no worked out stopes to backfill, there does not seem to be an advantage in underground concentration, as the tailins would have to be pumped to surface separate from the concentrates.

    From J.H., Canada

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  5. Plenty of open spaces down Crofty. Just pop a borehole into an old stope?

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  6. This is what Kidd Creek needs to do, start processing underground to reduce tonnage to surface. Even with a new shaft the weight of ore is considerable, when trying to hoist from such a great depth. Concentrating it underground is the efficient way to go, no one listened when I mentioned it. Maybe they did and just thought I was nuts!!!!!!!!!!!

    By Sean paterson at BB Power Construction and Mining Inc.

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  7. to J.H.

    The aim of the Python is to produce a tailings material that can be backfilled. The present Python design is at a fine crush, P80 down to 500-600microns, thus the tailings material is coarse and dewaters well. Obiviously the material would have to be assessed for backfill suitability for the specific operation and then treated accordingly on a purpose built backfill Python-skid.

    You've also hit on an important factor for successful underground processing integration, that is to adusting the mine planning regime to ensure there are stopes ready to be filled.

    Ben Murphy
    Gekko Systems

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