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!

Short Course Nightmares

I met up with Fathi Habashi at the SME Meeting in Phoenix, and he mentioned that he is presenting a 2-day course “Introduction to Extractive Metallurgy” this month. I do not envy him, as I know how hard these intensive courses can be. In the early 1980s I gave a few introductory 2-day courses to mining engineers and geologists in Johannesburg, and it was exhausting.

Nothing like my nightmare short course though! In 1994 I was invited to give a 25-hour lecture course on mineral processing at the Alès School of Mines in France. Foolishly I agreed- the course was over a four day period, after which I had to set and mark an examination for the 5th day! It was exhausting; the students spoke good English, but I’m not sure that they really came to terms with my Lancastrian accent.

Never again! I just wondered if anyone else has had interesting short course experiences, either as a lecturer or participant.

Undoubtedly my most memorable short course was a 5-minute presentation on froth flotation to Her Majesty the Queen in 1980. It must also have been a memorable experience for Her Majesty, as she is obviously enthralled by my efforts.

New Comments Alert

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Comminution '10 is the biggest yet  2 new comments
Grinding Mill DEM Modelling  2 new comments
Stranded in darkest Africa  4 new comments
Post-Comminution '10- 2 new comments
Are rod and ball mills set to become obsolete?  5 new comments

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Maybe rod mills are at the dusk of their usefulness?

My last blog posting has already had two interesting comments, and I think a lively discussion is building up on LinkedIn, on the Minerals Engineering and Grinding Mills Technology groups.

One of the comments, by Dave Almond, Global Product Manager, Process Control Systems at FLSmidth Automation, USA, I highlight here:

This is an interesting question. Although new rod mills were being installed in PGM's as recently as 8 years ago (Northam Platinum) and are still installed in phosphates I do think they are at the dusk of their usefulness. There are limits to the length of the rods manufactured and consequently rod mill sizes are limited to fairly small dimensions (~15' diameter) and thus capacity is limited and not really suited to the low grade, high capacity operations being built today. Pity in some ways as rod/ball circuits were more energy efficient than the new SABC circuits of today.


I am less inclined to agree that ball mills have reached the end of their usefulness. Once again mainly due to the economies of scale needed to make many new projects viable and stirred mills also have limited capacity making multiple lines necessary which in turn brings back the old headaches of maintenance intensity and associated costs. Ball mills are now as large as 28' diameter (yes, the first ones have been ordered for a copper project in Peru) making single line, high throughput grinding lines still very practical.


HPGRs are also still limited on throughput resulting in the same issues as for stirred mills. They may eventually get there but the large HPGRs installed today already have grinding rolls exceeding 100 tonnes in mass! These are not small components to change out!


I guess to answer your question, my perspective is that SAB circuits will still be around for some years to come. Rod mills are about done. HPGRs are interesting but not a silver bullet or that innovative given that roller crushers were used in the same applications years ago and the Randol conference in Perth (2005) seemed to support that HPGRs worked better at medium pressures than high pressures. These machines all have their place under the right conditions (Mogalakwena North in SA and Boddington in Australia seem to be good examples). What is a little worrying is that many minerals processing professional consultants I have talked with claim they are beginning to be concerned that they are being asked to justify selections of equipment types based on trends/fashion rather than good scientific investigations.


I would be interested to hear other perspectives on this subject as it is an interesting one.

Are rod and ball mills set to become obsolete?

This was the provocative question I asked delegates at Comminution '10, during the final summing up of the conference.

At the beginning of the 20th century the advent of rod and ball mills led to the demise of stamp mills, and rod and ball mills then dominated 20th century grinding circuits.

Are we about to see a new revolution, with rod and ball mils superceded by circuits involving HPGR/SAG mills and stirred mills?  It was apparent at the conference that HPGR are being increasingly utilised, while the use of stirred mills, originally designed for ultrafine grinding, is extending slowly into the coarser grinding ranges.

Froth Flotation news

LinkedIn members may not be aware that a new group, Froth Flotation, was formed very recently.  As yet there are only 15 members, but I am sure that the size of the group will increase as people become aware of its existence.  Members so far seem to be also associated with the Minerals Engineers group, which currently has 464 members.

Dr. Stephen Grano is well known to sulphide flotation researchers. Formerly with the Ian Wark Research Institute in Australia, he was also MEI's consultant on our first flotation conference, held in Adelaide in 2000. Stephen has now been appointed to lead the University of Adelaide's new Institute for Mineral and Energy Resources.  The full story can be found on MEI Online.

Later this year Minerals Engineering will publish a special Froth Flotation issue, containing selected papers from last year's Flotation '09 conference in Cape Town. Ninety-eight papers were presented at the conference, of which 50 have been submitted for peer-review. It is expected that around 40 papers will be in the special issue, currently scheduled for Volume 23 Issues 11-13 in October.