Sunday 25 February 2024

Sunday in Phoenix

I arrived in Phoenix last night after an 11 hour flight from London. For once everything went to schedule including, remarkably, the trains from Falmouth to Heathrow.

Due to the seven hour time difference I was up very early this morning and after breakfast ventured out into a very balmy downtown, the temperature similar to a good summer day in Cornwall.

The short walk from my hotel took me to the Phoenix Convention Centre, where not surprisingly at 7.30 in the morning the registration area for MINEXCHANGE2024 was very quiet.

After completing registration I called in at the SME Bookshop to say hello to Theo Warrior and Melissa Serdinky and to see what the latest mineral processing offerings are this year.

Melissa and Theo

Tailings Case Studies: Real-World Lessons in Tailings is edited by Kimberly Finke Morrison, Senior Director for Global Tailings Management at Newmont Corporation, USA.

Basic Cyanide Chemistry: a simple guide for gold and silver leaching by Michael Botz equips readers with basic knowledge about cyanide's interactions with gold, silver, and other metals, enhancing understanding of these processes and their influence on leach solutions and ore processing.

Leaving the convention centre I strolled around downtown passing by Heritage Centre, an historic site anchored by the Rosson House, a fully-restored 1895 Queen Anne Victorian house, now a museum which interprets the history of Phoenix. 

Passing by the convention centre again I had coffee with Kriss Waters and Alex Doll. Kriss is the Canadian Editor for Minerals Engineering and Alex, Principal Consultant with Alex G Doll Consulting Ltd, has agreed in principle to present a keynote lecture at Comminution '25 in Cape Town next year.

With Kriss and Alex
I met up with Kriss again a couple of hours later for lunch at the ever excellent Seamus McCaffrey's Irish Pub on Monroe Street, not in the least being tempted by the restaurant opposite!

Then it was back to the hotel, a quick change and back to the convention centre for the opening reception for the exhibition, the start of MINEXCHANGE2024.

Thursday 22 February 2024

Deep diving in the 1970s

I recently caught up with an old Cornish miner who I had not seen for around 45 years. Terry Angove had been involved with shaft sinking at the old tin mines of the 1970s, South Crofty, Wheal Jane and Mount Wellington, but I knew him not as a miner but as a very competent diver and we talked a lot of our dives in the 1970s, particularly a deep dive in Falmouth Bay on the wreck of the HMT Rinovia.

The HMT Rinovia was a steam fishing vessel, requisitioned as a mine sweeper in 1939. In 1940, it hit a mine and sank and although its approximate location was known, about 2 miles off Falmouth, there was no search by local divers, probably due to the depth of water, about 180 ft (55m), considered to be too deep for diving breathing compressed air. 

In October 1977 a local fisherman spotted the wreck on his echo sounder and identified transit bearings, two fixed and visible objects lining up on the Falmouth shoreline. He reported the wreck location to the Falmouth Branch of the British Sub-Aqua Club (BSAC). At the time I was Diving Officer for the Falmouth and Camborne School of Mines branches of BSAC and as such was responsible for dive planning and safety. The opportunity to dive on a 'virgin' wreck was too good to miss, but it would have to be undertaken by the most experienced deep divers in the clubs, as anything over 100 feet (30m) was regarded as deep and 132 feet (40m) was recommended as the limit for compressed air diving. It was always a source of amusement that non-divers referred to our air bottles as 'oxygen tanks'. Compressed air was used not because it was cheap, but because pure oxygen could be lethal when breathed at only around 2 atmospheres pressure, a depth of only 10m, many wartime divers dying due to oxygen poisoning.

It was decided that a four man team would dive on the Rinovia, Terry and me, Mike Tuffery, a local tug captain and Ken Dunstan, a local fisherman and owner of the 24 ft Pisces, Falmouth Branch's regular diving boat. All of us had many +100 ft dives under our belts, the most recent and deepest being 160 ft (49 m) off the Wolf Rock Reef between Land's End and the Isles of Scilly.


Diving to such depths is not just a matter of strapping on an aqualung and plunging below the surface, it requires careful planning and a knowledge of the physics and physiological effects of diving. In planning the dive there were a few things to take into account:

Air Supply: On the surface the average human breathes about 1 cubic feet (0.03 m3) of air per minute. I would be using two (twin) bottles, containing 110 ft3 of air compressed to 160 atmospheres (ats) pressure. The bottles were connected to a regulator on the mouthpiece which supplied air on demand at the pressure of the surrounding water. Every 33 ft (10 m) of depth increased the surrounding pressure by 1 atmosphere so at 10m a diver would be breathing air at 2 ft3 per minute and at 180 ft the pressure would be 6.5 ats, so we would be consuming 6.5 ft3 per minute, imposing a severe limit to the time we could spend at depth. 

Also taken into account was that air at a pressure of 6.5 ats is very dense and there would be an increase in exertion just by breathing it in. This would also be exacerbated by the effect of cold water at depth and the effect of pressure on our neoprene wetsuits. Neoprene is a synthetic material which is full of minute 'closed cells' of nitrogen which provide insulation. It provides buoyancy such that the diver requires a weighted belt (7 kg in my case) to achieve neutral buoyancy at the surface. However as the diver descends, the pressure squeezes the nitrogen in the cells, the wetsuit becomes thinner and loses its insulation properties, and also its buoyancy, so to maintain neutral buoyancy it is necessary to bleed air from the bottles into the adjustable buoyancy lifejacket (ABLJ), an essential part of the equipment. On returning to the surface this added air must be bled out of the ABLJ to avoid an uncontrolled ascent.

So we could plan the dive, and its duration according to our air supply, but the main concern with deep diving with air is the effect of nitrogen on the body.

Nitrogen: Air contains 78% nitrogen, an inert gas which causes no problems when breathed at normal atmospheric pressure, but is a major worry when breathed at high pressure. At depth nitrogen is absorbed in the bloodstream and if the ascent is made too quickly this can be released as bubbles in the bloodstream, which can be fatal. So all divers are trained to make a slow ascent to the surface to avoid this and it isn't of major concern to an experienced diver. 

However at great depth nitrogen is also forced into tissues and ligaments and a slow ascent to the surface may not give sufficient time for this to be released. The gas can bubble out into the joints causing crippling pain- decompression sickness, commonly know as 'the bends'.

Decompression sickness was originally known as Caisson Disease and was first identified in mining in the mid 19th century after the invention of the steam engine, which was eventually adapted to run air compressors. The first use of a pressurised chamber was to mine coal in the Loire Valley of France in 1840, in what was called a caisson (“box” in French). A chamber with an open bottom was lowered down into the ground, and compressed air was pumped into it, forcing water down and out of the bottom. This allowed workers to dig below the water table and into valuable stores of coal.  Miners worked 7 to 10 hour shifts and cases of the curious “mal de caisson,” were soon seen, described as joint pain and soreness that appeared approximately half an hour after returning to the surface.;  These were the first known injuries from compressed air and represented the start of a decades-long journey to find the cause of the mysterious and deadly “caisson disease.”

Although decompression sickness is a serious condition it is totally avoidable by making stops of several minutes en route to the surface. These decompression stops are undertaken at relatively shallow depths where the relative pressure changes are at their greatest, and in our planning we decided on 5 minute stops at 30 ft and 15 feet to allow the nitrogen to dissipate after a maximum of 10 minutes at the greatest depth.

Testing out a prototype decompression meter (on my right wrist) in 1976.
For the Rinovia dive we made use of trusted decompression tables

So, we could avoid decompression sickness but the other effect of nitrogen we could not control, and it was the narcotic effect of nitrogen at high pressure which was our major concern. Nitrogen narcosis manifests itself around 100 ft (30m) and rapidly worsens with increasing depth, such that 132 ft (40m) was recommended as the safe limit for sports divers. The legendary pioneer Jacques Cousteau called it the 'rapture of the deep' and it has also been known as "Martini's law", the idea that narcosis results in the feeling of one martini for every 10 m (33 ft) below 20 m (66 ft) depth. 

Although in retrospect we could have assessed our susceptibility to nitrogen narcosis by downing martinis in the pub, we did this by carrying out progressively deeper dives and by a session in the recompression chamber at Fort Bovisands in Plymouth. A recompression chamber is a cylindrical steel vessel into which air is introduced under pressure (as with the caisson) and is used to force nitrogen bubbles back into the tissues of any diver suffering from the bends, after which the pressure is slowly reduced to allow the nitrogen to diffuse safely. We were subjected to a pressure equivalent to a depth of 165 ft (50m) with no serious effects apart from a slight slowing down in the performance of simple mental tasks, but one of the CSM students succumbed to uncontrollable fits of giggling even at 95 ft (30m) so needless to say he was not asked to audition for the Rinovia dive.

And so, after all the planning we were all set for the dive.

On the morning of October 22nd 1977 Terry, Mike, Ken and I met at Mylor Harbour, Falmouth, and set off in Pisces into Falmouth Bay.  We soon picked up the fisherman's transit bearings and after about 2 miles the wreck showed clearly on the echo sounder in 180 ft (55m) of water. We dropped a 'shot line' a weighted rope, onto the wreck and prepared to dive.

Terry and Mike dived first and as they descended we watched their twin sets of bubbles bursting on the surface, becoming more voluminous the deeper they went as the volume of air in each bubble increased on ascent due to the fall in pressure.

After around 20 minutes we could see them clearly holding the shot line at 15 ft (4.5m) on their second 5 minute decompression stop, after which they appeared on the surface, Terry holding aloft a hurricane lamp which he had found in full view on the wheelhouse, a clear indication that no one had dived the wreck previously.

Terry with the hurricane lamp back at Mylor Harbour

Ken and I then dived and reached 175 ft (53m) before we arrived on the wreck but unfortunately the shot line had moved and we were somewhere on the deck with nothing recognisable. We circled the shot line but there was nothing to see of interest so after 11 minutes we terminated the dive and returned to the surface and our two stops, then the long journey back to Mylor.

At Mylor after the dive, Terry, Mike, Ken and me

We agreed that it had been a rather disappointing venture and it remained my deepest dive until I abandoned diving in 1979 to devote my spare time to cricket! In later years I had a few reef dives in Thailand, Madagascar and the Great Barrier Reef, but diving off the Cornish coast still holds the fondest memories (see posting of 8 March 2012). 

Nowadays the Rinovia is listed in Falmouth's Dive Site list and Atlantic Scuba describes it as a really nice shallow trimix dive. Shallow!  How times have changed. Nowadays advanced sports divers can descend to greater depths by using gas mixtures such as trimix, a blend of oxygen and helium and a reduced amount of nitrogen, which allows safe diving to 210ft (65m) with little worries about narcosis, although decompression stops are still needed. Helium has no narcotic effect and its low density reduces breathing resistance at depth.

Deep sports diving is obviously much different now than in the 1970s. I know that many people that I meet around the world are keen divers so I would very much like to hear of your own deep diving experiences.

Sunday 18 February 2024

SME Annual Meeting in Phoenix is only a week away

Next week I will be in Phoenix, Arizona, reporting on one of the mining industry's biggest events, the Annual Meeting of the Society for Mining, Metallurgy and Exploration (MINEXCHANGE2024).

This will be my 21st SME Annual Meeting, and my 4th in Phoenix. The last one in Arizona was in 2020, attended by over 5700 delegates from all areas of the mining industry. I was lucky to escape back to the UK after that one, narrowly avoiding the first pandemic lockdown, and my next visit to the USA was two years later for the meeting in Salt Lake City.

I have reported on these events annually for the blog, featuring mineral processing people and innovations. As always I would very much like you to say hello if you see me wandering around the huge exhibition. 

If you have an exhibition booth, please contact me prior to the event and I will arrange to meet at your booth for a photo and to hear your latest news.

Phoenix 2020

You can also catch up with me on the final afternoon at the Sheraton Phoenix where MINEXCHANGE2024 will end with the SME Awards Celebration, which includes a reception with beverages and hors d’oeuvres, a great final networking opportunity.

I look forward to meeting you in Phoenix.


Friday 16 February 2024

February Cornish Mining Sundowner and news of a new book on Cornish tin mining

Despite the atrocious weather around 15 Cornish mining folk made it to the sundowner last night, the first of the year at Falmouth's Chain Locker.

All but one of the attendees were 'locals' from West Cornwall, so it was good to see East Cornwall's representative Alex Newns, Minerals Technology Manager at Imerys Minerals Ltd. Imerys specialises in the production and processing of industrial minerals and operates the china clay mines in the St. Austell area of East Cornwall. Last year Imerys acquired an 80% stake in British Lithium, based in the same area, the transaction bringing together Imerys's lithium mineral resources, found in the micas in the china clay residues, and British Lithium’s technology and state-of-the-art lithium pilot plant, which is now producing battery-grade lithium carbonate.

The resources give sufficient confidence to target a life of mine exceeding 30 years at a production rate of 20,000 tonnes of lithium carbonate equivalent per year, potentially enough to equip 500,000 electrical vehicles per year by the end of the decade, meeting roughly two-thirds of Britain’s estimated battery demand by 2030 when all UK car manufacturers convert to electric vehicles. It was good to talk to Alex about the latest developments, and to hear that he was at CSM in my class within the MSc course in mineral processing in my final year in 1996.

Alex Newns (4th left) with me, Dean Eastbury, KP van der Wielen, Pat Foster and Nick Clarke

There was no major mining news from West Cornwall this month, but a new book might be of interest- Tin mining in Cornwall 1900 to 1950 - decline, fall and resurrection

In histories of the Cornish Tin Industry, the period after the death of Queen Victoria often receives scant attention and is treated as a mere tailpiece. This omission is now significantly remedied by Roger Burt's history of the first half of the twentieth century. The book provides a new analysis of this era which examines its successes and failures both generally and through major players. East Pool, Geevor and South Crofty. There are also portraits of several key individuals. This is an important original work from an author who has made an extensive study of metal mining with particular reference to Cornwall, and a major addition to the story of Cornish Tin. It also provides interesting perspectives on the problems facing any revival of Cornish mining now or in the future.

The next Cornish Mining Sundowner will be on Thursday 21st March from 5.30pm at the Chain Locker, Falmouth.

Monday 12 February 2024

The Future of Geometallurgy

Geometallurgy is an interdisciplinary research field concerned with the planning, monitoring, and optimization of mineral resource extraction and processing. Geometallurgy requires a quantitative understanding of primary resource characteristics such as mineralogical composition and texture, the distribution and variability of these characteristics across the target ore body, and how these interact with mining and beneficiation processes.  This requires accurate analytical data for resource characterization, a detailed under­standing of ore body geology, process technology, economics, and the often­complex interactions between them.

Complex, polymetallic, lower-grade and deeper mineral deposits are forecast to be the future source of the metals and minerals required to decarbonise the global economy. The sustainable and economic extraction of these minerals will require the expert application of geometallurgy across the mining value chain, from concept through to closure.   However, geometallurgy is unique amongst disciplines in that it does not have a broad and deep external ecosystem that extends from academia through research institutes, member-led industry bodies, mining companies, testing laboratories, software developers and consultants. Rather, it is defined by loosely connected pockets of excellence and innovative adaptation.  

In a keynote lecture at November's Process Mineralogy '24 in Cape Town, Stewart Brand will suggest that a new approach to geometallurgy is required if we are to successfully mine the complex orebodies of the future. The substantial technical challenges ahead require a step change increase in collaboration and creativity to leverage collective knowledge and drive innovation. We will need to deliberately nurture the external ecosystems that are required to support and develop geometallurgy into a broad and deep discipline. Stewart Brand is Principal - Global Geometallurgy at BHP, Australia where he leads strategic geometallurgy projects and supports geometallurgical teams around the world. 

The fundamental concepts of geometallurgy are explored in the December 2023 issue of Elements, an international magazine of mineralogy, geochemistry and petrology. Guest editors Max Frenzel, Raimon Tolosana-Delgado, and Jens Gutzmer review how current geometallurgical research is opening up opportunities for geoscientists to generate better economic and environmental outcomes for the global raw materials industry as part of a sustainable economy. 


Wednesday 7 February 2024

FLSmidth's major involvement with Mill Circuits '24

It was great to hear that major mineral processing equipment company FLSmidth is to sponsor Mill Circuits '24 in Cape Town in June, joining Capstone Copper and Conundrum.

FLSmidth has long been associated with MEI Conferences, and the company is also sponsoring Comminution '25 and Flotation '25 next year. 

FLSmidth is a full flowsheet technology and service supplier to the global mining and cement industries, aiding its customers in improving performance, lower operating costs and reduce environmental impact. Its MissionZero programme has set a target of providing solutions for zero-emission mining and zero-emission cement production by 2030, supporting a green transition built upon sustainable materials.  And congratulations to FLSmidth for winning the Mining Magazine Award 2024 for Technology and Innovation for the Reflux Classifier™ and Reflux™ Flotation Cell.

Dr. Dariusz Lelinski, the Global Director for Flotation at FLSmidth, USA, will present the keynote lecture at the conference,  exploring how different flotation technologies can improve both productivity and sustainability performance. 

We will be drafting the provisional programmes for Mill Circuits '24 and for Physical Separation '24 which immediately precedes it, later this month, so it is not too late to submit abstracts via the conference websites.